Der&qmients in Petroleum Science, 14
Paraffin products Prapedcs, rechplloivggit?,~,appliuu iiot 1s
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Der&qmients in Petroleum Science, 14
Paraffin products Prapedcs, rechplloivggit?,~,appliuu iiot 1s
FURTHER TITLES IN THIS SERIES 1 A. GENE COLLINS GEOCHEMISTRY OF OILFIELD WATERS 2 W. H. FERTL ABNORMAL FORMATION PRESSURES 3 A.P. SZILAS PRODUCTION AND TRANSPORT OF OIL AND GAS 4 C.E.B. CONYBEARE GEOMORPHOLOGY OF OIL AND GAS FIELDS IN SANDSTONE BODIES 5 T.F. YEN and G.V. CHILINGARIAN (Editors) OIL SHALE
6 D.W. PEACEMAN FUNDAMENTALS OF NUMERICAL RESERVOIR SIMULATION
7 G.V. CHILINGARIAN and T.F. YEN (Editors) BITUMENS, ASPHALTS AND TAR SANDS 8 L.P. DAKE FUNDAMENTALS OF RESERVOIR ENGINEERING
9 K. MAGARA COMPACTION AND FLUID MIGRATION 10 M.T. SILVIA and E.A. ROBINSON DECONVOLUTION OF GEOPHYSICAL TIME SERIES IN THE EXPLORATION FOR OIL AND NATURAL GAS 11 G.V. CHILINGARIAN and P. VORABUTR DRILLING AND DRILLING FLUIDS
12 T. VAN GOLF-RACHT FRACTURED HYDROCARBON-RESERVOIR ENGINEERING 13 F. JOHN FAYERS (Editor) ENHANCED OIL RECOVERY
Developments in Petroleum Science, 14
Paraffin products Properties, technologies, applications by M. FREUND Member of the Hungarian Academy of Sciences
R. CSIKdS Hungarian Oil and Gas Research Institute
S. KESZTHELYI Hungarian Oil and Gas Research Institute
GY. M6ZES ffungarian Oil and Gas Research Institute
edited by GY. M6ZES
ELSEVIER SCIENTIFIC PUBLISHING COMPANY AMSTERDAM -OXFORD - NEW YORK 1982
Joint edition published by Elsevier Scientific Publishing Company, Amsterdam, The Netherlands and Akadkmiai Kiadb, The Publishing House of the Hungarian Academy of Sciences, Budapest, Hungary Revised and updated translation of ‘Kaolaj paraffinok’ published by Milszaki Konyvkiadb, Budapest Translated by E. JAKAB The distribution of this book is being handled by the following publishers for the U. S. A . and Canada
Elsevier Science Publishing Company, Inc. 52 Vanderbilt Avenue, New York, New York 10017, U. S. A. for the East European Countries, People’s Republic of China, Democratic People’s Republic of Korea, Republic of Cuba, Socialist Republic of Vietnam and People’s Republic of Mongolia Kultura Hungarian Foreign Trading Co., P. 0. Box 149, H-1389 Budapest, Hungary,
for all remaining areas Elsevier Scientific Publishing Company Molenwerf 1 P. 0. Box 211, 1000 AE Amsterdam, The Netherlands
Library of Congress Cataloging in Publication Data K6olaj p a r p n o k . Paraffin products.
English.
(Developments in petroleum science; 14) Translation of: Ki3olaj paraffinok. Bibliography: p. Includes index. 1. Paraffins. I. Freund, MihAly, 1889TI. Mbzes, Gyula. 111. Title. IV. Series. TP692.4.P3K6513 665.5’385 81-15246 ISBN G-444-99712-1 AACRZ
ISBN 0-444-99712-1 (Vole 14) ISBN 0-444-41625-0 (Series)
0AkadPmiai Kiadd, Budapest 1982 Printed in Hungary
CONTENTS
PREFACE
9
INTRODUCTION
11
I. CHEMICAL, CRYSTALLOGRAPHICAL AND PHYSICAL PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
13
(A) Liquid paraffins and paraffin waxes from petroleum 1. Composition of petroleum distillation products 2. Nomenclature of liquid paraffins and paraffin waxes Literature (B) Chemical properties of liquid paraffins and paraffin waxes 1. Preparative and analytical methods for studying the chemical composition of liquid paraffins and paraffin waxes (a) Separation methods (b) Chemical classification o n the basis of physical characteristics (c) Analytical methods for the determination of individual hydrocarbons or of compositions of their mixtures 2. Chemical composition of liquid paraffins and paraffin waxes 3. Chemical properties of individual alkanes and their mixtures (a) The reactions of paraffins with halogens (b) Sulfochlorination of alkanes (c) Reactions of liquid paraffins and paraffin waxes with sulfur dioxide, sulfur trioxide, sulfuric acid and fuming sulfuric acid (oleum) (d) Reaction of liquid paraffins and paraffin waxes with nitric acid (e) Oxidation of liquid paraffins and paraffin waxes ( f ) Thermal decomposition and isomerization of alkanes Literature (C) Crystal structure of paraffin waxes 1. Crystal structure and crystallization 2. Crystal structure and habit of individual alkanes and their mixtures Literature (D) Physical properties of paraffin waxes 1. Melting point, boiling point and melt viscosity 2. Density and thermal expansion
13 13 17 20 21
21 21 26 28 29 54 54 58 59 60 62 65 68 70 70 75 89 90 91 94
6
CONTENTS
3. Optical properties 4. Rheological properties 5. Thermal properties 6. Solubility 7. Adhesive properties 8. Water vapour permeability 9. Water resistance 10. Electrical properties Literature
II. MANUFACTURE OF PARAFFIN WAXES AND CERESINS FROM PETROLEUM (A) The origins and development of dewaxing processes Literature (€3) The role of the crystal structure of paraffin waxes in the dewaxing process Literature (C) Dewaxing processes using solvents 1. Methyl ethyl ketone dewaxing 2. The propane dewaxing process 3. Dewaxing with a mixture of propylene and acetone 4. Dewaxing with chlorinated hydrocarbons 5. Dilchill dewaxing process 6. Filter aids Literature (D) De-oiling and fractional crystallization of slack waxes and petrolatum Literature (E) Manufacture of n-alkanes 1. n-Alkane manufacture based on adduct formation with urea (a) Mechanism of adduct formation, factors affecting adduct formation, structure of adducts (b) Technology of adduct formation 2. Manufacture of n-alkanes using molecular sieves (a) Composition, structure and adsorption properties of synthetic molecular sieves (b) Manufacture of n-alkanes using molecular sieve processes Literature (F) Purification of paraffin waxes 1. By treatment with chemicals 2. By adsorption processes 3. By hydrogenation Literature (G)Blending of paraffin waxes 1. Blending with microcrystalline paraffin waxes 2. Blending with polymers Literature
102 107 118
123 130 136 137 138 140 141 141 143 143 144 145 146 160 163 1 64 165 166 167 168 174 175 175 177 185 193
194 195 202 204 205 207 215 222 223 224 225 239
CONTENTS
III. APPLICATIONS OF PARAFFIN WAXES AND LIQUID PARAFFINS (A) Direct applications of paraffin waxes and liquid paraffins Literature 1. Paraffin waxes in the paper industry (a) Paraf6n waxes for impregnation (b) Paraffin waxes in coatings (c) Paraffin waxes for lamination (13)Paraffin waxes as additives to paper sizes Literature 2. Application of paraffin waxes in household chemicals (by Gy. Buktuy) (a) Polishes with paraffin wax as an additive (b) Candles Literature 3. Application of paraffin waxes in the cosmetics industry (by Gy. Baktay) (a) Solid perfumes (b) Cosmetic creams (c) Beauty masks (d) Protective creams for industrial workers (e) Facial care and beauty products (f) Hair preparations (g) Anti-perspirants Literature 4. Application of paraffin waxes in the food industry and in agriculture Literature 5. Other fields of application for paraffin waxes (a) The match industry (b) The rubber industry (c) Precision casting (d) The manufacture of refractory ceramics (e) The electrical industry ( f ) Paraffin wax emulsions in building construction Literature (B) Paraffin waxes and liquid paraffins as starting materials for the chemical industry 1. Manufacture and utilization of chlorinated paraffins (a) The chlorination process (b) Batchwise and continuous chlorination of paraffins (c) Factors affecting the manufacture and grade of chlorinated paraffins (d) Applications of chlorinated paraffins Literature 2. Sulfochlorination of paraffins and utilization of the products obtained Literature 3. Manufacture of fatty acids, dicarboxylic acids and alcohols by the oxidation of paraffins, and utilization of the products (a) The main variants of paraffin oxidation
7 240
240 24 1 241 241 242 241 248 249 249 249 260 26 1 262 263 263 266 266 266 268 268 269 269 27 1 27 1 211 212 272 213 214 215 276 276 216 216 211 280 283 286 287 289 290 290
8
CONTENTS
(b) The manufacture of fatty acids by paraffin oxidation (c) Manufacture of alcohols by paraffin oxidation (d) Utilization of paraffin oxidation products Literature 4. Manufacture of olefins, liquid at ambient temperature, from paraffins, and utilization of the products (a) Manufacture of olefins from paraffin waxes and paraffin crudes (b) Applications of high molecular weight alpha-olefins Literature ( C ) The manufacture of proteins and organic acids from hydrocarbons by biosynthesis 1. Protein manufacture from hydrocarbons (a) Significance of the problem and present situation (b) Manufacture of single cell protein (petroleum yeast) (c) Properties and use of single cell protein 2. The manufacture of organic acids from paraffins Literature Subject index
290 298 302 304 305 305 315 321 323 323 323 325 327 328 329 331
PREFACE
On a world-wide basis, the share of petroleum waxes related to the total o petroleum products is tiny. In 1975, for example, only 1.5 million tons of paraffin waxes were produced from a total output of 2,700 million tons of crude oil, thus amounting to only 0.06%. Even if lower molecular weight paraffin products are included, the share - as compared to other petroleum products - remains insignificant. When, however, the greatly varied direct applications of solid and liquid paraffins in industry, and their utilization as raw materials in the petrochemical industry are considered, their importance becomes immediately obvious. For this reason it appeared of interest to summarize - without claiming completeness the basic facts and data on the manufacture, applications, physico-chemical and chemical properties of these products in a monograph suited to both research and to industrial audiences. Nomenclature is also discussed. The authors hope that the present book will be of assistance to all who wish to obtain an overall coherent view of paraffin waxes and related products, their properties, manufacture and applications. This English edition is a revised version of the Hungarian original. It includes the most recent information available to the authors on the topics covered. I
The Authors
This Page Intentionally Left Blank
INTRODUCTION
Paraffinic hydrocarbons, or paraffins are straight-chain or branched saturated organic compounds with the composition C,,H2,,+2.The term paraffin waxes is used for mixtures of various hydrocarbon groups, especially paraffins and cycloalkanes, that are solid at ambient temperature. Paraffins are present in large amounts in nature, but can also be produced synthetically and are formed as by-products in processing certain natural substances. Paraffins of low molecular weight are found in natural gas, paraffins of medium and high molecular weight in petroleum and ozokerite. On industrial scale, paraffins can be manufactured from coal by the well-known Fischer-Tropsch synthesis. Paraffins are also obtained from the tar-like products obtained by the dry distillation of coal (mainly brown coal) and other organic materials (wood, lignite, bituminous shales, fish tallow etc.). In view of present trends, this book will deal with the Structure, properties, manufacture and application only of paraffins obtained from petroleum, and that are liquid or solid at ambient temperatures. Among liquid paraffins, only mixtures containing higher than Clo alkanes, cycloalkanes and, in smaller amounts, aromatic hydrocarbons will be discussed in detail. Alkanes that are gaseous at ambient temperature will not be considered in this book. Paraffins, liquid at ambient temperatures and containing higher than Clq alkanes are produced from the kerosine and gas oil fractions obtained by the distillation of hydrocarbon crudes at atmospheric pressure. Paraffinwaxes, solid at ambient temperature, are obtained from lubricating oil fractions having various average boiling-points, from distillation residues resulting from the vacuum distillation of hydrocarbon crudes, and from the so-called tank waxes and pipeline waxes separated during the storage and transport of such crudes. In the following, the terms liquid paraffins and solid paraffin waxes will always be used in the above sense. Whenever individual members of the homologous series of paraffins are in question, they will be termed alkanes to avoid confusion. Liquid paraffins from petroleum consist of ClO-Cl8,mainly normal hydrocarbons that are liquid at ambient temperature. The average molecular weight varies from 150 to 250. The nomenclature of paraffin waxes with different crystal structures will be discussed in detail in the following. However, we wish to mention in advance that
12
INTRODUCTION
the various types of paraffin waxes form essentially two groups. Macrocrystalline paraffin waxes are mixtures which consist chiefly of saturated, normal C1,-C, hydrocarbons and smaller amounts of iso-alkanes and cycloalkanes. The molecular weight of the components varies between 250 and 450, their melting point between 40 and 60 "C.Their crystals are plate- or needle-shaped. Microcrystalline paraffin waxes contain, in addition to normal hydrocarbons, large amounts of iso-alkanes and naphthenes with long alkyl side-chains. The iso-alkanes form microcrystals and the major part of these waxes consists of C,o-C,, compounds. The melting point of microcrystalline paraffin waxes varies between 60 and 90 "C. The world production of paraffin wax increases from year to year. However, whereas this increase was around 60% between 1950 and 1960, the growth rate has decreased since 1960. This is mainly due to plastics (polyethylene, PVC, polystyrene, cellophane etc.) being increasingly used in packaging. It is of interest to note that while around 90% of the world production of paraffin wax in 1960-1961 consisted of macrocrystalline paraffin wax, the present growth rate of microcrystalline paraffin wax production is substantially higher than that of macrocrystalline paraffin wax. Sherwood's data indicate that application of microcrystalline paraffin wax in the U.S.A. increased by 170% as early as in the period 1948-1958, whereas for macrocrystalline wax the increase over the same period was only 10%. This shift is the result of the already mentioned expansion in the use of plastics in packaging. This same reason urged paraffin wax producers to improve the properties of both macro- and microcrystalline paraffin waxes by means of additives. A rich choice of such products is now available on the world market.
I. CHEMICAL, CRYSTALLOGRAPHICAL AND PHYSICAL PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
(A) Liquid paraffins and paraffin waxes from petroleum 1. Composition of petroleum distillation products /
Crude oils and their products contain a large number of individual paraffins. The main physical characteristics of the most frequently occurring alkanes are listed in Table 1-1, indicating that n-pentane is already liquid and n-hexadecane solid at ambient temperature. Table I-I. Physical characteristics of some alkanes occurring in petroleum
Methane Ethane Propane
CH, CZH, CaH,
16 30 44
Butane n-butane iso-butane
C.810
58
Pentane n-pentane 2-methylbutane (iso-pentane) 2,2-dimethylpropane (neopentane)
C,Hn
Hexane n-hexane 2-methylpentane
GHi,
72
86
3-methy lpentane
- 161.5 - 88.5 -42.0
0.424' 0.546' 0.582'
-82 32 96
4.2
- 138.5 - 159.5
- 0.5 - 12.0
0.602' 0.596'
153 134
3.7 3.8
- 129.5
36.0
0.625
197
3.3
- 159.5
28.0
0.620
188
3.4
- 16.5
9.5
0.6139
184
3.5
-94.0 - 153.5
69.0 60.0 63.0
0.659 0.656 0.664
235 228 227
-
-98.0
49.5
0.649
212
-
- 129.0
58.0
0.662
221
3.1
-99.5 between
98.5 19-93
0.684
267
:.%)
%)
2.7 2.12.9
-118.0
2,2-dimethylbutane 2,3-dimethylbutane Heptane n-heptane iso-heptanes
-182.5 -183.0 -187.0
C7H16
4.6 5.0
2.9 3.2
100
and
-25
14
I. PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
Table I-1 (cont.)
I
Compound
I
Formula
~
Octane n-octane 2,2,3-trimethylpentane 2,2,4-trimethylpentane (isooctane) other iso-octanes
$:
I I
I I
Melting point, "C (101 kPa)
Boiling point, "C (101 kPa)
-57.0
125.5
0.703
296
2.5
110.5
0.716
285
-
99.5
0.692
268
-
Density
at 2ooc
crit. t e m ~ , . Crit. oc press,, MPa
114
- 107.5 between and
+ 1046
Nonane n-nonane iso-nonanes
128
Decane n-decane iso-decanes
142
n-Hendecane n-Dodecane n-Tetradecane n-Hexadecane n-Octadecane n-Eicosane n-Pentacosane n-Triacontane n-Pentatriacontane n-Pentacontane
-53.3
-
150.5
0.718
323
-29.5
173.5 147-1 168
)-\:.0.730
347
-
156 170 198 226 254 282 352 422 492 702
-25.5 -9.5 5.5 18.0 28.0 36.5 53.5 66.0 74.5 92.0
196 216 254 287 308 2054 25g4 3044 3314 4214
0.740 0.749 0.763 0.174 0.782 0.789 0.801 0.810 0.7813 0.7943
-
369 391 429 462 49 1 513
2.3
-
2.1
-
593
2.0 1.9 1.7 1.5 1.4 1.3 1.o
708
0.7
-
-
-
At the boiling point *At0°C
Liquid density at the melting point ' A t 2.1 kPa 104 'C: Hexamethylethane a
+
Even the lower boiling-point fractions of petroleum contain, depending on the source of the crude, in addition to alkanes, varying amounts of other hydrocarbons, namely cycloalkanes and aromatic compounds. Table 1-2 presents the alkane and cycloalkane content of gasoline products over the 40-120 "C distillation range, obtained from different crudes. With increasing average molecular weight, the composition of petroleum fractions is more and more complex. The alkane, cycloalkane and aromatics content of different gasoline and naphtha fractions obtained from three different crudes
15
(A) LIQUID PARAFFINS AND PARAFTIN WAXES FROM PETROLEUM
Table 1-2. Alkane and cycloalkane content in gasolines from different sources Vol- % Sources n-Alkanes
Ponca field, Oklahoma Greendale-Kawkalinfield, Michigan Conroe field, Texas Loviszi field, Hungary Budafa field, Hungary
1
iso-Alkanes
1
Cyclopentanes
I
Cyclohexanea
35.7
20.5
23.4
20.4
63.1 18.2 26.0 30.8
13.2 20.3 17.2 18.9
8.O 17.3 27.0 29.5
15.7 44.2 29.8 20.8
is shown in Table 1-3. It can be noticed that in the case of the fractions from the Yates field the alkane content decreases, while the cycloalkane content substantially increases with the boiling range. In the case of the other two crudes no such unequivocal change could be observed with regard to alkanes and cycloalkanes, while their aromatics content was the highest in the 95-1 15 "Cfraction. Table 1-4 lists the hydrocarbon composition of the kerosine and light gas oil fractions of Table Z-3. Alkanes, cycloalkanes and aromatics content of petroleum fractions from different sources Boiling point range, O C (101 kPa)
_ _ ~ ___
I
Slaughter field
AIkanes
~
Cycloalkanes
Aromatics
1
VOl- %
I
1
Wasson field
Alkanes
Cycloalkanes
Aromatics
I
1
Yates field * Al-
kanes
Cycloalkanes
Table 1-4. Hydrocarbon composition of kerosine and gas oil fractions of petroleum from the Ponca field
Hydrocarbon
Boiling point range_ (101 kPa) _ _ 180-23OoC
n-Alkanes Iso-afkanes Monocycloalkanes Bicycloalkanes Tricycloalkanes Monocyclic aromatics* Bicyclic aromatics
23 16 32 11 0 15 3
I
230-300°C
22 8 29 17 4 12 8
Monocyclic aromatics include alkylbenzencs and aromatic cycloalkanc-type hydrocarbons
1
Aromatics
16
I. PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
crude from the Ponca field. It can be observed that the content in bicycloalkanes and bicyclic aromatics increases with the boiling point. The fractions and the distillation residues suitable for the manufacture of lubricating oils have a still more complex composition. In these distillation fractions the carbon atom number of the components varies between 25 and 40. In the residual oil compounds with 50 to 60, and in some cases up to 80 carbon atoms are found. The chemical composition of the lubricating oils obtained by refining these materials differs from the composition of the starting distillates and residual oils actually as a result of the refining operations. This theme, however, is outside the scope of this book. The different compositions, depending on their average molecular weight (viscosity) and extent of refining (viscosity index) are shown in Table 1-5, presenting the carbon atom distribution determined by the so-called Table Z-5. Carbon atom distribution among aromatic, cycloalkane and alkane compounds in refined lubricating oils Viscosity at 98.9 "C
Oil type
_____
High viscosity index aircraft oil High viscosity index motor oil Medium viscosity index motor oil Low viscosity index oil Medical-grade oil
Viscosity index
Carbon atom distribution, % aromatic
1 cycloalkane 1
alkane
101 49
63 62 48
* S.S.U.: flow time in seconds, measured with a Saybolt Universal viscorneter
n-d-M method, that is, the distribution of the total number of carbon atoms contained in the compounds constituting the lubricating oil between the individual groups of hydrocarbons. The highly complex composition of high boiling-point fractions is represented by the data in Table 1-6 referring to a lubricating oil fraction composed of C25-C35 Table 1-6. Composition of a CzsC,, lubricating oil fraction
-
_.____
Compounds
n-Alkanes Iso-alkanes Monocycloalkanes Bicycloalkanes Tri- and polycycloalkanes Monocyclic aromatics with cycloalkane rings Bicyclic aromatics with cycloalkane rings Tricyclic aromatics with cycloalkane rings Polycyclic aromatics with low hydrogen content and non-hydrocarbon compounds
Vol- %
13.7 8.3 18.4 9.9
16.5 10.5 8.1
6.6 8.0
(A) LIQUID PARAFFINS AND PARAFFIN WAXES FROM PFTROLEUM
17
compounds, obtained by fractional distillation from the Ponca field crude. A comparison with the data of Table 1-4 unequivocally confirms that the higher-boiling fractions contain much more cycloalkanes and aromatics than the lower-boiling fractions. From this short summary of the composition of crude petroleums it may be seen that paraffin waxes produced mainly from higher-boiling distillates and residual oils contain normal hydrocarbons as well as large amounts of iso-alkanes. Also, significant amounts of one, or more ring hydrocarbons with straight side chains can be found. 2. Nomenclature of liquid parafis and paraffin waxes All classifications regarding a range of products are more or less arbitrary, or valid only with certain restrictions. It is, however, a basic postulate, when establishing some nomenclature system, that in addition to an endeavour at simplicity, both the technological and application aspects of the products in question should assert themselves. The manufacture of liquid paraffins and paraffin waxes will be discussed in Chapter 11, their application in Chapter 111. In conformity with these chapters we established a nomenclature system, which, in our opinion, satisfies the above basic requirements. This nomenclature will be applied in the course of this book. Widely varying terms are used in the literature, in the technological practice of the petroleum industry and in commerce for different grades of liquid paraffin and paraffin waxes. The terms slab paraffin wax, slack wax, scale wax, and pipeline or tank wax were established in earlier petroleum industrial practice. The term slab wax was used exclusively for paraffin waxes obtained by cooling, pressing and sweating from low-viscosity distillates. Only pressing and sweating were feasible for the separation of the oily part and the solidified paraffin wax, since centrifuging could not be applied. The term slack wax, or slacks, was used for the intermediate product of cooling and pressing without sweating or refining, and the product produced by sweating was called scale wax. On the other hand, petrolatums from residual oils and pipeline or tank waxes cannot be pressed, but only centrifuged in solvent media. This was an important aspect at the time when dewaxing by means of solvents was not yet known. The fraction distilling over between those that could be dewaxed by pressing and sweating and those that could be dewaxed by centrifuging was called the intermediate fraction. This intermediate, that is, paraffinic medium and heavy distillate, could be dewaxed only under great dif€iculties and with very poor yields either by pressing or by centrifuging. The paraffin waxes obtained from the intermediate fraction were called slop wax. The intermediate fraction was often used as fuel without recovering its paraffin wax content. At present, when solvent dewaxing processes have completely conquered the field, these aspects, and the terms connected with them, will obviously lose their importance. 2
18
I. PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
Classification of paraffin waxes : Paraffin waxes with macrocrystalline structure can be classified e.g. with respect to their melting point or to the extent of refining. On the basis of the melting p o b t one can distinguish between soft paraffin waxes with melting points below 45 "C, and hard paraffin waxes with melting points between 45 and 60°C and needle penetration values below 20 mm/lO at 25 "C. Depending on the degree of refining, one can classify paraffin waxes as technical, semi-refined and refined grade waxes. Technical grade paraffin waxes usually contain less than 6 wt-% oil; these are products obtained by dewaxing from slacks. Semi-refined paraffin waxes may contain a maximum of 3 wt- % oil, and their colour is light yellow to white. Finally, refined paraffin waxes contain 0.4 to 0.8 wt- % oil, they are completely colourless, odourless and do not contain substances detrimental to health. Our nomenclature system is based on the classification of paraffin waxes into macrocrystalline and microcrystalline groups. The crystal structure of macrocrystalline (slab) paraffin waxes can be observed visually, while that of microcrystalline paraffin waxes only with a microscope. The term amorphous is thus sometimes found in the literature for paraffin waxes obtained from residual oil. As it is known all paraffin waxes obtained from petroleum are crystalline below their setting point. The size of the crystals, however, decreases with the increasing boiling point of the paraffin wax. Microcrystalline para& waxes have higher molecular weights, densities and refractive indices than macrocrystalline paraffin waxes. From the view of both processing and application, it is an important property of microcrystalline para& waxes that they are capable of retaining more oil than macrocrystalline waxes. The structural difference is also confirmed by the observation that blending macrocrystalline slab wax with only a few tenths of a per cent of microcrystalline paraffin wax changes the ease of pressing and sweating the former. After these preliminary remarks, our classification system is shown in Fig. 1-1. The raw materials for liquid paraffins are the distillates obtained by the distillation of petroleum crudes. The raw materials for paraffin waxes are the light, intermediate and heavy hydrocarbon oil distillates obtained by the vacuum distillation of the latter, the residual oils of vacuum distillation, and pipeline and tank waxes. The semiproducts obtained in the first stage from light, intermediate and heavy distillates, from residual oils and from pipeline and tank waxes cannot yet be regarded as paraffin waxes. They are termed slacks and petrolatums, respectively. The difference between paraffin waxes and slacks and petrolatums is in their oil content, and hence in their chemical composition. The differences in chemical composition are obviously affected by the conditions of de-oiling. Macrocrystalline paraffin wax is produced from the slacks obtained from paraffin light oil distillates. Microcrystalline paraffin waxes, both of the brittle and the ductile type, are obtained from petrolatum. Ductile microcrystalline paraffin waxes include two sub-groups, namely plastic and elastic paraffin waxes. Another term used for the low oil-content macrocrystalline paraffin waxes is slab paraffin waxes. The term ceresin is reserved exclusively for brittle microcrystalline paraffin waxes.
Paraffin light distillates (atmospheric distillation)
Paraffin medium distillates (vacuum distillation)
n
&
c 2 U
0
0 I Slack wax
3 5
* 3
Macrocrystalline paraffins
2
4 Brittle microcrystalline paraffin waxes
Ductile microcrystalline paraffin waxes
micro crystalline paraffin waxes
Fig. I-I. Sources and classification of liquid paraffins and paraffin waxes from petroleum
Plastic microcrystalline paraffin waxes
&L
20
I. PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
The products obtained from slacks and petrolatums, named according to our nomenclature, are products not subjected to further purification. Whatever method is used for further purification, it will not change, or only change insignificantly, apart from colour, odour and content in bi- and tricyclic aromatics, the characteristics of these products. The products that have undergone further purification are distinguished by the attribute "purified". The differences between the characteristics of macrocrystalline, intermediate and microcrystallineparaffin waxes not subjected to purification, and their classification based on these differences is shown in Table 1-7. The basis of our classification is the melting point, kinematic viscosity at 100 "C, penetration at 25 "C, breaking point (Fraass) and oil content (ASTM). In our view, the totality of these characteristics is necessary and sufficient for an unequivocal characterization of the paraffin wax in question, its structure, oil content and mechanical characteristics. Table I-7. Classification of macrocrystalline, intermediate and microcrystalline paraffin waxes by their characteristics
I Intermediate
Characteristics
1
brittle (ceresin)
1-
Microcrvstallino ductile elastic
I
plastic
I
Melting point, "C Viscosity at 100 OC,mm*/s Penetration at 25 O , 0.1 mm (ASTM needle) Breaking point (Fraass), O C Oil content (ASTM), wt-%
40-60 c5.5
58-70 5.5-10
74-85 >10
12-20 >+25 <0.8
>15 >+15 <5.0
<10 >+25
<2.0
50-60
> 10
20-35 -20-0 0.5-3.0
50-70
> 10
20-50 -30-+ 10 3.0-7.0
Literature Asinger, F., Paraffins, Chemistry and Technology. Pergamon Press, Oxford (1968). Finck, E., Fette, Seifen, Anstr-Mittel, 62, 502 (1960). Forziati-Willingham-Mair-Rossini: J . Res. natn. Bur. Stund., 82, 11 (1944). Gruse-Stevens: Chemical Technology of Petroleum. MacGraw Hill, New York (1960). Hoffmann, H. J., Erdol, Kohle, 17, 717 (1964). Ivanovszky, L., Chem. Tech. Berf., 11, 315 (1959). Kreuder, W., Seifkn-ale-Fette- Wachse, 84, 665, 699, 735, 773, 849 (1958). - : Seifen-ale-Fette-Wachse, 85, 19, 41, 67, 93 (1959). Mair-Rossini: Ind. Engng. Chem., 47, 1062 (1955). Marx-Presting: Chem. Tech. Berl., 7, 662 (1955). Mazee, W. M., Modern Petroleum Technology, 3rd ed. (Ed. E. B. Evans), Institute of Petroleum, London (1962). Perry, J. H., Chemical Engineers' Handbook. McGraw-Hill, New York (1950). Phillips, J., Petrol. Refiner, 38, 193 (1959). Rossini-Mair: Adv. Chem. Ser., No. 5, 334 (1951).
(B) CHEMICAL PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
21
Rumberger, J., Symposium on Composition of Petroleum Oils, Determination and Evaluation. ASTM, p. 283 (1958). Teubel-Schneider-Schmiedel :Erddlparajine. VEB Deutscher Verlag fur Grundstoffindustrie, Leipzig (1965). Tuttle, J. B., Petroleum Products Handbook. (Ed. V. B. Guthrie), McGraw-Hill, New York (1960).
Wolff, G., Coating, 9, No. 1. 13 (1976).
(B) Chemical properties of liquid paraffins and paraffin waxes The chemical properties of liquid paraffins and paraffin waxes obtained from petroleum are in relation with the following steps : - preparative and analytical methods for studying the chemical composition of liquid paraffins and paraffin waxes, - determining the chemical composition of the paraffins, - determining the chemical properties of individual paraffin hydrocarbons.
1. Preparative and analytical methods for studying the chemical composition of liquid paraffins and parailin waxes The determination of the chemical composition of liquid paraffins and paraffin waxes can only be carried out after cumbersome separation procedures and subsequent analyses including spectral analysis, gas chromatography, etc. In the case of paraffin waxes with higher average molecular weight it is almost impossible, even using the most laborious operations, to achieve complete separation of individual compounds. In general, the objective is to produce narrow fractions whose components are closely similar or identical with regard to chemical structure. An approach to the chemical nature of a given paraffin wax is also yielded by physical characteristics, whose values are closely related, for a given molecular weight, to the structure of the molecule. For determining and characterizing the chemical composition of paraffin waxes, essentially three groups of preparative and analytical procedures are available: - separation methods, - classification methods based on physical characteristics, - analytical methods for the determination of individual components.
(a) Separation methods For a partial separation of the components differing in molecular weight and chemical structure, the following methods can be considered : - fractional distillation,
22
I. PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
- fractional crystallization, adduct formation with urea and column chromatography on urea, separation using molecular sieves, - elution chromatography, - thin layer chromatography. Separation by distillation is based on the differing boiling points of the components. This separation method is much limited, since the boiling points of the successive members of the n-alkane series, particularly in the case of compounds containing more than 25 C-atoms, are very close to one another. Therefore; preparative separation by distillation is effective mainly in the case of < C , n-alkanes. This separation method is difficult to apply to iso-alkanes and cycloalkanes, since the boiling points of the members of these two homologous series overlap. If a mixture of pure n-alkanes has been ffrst separated, by some method, from the material to be analyzed, the distribution of the compounds in the mixture can be determined by molecular distillation. It is obvious from what has been said that separation by distillation is much less effective in the case of microcrystalline paraffin waxes than in the case of liquid paraffins and macrocrystalline paraffin waxes. A successful method for the separation of microcrystalline paraffin waxes is fractional crystallization based on differential solubility. Ketones, mixtures of ketones and aromatics, halogenated hydrocarbons and different gasoline grades have been used as solvents in research up to the present. Fractional crystallization yields fractions of both macrocrystalline and microcrystalline paraffin waxes differing in molecular structure and molecular dimension. At higher temperatures of crystallization, fractions containing higher molecular weight and less branched alkanes, as well as cycloalkanes with long side chains will crystallize. With successive lowering of the temperature, the fractions will contain more and more iso-alkanes and cycloalkanes with shorter side chains; simultaneously the average molecular weight of the fractions will decrease. n-Alkanes can also be separated from iso- and cycloalkanes by urea adduct formation. X-ray studies have shown that the long chains of n-alkanes as well as long chains, if present, of iso- and cycloalkanes are enclosed in the tubular channels of the adduct, and this results in a hexagonal urea lattice. Urea crystallizes in the hexagonal system only when an adduct is formed, its normal crystal system being tetragonal. Straight-chain derivatives of n-alkanes, e.g. carboxylic acids, alcohols, esters, amines etc. are also capable of adduct formation. Adduct formation between n-alkanes and urea takes place in solutions of the former in gasoline, benzene or halogenated hydrocarbons when solid urea or an aqueous or alcoholic urea solution is added. When solid urea is applied, a small amount of a wetting agent, i.e. water, alcohol or some other substance with a s h i lar effect is necessary. Adduct formation is inhibited by resins, bituminous substances, sulfur compounds, etc. It is, therefore, important to remove such substances from the material before adduct formation, by elution chromatography or some other method. -
-
(B) CHEMICAL PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
23
Adduct formation is an equilibrium reaction, the equilibrium being dependent on temperature, concentration of urea and adduct-forming components, and nature of the solvent. Adduct formation is exothermic, the heat of reaction is the higher, the longer the alkane chain. Hence the stability of the adduct is the greater the longer the adduct-forming molecule chain. Short-chain n-alkanes form adducts only at low temperatures, and these products will readily decompose. The following method was used by Hessler and Meinhart. Dilute solutions of macro- and microcrystalline paraffin waxes in carbon tetrachloride were prepared, methyl alcohol saturated with urea was added and the mixture vigorously agitated. The crystalline precipitate formed was filtered, washed with alcohol and dried. The decomposition of the adduct was carried out with distilled water at 70 "C. A diagram of the urea adduct method developed in the Hungarian Oil and Gas Research Institute is shown in Fig. 1-2. As well as urea, thiourea can also successfully be used for studying the chemical composition of complex mixtures of hydrocarbons and their derivatives. Thiourea forms adducts most readily with branched compounds. The essence of columnchromatography, using urea, is as follows. The substance to be studied is introduced, in the form of a solution, into a column filled with urea. Those components of the substance which, under the given conditions, namely thermostatted temperature, presence of activator in the column and percolation time, form an adduct with urea will be bound, 'while the unreacting components will remain in solution and will be eluted from the column by washing with solvent, and determined quantitatively. Subsequently, those components having formed adducts will be eluted by successive stepwise increases of the temperature. The temperatures corresponding to these steps will determine the structure and average molecular weight of the eluate fractions. Molecular sieves are zeolites consisting of aluminium, calcium, alkali and hydrogen orthosilicates. Their characteristic feature is the ready compensation of the negative charges of their tetrahedral and A10i5 crygtal lattices by cation exchange. The interconnected voids in their lattices contain combined water that can reversibly be removed by heating. Dehydrated zeolite is capable of binding molecules having suitable dimensions to fit into the voids. For the separation of n-alkanes from hydrocarbon mixtures, synthetic molecular sieves of the so-called 5 '8, type are suitable. The average diameter of their pores is 5 A, their chemical composition is Me,,/n[(A1OJl, * (Si02)lz] 27 H,O. For chemical group analysis of liquid paraffins and macro- and microcrystalline paraffin waxes, column chromatographic separation methods based on the work of Mair, Rossini, Spengler, Snyder and Heinze are well suited. Silica gel or activated alumina is preferably used as adsorbent. The ratio of adsorbent to sample is between 20 : 1 and 30 : 1. The sample is introduced in the form of a dilute solution in gasoline or hexane. The succession of the eluents is that of the increasing polarity, e.g. hexane, mixture of hexane and benzene, benzene, methanol and chloroform. This method allows separation of saturated hydrocarbons, and mono-, bi- and tricyclic aromatics with satisfactory sharpness.
-
24
I. PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
Benzene (solvent for paraffin wax)
Dissolution of paraffin wax (25-30"C).
-.
water (90°C)
Wash and separation
Adduct formation (25"C, 96 h)
Wash liquor ~
Solution of ;so-alkanes Aqueous in benzene solution of urea
with 10 wt-% methanol
Wash
-
Benzene
t
Washed adduct
Distilled Removal of solvent
Is0 - alkanes
Aqueous solution of urea n-Alkanes +solvent
Removal of solvent
n -Alkanes
Fig. 1-2. Method for determining the n-alkane and iso-alkane content in macrocrystalline
and microcrystallineparaffin waxes
(B) CHEMICAL PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
I
Slack wax
25
]
Separation' of olefins with mercury acetate
i Olefin - free slack wax
Adduct formation
c
I
n-Alkanes and
1 Iso-alkanes, aromatics, resins
I
1
Column chromatogr.aphy
Column chromatography on silica gel
on silica gel
Iso-alkanes
A l k y l - substituted aromat tcs A
Column chromatography on activated carbon
I Column chrdmatographtj
n-alkanes
a1k y I - substituted aromat ics
Fig. 1-3. Combined separation method of Spengler and Jantzen
A more detailed chemical study of macro- or microcrystalline paraffin wax requires a combination of separation methods. A diagram of a combined separation method developed by Spengler and Jantzen is shown in Fig. 1-3. Separation of macro-and microcrystallineparaffin waxes by thin-layer chromatography was developed, among others, by Dietsche and Sucker. They used a 250
26
I. PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
Gm silica gel support layer impregnated with 40 % urea. To avoid recrystallization of the urea, a small amount of sorbite was applied. The paraffin wax to be studied was applied in a 1 % solution in benzene, at 50 to 60 "C. The solvent used for runs was a mixture of carbon tetrachloride and ethanol saturated with urea. By using a suitable solvent composition and temperature (around 50 "C), they succeeded in obtaining satisfactory separation of the paraffin wax with respect to chain length and degree of branching. By using appropriate conditions and simultaneous runs with reference standard materials, they could determine the ratio of n- and iso-alkanes in macrocrystalline paraffin waxes.
(b) Chemical classijcation on the basis of physical characteristics According to Etessam and Sawyer, the relationship between the melting poirlt and the molecular weight for n-alkanes is
M m.p. = 415 ____ - 273 M + 95 where m.p. is the melting point and M the molecular weight. According to Ivanovsky, an analogous relationship can be established between the melting point and the density : lo3 * d y = 716 f 0.75 m.p. (1-2) where d: is the density at 90 "C relative to that of water at 4 "C. From these equations the so-called ring value is derived, since
-
lo3 d: = 511
+ 311 M M+ 95
(1-3)
and the ring value, indicating the density increases due to ring closure as compared to the equimolecular n-alkane, is (1-4)
The so-called asymmetry value is obtained from the Etessam and Sawyer relationship by introducing a factor of 0.75: a.v. = 311
M M
+ 95
- 205 - 0.75 m.p.
(1-5)
The asymmetry value indicates the melting point decrease due to iso-alkanes as compared to the equimolecular n-alkane. For n-alkanes, both the ring value and the asymmetry value are zero. For isoalkanes the ring value differs only slightly from zero, its maximum value can reach 5, while for cycloalkanes the ring value can be as high as 100. In the simultaneous presence of iso-alkanes and cycloalkanes, the ring value will have inter-
27
(B) CHEMICAL PROPERTIES OF LiQUID PARAFFINS AND PARAFFIN WAXES
mediate values, depending on the number and nature of branchings. To decide for mixed paraffin waxes whether they are composed mainly of iso-alkanes or cycloalkanes, it is necessary to know both the ring value and the asymmetry value. In such cases the so-called sum value (s.v.) yields the answer, its value for n-alkanes being zero: S.V. =
r.v.
+ a.v. = lo3
*
d: - 716 - 0.75 m.p.
(1-6)
According to Spengler and Jantzen the relationship between refractive index and melting point permits calculations on the iso-alkane, cycloalkane and alkylsubstituted aromatics content in paraffin waxes. For n-alkanes, this relationship has the form: 70 nD = 4.2 * m.p. 1.4076 (1-7)
+
where n: is the refractive index at 70 "C. Similar relationships are valid for iso- and cycloalkanes and alkyl-substituted aromatics. However, the straight lines representing the latter rekdtionships intersect the substantially steeper straight line for n-alkanes. The point of intersection is not known exactly, but is around the melting point values of 125 to 130°C 70 and nD = 1.4580. Such a refractive index versus melting point diagram is shown in Fig. 1-4. If the measured values of some paraffin wax or of one of its fractions are placed into this diagram, certain conclusions can be made regarding its composition.
Melting point, 'C Fig. 1-4. Relationship between the refraction index and melting point of hydrocarbons
28
I. PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
Hersch and Fenske found that the naphthenic ring content of aromatics-free paraffin waxes or their fractions can be determined using the Watterman n-d-M ring analysis modified by them. Their methods are as follows:
- the average number of naphthenic rings per molecule is
RN = 0.284 [(n: - 1.4750)M + 8.79]0*8';
(1-8)
- the number of carbon atoms combined in naphthenic rings is
CN = 2.08 [(n: - 1.4750)M + 8.79]0*73;
(1-9)
- the percentage of naphthenic rings is N = - 2890 [(n: M
-
1.4750)M + 8.79]0-73,
(1-10)
where n z is the refractive index at 20 "C. ( c ) Analytical methods for the determination of individual hydrocarbons or of compositions of their mixtures The methods discussed in the previous paragraphs are suitable to give an overall approach to the chemical composition of macro- and microcrystalline paraffin waxes. This is satisfactory in many cases for manufacturing and application purposes. If, however, individual hydrocarbons must be determined, gas chromatography, mass spectrometry and infrared spectrometry method have to be used. High-temperature gas chromatography and mass spectrometry methods suitable for the analysis of paraffin waxes have been frequently discussed in the recent literature. For the gas chromatography of macrocrystalline paraffin waxes, temperatures between 250 and 350 "Care used. The paraffin wax is retained by stationary liquid phase and individual components are stripped from the column, according to their volatility, using hydrogen or helium as carrier gas. The fractions eluted are recorded with thermal conductivity or flame ionization detectors. Different selective liquid stationary phases are in use, e.g. silicone oils, distillation methyl silicone fluid, carborane (methyl silicone fluid) etc. Gas chromatographic analysis of paraffin waxes will not be discussed in detail here. It will only be mentioned that apparatus and techniques exist that allow the determination of individual hydrocarbons up to CS5. The results of Levy and co-workers are particularly worth mentioning. They combined high-temperature gas chromatography and mass spectrometry methods, and achieved qualitative and quantitative determination of 67 individual components in a refined macrocrystalline paraffin wax. It is, in general, effective to use a suitable form of gas chromatography for separation, and mass spectrometry for subsequent identification.
(B) CHEMICAL PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
29
There are many reports on infrared spectrometric studies of paraffin waxes. However, no generally accepted analytical method has yet been established for the determination of other than normal hydrocarbons. In the IR spectrometry of paraffin waxes, absorption bands are, in general, within the 600 to 3530 cm-' range. Such analyses were successful in differentiating and detecting primary, secondary and tertiary carbon atoms. The presence of iso-alkanes and cycloalkanes in paraffin waxes forming urea adducts could qualitatively be confirmed. Using IR spectroscopy, some authors succeeded in determining the extent of branching, whilst others determined the numbers of methyl and methylene groups. In addition to these instrumental analytical methods, various chemical analytical procedures were developed for identifying or determining a given group of compounds. The antimony pentachloride method shall be mentioned as an example. This is based on the finding that n-alkanes, in carbon tetrachloride solution, do not react with antimony pentachloride, whereas iso-alkanes form an insoluble, pitch-like substance. Thus, the n-alkane content in macro- and microcrystalline paraffin waxes can be determined. 2. Chemical composition of liquid paraffins and parnffin waxes Liquid paraffins have a relatively simple chemical composition, as they consist almost entirely of n-alkanes. The products manufactured by different companies for different purposes show only slight variations in the molecular weight range. On the other hand, the chemical composition of macrocrystalline and microcrystalline paraffin waxes varies over an almost infinite range of combinations, varying according to the source of the crude petroleum and to processing technology. To characterize the chemical composition of paraffin waxes, let us first summarize the general ideas, and subsequently present the composition of some paraffin waxes from different sources. As demonstrated by spectroscopic studies, paraffin waxes consist mainly of saturated hydrocarbons. The number of aromatic ring compounds, particularly in the case of macrocrystalline paraffin waxes consisting of compounds of lower molecular weight, is so small that they have practically no effect on the properties of the waxes. In fact, the majority of these rings are present as alkylbenzene derivatives and in condensed forms, and hence detrimental to health. In studying the composition of liquid paraffins let us consider the work of Mikhaylov and co-workers who studied the composition of a liquid paraffin obtained by urea dewaxing of a Diesel fuel from a high sulfur-content crude, and subsequent refining by adsorption. This liquid paraffin contained 0.2 wt- % aromatics, the amount of hydrocarbons forming no adducts with urea was relatively small. Table 1-8 lists the most important properties of the liquid paraffin, and the products obtained by twice repeated treatment with urea. As may be seen, the fractions forming no adducts with urea become enriched in iso-, cyclo-
30
I. PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
Table 1-8. Chemical composition and physical properties of liquid paraffin, of its urea-adduct forming parts and parts forming no adduct with urea I
1
Product
First urea treatment 1 Starting material 2 Adduct-forming compounds 3 Compounds forming no adduct
Total : Second urea treatment 4 Adduct-forming compounds 5 Compounds forming no adduct Total:
1
1
Hydrocarbon content, wt- % relative to starting material Yield, %
n-alkanes
phenylalkanes
Properties
-__
iso-alkanes and cYclOalkanes
~~~~i~~ dl0
1
i
___
Refr. index Melting point
"C
100.0
96.4
0.2
3.4
0.8043
1.4370
24.5
95.0
92.5
traces
2.5
0.8054
1.4370
27.0
5.0
3.7
0.21
1.07
-
-
-
-
-
100.0
96.2
0.21
3.57
2.45
2.18
0.027
0.243
0.7743
1.4350
2.55
1.55 3.73
0.165 0.192
0.837 1.080
0.7922
1.4385
-
-
5.0
Table 1-9. Composition of the liquid paraffin in Table 1-8 Hydrocarbons
Identified n-Alkanes Iso-alkanes 2- and 4-methylalkanes 3-methylalkanes 5-methylalkanes 6-methylalkanes Cycloalkanes 1-cyclopentylalkanes 1-cyclohexylalkanes Phenylalkanes 2-phenylalkanes Total identified :
I
Carbon atom range
1
Share, wt-%
I
Number of compounds
C11-Cz4
96.400
14
C,,-Czo
1.168 0.484 0.126 0.061
12 6 6 4
C,,-C1*
0.132 0.299
6 6
c,,-czo
0.047 98.717
6 60
1.283
-
cI7-czo
C11-C24
Non-identified Iso-alkanes
Cycloalkanes Phenylalkanes Total non-identified:
-
9.0 7.2
-
31
(B) CHEMICAL PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
and phenylalkanes. The total hydrocarbon composition of the liquid paraffin is listed in Table 1-9, showing that 60 compounds could be identified, among these 14 different n-alkanes, 28 iso-alkanes, 12 cycloalkanes and 6 phenylalkanes. The amount of non-identified hydrocarbons did not exceed 1.3 %. The authors also stated that the iso-alkanes contained in the fraction forming no adduct with urea are monosubstituted methylalkanes, with the methyl group attached to one of the C, to C, carbon atoms. The cycloalkanes contained in the fraction are rings of five or six carbon atoms, with straight-chain alkyl groups attached. In the phenylalkanes present, the benzene ring is attached to the second carbon atom of the alkane. Paraffin waxes consisting of C,&30 hydrocarbons are mainly composed of n-alkanes. Compounds containing rings, or branched at the end of the chain, are also present, but in small amounts and especially in the higher fractions. In microcrystalline paraffin waxes consisting of >C3,C3, hydrocarbons, obtained from fractions distilling over at higher temperatures or from vacuum distillation residues, the other than normal character dominates. Hydrocarbons other than normal cover the total carbon atom number range from C30 to Cs0. n-Alkanes in microcrystalline paraffin waxes are also mainly within this range. In addition to n-alkanes and iso-alkanes, macrocrystalline and microcrystalline paraffin waxes contain naphthenes, especially alkyl-substituted derivatives of cyclopentane and cyclohexane. Depending on the source of the crude and on the extent of refining, larger or lesser amounts of cyclic sulfur and nitrogen compounds are also present. The decisive factors determining the properties of low oil-content paraffin waxes are hence the distribution, by carbon atom number, of n-, iso- and cycloalkanes and their relative quantities. This appears quite evident, knowing that substantial differences exist between the properties of isomeric n- and iso-alkanes. As an example, Table 1-10 (based on data by Mazee) records the physical properties of two n-alkanes and their iso-alkane isomers, both within the carbon atom number range of macrocrystalline paraffin waxes. To characterize the chemical composition of paraffin waxes some characteristic values for three microcrystalline paraffin waxes from different sources will first be presented, based on data from Ridenour, Spilners and Templin. These values Table I-10. Physical properties of two n-alkanes and their branched isomers in the range of macrocrystalline paraffin waxes Alkane
n-Tetracosane 2-Methyltricosane 2,2-Dimethyl-n-docosane n-Octacosane 10-Nonylnonadecane
1 1 Formula
CZaH,o CZ4H,, CllHSO CzsH,, CzsH,,
Boiling point at 0.5.F
Melting point; "C
1 1 Density
di0
208.6 205.0 201.5 242.0 228.3
50.7 37.6 34.8 61.3 -5.5
0.7562 0.7539 0.7536 0.7639 0.7650
1.4205 1.4201 1.4191 1.4248 1.4247
2.42 2.48 2.71 3.40 2.68
32
I. PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
Table I-11. Main characteristics of microcrystalline paraffin waxes from different sources Wax identification mark
Characteristics
Melting point, OC Refractive index, &' Density at 70 "C Average molecular weight Ring analysis (n-d-M) RA
RN Oil content, wt- %
76.0 1.4514 0.8122 629
74.1 1A 8 3 0.8065 574
62.5 1.4547 0.8184 682
0.20 0.60 8.2
0.12 0.48 4.5
0.20 0.90 0.8
are summarized in Table 1-11. Sample A is a typical microcrystalline paraffin wax, sample B a hard, brittle product, sample C a highly flexible, ductile microcrystalline wax with high adhesive power. Portions isolated from these samples by adduct formation with urea, and fractions obtained from these portions by molecular distillation are characterized in Tables 1-12-1-14. The symbols used are: RT = = total ring content per molecule, R, = aromatic ring content per molecule, R, = naphthenic ring content per molecule. In the first eight distillation fractions of the adduct-forming portion of sample A , the total ring content determined by the n-d-M method is less than 0.2 rings/molecule. The value of R N in distillation fraction 9 is 0.4, in the distillation residue 0.8. According to infrared absorption
No. of fraction
Adduct-forming part 1 2
3 4 5 6 7 8 9
Distillation residue
wt-%
M.p.
"C
Refr. ind.
,,g
Aver. Dens. at 70°C
b:
100 10.5 9.0 11.8 11.8 10.2 9.5 10.0 8.0 10.2
79.0 68.9 71.6 72.8 75.8 77.0 78.6 80.9 83.4 87.4
1.4422 0.7919 1.4374 1.4388 1.4390 1.4408 1.4408 1.4413 1.4426 1.4438 1.4458 0.8028
548 447 486 489 510 537 550 572 590 662
9.0
93.6
1.4531 0.8165
910
Ring analysis (n-d-M)
__ RT
I 1 RA
RN
0.0 -
0.0 -
Corresponding n-alkane
1 vz
~;a:
c,
-
C,, C,, C,, C,, C,,
c,
0.4
0.0
0.4
C.1 C,, C,,
79.4 69.3 72.7 74.0 75.6 78.1 79.5 82.9 82.9 87.5
0.9
0.1
0.8
C,,
98.1
0.0
-
-
-
-
-
-
33
(B) CHEMICAL PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
Table 1-13. Characteristics of the fractions obtained by molecular distillation from the adduct-forming part of the microcrystalline paraffin wax marked B in Table 1-11 n-alkane No. of fraction
Adduct-forming part 1 2 3 4 5 6 7 8 9
Distillation residue
No. of fraction
Adduct-forming part 1 2 3 4 5 6 7 8 9
Distillation residue
100 10.1 10.4 10.6 10.5 10.0 10.0 9.1 8.6 11.4
76.0 67.0 69.4 71.2 73.8 76.0 77.6 79.4 80.5 82.2
1.4410 1.4356 1.4368 1.4377 1.4390 1.4399 1A 0 8 1.441 8 1.4425 1.4439
9.3
85.0
1.4488
Yield wt-%
M.P.
"C
526 439 464 475 509 518 536 557 565 594 0.8066
684
CS7 C,, C33 Cs C,,
76.8 67.2 70.8 72.7 75.6 (2.37 76.8 Ca8 78.1 Cd0 80.7 Cl0 80.7 Cd2 82.9 0.4
0.05
Ring analysis (n-d-M)
Refr. ind.
Dens. at
Aver.
% '"
7O"C
Wt.
0.7882 0.7797
0.1 0.3
0.0 0.0
0.3
1.0
0.0
1.0
mol.
100 9.6 11.0 10.4 9.9 11.5 11.7 8.5 9.0 8.9
67.0 62.0 66.2 67.2 68.3 69.6 71.4 72.4 74.2 76.0
1.4400 1.4340 1.4363 1.4371 1.4377 1.4387 1.4402 1.4419 1.4435 1A450
0.7959 0.7994
478 407 436 455 458 471 492 520 543 575
9.5
82.0
1.4529
0.8167
743
-
-
-
__ RT
0.0 0.0
-
I 1 Rk
0.0 0.0
-
-
-
C,
0.35
C
89.0
o
~
1
RN
; !? 72.7 62.3 67.2 69.0 70.8 72.7 74.0 76.8 79.5 81.9
0.0 0.0 -
-
0.1
Cs,
91.7
measurements this consists of monocyclic alkanes and their substituted derivatives. The adduct-formingportion of sample B, and its fractions have a similar composition, the differences showing only in the range of molecular weights and in the total ring content of distillation fraction 9 and of the residue. Fractions from sample C have lower melting points and higher refractive indices than fractions from samples A and B with identical molecular weights. This indicates that 3
-
~
34
1. PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
sample C contains a higher percentage of iso-alkanes. However, the slight differences in the melting points demonstrate that these iso-alkanes are branched to a small extent only. The characteristics of the portions of the three samples forming no adduct with urea, as well as of their distillation fractions, are listed in Tables 1-15-1-17. It may be observed that the portion of sample C forming no adduct has a substantially higher average molecular weight, a broader molecular weight range, a lower average melting point and a narrower melting point range than those of the other two samples. This difference is in conformity with its composition: sample C and its portion forming no adduct contains more branched alkanes and the share of aromatic and naphthenic rings is higher than in sample A and B. The ring Table 1-15 Characteristics of the fractions obtained by molecular distillation from the part forming no adduct of the microcrystalline paraffin wax marked A in Table 1-1 1
Part forming no adduct 1 2 3 4 5
6 7 8
100 8.75 9.75 9.75 9.55
10.45 9.85 10.7 10.4
Distillation residue 20.8
63.0-65.0 51.0 57.0 61.0 66.0 66.0 69.0 71.0 72.0
1.4592 1.4580 1.4566 1.4556 1.4559 1.4567 1.4578 1.4595 1.4644
0.8305 0.8291 0.8244 0.8243 0.8239 0.8246 0.8264 0.8310 0.8338
706 490 535 579 623 661 758 783 910
1.9 1.8 1.5 1.6 1.6 1.5 1.6 1.9 1.7
0.15 0.2 0.2
0.6
1.75 1.6 1.3 1.55 1.5 1.35 1.45 1.75 1.1
68.0
1.4677
0.8440
1340
3.0
0.6
2.4
0.05
0.1 0.15 0.15
0.15
Table 1-16. Characteristics of the fractions obtained by molecular distillation from the part forming no adduct of the microcrystalline paraffin wax marked B in Table 1-11
Part forming no adduct 1
6 7
10.1 10.4 10.0 10.1 10.5 9.2 11.9
63.0-63.3 55.6 58.6 60.6 62.7 64.3 65.3 66.0
1.4617 1.4596 1.4559 1.4559 1.4562 1.4573 1.4583 1.4606
0.8325 0.8304 0.8217 0.8217 0.8220 0.8245 0.8255 0.8306
686 500 540 561 602 643 653 712
1.8 1.8 1.3 1.3 1.3 1.4 1.4 1.7
0.25 0.30 0.30 0.35 0.35
1.4 1.55 1.05 1.05 1.00 1.10 1.05 1.35
Distillation residue
27.8
65.6
1.4695
0.8434
930
2.2
0.8
1.4
.
L
3 4 5
100
0.4 0.25 0.25
35
(B) CHEMICAL PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
Table Z-17.Characteristics of the fractions obtained by molecular distillation from the part forming no adduct of the microcrystallineparaffin wax marked C in Table 1-11 No. of fraction
Part forming no adduct 1 2 3 4 5 6 7
Distillation residue
Refr. ind. n&O
Dens. at 70 "C
Aver.
Ring analysis RT
I
RA
I N'
100 13.7 9.3 9.8 9.7 9.5 9.6 14.2
56.0 56.6 56.9 56.6 55.6 55.0 51.0
1.4598 1.4466 1.4481 1.4509 1.4536 1A563 1.4598 1.4644
0.8256 0.8030 0.8087 0.8130 0.8188 0.8232 0.8297 0.8390
773 503 544 603 656 750 839 967
1.2 0.6 0.9 1.0 1.2 1.4 1.7 2.4
0.4 0.1 0.0 0.0 0.0 0.1 0.2 0.4
0.8 0.5 0.9 1.0 1.2 1.3 1.5 2.0
24.2
45.0
1.4727
0.8529
1700
4.0
0.9
3.1
55.0
compounds in sample C are concentrated to a higher extent in the higher molecular weight fractions than is the case with samples A and B. The cited authors achieved further separation by thermodiffusion of the distillation fractions obtained from the part of sample A that forms no adduct. As a result of subsequent analyses, they succeeded in determining the chemical composition of this part of the sample. They found that it consists of about 17 wt-% monocyclopentylalkanes, 24 wt- % monocyclohexylalkanes, 6 wt- % dicyclopentylalkanes, 20 wt- % dicyclohexylalkanes, 6 wt- % monocyclic aromatics, 5 wt- % polycyclic aromatics and 22 wt- % polycyclic alkanes. The distribution among these compound types is shown in Fig. 1-5, where, on the one hand, dicyclopentyl-
Distillation yield, wt-%
Fig. 1-5. Distribution of compounds in the part forming no adduct of the microcrystalline
paraffin wax marked A
3+
36
I. PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
and dicyclohexylalkanes, and on the other, aromatics and polycycloalkanes are combined into one group each. Bornemann and Heinze used the combined analytical procedure shown in Fig. 1-6 for characterizing the composition of microcrystalline paraffin waxes. Their starting material was slack wax. In the first stage they prepared - by fractional crystallization - vaseline, plastic and hard microcrystalline paraffin wax (these terms correspond to the classification of Kreuder). The hard paraffin wax was then separated into several fractions by chromatography on columns filled with silica gel. The iso-octane eluates were separated into portions forming adducts and forming no adducts, and these were subsequently subjected to further separation by fractional crystallization from dichloroethane, by chromatography on activated carbon and silica gel, and by molecular distillation. The results that the cited authors obtained with petrolatum from the heavy distillate of Romashkino crude are presented in the following tables. Table 1-18 Table Z-18. Main characteristics of products obtained by fractional crystallization of a petrolatum from the heavy distillate of a Romashkino crude Characteristics
Yield, wt-% Refractive index, ng Density at 90 OC Average molecular weight Melting point, *C Viscosity at 90 O C , mmZ/s Penetration at 25 OC, 0.1 mm Oil content, wt- % Part forming adduct with urea, wt-
%
Part forming no adduct, wt- %
Starting
1.4497 0.8102 450 63.6 16.7 40 (cone) 25.5 27.4 72.6
69.7 1.4546 0.8193 422 40.9 18.1 120 (cone)
-
-
20.7 1A430 0.7977 535 63.4 14.0 27 6.5 48.5 51.5
9.6 1.4393 0.7866 550 77.9 14.4 9 1.7 84.5 15.5
shows the main characteristics of the products obtained by fractional crystallization from the petrolatum. The hard paraffin wax fraction was separated by chromatography on 0.1-0.4 mm silica gel activated at 180 "C.The fractions obtained in this operation are shown in Table 1-19. The iso-octane eluates separated into adduct-forming and non-adduct-forming portions were further separated by fractional crystallization, by molecular distillation at 200-265 "C in a vacuum of 1 cPa, and by chromatography. The narrow fractions obtained by these procedures were analysed by determining the usual physical characteristics (refractive index, density, melting point, etc.), the Hersch-Fenske data and the n, versus b.p. diagram shown in Fig. 1-7. Their experimental results can be summarized as follows. The hard paraffin wax studied consists of C,,-C,, compounds. The n-alkane content represents 25 to 35 %, the majority of these being C,&, compounds. The share of iso-alkanes
Slack wax from heavy distillate I
Fractional !istillation
EIzI
crl
a
Plastic paraffin wax
Vase1ine
Hard paraffin wax
Resins Iso-octane eluate
Iso-octane eluate
Iso-octane eluate
I
I1
III
f
Iso-octane eluate IV
Benzene eiuate
8
, I
distillation
carbon
I I I Chromatographic separation I
carbon
I
carbon
I
I
I
I
carbon
Chromatographic separation on active carbon w
4
Fig. 1-6.Group analysis of microcrystalline paraffin waxes according to Bornemann and H e i m
38
I. PROPERTIES OF LIQUID PARAFFlNS AND PARAFFIN WAXES
Table 1-19. Characteristics of fractions obtained by chromatography on silica gel of the hard microcrystalline paraffin wax (source: Romashkino crude) figuring in Table 1-18
1-
characteristics
Refractive index, :n Density at 90 OC Average molecular weight Melting point, OC Viscosity at 90 OC, mm2/s Penetration at 25 OC, 0.1 mm Oil content, wt- % Part forming a n adduct with urea, wt-% Part forming no adduct, wt- %
___Eluates _ _with. iso-octane~-_ _ _ _Eluate with
__
I
1
111
I I1 _________-___
1.4372 0.7854 620 78.4 12.9 9 0.4
1.4381 0.7868 550 77.4 13.3 9 0.7
87.8 12.2
85.3 14.7
~
1.4402 0.7901 565 77.0 14.4 9 1.2 81.5 18.5
IV
benzene
1.4478 0.8032 610 75.8 16.9 10 2.7
1.4750 0.8553 610 71.2
74.7 25.3
-
15 12.4 -
-
and naphthenes is 55 to 65 wt-%, around 10 wt-% of which are C45-C55 alkyldicycloalkanes and alkyltricycloalkanes. The C35-C50 compounds are iso-alkanes, alkylcyclopentanes and alkylcyclohexanes. Aromatics represent about 1 wt- %, resinous substances around 1.5 wt- %.
0
1.4600
lC200
I 0
7
/ ' 20
"
40
Boiling point,
60
80
"C (1 cPa)
Fig. 1-7. Part of the diagram of refractive index versus boiling point. A hard paraffin wax, B I-IV iso-octane eluates, C adduct-forming part of iso-octane eluate I, D part of iso-octane eluate I forming no adduct
The authors of this book studied how and to what extent the chemical composition of macrocrystalline and microcrystalline paraffin waxes from Romashkino crude is changed by the effect of de-oiling and subsequent refining by the hot
39
(B) CHEMICAL PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
Table 1-20. Characteristics of slack wax and petrolatums from Romashkino crude Characteristics
Macrocrystalline slack wax from light distillate
Microcrystalline petrolatum from heavy distillate
Microcrystalline. petrolatum from residual oil
0.7683 2.75 48.5 27 8+ 1 7.8 1.4269 319 0.19
0.8357 9.91 57.9 146 8 21 42.8 1.4604 480 0.89
0.8264 12.43 65.5 112 4.5+ 6 23.7 1.4551 583 0.65
Density at 80 OC Viscosity at 100 'c,mmZ/s Melting point, OC Penetration at 25 OC, 0.1 mm Colour index ASTM (1/4") Extinction (Pulfrich filter 8, 100 mm) Oil content, wt- % Refractive index &' Molecular weight Sulfur content, wt- % Aromatics, wt- % monocyclic bicyclic tricyclic
13.1 15.1 1.8
20.0 6.0 3.9
1.3 1 .o 0.7
contact method. The main characteristics of the materials investigated are shown in Table 1-20. De-oiling was carried out at + 10 and +30 "C with methyl ethyl ketone, hot contact treatment with 196 m2/g specific surface area activated clay of the bentonite type. The characteristics of the de-oiled products are listed in Table 1-21. Those in Table 1-22 are of products refined by hot contact under Table 1-21. Characteristics of the slack wax and petrolatums figuring in Table 1-20 after deoiling Macrop
Characteristics
Temperature of de-oiling, O C Yield relative to starting material, wt- % Density at 80 "C Melting point, "C Penetration at 25 OC, 0.1 mm Colour index ASTM (1/4") Extinction (Pulfrich filter 8, 10 mm) Oil content, wt- % Refractive index, n? Molecular weight Sulfur content, wt- % Aromatics, wt- % monocyclic bicyclic tricyclic
Microcrystalline paraffin ~ wax from~ heavy distillate
~
from paraffinic distillate
10
~
A
10
I
B
30
13.0 17.9 37.5 0.7884 0.7635 0.7930 51.9 73.1 66.8 19 15 28 1 8+ 8+ 0.85 1.03 14.2 5.7 0.7 5.1 1.4236 1.4360 1.4360 540 341 517 0.03 0.21 0.10 0.3 0.1 0.1
9.8 4.9 0.5
4.8 1.3 0.2
Microcrystalline paraffin wax from ~ ~ residual oil
_~_______ A
10
J
B
30
21.5 52.9 0.8065 0.7955 78.0 70.5 9 33 5.5+ 5+ 5.0 6.2 1 .o 6.7 1.4391 1.4442 636 694 0.17 0.36 13.7 2.0 1.3
7.0 0.7 0.6
~
40
I. PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
Table 1-22. Characteristics of the macro- and microcrystalline products figuring in Table 1-21 after hot contact refining
Characteristics
Macrocrystalline paraffin wax from light uaraf-
Microcrystalline paraffin wax from heavy distillate
Microcrystalline paraffin wax from residual oil
- - _ _ _ ~ _ _ _ _ _ . _ _
Density at 80 OC Melting point, OC Penetration at 25 OC, 0.1 mm Colour index ASTM (1/4") Extinction (Pulfrich filter 8, 10 mm) Oil content, wt- % Refractive index, ng Molecular weight Sulfur content, wt- % Aromatics, wt- % monocyclic bicyclic tricyclic
0.7900 0.7566 0.7846 0.8038 0.7892 51.9 66.8 73.1 70.5 78 15 33 9 19 28 1 0 1 1.5+ 0.20 0.36 0.00 0.16 0.17 0.7 5.7 5 .O 7.0 1 .o 1.4219 1.4418 1.4403 1.4488 1.4450 540 636 694 517 341 0.36 0.13 0.03 0.10 0.19 0.2 0.1 0.1
8 .O 4.6 0.3
4.0 0.6 0.2
13.3 0.2 0.2
4.4 0.4 0.1
optimum conditions. It may be seen that the aromatics content of all three products is reduced by one order of magnitude as a result of de-oiling, demonstrating that the aromatics and sulfur compounds are contained chiefly in the oily portion, as determined according to ASTM. Hot contact treatment mainly reduces the amount of bicyclic and tricyclic aromatic compounds. The starting materials, the de-oiled products and the products refined by hot contact were separated by chromatography on 0.10-0.18 nim silica gel, the weight ratio of adsorbent to sample being 20 : 1 and temperature 60 "C. Eluents applied successively were aromatics-free gasoline, a mixture of benzene and gasoline, benzene, and a mixture of methanol and chloroform. The mono-, di- and tricyclic aromatics content of the fractions was determined with a H-700 Hilger spectrometer. The distribution (in percentage) of carbon atoms in paraffinic and naphthenic bonds, and the number of methyl and methylene groups per molecule was determined by IR spectrometry. Figure 1-8 shows the refractive index at 80 "C plotted against the chromatographic yield for the petrolatum obtained from the residual oil, for the de-oiled and for the hot-contact purified products. It may be observed that, as was to be expected, both de-oiling and refining by hot-contact result in an increased n-alkane content. The vertical dash lines in the figure indicate the yields corresponding to the refractive index value of 1.4500. Before de-oiling, this yield is only 46 wt-%. After de-oiling at + 10 "C, the yield is 77 wt- %, after de-oiling at +30 "C, it increases to 94 %. By further refining, the 77 wt- % value is increased to 86 wt- %, the 94 wt- % yield to 96 wt- %. The distribution of n-alkanes, sulfur content and aromatics content versus chromatographic yield in the slack wax from light distillate and in the products
(B) CHEMICAL PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
41
1.51 I 1.50 1.49 1.48 1.47 1.46 1.45 I ,
I
,
I
1.441 I I I I 0 10 20 30 40 50 60 70 80 90 1 0 1.49 I
1
1.47
-
1.46 1.45 1.49 I
1
X
De-oiled at t10 O C and refined by hot contact
C
a,
cc
1
-
440
10 20 30 40 50 60 70 80 90 100
t
1.46 1.45
1'440 1 /.O
10 20 30 40 50 60 70 80 90 100
refined by hot contact
1.46 1.45 1'440
10 20 30 40 50 60 70 80 90 100 Yield, w t - %
Fig. 1-8. Refractive indices of chromatographicalfractions of paraffin waxes from residual oil
42
I. PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
-
'0
20
40 60 60 Yield, w t - %
100
100
"1
De-orled at +10 "C 3 60~a-
I
0
-
-3
p c
-
s I
,+ r
s
e-oiled at +10T and
I c
3
' - 2
40-
20-
Y
9
4
3
3
-1
2 U I
I
C
20
0 Yield, w t - %
40 60 80 Yield, wt- %
100
Fig. I-9. Distribution of n-alkanes and sulfur in macrocrystalline paraffin waxes
---
monocyclic aromatics bicyclic aromatics
-.---
tricyclic aromatics
a Yield, w t - %
60
1 De-oiled at +10 "C and refined by hot contact
LO
2ol 1 10
0
70
Yield, w t - %
,
,
80 90 Yield, w t - %
100
Fig. I-IO. Distribution of aromatic compounds in macrocrystalline para& waxes
43
(B) CHEMICAL PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
obtained from this material is shown in Figs 1-9 and 1-10. Similar plots for the microcrystalline paraffin wax from heavy distillates and residual oil are presented in Figs 1-1 1-1-14. The data indicate that the fractions from 0 to 80 wt- % of the macrocrystalline slack wax contain 98 to 75 wt- % n-alkanes, while the corresponding data for petrolatum from heavy distillate are 40 to 55 wt-%, and the n-alkane content of the petrolatum obtained from residual oil in the fractions up to 50 wt- % is as low as 62 to 30 wt-%. 90 I
I
4 3
100
_i 0
-t
10 Yield, w t - %
1001
I
90 De-oiled at t10 "C 80
P
4 -14
80
L-
I I I
:2010
I
[ -22 2 A -11
I
I
-
0 ' 0
I )
20
'
!
!
60 80 Vield, wt-"lo
40
'
100
0
. 70
< 3 60-I
3
I
De-olied ot +30 "C
..
-
< 0 C
50
LO-
30-
I I
20 10 - OO
-1
I I
I
' 804& 0 Yield, wt-
VO
100I
I
-De-oiled at +30 "C and 80 - refined by hot contact
70 60 '50A0 30 20 10 -
'0
20
40
60
80
-
*------
-4
z?
0
- s 3 .!3
I
-2 c 3
I I
-1
1I I
' L
3
Ln
100 Yleld, wt- 'fa
Yield, wt-'lo
Fig. I - I I . Distribution of n-alkanes and sulfur in microcrystalline paraffin waxes from heavy
distillates
44
1. PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
De-oiling, and, to a lesser extent also refining, lead to an increase in the percentage of n-alkane content in the case of all three starting materials. As to the distribution of aromatic compounds, these are present, in the case of macrocrystalline products, only in the last chromatographic fractions, in the final 7-10 wt-% of the substance, whereas in microcrystalline products, aromatics appear even at a yield of 40 wt- %. De-oiling and refining by hot contact significantly increase this limit. Similar relationships are found in the distribution of sulfur compounds. The sulfur content is maximum in all cases in the fractions where the content in diand tricyclic aromatics is maximum. The sulfur atoms are consequently sited mainly in aromatic compounds. In the following, the chemical composition of some paraffin waxes determined by mass spectrometry is presented, based on data by Edwards. These substances represent the total range of macrocrystalline waxes, and include paraffin waxes 80 70 $ c 60 3 50 6 40 U 30 E 20 10
-monocyclic aromatics ---
bicyclic aromatics
-.-.-
tricyclic aromatics
$
$0
50
60 70 80 Yield, wt-%
90
100
7
60-De-orled 50-
at + 3 0 T
w- 40-
2
30209 10Q.
g
Yield, wt-%
Yield, w t- %
70
?
70
6OCDe-oiled at +10 O C and
60-De-oiled at +30 "C and 7 50refined bg hot contact w-
4030-
:
20-
2 10Q. Yield, w t - %
Fig. 1-12. Distribution 9f aromatic compounds in microcrystalline paraffin waxes from heavy
distillates
45
(B) CHEMICAL PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
whose compositions may be regarded as typical cases. The main characteristics and analytical data of the six paraffin waxes studied are contained in Table 1-23. Figure 1-15 shows the distribution of n- and iso-alkanes relative to the number of carbon atoms. These data also confirm the significant differences in the chemical composition of paraffin waxes depending on their source and manufacturing conditions. The samples investigated consist mainly of n-alkanes ;however, in samples A and F the iso-alkane content is rather high. The distributions demonstrate that hydrocarbons other than normal are concentrated in the higher molecular weight 4
80 70 - Starting material
-3s
* r -2
5-
c J
=
-1
v,
100 Yield, wt-"lo
90 80
De-oiled at +lo "C
4
s
70 -
90 I 80 De-oiled at +30 "C 70
I
t
c
3 50
3
aC
-0 Y
30 20 10 -
7C Yield, w t
--
-
'0 10
at +I0 "C and
70- refined by hot contact
6050 -
-
*----
30
50
70
90
Yield, wt-"lo
"10
sn BoI-De-oiled
20 10
44
s
90 t 80 - De-oiled at +30 "C and 7 0 - refined bg hot contact
I
r a-
s 4030 --
40 -
30 -
Y
7C 20 -
20 10 -
10 -
- OO Yield, wt-"lo
Yield, wt-"10
Fig. I-13. Distribution of n-alkanes and sulfur in microcrystalline paraffin waxes from residual
oils
46
I. PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
1001
n
1
-monocyclic aromatics --- bicyclic aromatics ----- tricyclic aromatics
s
.3 I
m-
u .c
0
E
2
Q
Yield, w t - %
80 4?
80 I
70 - De-oiled at +10 "C
I
I
I
De-oiled at +30
"c
I
3 m-
.-V
a ..
0
30
I
E 20
0,
a
'40
50
60
70
80
$0
Yield, wt-"lo
70 I 6 0 - De-oiled
1
at +10 "C and I c 50- refined b y hot contact 3 40 mu .- 30 -
P
50
60 70 80 Yield, w t - %
70 S 60-De-oiled at +30 "C and 50- refined by hot contact
90
100 I
'3
c
0
E 20 2 .I0 -
4
0
I
Yield, wt-%
Yield, wt-"lo
Fig. 1-14. Distribution of aromatic compounds in microcrystalline paraffin waxes from
residual oils
fractions. Disregarding sample A , the share of hydrocarbons other than normal increases with the melting point of the paraffin wax. Sample A was obtained by blending high and low melting-point paraffin waxes, and hence this sample cannot be directly compared with the others. The above samples were further separated by fractional distillation, and the composition of the fractions were also determined by mass spectrometry. Table 1-24 lists the results of these analyses. Fractions from wax B were not examined since the non-normal hydrocarbon content of this wax was low and the distribution appeared to be of less interest. Figures I-16,1-17 and 1-18 present the dis-
47
(B) CHEMICAL PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
Table I-23. Main characteristics and chemical composition determined by mass spectrometry of various paraffin waxes Characteristics and composition
Melting point, "C Oil content (ASTM), wt- %
n-Alkanes, wt- % Branched alkanes, wt- % Monocycloalkanes, wt- % Polycycloalkanes, wt- % Monocycloaromatics, wt- % Aromatic cycloalkanes
I
--
i
A
50.7 <0.2 75.5 13.5 10.2 0.6
I
i 57.3
57.5
58.7
62.8
0.3
<0.2
94.0
<0.2 81.9 10.4 0.3
<0.2 82.2 8.2 9.0 0.5
0.5 66.5 17.9
3.4 0.0
86.4 6.3 7.1 0.1
0.0 0.0
traces 0.0
0.0 0.0
0.1 0.0
paraffin wax A
1.9 0.3
traces
l5
s-
10
g
5
Carbon atom number 15
15
Paraffin wax &
10
s-
0'
10
I
I
z0
13.4
7Paraffin wax D
I
Carbon atom number
-
1.4
I Iso-alkanes
I] n-Alkanes I
+
52.9
2.6
0.2 0.0
i
5
1' 5
15
r " 5
20 25 30 35 Carbon atom number Paraffin wax
'15
40
20
25
30
35
40
45
Carbon atom number
15
c1
s
10
8
5
-
Paraffin wax F
I
1' 5
20 25 30 35 Carbon atom number
20 25 30 35 40 Carbon atom number Fig. I-IS. Distribution of n-alkanes and iso-alkanes in various paraffin waxes
40
1' 5
45
48
I. PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
Table I-24. Composition of distillation fractions of the paraffin waxes
listed in Table 1-23, determined by mass spectrometry Parafin wax A Components
I-
n-Alkanes Branched alkanes Monocycloalkanes Polycycloalkanes Monocycloaromatics Aromatic cycloalkanes
40-45 wt-%
'
60-65 wt-%
~
85-90 wt-%
part of heads
95.7 4.2 0.1 0.0 0.0 0.0
82.4 13.9 3.6 0.0 0.1 0.0
52.1 28.6 17.7 13 0.3 0.0
6.5 wt-% residue
37.6 25.9 30.5 4.4 1.4 0.2
Parafin wax C Components
I-
1
20-25 wt-%
60-65 wt-%
1
85-90 wt-%
5.0 wt-% residua
1
85-90 wt-%
5.0 wt- % residue
part of heads
n-Alkanes Branched alkanes Monocycloalkanes Polycycloalkanes Monocycloaroma tics Aromatic cycloalkanes Parafin wax D 20-25 wt-%
Components
n-Alkanes Branched alkanes Monocycloalkanes Polycycloal kanes Monocycloaromatics Aromatic cycloalkanes
60-65 wt-%
part of heads
n-Alkanes Branched alkanes Monocycloalkanes Polycycloalkanes Monocycloaromatics Aromatic cycloalkanes
Components
1
91.4 7.5 11 0.0 0.0 0.0
l-
20-25 wt-%
78.7 16.0
60.6 24.0
14.0 1.4 traces 0.0
5.0
0.3 0.0 0.0
1
60-65 wt-%
I
85-90 wt-%
79.2 13.6 6.5 0.4 0.3 0.0
traces traces
5.0 wt-%
residue
part of heads
94.5 5.5 0.0 0.0 0.0 0.0
37.3 34.0 23.8 4.9
64.4 19.4 14.4 1.5 0.2 0.1
48.1 23.0 24.3 3.7 0.8 0.1
(B) CHEMICAL PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
49
Table I-24 (cont.) Parafin wax F 20-25 wt-%
Components
1
6C65
1
wt-%
85-90 wt-%
part of heads
n-Alkanes Branched alkanes Monocycloalkanes Polycycloalkanes Monocycloaromatics Aromatic cycloalkanes
78.6 14.9 6.5 traces traces 0.0
54.6 26.7 16.5 1.9 0.2 0.1
42.8 32.4 20.5 3.6 0.6 0.1
5.0 wt-% residue
44.6 23.9 24.1 6.1 1.o
0.3
tribution of normal and branched alkanes in different fractions of samples A, D and F. Turner and co-workers also used mass spectrometry to investigate paraffin waxes. The characteristics of their samples are listed in Table 1-25. Sample A
1n-Alkanes
IIso-alkanes
35 30 25 20 15 10
5
1
35
60 %- 65 ' l o head product
$ 30-
.t; 25 2 20+ c 15.-
r
10 -
85 %- 90 '10 head product
10
10 -
50 15
I
20
I
25
30
35
40
45
Carbon atom number
Fig. 1-16. Distribution of n-alkanes and iso-alkanes in the fractions of the paraffin wax
marked A 4
50
I. PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
Table 2-25. Characteristicsand chemical composition of various paraffin waxes Characteristics, composition
I
Melting point, OC Oil content, wt- % n-Alkanes, wt- % Iso-alkanes, wt- % Cycloalkanes, wt- % Alkylbenzenes, wt-
57.8 -
98.1 1.5
0.4
53.4 0.7 86.1 6.3 7.1 0.5
53.2 0.8 76.4 13.4 10.2
51.8 0.1 82.9 7.7 9.4
-
-
53.7 0.4 91.4 5.6 3.0
54.0 0.3 81.4 10.1 8.5
-
54.4 0.3 92.3 3.5 4.0 0.2
-
60.9 0.2 89.2 5.8 5.0
-
51.0 -
25.0 21.0 54.0 -
was a product obtained by repeated crystallization from a commercial paraffin wax de-oiled by sweating. Samples B, D, N and P were usual commercial grades. Samples E, F and H were obtained from slack waxes by laboratory-scale sweating. Sample J was prepared by a combination of various separations and enriching operations. First, a narrow boiling-point range fraction (b.p. 232°C a t 80 Pa) was obtained by vacuum distillation of a blend of commercial paraffin waxes. The cycloalkane content of this fraction was further enriched by thermodiffusion. The sample J was the bottom product of the thermodiffusion column, obtained with a yield of 7 wt-%. The data in the table and mass spectrometry analyses allowed the following conclusions :
0
n-Alkanes
I
Iso-alkanes ._
-
20% - 2 5 "lo head product
head product
10 -
Carbon atom number
Fig. 2-17. Distribution of n-alkanes and iso-alkanes in the fractions of the paraffin wax
marked D
(B) CHEMICAL PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
0 -
25 20 15 10 5
t.
0 5 15
-
d, 10 -C 5 --
$
IIso-alkanes
n-Alkanes
20 % - 25 "lo head product
-. n
I
.-5
51
I
I
r
60 ' l o - 65 '10 head product
~
-
0 15
5 101 " 5 0
10 5Carbon atom number
Fig. 1-18. Distribution of n-alkanes and iso-alkanes in the fractions of the paraffin wax
marked F
(i) In all macrocrystalline paraffin waxes with melting points between 53 and 61 "C,the majority of n-alkane molecules are in the C,, to Gorange. It is interesting to note that in spite of the only 1 "Cdifference between the melting points of samples B and D, on the one hand, and sample N , on the other, the share of this fraction is 68 wt- % for the former two samples, in contrast to 86 wt- % for sample N , while the C,,-C,, n-alkane content in sample N is substantially lower than in samples B and D. (ii) The melting point of sample P is substantially higher than that of samples B, D and N . This is due, as shown by mass spectrometric data, to a share of 26 wt- % of C,l-C,, n-alkanes in sample P,as compared to 3-4 % in the other three samples. Sample P also contains 3 wt-% C,,-C,, n-alkanes, and its iso-alkane components, making up 5.8 wt- %, are >C,, compounds. (iii) Sample A is characterized by the finding that its n-alkane share of 98 wt-% is made up almost entirely of C,,-C,, compounds. This is presumably due to the repeated crystallization. The melting point of 58 "C corresponds to this composition. (iv) The melting points of samples E, F and H obtained by laboratory-scale sweating are also in conformity with the distribution by carbon atom number. (v) The melting point and composition of sample J clearly demonstrates that a relatively high melting point can also be reached, even with a low content of n-alkanes, if the iso-alkane and cycloalkane components present in larger amounts are suitable carbon atom number compounds. 4'
52
I. PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
Different paraffin wax grades are manufactured by de-oiling of slack waxes and petrolates. It is, therefore, of interest to give a short characterization of the composition of slack waxes. This subject was studied in detail by Kajdas et al., among others. Table 1-26 summarizes their results concerning the composition Table 1-26. Composition of three slack waxes Content, wt-% Hydrocarbon group Sample B
[
Sample c
Methods of analysis
I Sample D
+ cycloalkanes
70.7 20.0
33.4 43.5
12.0 48.5
Adduct formation with urea Deduction of n-alkane content from total alkanes
Alkyl-substituted monocyclic aromatics
6.0
16.0
33.5
Column adsorption on silica gel. Eluent: hexane
Alkyl-substituted polycyclic aromatics
2.5
4.0
2.0
Olefins Resins
0.3 0.5
0.6 2.5
1.5 2.5
Column adsorption on silica gel. Eluent : benzene Iodine number Calculated from difference
n-Alkanes Iso-alkanes
~
of three different slack waxes. Sample B was obtained from spindle oil, sample C from lubricating oil, and sample D from residual oil. The slack waxes were separated by a combination of different methods (adduct formation with urea, chromatography, various chemical methods). It may be seen from the data that with increasing average boiling point of the distillate, i.e. average molecular weight of the slack wax, the n-alkane content significantly decreases, while the share of isoand cycloalkanes and alkylated aromatics substantially increases. The composition of a slack wax obtained from a so-called ,,neutral oil 11” fraction of a Polish crude was determined by means of the procedures shown in Fig. 1-19. The results are summarized in Table 1-27. The fractions were analysed by IR spectrometry, NMR, mass spectrometry and UV spectrometry.
Table 1-27. Composition of slack wax from neutral oil I1 Hydrocarbons
n-Alkanes Naphthenes with few side chains Iso-alkanes (slightly branched) Naphthenes with many side chains Iso-alkanes (very branched) Naphthenics-aromatics Polycyclic aromatics and resins
I
Carbon atom range
Mark
16 13 9 33 6 17 6
2 1-3 3-4 7-8
-
4-5
-
53
(B) CHEMICAL PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
r
Extractive crystallization with urea
e Adduct - forming part
= I
Part forming no adduct
Vacuum distillation
r
1
Part forming no adduct
Adduct-forming part
b
10 fractions
I
Chromatographic separation on silica gel
Naphthenes and
Naphthenes and
iso-alkanes
(10 fractions)
(10 fractions)
B
C
D
n - Alkanes
P
.
Fig. I-19. Diagram of the separation of slack wax
The hydrocarbon composition and distribution by carbon atom number of group B (Fig. 1-19, Table 1-27) is presented in Fig. 1-20. By further distillation of group C , three different fractions were prepared with boiling ranges of 426-446, 484-492 and 519-557 "C. The IR and NMR spectra of these fractions are very similar, and hence the differences in their structures are presumably explainable from the length of the side chains of the naphthenic rings. An average molecule of the above three fractions consists presumably of one isolated or condensed ring, seven CH, groups, and the longest side chain does not contain more than 20 carbon atoms.
54
I. PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
n Fig. 1-20. Hydrocarbon composition of fraction B obtained from the slack wax from neutral oil 11
3. Chemical properties of individual alkanes and their mixtures Alkanes are neutral compounds fairly resistant to the action of chemicals. This behaviour is reflected in their earlier name paraffins (parum affinis = of little affinity). A more detailed study of the chemical properties of alkanes, however, led to the recognition that they are far from being totally inert to chemicals. Many examples of the radical-type homolytic activation of the C-H bond in alkanes are known. Their most important reactions are summarized in Table 1-28. (a) The reactions of paraffins with halogens Direct halogenation of alkanes takes place according to the following substitution reaction : C"H2, + 2
+&
-+
CnH,,
4.1
- x + HX
This reaction can be considered above all for preparing fluoro-, chloro- and bromoderivatives. Iodine cannot be introduced by a direct substitution reaction, however, this process takes place only a t higher temperatures. The HJ formed in the reaction will dehalogenate, in a reduction reaction, the alkyl iodide formed. Hence, the reaction is reversible and the equilibrium is shifted towards the left-hand side of the above general equation. Therefore, direct substitution with iodine is feasible only in the presence of certain additives (e.g., nitric acid, mercury(I1) oxide, silver
(B) CHEMICAL PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
55
Table 1-28. Chemical reactions of alkanes No.
~
I
Agent
Process
Product
Halogens Sulfuryl chloride (+dibenzoyl peroxide)
Light-catalysed substitution
Saturated halogensubstituted derivative
Phosgene or oxalyl chloride
Light-catalysed substitution (chlorocarbonylation)
Chloride of carboxylic acid
Sulfur trioxide Sulfur dioxide 4-chlorine Sulfur dioxide oxygen
Substitution
Alkanesulfonic acid, Alkanesulfonic chloride
Nitric acid or nitrogen dioxide
Substitution
Nitroalkane
Oxidizing agents
Oxidation
Alcohol, aldehyde, ketone, carboxylic acid
Chain splitting, Catalytic isomerization, Dehydrogenation
Short-chain hydrocarbons, Branched alkane isomer, Unsaturated hydrocarbons
+
High temperature
perchlorate) that bind or decompose, by oxidation, the hydrogen iodide formed and thereby render the process irreversible. In contrast to iodine, fluorine reacts with explosive violence, resulting in chain splitting of the alkane which will then yield carbon tetrafluoride and hydrogen fluoride. The heat of reaction of the fluorination process is as high as 419 kJ/mol, as compared to the 101-109 kJ/iiiol for chlorination. Therefore, direct fluorination can only be carried out in the presence of retarding catalysts, e.g. silver-plated copper chips, or by using fluorine gas diluted with nitrogen. In such retarded reactions no chain splitting will occur. However, no control of the reaction to obtain monovalent alkyl fluorides is possible, and a mixture of multiple-fluorinated hydrocarbons will be formed. Fluorine derivatives are manufactured by indirect methods, by exchanging chlorine against fluorine in chlorine derivatives. Chlorine and bromine are capable of direct substitution reactions with saturated hydrocarbons. Chlorine reacts with alkanes directly at ambient temperature. With increasing temperature, the rate of the reaction increases. The process can also be accelerated by catalysts or light. Photocatalytic chlorination is a radical chain reaction proceeding according to the following stages : C1, + hv -+ 2 C1* R-H + C1* + R* + HCl R*
+ C1,
-+
R-Cl
+ C1*
56
I. PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
The first reaction step is the absorption of light energy by the chlorine molecule, resulting in the formation of excited chlorine atoms. These immediately react with alkanes, yielding alkyl free radicals. In the next step, the free radicals react with chlorine molecules, and alkyl chlorides or polychlorinated alkanes substituted at different sites will be formed, as well as excited chlorine atoms which maintain the chain reaction. The chain reaction can be broken off as a result of several reactions. The most important reactions are: recombination of excited chlorine atoms on the wall of the equipment (wall effect); reaction of alkyl-free radicals with excited chlorine atoms (instead of chlorine molecules); if oxygen is present, reaction of oxygen with alkyl-free radicals, yielding peroxides (subsequently reacting with one another or with further alkyl-free radicals and thereby forming stable products); finally the reaction of the excited chlorine atoms with oxygen, yielding chlorine dioxide. Irradiation with light in the wavelength range of 2500 to 4000 A, corresponding to the absorption range of chlorine, is used in photochemical chlorination. The energy of such radiation amply provides for the activation energy of the dissociation of chlorine molecules (239 kJ/mol). Photochemical chlorination is mainly of importance in the chlorination of liquid paraffins. In this process, chlorination can be carried out at low temperatures (30-50 "C), since the rate of the reaction depends only sIightIy on temperature. For example, normal dodecane is readily chlorinated already at 30 "C with a chlorine consumption of about 1.7 litres/kg s. Paraffin waxes can also be chlorinated by the photochemical process. Parallel to the higher melting point, chlorination is carried out at somewhat higher temperatures, around 7G90 "C. Paraffin waxes melting below 75 "C are usually chlorinated in the melt, those with higher melting points in solution, using chlorinated hydrocarbons, e.g. carbon tetrachloride, as solvent. Depending on the nature of the paraffin wax and conditions, several products, mono-, di-, tri- and polysubstituted alkanes, are formed simultaneously :
-
+
+ +
C,H,, + ,C1 C1, + C,H,,Cl, HCI C1, .+ C,H,, - C1, HCI etc. C,H,, C1, In the chlorination of alkanes one must reckon with the formation of all theoretically possible chloroalkane isomers. The ratios of the isomers are defined by the number of different-order hydrogen atoms and by the relative rate of reaction of the hydrogen atoms. In liquid-phase chlorination at about 30 "C, the relative rate of reaction of primary, secondary and tertiary hydrogen atoms is approximately 1 :3.25 : 4.43. These proportions are only slightly changed by catalysts or by light irradiation. The values depend above all on the temperature and pressure of the chlorination process. With increasing temperature the difference between the rates decreases. The number of mono- and polysubstituted products of saturated hydrocarbons, also taking into account isomerization, rapidly increases with increasing numbers of carbon atoms in the molecule.
+
(B) CHEMICAL PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
57
In addition to photocatalytic chlorination, homogeneous catalytic chlorination is also known. This process can be applied both to liquid paraffins and to paraffin waxes. In liquid-phase chlorination, usually catalysts readily soluble in liquid hydrocarbons or in their mixtures with chlorinated hydrocarbons, e.g. carbon tetrachloride, are used. In these processes, chlorine will readily dissociate into active chlorine ions. The most important catalysts are chlorides of iodine, phosphorus, sulfur, antimony, iron and tin. Liquid paraffins are usually chlorinated in the presence of dissolved iodine or phosphorus pentachloride. Bolley was the first, in 1858, to chlorinate paraffin waxes with the cited methods. He obtained a viscous oil-like liquid at ambient temperature. Upon continuing chlorination up to a chlorine content of about 62 wt-%, an amorphous product was formed, which he termed chloroparaffin. In addition to homogeneous catalytic chlorination, heterogeneous catalytic chlorination processes carried out in the gas phase are also known. Among heterogeneous catalysts are copper chloride and iron, usually applied on alumina and silica gel supports. These processes have no great importance for alkane chlorination, since the activity of the catalysts decreases, especially due to coke formation. In thermal chlorination neither catalysts nor light irradiation are used. In this process excited chlorine atoms are formed by the thermal dissociation of chlorine molecules. In the first step, the chlorine radicals attack the C- H bonds and start a chain reaction. Correspondingly, the activation energy is substantially higher, 83.7 kJ/mol, as compared to 50.3 kJ/mol in catalytic chlorination. Thermal chlorination is a chain reaction strongly inhibited by the presence of oxygen. In thermal chlorination, depending on reaction conditions, unsaturated hydrocarbons are also formed besides chloroalkanes. On the other hand, the formation of hydrogen chloride by dehydrochlorination of alkyl chlorides does not take place, or only to a slight extent. Thermal chlorination is used chiefly for lower molecular weight hydrocarbons, but higher molecular weight paraffin hydrocarbons are also chlorinated by this process, at temperatures between 70 and 100 "C, to the desired chlorine content. In fact, even polyethylene can be chlorinated in this manner. Alkanes react slowly with phosgene or oxalyl chloride, yielding the chlorides of the corresponding carboxylic acids according to the following equations:
R-H
+ COCl,
R-H+
COCl
1
COCl
hv or peroxide
R-COCl
+ HCl
R-COCl
+ HCI
hv
-co
58
1. PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
(6) Sulfochlorination of alkanes
The first mention of the simultaneous reaction of sulfur dioxide and chlorine with liquid alkanes was made in the patent "Procedure for the Halogenation of Hydrocarbons" issued by Cortes F. Reed and Charles Horn in 1936. In this reaction, alkyl sulfochlorides are formed : R-H
+ SO2 + C12
R-SOZ-CI
+ HCl
In addition to the simultaneous introduction of sulfur dioxide and chlorine into the molecule, chlorination without the participation of sulfur can also take place, and subsequently these chlorinated molecules can undergo sulfochlorination. Generally in substitution reactions, di- or polysulfochlorination also takes place, so that finally a mixture of mono-, di- and polysulfochlorides, alkyl chlorides, chloromono- and disulfochIorides and unreacted alkanes is obtained. Similarly to chlorination, sulfochlorination is also a chain reaction :
+ hv Cl* + C1* R-H + C1* -+ R* + HCl R* + SO, -+ R- SOB R-SO,* + C1, -+ R-SOz-Cl + C1* C1,
-+
At identical intensities of irradiation, shorter wave-length light will result in a lower chlorine to sulfur ratio in the products. The chlorination of the hydrocarbon can be avoided by using UV light. Recently some organic catalysts were discovered which are capable of starting and maintaining the sulfochlorination reaction without requiring light. For instance, diazomethane, lead tetraethyl, triphenyl-methylmethane, acetone peroxide, dialkyl peroxides and benzoyl peroxide are such radical-forming substances; their catalytic effect being due to their reaction with chlorine molecules yielding alkylfree radicals and excited chlorine atoms. To suppress chlorination of the alkane chain it is preferable to operate with excess sulfur dioxide pf about 100 mol- % (higher excesses are unfavourable). The formation of polysulfochlorides can be reduced by only partial sulfochlorination. Under optimum conditions, sulfochlorination to 50 wt- % yields 85 wt- % mono- and 15 wt- % disulfochloride, as compared to full sulfochlorination when 60 wt- % mono- and 40 wt- % disulfochlorides are formed. When alkanes are reacted with a 3 : 1 mixture of sulfur dioxide and chlorine, the main product is alkyl monosulfochloride, with minor amounts of polysulfochlorides, alkyl chlorides and chloroalkyl sulfochlorides as side products. Isomeric monosulfochlorides can also be formed in sulfochlorination. Sulfochloride groups are only bound to primary and secondary carbon atoms, the hydrogen atoms bound to tertiary carbon atoms do not enter into reaction. However, the latter are sensitive to chlorination. Therefore, the sulfochlorination
(B) CHEMICAL PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
59
of compounds containing tertiary carbon atoms results in substantial chlorination of the carbon chain. In higher molecular weight hydrocarbons, the sulfochloride groups are distributed evenly along the methylene groups. Aliphatic sulfochlorides are not heat-resistant : when heated, sulfur dioxide is split off and alkyl chlorides are formed. Such desulfonation reactions take place readily with higher molecular weight aliphatic sulfochlorides. However, in contrast to sulfochlorides, aliphatic sulfofluorides obtained from sulfochlorides with potassium fluoride solution are thermally stable.
(c) Reactiondliquid parafins and parafin waxes with sulfur dioxide, sul&&.rnQkide, sulfuric acid and .fuming suljiuric acid (oleurn) The term sulfonntion designates the chemical reaction in which a bond is 0
I/
formed between the-S=O
group and a carbon or nitrogen atom of an organic
I
OH cornpound.6ulfonic acid groups and sulfonic acids must not be mixed up with the esters of sulfuric acid, that is, with alkyl sulfates having the general formula R-0-SO,-OH, like e.g. ethyl sulfate C,H,-0-SO,-OH, in which the -SO,H group is bound to an oxygen atom and not directly to a carbon or nitrogen atom as in sulfonic acids. In aliphatic hydrocarbons three sulfonic groups can be bound to one and the same carbon atom. Direct sulfonation is usually carried out with concentrated sulfuric acid, oleum, mixtures of sulfur dioxide and chlorine and mixtures of sulfur dioxide and oxygen. At ambient temperature concentrated sulfuric acid, and even fuming sulfuric acid containing less than 15 wt-% sulfur trioxide, does not react with alkanes. Studies by Engler and Hofer showed that in particular medium and high carbon atom number branched alkanes yield alkylsulfonic acids with hot concentrated sulfuric acid according to the following reaction : C,H,,
+2
+ HOSO2OH
+ C,H,,
+ 1-
S 0 2 0 H + H,O
Pure sulfur trioxide, in the liquid or gaseous state, also yields sulfonic acids with alkanes under appropriate conditions. In this case the reaction is essentially an addition: R-H SO, + R-SOaH
+
The dehydrating effect of sulfur trioxide is so vigorous that it carbonizes organic compounds when added directly. Therefore, sulfonation with sulfur trioxide, free of such side reactions, is feasible only at lower temperatures and in the presence of solvents or sulfuric acid.
60
I. PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
With mixtures of sulfur dioxide and oxygen, alkanes yield aliphatic sulfonic acids according to the following reaction : R-H
+ SO, + 1/20,-
light
R-SO,-OH
This sulfoxidation takes place in the presence of UV light or various catalysts, e.g. chlorides or anhydrides of acids, peroxides, peracids. Sulfoxidation of higher alkanes proceeds only under permanent irradiation or the addition of anorganic catalyst. The sulfo group is statistically distributed along the carbon chain. Sulfonic acids with chain-end sulfo groups will be the scarcer the longer the alkane molecule is. In the sulfoxidation of higher alkanes in the presence of acetic anhydride, it is assumed that a mixed anhydride of sulfonperacid and acetic acid is formed, which subsequently reacts with the water present and is transformed into sulfonic acid : R-H
+ (CH3CO),O 0 - 0 - COCH, + HZO
+ SO, +
R- SO,-
0 2
+
R-SO2-O-O-COCH3
R- SOZOH
i
+ CH,COOH
+ CHSCOOH, + 1/2 0 2
(d) Reaction of liquid parafins and parafin waxes with nitric acid Concentrated nitric acid reacts only to a slight extent with alkanes, even at 100 "C. Konovalov found that alkanes can readily be nitrated with dilute nitric acid (13 wt-%) at 130 to 150 "C under pressure, that is, heated in a closed vessel, and yield nitroalkanes :
C,H2,
+2
+ HONO,
-+
C,H,,
+ 1-
NO,
+ HZO
He stated that the reaction is a radical chain reaction accelerated by radicalforming substances, e.g. lead tetraethyl, and retarded by substances inhibiting the chain reaction, e.g. nitrogen monoxide. The nitration of alkanes is accompanied by oxidation, chain splitting and degradation. Alkanes, above all n-alkanes react only slowly with the so-called nitrating mixture, a mixture of concentrated nitric acid and concentrated sulfuric acid. This mixture, eminently suitable for the nitration of aromatic hydrocarbons, when applied to alkanes, results in rapid hydrolysis, by the hot sulfuric acid, of primary nitroalkanes, and conversion of secondary and tertiary nitroalkanes into brown, tar-like products. Nitro compounds are classified by the order of the carbon atom to which they are bound. Correspondingly, primary, secondary and tertiary nitro compounds exist. Iso-alkanes containing tertiary carbon atoms are readily oxidized by hot fuming nitric acid. In this process, called oxidative degradation, carbon dioxide and carboxylic acids with one less carbon atom are formed. Markovnikov observed that hydrogen atoms bound to primary carbon atoms are the most resistant to substitution by nitro groups, hydrogen atoms at secondary
(B) CHEMICAL PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
61
carbon atoms will enter more readily into reaction, and hydrogen atoms at tertiary carbon atoms react at the highest rate. The most important experimental results of the liquid-phase nitration of alkanes with nitric acid are as follows: (i) The rate of reaction is low, conversion increases With temperature. (ii) Nitration is accompanied by oxidation, and polynitro compounds are also formed, presumably because nitroalkanes are readily soluble, nitratable and hydrolysable. Higher molecular weight alkanes can readily be nitrated in the melt with nitric acid vapour, at relatively low temperatures. At high ratios of nitric acid to alkane, polynitro compounds and fatty acids are primarily formed. When the ratio is reduced to 1 :2, only about 40 wt-% of the alkanes react and the main product consists of mononitro derivatives. The mixtures of alkanes can be nitrated with nitric acid vapour in liquid phase, when their initial boiling point is at least 160-170°C. Alkanes of 7-12 carbon atom numbers cannot be subjected to nitration with nitric acid vapour in liquid phase because of their low boiling points. On the other hand, in the case of gasphase nitration of these alkanes the risk of pyrolysis is present. These alkanes can be nitrated under pressure, at 160-170 O C , with dinitrogen tetroxide.
Table 1-29. Some reactions taking place in the alkane oxidation process
R1\c/o-o~ R2/ H \
">,,-ORz
Rl
R,
'CH-0-+
OH
)CH2+R1>
R 'z
'><:-'3
R
0
R,-C&H
0
0 R-C
+ OH- +
R-C(
-P
+
-
R4
9-
+ Rz-
0 R-C
0
-+ R-CfOOH + R-<
Now: R
R,
0 HO) C H - R + 2 R - C 4
0-0 dkyl group
+ 0
\OH
62
I. PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
(e) Oxidation of liquid parafins and parafin waxes
Liquid paraffins and paraffin waxes do not react with oxygen at ambient temperature. The oxidation process begins to a significant extent only at temperatures of 80 to 100 "C. The oxidation of alkanes is a radical chain reaction. R* radicals formed by the effect of light, initiators, etc. react with oxygen to form active peroxide radicals R-00*. The reaction of the latter with alkane molecules R - H results in the formation of alkane hydroperoxide R-OOH and alkyl free radicals R* maintaining the chain reaction. Alkyl-free radicals, peroxide radicals and hydroperoxide are of the greatest significance in the progress of the oxidation process. Some examples of the manifold reactions taking place in the course of the oxidation of alkanes are presented in Table 1-29. Obviously, the number of products is very high, and includes esters, ketones, aldehydes, alcohols, acids, water and hydrogen peroxide. Since all radicals are capable of reacting with all compounds in the reaction product, lactones, hydroxyacids, dicarboxylic acids, etc. can also be formed. It should, however, be stressed that the mechanism of alkane oxidation is not yet fully clarified. Different authors assume various intermediate reactions within the oxidation process. Only some examples shall be mentioned. For example, Rieche maintains that the starting reaction of oxidation is the formation of alkyl hydroperoxides, involving molecular oxygen, according to the following:
R1CH2CH2CH2R2+ 0, -+ RlCH2- CH -CH, - R2
I
0
I
0
I
H The subsequent step is the rearrangement of the alkyl hydroperoxide into the semi-acetal, which is then converted into the aldehyde and alcohol :
RICH, - CH - CH, - R,
+
RICH, - CH - 0 - CH2R2
1
I
0
OH
I
0
I
H 0
/I
+
R,CH,-C-H
+ R2CH2OH
+
(B) CHEMICAL PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
63
The aldehyde formed in the above reaction yields the peracid with oxygen:
0
0
II
I1
+0 2
R-C-H
-+
R-C-0-OH
The peracid forms a very labile adduct with the aldehyde:
0
0
0
H
II
I/
I1
I
+ R-C-H
R-C-0-OH
-+ R - C - 0 - 0 - C - R
I
OH This adduct is transformed, in the presence of water, into two molecules of fatty acid : 0 H
II
R-C-0-0-C-R
I -+
2R-COOH
I
OH If no water is present, two molecules of the adduct yield one molecule of the fatty acid anhydride and two molecules of the fatty acid:
0
H
II
I
2R-C-0-0-C-R
-P
I
II
0
OH
+ 2R-COOH + HSO
R-C-0-C-R
I1
0
The primary alcohol formed parallel with the aldehyde reacts with molecular oxygen. The primary product is aldehyde peroxide hydrate, which is rearranged into the ortho-acid, immediately dehydrated to the carboxylic acid :
H
H
I
I
R-C-H
I
OH
+ 0,
-+
R-C-0-OH
I
OH
OH
I
+ R-C-OH
-+
RCOOH f H2O
I
OH
According to Langenbeck and Pritzkow, alcohols, in the course of alkane oxidation, are not oxidized to the corresponding fatty acid homologue, but because oxygen first attacks the hydrocarbon chain, lower fatty acids and hydroxycarboxylic acids are formed. These authors, along with many others, assume that the first stage of the oxidation is the formation of hydroperoxides. In the second stage, however, the secondary hydroperoxides decompose, yielding ketones and alcohols:
64
I. PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
main reaction R1- CH, - CH - CH2 - R2 I \ I side reaction OOH
R1-
CH, - CO - CH2 - Rz
L
Rl-CHz-CH-CH2-R2
+ H,O
+ 1/20?
I
OH The ketone formed as main product is further oxidized, yielding alpha-ketohydroperoxide, which, in the following stage, is rearranged into aldehyde and fatty acid :
Rl-CHZ-CO-CH2-R2
+
0 2
+ R,-CH-CO-CHZ-RZ
-+
I
0
I
+
R1-CHO
+ R2 - CHZ-COOH
OH
Since substantial amounts of esters are also found in the oxidation products, Langenbeck assumed that the esters are formed according to the Bayer-Villiger reaction, from peracids and ketones : 0
I1
R-C-0-OH
+ R1-CO-CH7-RZ
+ RCOOH
+ R,-COO-CH,-R,
Alpha-ketohydroperoxides can, in part, be transformed into diketones, the latter reacting, according to Karrer and Schneider, with peracids, and yielding fatty acid anhydrides and fatty acids: RI-CH-CO-R,
--+
R1-CO-CO-R2
I
+ HZO
0
I
OH R1-CO-CO-Rz
+ R3-COO-OH
+ R1-CO-0-CO-R2
+ R3COOH
These anhydrides form esters with compounds containing hydroxyl groups. In the case of n-alkanes, the rate of oxidation increases with chain length, since the C-H bond energy in -CH,, =CH2 and -CH groups decreases in the ratio of 1 :4 :76, and consequently the effect of -CH2- groups becomes more and more important as the chain length increases. The relative oxidation rates of some n-alkanes are presented in Table 1-30. Another important feature is the higher rate of oxidation of n-alkanes than that of their branched isomers. The relative oxidation rates of n-hexane and of its isomers are listed in Table 1-31. Primary and secondary hydroperoxides are formed more reluctantly and decompose more readily than tertiary hydroperoxides. Tertiary hydrogen reacts relatively readily and rapidly, and the tertiary hydro-
(B) CHEMICAL PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
Table 1-30. Relative oxidation rates of some n-alkanes 0,(mol) Oxidation rate = alkanes (mol) timi)
, Hydrocarbons
n-Pentane n-Hexane n-Octane n-Decane
I
oxiZE;ate
1 .o 7.5 200 1380
(
65
Table I-31. Relative oxidation rate of hexane isomers 0 1 (moo Oxidation rate = alkane (mol) time
-
Hydrocarbons
2,3-Dimethylbutane 2,ZDimethylbutane 3-Methylpentane 2-Methylpentane n-Hexane
I
Relative oxidation rate
1 12 60 560 1580
peroxides are stable reaction products. Thus, the rate of reformation of the chain transfer radicals is greater in the case of primary and secondary hydroperoxides, and hence the rate of reaction is higher. Salts of multivalent metals, e.g. manganese, cobalt, iron, copper, and radicalforming substances, such as hydrogen bromide, manganese(J1) bromide etc., accelerate the oxidation reactions. Oxidation processes of alkanes can be changed by using so-called modifiers. These are of particular interest in the oxidation of higher alkane mixtures. By using boric acids as modifiers, the ketone to alcohol ratio can be shifted towards the latter in the reaction product. Apparently the effect of boric acids consists not only in their protecting the alcohols against esterification, but also in the reaction of boric acids and their anhydrides, with R-00* radical;, yielding, via intermediate products, alcohols and esters, respectively.
(f)Thermal decomposition and isomerization of alkanes At temperatures above 350 "C,alkanes suffer thermal decomposition. The two major reactions in this process are dehydrogenation and chain splitting :
Chain splitting is thermodynamicallymore feasible than dehydrogenation. According to Haber's rule, the lower molecular weight hydrocarbon formed in chain splitting is the alkane, the higher molecular weight hydrocarbon the alkene (olefin). In the course of thermal decomposition, isomerization reactions also take place as side reactions. Alkylation of alkanes and aromatics formed by the thermal decomposition of olefins, cyclization of alkanes and olefins, further decomposition of olefins formed in primary reactions and polymerization of olefins are also involved. The products of the thermal decomposition that are liquid at ambient temperature, contain in addition to diolefins, naphthenes, and aromatic compounds al5
66
I. PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
kanes and olefins with lower carbon atom numbers than those of the starting alkanes, too. Depending on the reaction conditions, a solid by-product, called petroleum coke, is also formed in greater or lesser amounts. The gaseous products, in quantities depending on the conditions, are hydrogen, methane, ethane, propane, butane, ethylene, acetylene, propylene and but ylene. The major factors affecting the thermal decomposition of alkanes are temperature, time of reaction, and, to a lesser degree, pressure. The temperature of thermal decomposition not only affects the rate of reaction, but also determines the thermodynamically possible processes. With increasing temperature the yield of gaseous reaction products, but also coke formation, increases. Polymerization side-reactionstake place at normal pressure up to about 400 "C. The formation of diolefins and aromatics starts above 600 "C. Increased reaction-time promotes secondary processes, so that the formation of low molecular weight olefins, of coke and of hydrogen then increases. Increased pressure promotes reactions involving volume reduction :it suppresses dehydrogenation, but does not affect chain splitting. Higher pressures are favourable to secondary polymerization and condensation reactions, the share of liquid reaction products increases and the yield of gaseous olefins is reduced. With increasing pressure, the rate of reaction also increases up to rates exceeding the rate corresponding to atmospheric pressure by a factor of 20 to 40. -In conformity to the reactivity of alkanes, the rate of reaction of thermal decomposition increases up to Cl0. However, for >C, alkanes, no difference in activation energy or rate constant is observed. Branched alkanes are cracked more readily than n-alkanes. Compounds containing a single methyl group on the secondary C atom behave similarly to n-alkanes, this similarity increases with molecular weight. The further the methyl group from the end of the molecule, the greater the difference between the behaviour of the iso-alkane and the n-alkane. Two methyl groups on the chain already cause significant differences. Among the various theories postulated for the thermal decompositionmechanism of alkanes, the free radical chain mechanism has been widely accepted. According to this theory, free radicals are formed, when C - C or C - H bonds are thermally split : R-CH2-CH,
+ R-CH,
4-CH,
*,
or
CH3
I
f
R-CH-CHZ-CHZ
CH
I
R - CH- CH,-CH,
\
CH3
(B) CHEMICAL PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
67
The free radicals react with alkanes forming new radicals:
CH,
*
+ R-CH,-CH,-CH,
+ CH,
+ R-eH-CH,-CH,
The new radical is always formed on internal carbon atoms, since the energy of secondary C - H bonds is lower (372 kJ/mol) than that of primary bonds (398 kJ/mol). Secondary free radicals subsequently form double bonds in the /3-position, and these yield a-olefins, primary free radicals are also formed : R- CH, -CH,- CH2- CH, - 6 H - CH,- CH, + R-CH,-CH,-CH,
R-CH,-CH,-CH,
+
+ CH,=CH-CH,-CH:, R-CH, + CH,=CH,
*
*
3
*
Internai rearrangement of long-chain free radicals leads to the formation of internal free radicals :
R- CH, - CHZ-CHZ- CH, - CH, - CH, - CH, * + --f R - CH,- 6 H - CH, - CH, - CH, - CH, - CH3 . Recombination of free radicals also occurs:
R-CH,
*
+ R-CH,
+ R-CHZ-CHZ-R
However, free radicals are incapable of producing branching and cyclization of the alkane chain. The quantities and the chemical compositions of gaseous, liquid and solid products formed by the thermal decomposition of alkanes are changed by the presence of catalysts. Amorphous catalysts consisting of Si02 and A1,0, can be set to achieve the required effect by varying the alumina content between 13 and 75 wt- %. Crystalline zeolites (molecular sieves) have recently gained importance as catalysts for thermal decomposition. In their presence, as compared to thermal cracking without using catalysts, the C, hydrocarbon content of the gaseous product, and the koalkane, cycloalkane and aromatics content of the liquid product significantly increases. The process of catalytic thermal decomposition is based on the formation of so-called carbonium ions. Carbonium ions are hydrocarbon ions with a free positive charge at one carbon atom, e.g. tertiary butyl cation:
CH,
I
CH3-C+
I
CH, By the use of catalysts, carbonium ions are formed in the course of catalytic thermal decomposition, and their reactions yield the further products.
68
I. PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
By treating n-alkanes containing four or more carbon atoms under relatively mild conditions with metal halides and hydrochloric acid, isomerization into branched alkanes is achieved. The reaction is reversible and accompanied by insignificant amounts of cracking, dehydrogenation and polymerization of the olefins formed. If pure alkanes are used as starting material, small amounts of hydrochloric acid, water, and various promotors act as carbonium ion sources. Table 1-32. Isomerization of n-alkanes n-Alkanes Conditions and products c.0
Temperature, OC Pressure, kPa Molar ratio hydrogen/alkane in feed Product distribution in wt- % relative to alkane Gas Liquid cracked Isomers : solid liquid Aromatics Unchanged alkane
I
c,.
1
c.0
430 3500 64
430 3500 67
420 3500 32
6 7
5 14
4 32
0 34 1 52
9 22 1 49
13 8 1 42
By their action, the isomerization continues as a chain reaction. High molecular weight n-alkanes can also be isomerized in the presence of Friedel-Craft catalysts. Isomerization conditions of various n-alkanes and the most important characteristics of the products are listed in Table 1-32.
Literature Andreas, F., Chem. Tech. Berl., 16, 449 (1964). Asinger, F., Parufins, Chemistry and Technology. Pergamon Press, Oxford (1 968). Asinger-Fell: Erdd, Kohle, 17, 74 (1964). Azizova-Chernozhukov-Kartinin-Grishin: Nef’i Guz, No. 10, 59 (1970). Bailey-Bannerot-Fetterly: Ind. Engng. Chem., 43, 2125 (1951). Bell-Raley-Rust: Discuss. Furuduy SOC.,10, 242 (1951). Bengen, F., Angew. Chem., 63, 207 (1953). Berty, J., Az asurinyolaj kEmiai feldolgozrisa. (Chemical processing of petroleum). Nehtzipari Konyvkiad6, Budapest (1952). Bornemann-Heinze: Chem. Tech. Berl., 20, 99 (1968). Borzsonyi-E. Kantor-Keszthelyi: MAFKIkiadvdny (Report of the Hungarian Oil and Gas Research Institute), No. 311 (1964). Brandes, G . , Brennst. Chem., 37,263 (1956). Buchler-Graves: Znd. Engng. Chem., 19, 718 (1927). Burwell, A. W., Ind. Engng. Chem., 26, 204 (1934). Burger-Combarnous: Revue Znst. r. Pgtrole, 30, 551 (1975). Clark-Smith: Ind. Engng. Chem., 23,697 (1931).
(B) CHEMICAL PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
69
Csik6s-E. KAntor-M6zes-Keszthelyi: MT A KCm. Tud. Oszt. K6zl. (Report of the Department of Chemical Sciences of the Hungarian Academy of Sciences) 25, 134 (1966). Dietsche, W., Fette, Seifen, Anstr-Mittel, 72, 778 (1970). Edwards, R. T., Mod. Packag., 26, No. 6. 123 (1953). - : Ind. Engng. Chem., 47, 2555 (1955). - : Ind. Engng. Chem., 49, 750 (1957). - : Petrol. Refiner, 36, 180 (1957). Eggertsen-Groennings: Anulyf. Chem., 33, 1147 (1961). Emanuel, N. M., The Oxidation of Hydrocarbons in the Liquid Phase. Perganion Press, Oxford (1965). Ernanuel-Maizus-Skibida: Angew. Chem., 81, 91 (1969). Etessam-Sawyer: J. Znst. Petrol., 25, 253 (1939). Ferris-Cowles: Ind. Engng. Chem., 37, 1057 (1945). Finkel-Heinze: Chem. Tech. Berl., 14, 299 (1962). Francis-Young: J . Chem. Soc., 73, 928 (1898). Franke, R., Energie Tech., 25, 388 (1975). Freund-BCithory: Erdd, Kohle, 9 , 237 (1956). Freund-Keszthelyi-Mbzes: Chem. Tech. Berl., 17, 582 (1965). Fuchs-Nettesheim: Erdtil, Kohle, 10, 362 (1957). George-Robertson: J. Znst. Petrol., 32, 382, 400 (1946). - : Proc. R. SOC.,185, 288 (1946). George-Walsh: Trans. Faraduy SOC.,42,94, 210, 217 (1946). Gip-Heinze: Acta Chim. Hung., 31, 85 (1962). Grodde, K. H., Erdd, Kohle, 3, 61 (1950). Gross-Grodde: 61, Kohle, 38, 419 (1942). Griinberg, M., Seifen-ble-Fette-Wachse, 90, 478 (1964). Gruse, W. A., Chemical Technology of Petroleum. McGraw-Hill, New York (1960). Guseva-Ashkinadze-Leifman: Izv. Akud. Nuuk. SSSR, Ser. Phys., 27, 104 (1963). Hass-McBee: Znd. Engng. Chem., 23, 352 (1931); 27, 1190 (1935); ,28, 333 (1936); 33, 185 (1941). Heberling, R., Freiberger ForschHff., A 201, 21 (1961). Hessler-Meinhardt : Fette, Seifen, 55, 441 (1953). Hildebrand-Teubel-Peper-Dahlke: Chem. Tech. Berl., 15,482 (1963). Hunter-Segester: US.Pat. 2 670 323 (1954). Isrnaylov-Terteryan: Khimiya Tekhnol. Topl. Musel, 20, No. 12, 6 (1975). Kaiser, R., Fette, Seifen, Anstr-Mittel, 60, 915 (1958). Kajdas, C., Seifen-Ole-Fette- Wachse, 96, 251 (1970). Kajdas-Tiimmler-Berthold: Erdd, Kohle, 23, 663 (1970). Kdntor, E., MdFKZ k6zlemdnyek (Report of the Hungarian Oil and Gas Research Institute), No. 274 (1963). Kharasch-Berkman: J. 01-gChem., 6, 810 (1941). Kisielow-Kajdas: Seifen-Ole-Fette- Wachse, 93, 719 (1967). Krasavchenko-Zemskova-Mikhnovskaya:Neftekhimiya, 11,803 (1971). Krasnova-Malnev-Putshkovskaya: Zzv. Akad. Nauk. SSSR,Ser. Phys., 27, 98 (1963). Kreuder, W., Fette, Seifen, 84, 665, 699, 735, 773, 849 (1958). - : Fette, Seifen, 85, 19, 41, 93 (1959). Larson-Becker: Anulyt. Chem., 32, 1215 (1960). Leibnitz-Hager-Heinze: J. Prukt. Chem., 4. Reihe, 3 , Heft 1-2 (1956). Leibnitz-Hager-Herrnann: J. Prukt. Chem., 4. Reihe, 5, Heft 1-2 (1957). Levy-Doyle-Brown-Melpolder: Analyt. Chem., 33, 698 (1961). Lomrnerzheim, W., Erdd, Kohle, 7,212 (1954). Lund, H. A., Petrol. Process., 7, 326 (1952). McCleary-Degering: Znd. Engng. Chem., 30, 64 (1938). McLaren, F. H., TAPPZ. Bull., 34, 462 (1961).
70
I. PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
Mikhaylov-Lulova: Khimiya Tekhnol. Topl. Masel, 20, No. 2, 15 (1975) Mikhaylov-Polyakova-Khmelnitsky : Khimiya Tekhnol. Topl. Masel, 10, No. 8 (1965). Minchin, S. T., J . Inst. Petrol., 34, 541 (1948). Moos-Haas: Erdd, Kohle, 1, 29 (1948). Nogare-Bennett: Analyt. Chem., 30, 1157 (1958) O’Connor-Norris: Analyt. Chem., 32, 701 (1960). Ogilvie-Simmons-Hinds: Analyt. Chem., 30, 25 (1958). O’Neal-Weir: Analyt. Chem., 23, 830 (1951). Padgett, F. W., Oil Gas J., 36, No. 38, 30, 45 (1938). Pavlova-Driyatskaya-Mokhtsiyan: Khimiya Tekhnol. Topl. Masel, 7, No. 3, 58 (1962). Philips, J., Petrol. Refiner, 38, 193 (1959). Postnov-Gafarova-Serikov: Khimiya Tekhnof. Topl. Masel, 17, No. 4, 15 (1972). Postnov-Lulova-Leonteva-Fedoszova: Neftepererab. Neftekhim., No. 2. 11 (1972). Reutner, F., Fette, Seifen, Anstr-Mittel, 70, 162 (1968). Rosner-Teubel: Chem. Tech. Berl., 15, 662 (1963). Schlenk, W., Justus Liebigs Annln. Chem., 565, 204 (1949). - : Fortschr. Chem. Forsch., 2 , 92 (1951). Stewart, R., Oxidation Mechanisms. Benjamin Inc., New York, Amsterdam (1964). Stull, D. R., Ind. Engng. Chem., 39, 518 (1947). Sucker, H., Fette, Seifen, Anstr-Mittel, 70, 849 (1968). Terres-Fischer-Sasse: Brennst. Chem., 31, 193 (1950). Terres-Brinkmann-Fischer : Brennst. Chem., 40, 279 (1959). Teubel-Schneider-Schmiedel : Erd6lparafine. VEB Deutscher Verlag fur Grundstoffindustrie, Leipzig (1965). Thorpe, T. C. G., J. Inst. Petrol., 37, No. 330, 275 (1951). Titschack, G., Fefte, Seijen, 67, 23 (1959). Triems-Heinze: Erdcil, Kohle, 18, 695 (1965). Turner-Brown-Harrison: Ind. Engng. Chem., 47, 1219 (1955). Vimos-M6zes-Keszthelyi-E. Kantor : MAhYI kiadvciny (Report of the Hungarian Oil and Gas Research Institute), No. 249 (1962). Vamos-E. Kintor: Erdd, Kohle, 17, 90 922 (1964). Willis, D. E., J . Chromat., 30, 86 (1967). Zhukhovitsky-Selenkina-Turkeltaub: Khimiya Tekhnof. Topl. Masel, 5 No. 11, 57 (1960). Zimmershied-Dinerstein-Weitkamp: Ind. Engng. Chem., 42, 1300 (1950).
(C) Crystal structure of paraffin waxes Paraffin hydrocarbons - whether individual compounds or their mixtures are always crystalline at temperatures below their melting point or melting range. 1. Crystal structure and crystallization
A crystal structure is one in which the constituent atoms or molecules oscillate about the points of a defined crystallographic arrangement, with frequencies and amplitudes depending on temperature. This arrangement, as regards shape, size and steric position, repeats itself continuously within a crystal. Such a structure is called a lattice structure. The shapes and sizes of crystal faces formed in the crystallization process of a given substance - although the crystallographic system remains unchanged -
(C) CRYSTAL. STRUCTURE OF PARAFFIN WAXES
71
differ according to whether crystallization takes place from the melt or from a solution. Well-developed crystals will only be obtained in the latter case. When crystallizing from the melt, the independently developing crystals will come into contact with one another as they grow, and will interfere with further growth in the places of contact. In the free spaces between the crystals, however, crystallization will continue until the whole of the melt becomes crystalline. As a result, the crystal boundaries - independently of the given crystallographic system - will depend on the relative position and mode of growth of the neighbouring crystals. These crystalline units, to distinguish them from crystals having regular faces, are termed crystallites. The crystals of crystalline organic compounds usually display a low order of symmetry. Only a few compounds crystallize in the cubic system, and tetragonal and hexagonal systems are also rare. The majority of organic crystals are rhombic or monoclinic. In organic molecular lattices with single bonds, the valence directions correqxmd to the tetrahedral arrangement. Hence aliphatic compounds containing no double or triple bonds are composed of carbon chains such as those occurring in the three dimensional lattice of diamond. Thus, aliphatic carbon chains may be regarded as derived from the diamond lattice. The distance between two carbon atoms in a single bond, in aliphatic chains containing no multiple bonds, is always 1.54 A, i.e. the same value as in the diamond lattice. In practice, the questions of crystallization and crystal structure are significant above all in the case of paraffin waxes solid at ambient temperatures. With liquid paraffins, crystallization is of no practical importance either in production or in application. In the course of the manufacture and application of paraffin waxes, crystallization almost always takes place from the melt. However, in the first stage of their manufacture - solvent dewaxing and de-oiling - and in fractional crystallization, parafiin max crystals are formed from solution. During the cooling of the melt, crystallization always starts with nucleus formation. The ability for crystallization of a melt is usually characterized numerically by the number of nuclei formed in the unit volume of the melt during unit time. Nucleus formation always starts below the melting point, that is, at a certain degree of supercooling. A further temperature decrease, that is, further increase in supercooling first leads td an increased capability for crystallization up to a maximum value, after which it decreases. This is due to the fact that by increasing supercooling up to a defined imit, the probability of establishing - by diffusion - the atomic or molecular arrangement required for crystallization will also grow. After, however,r eaching this limit, the viscosity of the melt will increase to such an extent that the viscous medium will hinder diffusion and thereby the establishment of such an arrangement. The slope of the ascending portion of the curve - relating to crystallization ability - changes from substance to substance. but decreases for all substances with lower cooling rates, i.e. slower cooling (Fig. 1-21).
12
I. PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
m. P Extent
of supercooling, "C
Fig. 1-21. Effect of the cooling rate on crystallization ability. I
- rapid cooling;
2
- slow
cooling
Crystal nuclei are already tiny crystals. The atoms or molecules fixed in them by lattice forces exert forces of attraction towards the melt and are capable in this way of binding further atoms or molecules from the melt. This enables the tiny crystals to grow. The rate of growth is called rate of crystallization, defined as linear growth of the crystals, in cm/s units. The rate of crystallization is a function of crystallographic directions, temperature of crystallization and extent of supercooling. Nucleation and growth of crystals are parallel processes. The relative rate of these two processes controls the final structure of the crystalline substance. When studying the relative rates of nucleation and crystal growth as a function of supercooling, several systems differing in properties are encountered in practice (Fig. 1-22). In case a, slight supercooling (1) leads to a great number of slowly growing crystals, resulting in a product consisting of small crystals. The contrary is the case with greater supercooling (2), when few, but large crystals are obtained. In case b, slight supercooling (1) and greater supercooling (3) both yield large crystals, while medium supercooling (2) results in small crystals. In case c, slight supercooling (1) results in large crystals, greater supercooling (2) in small crystals. It is a well-known phenomenon - also occurring with paraffin waxes - that if crystal nuclei of the same species as the melt are initially present, crystallization starts in more points, and the crystal texture of the product will be finer. Consequently, by heating such substances above their melting point and subsequently cooling, crystal sizes will increase, and the texture will become coarser. However, not only nuclei of their own species, but foreign nuclei also affect the texture of substances solidifying in crystals. The nature and extent of the effect of such impurities largely varies: in some cases they act as nuclei, while in others they interfere with the growth of the crystals. The crystallites in substances crystallized from the melt are unoriented. Therefore, the anisotropy of crystals does not appear in such so-called quasi-isotropic systems.
73
(C) CRYSTAL STRUCTURE OF PARAFFIN WAXES
In large paraffin wax castings, fineness of texture within a cross-section changes along the radius. On the surface the texture is finer, owing to rapid cooling, than in the middle. Equations of cooling curves for crystallization from the melt can be derived and considered. If, in a given moment 9, the temperature of a system is t "C and ambient temperature is to "C,the cooling rate of the system is y = - -
dt k - - -(t dB mc
- to)
(1-11)
where m is the mass of the system (g), c the mean specific heat of the substance of the system in the temperature range in question (J/kg"C), and k a constant depending on the surface of the system and on the conditions of cooling.
1
(6) Crystal growth
Crystal growth
I
2 Extent of supercooling, "C 1
3 1 Extent of supercooling;
Extent of supercooling, "C
F&. 1-22. Rates of crystal formation and growth
b
O C
74
I. PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
The functional relationship between the temperature of the system being cooled and time is represented by the so-called cooling curves. Their general equation is
t = (ti, - to)re'+
(1-12)
to
where tin is the initial temperature of the system. If the system is crystalline in the solid state (Fig. I-23b), the cooling curve displays a break at the melting point and proceeds horizontally for some time, indicating that the system stays at the temperature of the melting point as long as crystallization continues. When crystallization is complete, temperature again decreases corresponding to the above logarithmic relationship. If supercooling occurs, a local minimum appears on the cooling curve (Fig. I-23c). If the system consists of several constituents having different melting points (Fig. 1-234, the la) Iu L
3
c
ea,
a
E
I-
Time
-
-
Time
(Cl
L3
:
c
a
E
t-
Melting point
1\ c
Time
Time-
Fig. 1-23. Cooling curves of amorphous and crystalline substances. (a) amorphous substance; (b) crystallizing substance; (c) substance crystallizing from the supercooled melt;
( d ) multicomponent crystallizing substance
(C) CRYSlAL STRUCTURE OF PARAFFIN WAXES
75
crystallization process is indicated on the cooling curve by a straight portion forming an angle with the abscissa. In this case, solidification starts at the temperature tl and is completed at the temperature t,. This is the case with macro- and microcrystalline paraffin waxes. Different types of cooling curves are presented in Fig. 1-23. With many crystalline substances, a further change of the crystal structure takes place in a temperature range below the melting point. These changes - termed allotropic transitions - occur at given, so-called equilibrium transition temperatures, provided that cooling is infinitely slow. Allotropic transitions are always displayed on the cooling curve by further breaks, since they too are accompanied by changes in the heat content. It is an important characteristic of allotropic transitions that they represent reversible processes, i.e. they will be repeated during heating when the corresponding equilibrium temperature is reached, provided that heating is infinitely slow. If the cooling or heating rate is finite, the transitions take place at temperatures lower or higher, respectively, than the equilibrium temperature. Therefore, the transition temperature will differ when reached by cooling or by heating, the difference being a function of the rate of temperature change. The condition for crystallization starting from a solution is supersaturation of the solution by cooling or by removal of part of the solvent. In this case also, the process consists of two parts: nucleation and crystal growth. The number of nuclei will be high when cooling is rapid, the solution is intensely stirred during cooling and its purity is high. Crystal growth is controlled by the diffusion of the solute particles, i.e. finally, for example, by the viscosity and density of the solution at the temperature of crystallization. Industrially, crystallization from solution is implemented in two ways : by solvent removal and by cooling. The latter technique is particularly favoured if the solubility of the substance to be crystallized sharply decreases with decreasing temperature. This technology is, therefore, applied in dewaxing and de-oiling, and in fractional crystallization. Fractionation of paraffin waxes is based on the differing solubility of constituents, having either different molecular weights or being isomers. 2. Crystal structure and habit of individual alkanes and their mixtures According to Mazee, Schaerer, BayK, Smith and others, C,, to C3, normal paraffin hydrocarbons display a well-defined transition point at some centigrades below their melting point. The so-called a-phase, stable below the melting point, is converted into the b-phase, and the transition is accompanied by the release of a relatively high amount of heat. At ambient temperature, normal alkanes between C,, and C,, containing an odd number of carbon atoms have an orthorhombic structure, even-numbered normal alkanes between C,, and c,, have a triclinic structure and those between C,, and c36 a monoclinic structure. At higher tempera-
76
1. PROPERTIES OF
LIQUID PARAFFINS AND PARAFFIN WAXES
tures, the stable structures are crystal systems of higher symmetry, in particular orthorhombic and hexagonal structures. Several authors report that normal alkanes from C,, onwards do not exhibit transition points: the phase stable below the melting point is the Q-phase. In hexagonal structures the long molecules are capable of free rotation around their longitudinal axis. Such paraffin waxes are relatively soft. The hexagonal structure is shown in Fig. 1-24. In the orthorhombic crystals - shown in Fig. 1-25 - free rotation of the molecules is not possible, therefore, such paraffin waxes are more rigid.
Fig. 1-24 Hexagonal structure of paraffin wax crystals
az7.45 A b=L.97W
0
d200=3.725 A dllo=4.14 A
Fig. I-25. Orthorhombic structure of p a r a f i wax crystals
(C) CRYSTAL STRUCTURE OF PARAFFIN WAXES
7 5 1 , ,
, , , ,
Melting point,
I
,
77
;
"C
Fig. 1-26. Transition temperature versus melting point for n-alkanes and their mixtures
Figure 1-26 represents the transition temperatures of individual n-alkanes and of n-alkane mixtures, plotted against their melting points. With increasing carbon atom numbers, i.e. with increasing melting points the temperature difference between the transition point and the melting point decreases and finally disappears at C,, compound. The figure also indicates that for equal melting points, the transition point of the mixture is always lower than that of the individual hydrocarbons. In the case of certain normal alkanes, transition between the different modifications is more complex. For the n-alkane C24H50,between 50.7 and 46.5 "C the stable structure is the hexagonal form, between 46.5 and 42°C the so-called monoclinic I (monoclinic primitive) form, and below 42 "C the triclinic form. In the temperature range below 42 "C, the metastable monoclinic I1 modification can also be formed. As mentioned earlier, substantial amounts of heat are evolved at the transition of the a-phase into the P-phase. Transition points and heats of transition for the transition of some n-alkanes from their P-modification, stable at lower temperatures, into their a-modification, stable at higher temperatures, are listed in Table 1-33. For hydrocarbons containing even numbers of carbon atoms, the transition point is closer to the melting point than for hydrocarbonswith odd carbon numbers. The difference between even-numbered and odd-numbered hydrocarbons also appears in the values of heat of transition.
78
I. PROPERTIES OF LIQUID PARAWINS AND PARAFFIN WAXES
Table 1-33. Transition temperatures and heats of transition of some n-alkanes Nurfber atoms
21 22 23 24 25 26 27 28 29 30 35 36
I
Melting point,
40.4 44.4 47.4 51.1 53.3 57.0 60.0 61.6 64.0 66.0 74.6 75.9
1
Transition temperature, "C
32.5 43.0 40.5 48.1 47.0 53.8 53.0 58.0 58.2 62.0 71.8 73.8
1
Heat of transition, J/mol
15 503 28 240 21 788 31 341 26 103 34 274 28 994 35 489 31 592 37 542
-
The heat of fusion values reported in the literature for the different n-alkanes usually include the heat of transition from the a-phase into the P-phase, since determinations start from the melt, and the total amount of heat evolved during cooling to ambient temperature is measured. In Table 1-34, this heat of fusion,
Table 1-34. Melting point, heat of fusion and heat of transition of some n-alkanes Number of carbon atoms
22 24 26 30 34 35
Molecular weight
310 338 366 422 478 492
Melting point, "C
44.4 51.1 57.0 66.0 72.8 74.6
Heat of fusion for the crystal modification stable a t lower temperature, Jjkg
251 065 254 752 256 260 249 598 267 867 259 193
Heat of fusion for the crystal modification stable a t higher temperature, J/kg
157 921 166 762 160 561 163 117 167 349 175 644
Heat of transition, J/kg
93 144 87 990 95 700 86 482 100 728 80 616
the heat of fusion of the crystal modification stable at higher temperature, i.e. the true value of the heat of fusion, and the heat of transition for some n-alkanes are presented in J/kg units. The latter values, when recalculated to J/mol units, differ from those listed in Table 1-33. The reason for this variance is that the data reported in the two tables originate from different authors who used different techniques of measurement.
79
(C) CRYSTAL STRUCTURE OF PARAFFIN WAXES
The specific heat of the 8-modification and of n-alkanes in the liquid state is around 2095 J/kg"C, while the corresponding value for the u-modification is about 4190 J/kg "C. Up till now, branched paraffin hydrocarbons have not been investigated in detail. Much more intricate conditions for transition are to be expected with such compounds, since for example 366 319 isomers of eicosane (C&,,) can theoretically exist. Investigations, however, demonstrated that iso-alkanes display no modification changes in the solid state. A comparison of the edge lengths of the unit cells in normal alkanes demonstrates that the longest edge regularly increases with the number of carbon atoms in the chain. Since even-numbered and odd-numbered alkanes form two series differing in physical and crystallographic properties, even-numbered compounds may only be compared with even-numbered compounds, and odd-numbered compounds with odd-numbered compounds. Alkanes form typical molecular lattices held together by weak van der Waals forces. For this reason it is difficult to prepare single crystals. The usual technique is to apply a thin layer of the compound onto a glass plate by melting. Then the net plane with the longest identity distance will be located parallel to the surface of the glass plate. For some odd-numbered alkanes, this spacing is as follows: C15H32 C17H36 C19H40 &,H,,
21.0 A 23.6 A 26.2 A 38.6 A
The figures indicate that two CH, groups increase the net plane spacing by 2.5 to 2.6 A. The other net plane spacings are much shorter and do not change with chain length. Many researchers have investigated the crystal structure of synthesized n-alkanes. Miiller and Hengstenbergfound the following values for the unit cell dimensions of the rhombic modification of normal C2,H6,: a = 7.45
A;
b = 4.97 A;
c = 77.2
A
They also stated that the unit cell is tetramolecular. Two chain molecules each are located following one another in the direction of the c axis. The C-C bond distances and bond angles in the zig-zag chain are known: 1.54 A and 129"28', respectively. The distance between the CH3 end groups of the chains is 3.1 A. For pentatriacontane (C35H-J and hexacontane (C,pH12,), a and b values were found to be essentiallythe same, while c values were higher, corresponding to what has been said above. According to a later report of Miiller and Lonsdale, the dimensions of the unit cell of n-Cl,H3, at 21 "C are a = 4.28
A;
b = 4.82 A;
c = 23.07
A
80
I. PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
In one of his papers, Mazee reports that x-ray diffraction measurements on n-C,,H, demonstrated the existence of this hydrocarbon in three crystal modifications. He found the following values for the dimensions of the unit cell of the hexagonal modification at 46.5 "C: a = 4.77 A; c = 33.30 A. For the monoclinic modification at 42 "C the corresponding values were found to be: a = 7.50 A; b = 4.99 A; c = 32.70 A; and for the triclinic modification at ambient temperature: a = 7.42 8 ;b = 5.35 A; c = 32.50 A. Based on the results of crystallographic studies, Warth, in the 194Os, came to the conclusion that the unit cells of n-alkanes having higher melting points are bimolecular. For example, n-CS5H,, crystallizes in the orthorhombic system with the unit cell dimensions: a = 7.43 A; b = 4.97 A; c = 46.20 A. Every further - CH, group leads to an increase of c by 1.27 A. It may be seen from the cited data that different values are found in the literature for the edge length c of the unit cell, partly owing to the phenomenon of polymorphism, and partly to the simultaneous presence of several crystal modifications, so that the values found depend largely on the actual modification or mixture of modifications investigated. In addition, experimental data are significantly affected by the purity of the tested material. This is confirmed by a paper by Stanley and Ohlberg which summarizes data found for the long spacings of different crystal modifications in some even-numbered normal paraffin hydrocarbons measured immediately after solidification and after storage for 3 years at 37.5 "C (Table 1-35). Data found by Patton and Simons for the lattice constants of some odd-numbered normal hydrocarbons crystallizing in the orthorhombic system, at 28 "C, are presented in Table 1-36. A comparison with data from other authors indicates that these authors have apparently reversed the positions of the axes a and b.
Compound
Long ing (*0.0'
__~_
*)
Phases initially (relative amounts)
Angle of tilt Equilibrium phase which paraffin chain makes after 3 with basal plane years ~~
__-
81
(C) CRYSTAL. STRUCI'URE OF PARAFFIN WAXES
Table 1-36. Lattice constants of odd-numbered n-alkanes at 28 O Compounds n-C21H44
n-C,,H,* n-CzsH52 n-CP7HE.6 n-C2QH60
1
ao, A
bo,A
4.96f 0.01 4.96f0.01 4.96f 0.01 4.95k0.01 4.95k0.01
7.47f 0.01 7.4650.01 7.4550.01 7.45f0.01 7.44f0.01
1
C
co, A
57.30f 0.08 62.31f0.10 67.41f 0.08 72.59f0.08 77.70f0.18
Studying the crystal structure of cycloalkanes present in microcrystalline paraffin waxes having higher molecular weights, Miiller, Howells, Philip, Rogers and Newman found that their configuration is similar to compressed rings, that is, the molecule, in its crystalline state, consists of two linear chains bound together at the chain ends by a few carbon atoms. The unit cell of the cycloalkane (CH& is unimolecular, the compound crystallizes in the triclinic system and the lattice constants of the unit cell are a = 8.17 A; b = 5.47 A; c = 18.91 A. The corresponding lattice angles are a = 87"18'; /?= 95'10'; y = 106'04'. In cases when the linear chains are sufficiently long, it may be assumed that at the ends of the chain, the carbon atoms are closely packed, and in this way form a subcell. In the case of the above-mentioned cycloalkane, the triclinic subcell has the following lattice constants: a = 4.25 A; b = 5.47 A; c = 2.56A; the correspondingangles are cc = 60'30'; fl = 74'08'; y = 96'47'. In this case the subcell consists of two methylene groups. Since paraffin waxes are mixtures containing mainly n-alkanes, studies related to the crystallization and phase changes of binary, ternary or even more complex n-alkane mixtures are of interest. n-C,,H,Mazee studied the following binary mixtures : n-C,,H,,-n-C,,H,,; -n-C,,H,,; n-C,,H,,-n-C,,H,,; n-C,,H,,-n-C,,H,s; n-C1,H4,-n-C,,H,,. He stated that the constituents of these mixtures are miscible in all proportions, both in the liquid and in the solid state. In the phase diagram of the system n-C,,H,,-n-C&H,, (Fig. 1-27) the two-phase areas (L S,) and (S, + S,) almost shrink
+
SP n-C35 H72
Md-%
nUC36H7L
Hg. 1-27. Phase diagram of the binary system n-CmH7z-n-C96H74
6
82
I. PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
Sa
0 n -c19 HLO
Mol-%
n-CZ1Hf.L
Fig. 1-28. Phase diagram of the binary system n-ClsH40-n-C21H44
to single curves. On the other hand, the other systems with lower molecular weight constituents display phase diagrams in which the two-phase areas are more significant and the area (S, + S,) exhibits a minimum value, as may be seen, e.g. in Fig. 1-28. From the phase diagrams of these systems it appeared that a given difference in the carbon atom numbers of the constituents gives rise to a deviation from the ideal behaviour. The difference is greater the lower the molecular weight of the constituents is. With these systems, M a z e observed no melting point depression. For a quantitative evaluation, he calculated the ideal melting point curves of the systems C21H44-C23H48 and C2,H5,-C2,H5,. The calculation was based on Raoult’s law, according to which - assuming that no heat of admixture and no volume change arise - the following relationship is valid between the molar fractions of the constituents in the solid phase Xl,s and X2,s and the temperature T where the mixture totally melts: (1-13)
where XI, I and X2,I are the molar fractions, respectively, of the first and second
83
(C) CRYSTAL STRUCTURE OF PARAFFIN WAXES
constituents in the liquid phase, Tland T2the melting points, and Ql and the heats of fusion. Combining the two equations,
QB
(1-14)
This equation enables us to calculate the value of T. Analogously, the temperature T3 corresponding to the first appearance of melting can be calculated by means of the following equation : (1-15)
The calculated and experimental values are presented in Table 1-37. The data are in good agreement in all cases, the calculated values being slightly higher. Presumably the area (S, + Sp) having a minimum affects the area (S, L) to a certain extent.
+
Table 1-37.Beginning and end of the melting of n-alkane mixtures, determined experimentally and by calculation
I
1
Observed
Calculated
Composition, mol- % _ _ _ _ _ _ _ ~_ _ _ . ~~
CZIHU
__________.
c23H48
50.0 80.0
50.0 20.0
C24H50
CZt3H64
95.0 75.1 50.3 25.2
5.0 24.9 49.1 74.8
43.1 41.6
44.4 42.2
43.6 41.6
44.7 42.4
50.8 51.5 52.9 54.4
50.9 51.8 53.4 54.7
50.9 51.8 53.3 54.1
51.0 52.3 53.8 55.1
Experimental work has shown that volume changes are very small even when normal alkanes whose molecular weights differ greatly are being mixed. For example, the heat of admixture for the system C,H,,-C1,H,, is only about 125.7 J/mol. It has also been observed that the difference between the temperature corresponding to the minimum of the (S, + S,) area and the melting point pertaining to this minimum is the greater the smaller the molecular weights of the constituents (Table 1-38). This finding also confirms that deviation from the ideal behaviour is greater in systems with lower molecular weights than in higher molecular weight systems. The deviation increases with increasing differences between the carbon atom numbers of the constituents. 6*
84
I. PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
Table 1-38. Difference between the temperature minimum of the (S, S,) area and the corresponding melting point for binary mixtures of n-alkanes
+
Temperature differoncs, 'C
Constituents
The depression in the (S, + S,) area indicates that crystallization first appears in the a-form. It has also been confirmed that in binary systems, the structure of the 8-form largely depends on the difference between the chain lengths of the constituents. Deviation from ideal behaviour increases with increasing differences between the chain lengths. This is shown in Fig. 1-29, representing two possible variants of the phase diagram of the C,,H,,-C,,H,, system. In both variants, a m h h u m appears in the liquid area, although less pronounced than in the transition area. The figure indicates that solid solutions in the S, area deviate to a geater extent from the ideal state than in systems where the chain lengths of the constituents differ only by one or two carbon atoms. The lower boundary of the ( S , + S,)
701 L '
68
Y
L
70
-
-
66
?- 64 c
2 62
al a
$ F-
60 58
56
t-
:;I 50
0
I
,
sp
1
100
Fig. 1-29.Two possible variants of the phase diagram of the binary system n-CsoH6s-n-C8,H,P
85
(C) CRYSTAL STRUCTURE OF PARAFTIN WAXES
area is remarkably flat, and the lowest temperature within this broad range is relatively high. Presumably this finding is associated either with a series of mixed crystals, or with phase separation in the solid phase. X-ray studies did not confirm the latter assumption. However, in systems with greater chain length differences, e.g. n-C,,Hu-C,lH,,, phase separation takes place, i.e. a normal eutectic will arise. Figure 1-30 represents yet another phase diagram type for binary n-alkane systems. Here compositions exist that are monotropic, i.e. undergo only a single phase change. Commercial macrocrystalline paraffin waxes consist, at ambient temperatures, mainly of hard orthorhombic crystals, but the hexagonal structure is also always present, even if only in small amounts. In addition, liquid branched hydrocarbons also participate in building up the final structure. The amount of the hexagonal form depends on the molecular mass range of the constituents. The melting rangL and the transition range become broader with more complex paraffin wax composition. For narrower molecular mass range fractions, the transition range is narrower. When this transition is abrupt, contraction of the paraffin wax during cooling can cause cracks due to deformation. The difference between the melting point and the transition range is the greater the broader the molecular mass range of the paraffin wax. Figure 1-31 demonstrates that the transition temperatures of commercial macrocrystalline paraffin waxes with broad molecular weight ranges and complex
I
‘i
18 38
50 Mol-Olo
11 0 n-C20h2
Fig. 1-30. Phase diagram of the binary system n-Ci8Hcn-C&H,s
86
I. PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
c
.-C 0
a
C 0
.+ ._ m C
0,
t-
Melting point, "C Fig. 1-31. Transition point versus melting point of paraffin waxes representing various molecular weight ranges. I approach curve for n-alkanes, 2 mixtures of n-alkanes, 3 narrow fractions obtained by sweating from 57-60 OC melting range paraffin wax, 4 commercial paraffin waxes having different melting points
compositions, are lower - at identical melting points - than those of individual n-alkanes, their mixtures and narrower molecular weight range products obtained by fractional crystallization. The true heat of fusion, related to the modification stable at the higher temperature, of commercial macrocrystalline paraffin waxes is 167 kJ/kg. The total heat of fusion, including heat of transition from the modification stable at the higher temperature into the modification stable at the lower temperature, is around 251 kJ/kg. An increased ratio of branched alkanes in the paraffin wax can act in two different ways : if these compounds are liquid, they soften the wax and reduce cohesion stresses. If, however, they are solid, they will plasticize the wax. With suitable types of branched alkanes, these will fill the voids between crystals and correct the cracks arising due to contraction in the transition range. According to recent studies, crystal structure transformation in the n-alkane content of commercial paraffin waxes is not complete and often takes place only to a limited extent. The various properties of commercial paraffin waxes change with the relative amounts of the polymorphous modifications. Macrocrystalline slab paraffin waxes contain C,,-C,, n-alkanes, microcrystaln-alkanes. In the solld phase no transition occurs line paraffin waxes C&,, with n-alkanes above C3,, as at this carbon atom number the transition point becomes identical with the melting point. Hence in microcrystalline paraffins the importance of polymorphism is much less than in macrocrystalline slab parafin waxes.
(C) CRYSTAL STRUCTURE OF PARAFFIN WAXES
87
Fig. 1-32. Habits of paraffin wax crystals. ( a ) plate crystals; ( b ) malcrystals; (c) needle crystals
In crystalline substances, the boundaries of individual crystals are often independent of the crystal systems in which the substance crystallizes. This is also the case with individual alkanes and their mixtures. Many hundreds of photographs confirm that paraffin wax crystals appear in three different habits, namely plates, needles and so-called mal-shapes. The latter are small-size, underdeveloped crystals, which often agglomerate. The cross-section of needle crystals is similar to the annual rings of trees, while plate crystals resemble paved roads. The different crystal shapes are shown in Fig. 1-32, The conditions for the formation of plate and needle crystals have been studied by many researchers. Based on different studies and theories, Ferris and other researchers have come to the following conclusions: ( i ) The three crystal habits of paraffin waxes are the resul4 of different factors. For a given wax, both the conditions of crystallization and the chemical composition of the wax are of decisive importance. (ii) As a first approach, it has generally been confirmed that within given molecular weight limits, the constituents having higher melting points crystallize in plates. The low-melting constituents crystallize in needles, the medium-melting constituents in mal-shapes. Also, as a first approach, one may say that this relationship is independent of the presence of solvent in the crystallization process and of solvent concentration, if solvent was a t all present. (iii) The above statement is closely related to the observation that normal alkanes crystallize in plates and the crystal lattice is simplest in these crystals. Needle crystals contain both aliphatic and cyclic hydrocarbons, while mal-shaped crystals are characterized by their content of branched hydrocarbons. With the latter, the crystal lattice is obviously more complex than with needle crystals. (iv) From the view of transformability into one another, the three crystal habits exhibit a preferential order of succession. Plate crystals will always readily be transformed into needle- and mal-shaped crystals. Within the two latter habits, needle crystals will be transformed - under appropriate conditions - into malshaped crystals. Consider a molten mixture of high-melting constituents that - in the pure state - crystallize in plates, with low melting constituents that - in the pure state - crystallize in needles or mul-shapes. Cooling of this melt
88
I. PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
will lead first to plate crystal formation, while the still liquid low-melting constituents that yield needle- and mal-shaped crystals will be present as diluting medium. Further cooling will then result in the slow formation of needle- or mal-shaped crystals on top of the existing plate-shaped crystals, occasionally transforming the latter. (v) Cooling rate during crystallization is also an important factor in the resulting crystal habit. For both plate and needle crystals, low cooling rates will result in large crystals. The size of mal-shaped crystals, however, only slightly depends on the cooling rate. Presumably their crystal lattice is so complex that the probability of the incorporation of further molecules into the lattice, i.e. crystal growth is very slight. (vi) When crystallization takes place from a solvent, the relative solubility of individual hydrocarbons must be taken into account. The solubility of alkanes - independently of the form in which they crystallize - is inversely proportional to their melting point. In the presence of solvent, alkane mixtures begin to crystallize at relatively low temperatures. However, the constituents crystallizing in needles are more soluble than those crystallizing in plates. Therefore, needle crystals will appear only at lower temperatures and higher concentrations. Crystallization starts with the appearance of plate crystals. They are followed by malshape crystals which in this respect occupy a medium position. For any given alkane mixture and solvent, one can always find a concentration limit and a corresponding crystallization temperature limit, below and above which, respectively, crystallization in needles can be suppressed. If, however, conditions are such that concentration and temperature are above and below, respectively, these limits, needle and mal-shaped crystals are capable of transforming plate crystals. In needle crystals, a vein system or ribbing proceeding along the total length of the crystal can always be detected. The location and origin of this vein system has been investigated by several researchers. According to Ferris and co-workers it consists of a central hole system within the crystals. As regards mal-shaped crystals, Ferris and co-workers found that as a result of very rapid cooling, aggregates of tiny crystals are formed from paraffin wax melts, and these appear as mal-shaped crystals. According to another assumption, mal-shaped crystals are actually plate crystals piled on one another. For instance, n-hexacosane crystallizes in this manner from both melt and solution. Earlier its crystals were believed to be mal-shaped. Certain relationships can be detected between the crystal habits of paraffin waxes and the manufacturing process of the lubricating oil fractions from which they are won. Plate crystals are obtained from paraffinic distillates having lower average boiling points. Compounds present in such fractions and crystallizing in needle and mal-shapes have melting points so low that they behave as oils at the usual dewaxing and de-oiling temperatures, and are, therefore, almost completely absent from the de-oiled paraffin waxes. In distillates having higher boiling points and in distillation residues, needle and mal-shaped crystals appear, and their
(C) CRYSTAL STRUCTURE OF PARAFFIN WAXES
89
proportion increases with increasing boiling points. This also indicates that macrocrystalline paraffin waxes mainly crystallize in plates consisting of n-alkanes, while microcrystalline paraffin waxes crystallize in needle- and mal-shaped crystals containing branched alkanes. Table 1-39 lists the distribution of crystal habits in microcrystalline paraffins as a function of the boiling point. Table 1-39. Per cent distribution of crystal habits in microcrystalline paraffin waxes of different boiling points Average boiling point at 1.4 kPa, "C
80 95 105 115 130 140 150
Crystal habits ~
plates
~
mu/-shapes
100 99 98 91 78 54 37
0 1 2 7 12 17 27
1
needles
0 0 0 2 10 29 36
The crystal habits of alkanes are important factors in paraffin wax manufacture. Cakes from light paraffinic distillates are easy to press. This can be attributed to the fact that they contain plate crystals at the temperature of dewaxing. Such cakes are also easy to sweat, since at sweating temperatures they crystallize in large interlacing needle-shaped crystals. The paraffin wax is identical at both dewaxing and sweating, but the conditions of crystallization largely differ. At dewaxing, the amount of oil present is still relatively high, so that it keeps in solution the compounds that tend to crystallize in needles to such an extent, that a plate crystal structure will be established. In the sweating operation, however, when the wax cake is being cooled and crystallizes, the amount of oil present is much less, so that both crystal habits will crystallize simultaneously, and the needle crystals will alter the shape of the plate crystals. With increasing average boiling points of the distillates, the proportion of mal-shaped crystals substantially increases in the paraffin wax. Mal-shaped crystals crystallize simultaneously with plate crystals and alter their shape. Therefore, such distillates cannot be pressed.
Literature Asinger, F., Paraffins. Chemistry and Technology. Pergamon Press, Oxford (1968). Brooks-Dunstan: The Science of Petroleum. Vol. V, Part 111, Oxford University Press, London (1955). Brown, R. G., J . Appl. Phys., 34, 2382 (1963). Buchler-Graves: Znd.Engng. Chem., 19, 718 (1927). Clarke, E. W., Znd. Engng. Chem., 43, 2526 (1951). Coffey, S., Rodd's Chemistry of Carbon Compounds. Vol. I, Part A, Elsevier Publishing Company, Amsterdam (1964).
90
I. PROPERTIES OF LIQUID PARAFFINS AND PARAFFlN WAXES
Edwards, R . T., Petrol. Refiner, 36, 180 (1957). - : Znd. Engng. Chem., 49, 750 (1957). - : TAPPZ. Bull., 41, 267 (1958). Evans, U. R., Discuss. Faraday SOC.,N o . 5, 77 (1949). Ferris-Cowles-Henderson: Znd. Engng. Chem., 23,681 (1931). Ferris-Cowles: Znd. Engng. Chem., 37, 1054 (1945). Fontana, B. J., J . Phys. Chem., 57, 222 (1953). Gray, C. G., J. Inst. Petrol., 29, 226 (1943). - : Petroleum Lond., 7, 94, 98 (1944). Hoffman-Smyth: J. Am. Chem. SOC.,72, 171 (1950). Hoffman-Decker: J. Phys. Chem , 57, 22 (1953). Howells-Phillips-Rogers: Acta Crystallogr., 3, 210 (1950). Johnson, J. E., Znd. Engng. Chem., 46, 1046 (1954). Katz, E., J. Inst. Petrol., 17, 37 (1931). Kinsel-Phillips: Znd. Engng. Chem., 17, 152 (1945). Kirk-Othmer : Encyclopedia of Chemical Technology.Vol. 15, Wiley Interscience, New York (1968).
Magill-Pollack-Wyman: J . Polym. Sci. A3, 3781 (1965). Mazee, W. M., R e d . Trav. chim. Pays-Bas, Belg., 67, 197 (1948). Miiller, A., Proc. R. SOC. A 120,437 (1928). - : Proc. R . Soc., A 38, 514 (1932). Newman, B. A., J . Appl. Phys., 38, 4105 (1967). Niegisch-Swan: J. Appl. Phys., 31, 1906 (1960). Ohlberg, S. M., J. Phys. Chem., 63, 248 (1959). Padgett-Hefley-Hendrickson: Znd. Engng. Chem., 18,832 (1926). Padgett-Killingsworth: Pap. Trade J., 122, No. 5, 9, 37 (1946). Piper-Brown-Dyment: J. Chem. SOC.,127, 2194 (1925). Rhodes-Mason-Sutton: Znd. Engng. Chem., 19, 935 (1927). Sachanen, A. N., The Chemical Constituents of Petroleum. Reinhold Publ. Co., New York (1945).
Schaerer-Bayle-Mazee: Recl. Trav. chim. Pays-Bas, Belg., 75, 513 (1956). Smith, A. E., J. Chem. Phys., 21, 2229 (1953). Sullivan-McGill-French: Znd. Engng. Chem., 19, 1042 (1927). Templin, P. R., Znd. Engng. Chem., 48, 154 (1956). Teubel-Schneider-Schmiedel : Erd6iparafine. VEB Deutscher Verlag fur Grundstoffindustrie, Leipzig (1965). Turner, A. J., J . Polym. Sci., 62, 53 (1962). Turner-Brown-Harrison: Znd. Engng. Chem., 47, 1219 (1955). Vand-Aitken-Campbell: Acta Crystullogr., 2, 398 (1949). Vand-Boer: Proc. K. Ned. Akad. Wet., 50.991 (1947). Warth, A. H., The Chemistry and Technology of -Waxes. Reinhold Publishing Co., New York (1956).
Wilman-, H., Proc. Phys. SOC.,64, 329 (1951). Wilson-Lipson: Proc. Phys. SOC.,53, 245 (1941).
(D) Physical properties of paraffin waxes It is a very complex task to establish relationships between the chemical composition of paraffin waxes and their applicability in various fields. In many cases these relationships cannot unambiguously be determined. It is, therefore, of great importance to know the physical properties of paraffin waxes, and to develop suitable methods for their measurement.
91
(D) PHYSICAL PROPERTIES OF PARAFFIN WAXES
The literature has dealt extensively with such functional properties as tensile strength, blocking point, sealing strength, modulus of rupture etc. A knowledge of these physical properties allows us to determine with greater certainty whether the paraffin wax in question is suited for a given application. 1. Melting point, boiling point and melt viscosity Some important physical properties of normal paraffins, liquid or solid at ambient temperature, are summarized in Table 1-40. The melting point of n-alTable 1-40. Physical constants of normal alkanes
Pentane Hexane Heptane Octane Nonane Decane Undecane Dodecane Tridecane Tetradecane Pentadecane Hexadecane
- 129.7 -94.0 - 90.5 - 56.8 - 53.7 29.7 -25.6 -9.7 6.0 5.5 10.0 18.1
36.1 68.7 98.4 125.7 150.8 174.1 195.9 216.3 235.5 253.6 270.7 287.1
Heptadecane Octadecane Nonadecane Eicosane
22.0 28.0 32.0 36.4
302.6 317.4 331.6 345.1
-
-
0.6263 0.6594 0.6838 0.7026 0.7177 0.7301 0.7402 0.7487 0.7563 0.7627 0.7684 0.7733
1.3577 1.3749 1.3876 1.3974 1.4054 1.4119 1.4172 1.4216 1.4256 1.4290 1.4319 1.4345
d at m.p.
0.7767 0.7767 0.7776 0.7777
1.4360 (at 1.4367 (at 1.4336 (at 1.4346 (at
25 "C)
28 "C) 38 "C) 40 "C)
0.7782 0.7782 0.7797 0.7786 0.7785 0.7587 (at 90 "C) 0.7788 (at 60 "C) 0.7792 0.7797 0.7795 (at 70 "C)
1.4240 (at 1.4358 (at 1.4270 (at 1.4283 (at 1.4380 (at
70 "C) 45 "C) 70 "C) 70 "C) 60 "C)
b.p. at 2.1 kPa
Heneicosane Docosane Tricosane Tetracosane Pentacosane Hexacosane Heptacosane Octacosane Nonacosane Triacontane Tetracontane Pentacontane Hexacontane HeDtacontane
40.4 44.4 47.4 51.1 53.3 57.0 60.0 61.6 64.0 66.0 81.4 91.9-92.3 98.5-99.3 105-105.5
215 224-225 234 243 259 262 270 279-281 286 304
-
420-422 -
-
-
92
I. PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
kanes increases with molecular weight. The melting point of hectane, the highest molecular weight normal alkane isolated in a pure state, is 115 "C.Over the carbon atom number range from C , to CZ5,the relationship between the melting point and the carbon atom number cannot be described with one single function for even-numbered and odd-numbered n-alkanes, i.e. the melting points are higher and lower, respectively, than the average values calculated from even- and oddnumbered n-alkane melting points. It should be stressed that branching of the carbon chain, at identical molecular weights, results in an important decrease of the melting point, since high melting points are inseparable from high symmetry of the crystals, and this condition will be satisfied above all in the case of straight-chain alkanes. The melting points of various normal and branched paraffins are presented in Table 1-41. For example it may be seen, that among C,,HS, alkanes, the melting point of n-hexacosane is 56.4 "C as compared to 0.0 "C for 11-n-butyldocosane. Figure 1-33 represents average melting point versus molecular weight for n-alkanes and various types of waxes, including petroleum waxes obtained by rectification and fractional crystallization. Several of these narrow boiling-pointrange fractions have very similar molecular weights, and yet, as demonstrated by the figure, their melting points differ substantially. The boiling points of identical molecular weight straight-chain and branched alkanes also differ, but to a much lesser degree than the melting points. In the
82 77 71
66
y
60 , 54 C
'g 49 .-
5
43
38 32 27
21 16
b-4 I
ns of soft wax from rnperature carbonof brown coal fractions of total wax from I t c of brown coal
' '
10 I I I 1 1 ~ 1 ~ ' l L l , 1 ~ 1 ~ ' ~ 1 ' 1 ~ ~ ' I 1 11 1 1, ~ 1 1 I 200 300 400 500 600 700 800900 Molecular weight
Fig. 1-33. Melting point versus molecular weight for normal alkanes and waxes from different sources
(D) PHYSICAL. PROPERTIES OF PARAFFIN WAXES
93
Table 1-41. Melting points of various normal and branched alkanes found in waxes ~~
~
Hydrocarbon
Melting point by capillary tubs method O C
~UHXl
n-Tetracosane 2-Methyltricosane 2,2-Dimethyldocosane 5-n-But yleicosane
51.5 42.0 34.6 8.0
c26H64
n-Hexacosane 5-n-Butyldocosane 7-n-Butyldocosane 9-n-Butyldocosane 11-n-Butyldocosane
56.4 20.8 3.2 1.3 0.0
CZIlH58
10-Nonylnonadecane
- 5 to - 6
GPHIO 22-Methyltritetracontane
66.6-66.7
C,,-C,, range, the boiling point of the branched alkanes is lower by only 4 to 15 "C (depending on the number, length and position of the side chains) than that of the corresponding n-alkane. No definite relationship between the viscosities of normal and branched paraffinic hydrocarbons can be established. While alkanes with one side chain often have lower viscosities than that of the normal alkane, the viscosity of alkanes with two or three side chains ishigher than that of the corresponding normal alkane. The temperature coefficient of the viscosity of normal alkanes decreases with increasing molecular weight. Among isomeric branched alkanes the temperature coefficient of viscosity is highest for the compound with the shortest side chain, while this coefficient is substantially lower for alkanes with long side chains and for normal alkanes. Paraffin liquids at ambient temperature and melts of paraffins solid at ambient temperature behave as Newtonian systems. For certain applications, the viscosity of macrocrystalline and microcrystalline paraffin waxes, above all in the 100150 "C temperature range, is of importance. Fig. 1-34 shows melt viscosities, measured at 100, 120 and 140"C, for blends prepared from a macrocrystalline paraffin wax (drop melting point 53 "C) and a microcrystalline paraffin wax (drop melting point 70 "C).As to rheological properties of macrocrystalline and microcrystalline paraffin wax melts, it should be noted that they behave as nonNewtonian systems within their melting range : they exhibit structural viscosity and rheodestruction. In such systems viscosity is a function of the shear stress applied and of load time.
94
I. PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
20 40 60 80 I( 0 Macrocry st wax, wt-% L . A L - J
100 80 60 40 20 0 Microcryst wax, wt-Oh
Fig. 1-34. Melt viscosities of blends of a macrocrystalline and a microcrystalline paraffin wax
2. Density and thermal expansion
The density of paraffin waxes increases with their melting point. Table 1-42 lists the densities of several macrocrystalline paraffin waxes with different melting points, over a temperature range starting much below and ending much above the melting point. Figure 1-35 represents density versus melting point curves for narrow boilingrange fractions obtained by repeated vacuum distillation from a commercial Table 1-42. Densities of macrocrystalline paraffin waxes having different melting points Melting point, "C
V 0
2
-
50
52
; ~1 7 14 27 38 66 74 85
1
55
1
57
I
61
Density, g/cm'
0.906 0.903 0.897 0.872 (28 "C) 0.849 0.776 (63 "C) 0.769 0.762
0.915 (2 "C) 0.911 (10°C) 0.909 (15 "C) 0.897 0.873 0.775 0.768 (77 "C)
-
0.917 0.914 (10 "C) 0.910 (15 "C) 0.902 0.877 0.780 (60 "C) 0.774 (71 "C) 0.766 (82 "C)
0.922 0.919 0.914 0.911 0.896 (35 "C) 0.779 (63 "C) 0.772 0.765
0.922 0.919 0.915 0.905 (28 "C) 0.903 (35 "C) 0.783 (63 "C) 0.775 0.769
95
(D) PHYSICAL PROPERTIES OF PARAPFIN WAXES
Melting point, "C
Fig. 1-35 Density versus melting point for narrow boiling-range fractions obtained by vacuum distillation from a commercial paraffin wax (melting point 65 "c)
paraffin wax (melting point 65°C). At identical boiling points and molecular weights, the density of these fractions is generally lower than that of the pure n-alkanes. For comparison, Table 1-43 lists the densities of some pure normal and branched alkanes measured at 70 and 90 "C. The coefficient of cubical expansion does not change in the C21-C31range. Expansion coefficients for branched 2,2-dimethyldocosane and 10-nonylnonadecaneare lower than for n-alkanes having the same molecular weight. Table I-43. Densities of some individual alkanes Density, glcm' ~
Compound at 70°C
CzlH,, n-Heneicosane Cz3H,, n-Tricosane C,,H,, n-Tetracosane CZ8Hs8 n-Octacosane C3,HB2n-Triacontane C,lH,, n-Hentriacontane Cs4H,, n-Tetratriacontane C3,H,, n-Pentatriacontane C38H,, n-Hexatriacontane Cd8Ha n-Tritetracontane C,,H,, 2-Methyltricosane C,,H,, 2,2-Dimethyldocosane C,,H,, 13-Methylpentacosane C,,H,, 10-Nonylnonadecane C,4H,, 22-Methyltritetracontane C,,H,, 1-Cyclohexyloctadecane
0.7587 0.7654 0.7682 0.7759 0.7795 0.7827
-
-
-
0.7662 0.7642 0.7720 0.7170 0.7938 0.7997
1
at 90°C
0.7468 0.7531 0.7562 0.7639 0.7676 0.7709 0.7728 0.7734 0.7783 0.7812 0.7539 0.7536 0.7595 0.7650 0.7816 0.7874
Temp. coeff. of density in the liquid phase dd/At
0.00060 0.00060 0.00060 0.00060 0.00060 0.00059
-
0.00061 0.00053 0.00063 0.00055 0.00061 0.00062
96
I. PROPERTm OF LIQUID PARAFFINS AND PARAF'FW WAXES
As with the macrocrystalline paraffin waxes, the densities of microcrystalline waxes in the liquid and solid state differ greatly. Density data of a microcrystalline paraffin wax with a melting point of 73 "C are presented in Table 1-44. Plots of paraffin wax density versus temperature always exhibit several sharp breaks. If starting from the melt, the first break in the cooling curve appears at the liquid-solid phase transformation. As generally known, this transformation Table 1-44. Densities of a microcrystalline paraffin wax (melting point 73 "C)in the solid and liquid phase Temperature, "C
6.7 15.6 26.9 52.8 71.1 76.7 82.2 93.3 100.0 115.6 137.8 160.0 182.2 204.4 225.6
1
Density, g/cm*
0.9343 0.9294 0.9236 0.8921 0.8300 0.8025 0.7999 0.7935 0.7890 0.7805 0.761 1 0.7535 0.7410 0.7380 0.7140
is isothermal in the case of individual hydrocarbons. In paraffin waxes, however, these being mixtures of individual hydrocarbons, the liquid-solid transformation takes place over a temperature range indicated by the break. After solidification of the wax, further cooling results in solid-phase transitions between different crystal modifications. These transitions appear on the curve as subsequent breaks, their number and temperature depending on molecular weight. The breaks indicate that the transformations in question are accompanied by greater or lesser volume changes. These changes can also be measured directly. Table 1-45 summarizes volume expansion data for various macro- and microcrystalline paraffin waxes. Expansion data include volume changes occurring at liquid-solid and solid-solid transformations as well as thermal expansion of the liquid and solid phases. Expansion values were measured using a dilatometer. Figure 1-36 shows, based on the above data, the specific volumes of these paraffin waxes against temperature. The curves referring to macrocrystalline waxes resemble each other. On each curve, a sharp break at about 10°C below the melting point can be observed indicating a change in crystal structure. The crystallization points listed in the table are defined as the temperatures corresponding to
97
(D) PHYSICAL PROPERTIES OF PARAFFIN WAXES
Table 1-45. Volume changes of macro- and microcrystalline paraffin waxes Characteristics
i
I
Macrocrystalline paraffin waxes
Density a t 100 OC, dAo0 0.7531 Viscosity a t 98.9 'C, mmZ/s 3.19 Needle penetration a t 25 O C , 100 g/5s, 0.1 mm; ASTM D-5 33 Melting point (cooling curve), OC; ASTM D-87 51 0.34 Oil content, wt- %; ASTM D-721 Average molecular weight 376 Crystallization point, O C 51.6 a-p phase transition point, O C 34.0 Temperature change required for total phase transformation, OC 8.6 at liquid-solid transform. at a-p phase transition 10.5 Expansion coefficient, cm3/g * OC in the liquid phase 0.0011 0.0016 in the a solid phase 0.0010 in the p solid phase Expansion at melting,* 0.1228 cm3/g vol- x 10.6 ,_ Expansion at a-,!I phase transition,* cm*/g 0.0356 vol- % 3.2 Volume change occurring between the transition point of the a phase and the crystallization point of the liquid, 0.1716 cma/g vol- % 15.5
0.7547 3.22 28
0.7543 3.51
0.7555 3.59
19
19
55
Microcryst. wax
0.7945 12.59 36
53 0.48 358 53.2 35.5
0.22 377 55.9 38.4
56 0.36 387 56.8 40.5
62 8.52 587 74.0 -
8.5 10.3
8.8 11.4
7.7 12.0
35.0 -
0.0011 0.0014 0.0009
0.0010 0.0013 0.0008
0.0010 0.0014 0.0008
0.0010 o.oO09
0.1237 10.7
0.1264 11.0
0.1262 11.0
0.1372 12.5
0.0369 3.3
0.0387 3.5
0.0390 3.5
0.1735 15.7
0.1763 16.0
0.1770 16.1
-
0.1372 12.5
* Since paraffin waxes are mixtures of several components, these processes are non-isothermal.
the initial deviations from the curves representing the liquid phase. The actual initial temperature of crystallization, i.e. at which the first crystals appear in the melt, is some degrees centigrade higher. Its accurate measurement, however, is difficult. The volume-temperature curve for the microcrystalline wax differs from the former curves above all in that the solidification process is not indicated by a wellobservable break : the process takes place within a much broader temperature range than in the case of macrocrystalline waxes. Also, no transformation in the solid phase can be observed, although such transformations may actually take place, but will be masked by the broad solidification range. When crystal forma7
98
I. PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
.
0 1 3000
0
E
u 1 2500
d E 1 1 2000 0
r" 1 1500 u
aJ
0
m l 1000
20
25
30
35
40
L5
50
55
60
65
70
75
00
Temperature. "C Fig. 1-36. Specific volume versus temperature for various paraffin waxes
1.3500
. 0
1.3000
rn
1.2500
U
= .-
1.1 500
U
Qi CL CT)
1.1000 1.0500 Temperature,
"C
Fig. 1-37. Specific volume versus temperature for some n-alkanes
tion starts, the volume of macrocrystalline waxes sharply decreases. In the case of the microcrystalline wax, however, the corresponding break occurs at some centigrades below the crystallization point, and the break, as noted before, is only slight. These differences between the two paraffin wax types are caused by the higher oil content and molecular weight range as well as by the iso- and cycloalkane content of microcrystalline paraffin waxes. It may also be seen from the data in Table 1-45 that the values of the expansion coefficients for macro- and microcrystalline waxes in the liquid and solid state are approximately identical. Total expansion of microcrystalline wax, however, is much less than that of macrocrystalline waxes. The difference found in total expansion is in good agreement with the volume change observed at the solid-phase transition in macrocrystalline paraffin wax. Hence the smaller expan-
(D) PHYSICAL PROPERTIES OF PARAFFIN WAXES
99
sion of microcrystalline wax is due above all to the absence of solid-phase transition. It is obvious that for a given commercial wax, the character of the relationship between specific volume and temperature will depend on the carbon atom number and structure of the constituting individual alkanes, as well as on the nature and amount of non-paraffinic compounds present in the wax. To demonstrate this relationship in the case of individual alkanes, Fig. 1-37 is presented, in which, by way of example, specific volume versus temperature is plotted for normal C,, CZ4,CZB,C,,, C,, and C,, alkanes. These expansion curves resemble those in the foregoing figure, but certain differences should be noted. In the case of C24,C2,, C,, and C,, alkanes, thesolid-phase transition takes place at some "C below the melting point. The curve for C,, displays no solid-phase transition, while the curve for C,, exhibits two such transitions. It is clear from the foregoing that if a sufficiently wide temperature range is being considered, a difference will be observed between the total change in specific volume of macro- and microcrystalline paraffin waxes. Kinsel and Phillips proposed to utilize this phenomenon for classifying petroleum waxes into macroand microcrystalline waxes, by introducing a so-called crystallinity index. The volume contraction occurring during cooling a liquid paraffin wax from a given temperature to another temperature consists of three parts : (i) The contraction Kl occurring while the liquid cools from the given temperature to the melting point. Its value depends on molecular weight, the macroor microcrystalline nature of the wax being of no importance. (ii) The contraction K, taking place during solidification and, if any, solidphase transition. Its value does not only depend on molecular weight, but on the crystallization tendency of the wax. In the extreme case, when the substance is amorphous, the value of K, will be zero. Its value is the higher, the greater the crystallization tendency of the wax. (iii) The purely thermal contraction Ks of the solidified wax when cooled from the melting point to the given final temperature. Its value depends primarily on the molecular weight range. Total contraction Kt is equal to the algebraic sum of the above partial contractions : Kt ( ~ 0 1 - x = ) KI K, K, (1-16)
+
+
Hence the value of K,, i.e. contraction taking place during solidification and solid-phase transition can be obtained by measuring K, and K, and subtracting their sum from the measured value of K,. Kinsel and Phillips cooled 100 cm3 paraffin wax samples of various origin and structure from 93.4 "C, at a cooling rate of 5.56 "C (10 O F ) per hour, to temperatures exceeding their melting points by 2.7 "C. The measured contractions for the various waxes yielded an average Kl value of 0.072 vol-%/"C. This value could be used for all paraffin waxes with a maximum error of k0.008 vol- %/T. In contrast, the values of K, for the solid state changed with temperature. Large con'7
100
I. PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
tractions were observed for all paraffin waxes immediately below their melting points, the values decreasing with further cooling. KJ'C values over different temperature ranges, for a 73 "C melting point macrocrystalline wax and a 71 "C melting point microcrystalline wax are presented in Table 1-46. Table 1-46. K , values of a macrocrystallineand a microcrystallineparaffin wax over different temperature ranges
I
Macrocrystallineparafin wax, melting point 73 "C Temperature range, "C
K , for 0.56 "C
Microcrystalline paraffin wax. melting Doint 71 "C
Temperature range, "C
temperature decrease
71-66 66-60 60-54 54-49 49-27
0.530 0.333 0.144 0.078 0.040 Average value 0.155
K* for 0'56
temperature decrease
69-64 64-58 58-53 53-47 47-27
0.230 0.188 0.170 0.130 0.077 Average value 0.130
The large contraction observed immediately below the melting point is the combined effect of both thermal contraction and structural change occurring in the solid phase. Hence, it would be incorrect to subtract the average value of K, from Kt in order to determine Kc. Kc includes, of course, contraction due to structural changes, but this cannot be experimentally determined. Kinsel and Phillips assumed that for amorphous waxes the purely thermal contraction per "C is identical in the solid and liquid state. Therefore, contraction of different waxes should be compared over temperature ranges identical with respect to their melting points and not over an absolute pre-set temperature range. The chosen ranges should be wide enough to include all contraction due to changes in crystal structure. Kinsel and Phillips chose a temperature range A t , = 5.56 "C (10 OF) above the melting point and A t , = 27.80 "C (50 OF) below the melting point for their experiments. The value of Kc and the crystallinity index serving to characterize the crystalline character of the structure were then derived as follows: For the above conditions (1-17) Since, as assumed above,
-K.- -- 4 At2
(1-18)
At,
Equation (1-17) will assume the following simplified form:
Kc = Kt - K1 A t, -
0
33.36
(1-19)
(D) PHYSICAL PROPERTIES OF PARAFFIN WAXES
101
Using the value K J d t , = 0.072 accepted to be valid for all paraffin waxes, it follows that K, = Kt - 0.072 * 33.36 = Kt - 2.4 (1-20) Kinsel and Phillips defined the crystallinity index as ten times the value of K,:
(1-21)
C.Z. = lo(& - 2.4)
where Kt is total contraction of the wax measured over the range from 5.56 "C above its melting point to 27.80 "C below its melting point; K, is that portion of the contraction of the solid wax which is due to thermal contraction only and independent from changes in crystal structure, and Kl is the contraction of the wax in the liquid state. Table 1-47 lists total contraction and crystallinity index values calculated from the former for microcrystalline, intermediate and macrocrystalline paraffin waxes. Table I-47.Total contraction and crystallinity index for macrocrystalline, intermediate and microcrystalline paraftin waxes Melting point, "C
Total contraction, vol- %
Crystallinity index
Macrocrystalhe parafin waxes 55 52 60 73 51 56 64
13.3 13.7 13.7 13.9 14.0 14.1 14.1
109 113 113 115 116 117 117
Intermediate parafin waxes 70 74 72 74 66
11.4 11.7 12.5 S2.5 12.7
90 93 101
Microcrystalline paraf i n waxes 71 82 71 64 83 71 83 60 86 86
8.9 9.2 9.3 9.3 9.4 9.4 9.5 9.8 10.0 10.4
65 68 69 69 70 70 71 74 76 80
101 103
102
1. PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
The crystallinity index of microcrystalline waxes does not exceed 80, while macrocrystalline waxes have values above 110. However, even the use of the crystallinity index does not allow the drawing of a sharp dividing line between macro- and microcrystalline structures. Any classification based on this index must always take into account the oil content of the Table f-48.Total contraction of mixtures of paraffin waxes with various percentages of white mineral oil Oil content, wt-%
Melting point,
Total contraction, vol- %
Macrocrystalline parafin white oil waxes 0 5 10 20 30 40
53 52 51 50 47 45
13.30 12.50 11.50 10.50 9.05 1.25
Microcrystalline para f i n waxes white oil 0 5 10 20 30 40 50 0 5 10 20 30 40 50
74 73 73 12 70 68 65 86 85 85 84 82 81 79
10.05 10.34 10.28 9.16 8.18 1.49 6.79 11.40 11.40 11.40 10.52 10.24 8.76 8.08
+
+
wax. As demonstrated by the data in Table 1-48, total contraction for microcrystalline waxes with 5 to 10 wt- % oil content, these being still acceptable grades, is practically identical with total contraction for waxes containing no oil, whereas 5 wt- % oil in macrocrystalline waxes will reduce total contraction by 0.8 vol- %. This appears a significant decrease, but since oil content in commercial refined macrocrystalline paraffin waxes is normally below 1 wt- %, its effect on the crystallinity index of such waxes will be negligible.
3. Optical properties The refractive index is a physical property frequently used for identifying substances and for determining their compositions. The refractive index of paraffin waxes is usually measured at 80 to 85 "C.
103
(D) PHYSICAL PROPERTIES OF PARAFFIN WAXES
The relationship between density, refractive index (both measured at the same temperature) and molecular weight is given by the Lorentz-Lorenz formula :
(1-22) where M , is molar refraction, n refractive index, M molecular weight and d density. Table 1-49 lists refractive indices in the solid state of some macrocrystalline paraffin waxes having different melting points. Table Z-49. Refractive indices of some macrocrystalline paraffin waxes in the solid state 50
Melting point, "C
I
'
52
55
1
57
_
I
_ 61~
_
Refractive index
At 1 0 ° C At 20°C At 25 OC At 40 "C At 5 0 ° C
1.5306 1.5268 1.5169 1.5040
-
1.5321 1.5278 1.5256 1.5071 -
1.5348 1.5305 1.5277 1.5103
-
1.5366 1.5332 1.5311 1.5163 1.5049
1.5350 1.5328 1.5241 1.5087
The refractive index and the molar refraction calculated from the former are functions of chemical composition and molecular weight. Relationships between the molar refraction and molecular weight of alkanes and alkenes, cycloalkanes and aliphatic esters are plotted in Fig. 1-38. Within each homologous series, molar refraction is the function of molecular weight. The refractive indices of macrocrystalline paraffin waxes at 84 "C vary between 1.4210and 1.4315, their molar refraction between 100 and 154. The corresponding values for microcrystalline waxes are 1.4320 to 1.4480 and 160 to 195. In Table 1-50, refractive index data measured a t 70 and 90 "C and molar refraction are listed for a number of hydrocarbons which are usual constituents of macrocrystalline and microcrystalline paraffin waxes. The data indicate that the temperature coefficient of the refractive index slightly decreases with rising molecular weight in the C,,-C,, normal alkane range. The value of this coefficient is identical for normal and branched alkanes having the same molecular weight. According to Mazee, the molar refraction of the compounds in Table 1-50 can be calculated, with a knowledge of the molecular weight, by using the following relationship : M , = 0.33063M -t 1.6165 (1-23) Plots of the refractive index against temperature always indicate liquid-solid and solid-solid phase transformations. Therefore, the refractive index can be utilized to a certain extent for studying the crystal structure of paraffin waxes. Figure 1-39 represents such a plot for a macrocrystalline wax having a melting point of 48 "C. In the liquid phase, one refractive index value is measured for
104
1. PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
9
160
0
150
c
0
5
140 ._ c V
2 130 .&? -2 120
P
'"3ZO
310
,d,
4AO I 4!?@*4b 4!iO G!O
Molecular weight Fig. 1-38. Molar refraction versus molecular weight for some hydrocarbons and aliphatic
esters. I alkanes and alkenes, 2 cycloalkanes, 3 esters
Table I-50.Refractive indices at 70 and 90 OC and molar refraction values for various hydrocarbons
I
Compound
I
CZ1H,, n-Heneicosane C,,H,, n-Tricosane CZ4H,,n-Tetracosane C,,H,, n-Octacosane C,,H,, n-Triacontane C,,H,, n-Hentriacontane C34H70 n-Tetratriacontane C,,H,, n-Pentatriacontane C,,H,, n-Hexatriacontane C,,H,, n-Tritetracontane Cs4H,, 2-Methyltricosane CZ4H,,2,2-Dimethyldocosane C,,H,, 13-Methylpentacosane CZsH,, 10-Nonylnonadecane C14HB022-Methyltritetracontane CtaH,, 1-Cyclohexyloctadecane
*n +*
-
refractive index,
f =
Refractive index at 7 0 ° C
1.4240 1.4210 1.4283 1.4324 1.4342 1.4354
-
-
1.4216 1.4269 1.4303 1.4322 1.4417 1.4416
1
at 9 0 ° C
1.4160 1.4190 1.4205 1.4248 1.4266 1.4278 1.4296 1.4301 1.4308 1.4340 1.4201 1.4192 1.4229 1.4247 1.4346 1.4339
I 1
An * At
~~-
0.00040 0.00040 0.00039 0.00038 0.00038 0.00038
-
0.00038 0.00039 0.00037 0.00038 0.00036 0.00039
99.46 108.64 113.23 131.83 141.03 146.16 159.65 164.38 168.25 201.37 113.48 113.31 122.68 131.60 206.17 111.09
temperature
M = molecular weight, d = density
every temperature. In the a- and /?-phaseof the solid state, double refraction appears owing to anisotropy. From the two curves referring to the solid state, it can clearly be determined that the transition from the a-phase into the /?-phase takes place in this case between 30.6 and 24.4 "C.The less the constituents that are contained in the wax in question, the narrower the transition temperature range. Individual alkanes have sharp transition temperatures, as has been shown in Fig. 1-37.
105
(D) PHYSICAL PROPERTIES OF PARAFFIN WAXES
1.58 156
1.54 1.52
- 1.50 a
2
1.48 146
5 (L
144 1.42 140
15
25
35
45
55
65
75
a5
95
Temperature, "C
Fig. 1-39. Refractive index kersus temperature of a macrocrystalline paraffin wax (melting point 48 "C)
When measuring refractive index as a function of temperature, it is more accurate to use polarized light, since when using non-polarized light there is a possibility of double refraction. Measurements of the refractive index can be used for technological control in paraffin wax manufacture. Fig. 1-40 shows Tiedje's experimental results. His starting material was a microcrystalline wax originating from a residual oil. From this he prepared fractions I , II and III by distillation. Subsequently he separated the starting material, as well as the three distillates, by fractional crystallization into fractions having different melting points. Simultaneously he prepared, as a
Boundary of naphthenes Boundary of is0 -alkanes
Melting point, "C
Fig. 1-40. Refractive indices of fractions prepared from a microcrystalline paraffin wax by distillation and crystallization
106
1. PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
first stage, a narrow melting-range fraction by crystallization of the initial microcrystalline wax. Its melting point was in the 58 to 67 "C range. From this material he prepared several further fractions by distillation (marked by IV in the figure). He then measured the refractive index of all fractions at 80 "C and plotted them against their melting points. The objective of this investigation was to find out whether the sequence of operations, when both crystallization and distillation are applied, affects the sharpness of separation. As seen in the figure, the relationships between melting points and refractive indices give a clear answer. The refractive indices of final fractions having identical melting points, that is, their chemical compositions vary largely according to which separating operation, crystallization or distillation had first been applied. Among further optical properties, the colour and colour stability of paraffin waxes are important characteristics in many applications. Among instruments used for measuring colour, are the Lovibond Tintometer, the Saybolt Chromometer and the Tag Robinson instrument. The colour of macrocrystalline waxes in the liquid phase is best determined with the Lovibond Tintometer or the Saybolt Chromometer. To measure the darker colour of microcrystalline waxes in the liquid state, the Lovibond Tintometer in which thin layers of the material are used, and the Tag Robinson instrument are suitable. The problem of measuring the colour of paraffin waxes in the solid state reappears from time to time. However, up to the present no generally accepted methods, like those for liquid-state measurement, have been developed. Most specifications require that paraffin waxes do not change their colour during storage or application. Colour stability is connected primarily with oxidative stability, since oxidation causes discoloration of the wax. No generally accepted method for evaluating colour stability has as yet been developed, owing to the fact that oxidation causing discoloration depends on many variables like temperature, oxygen concentration, intensity and spectrum of light, effect of metal catalysts, etc. The methods developed so far can be classified into two groups. In one group measurements are made in the liquid state, in the presence of metal catalysts and air. In the other group, colour stability is investigated in the solid phase, in daylight, at a specified temperature. For applications in the paper industry a glossy surface of the paraffin wax film is required. Glossy films are obtained by rapid cooling which results in the formation of small-size crystallites. These reflect a large proportion of the incident light, whereas relatively large-size crystallites obtained by slow cooling yield dull surfaces. Initially glossy surfaces of paraffin waxes become duller with time, due to recrystallization and oxidation. The extent of gloss is measured by photometry of the reflected light. However, no method yielding satisfactorily reproducible results has as yet been developed.
(D) PHYSICAL PROPERTIES OF PARAFFIN WAXES
107
4. Rheological properties
The rheological behaviour of macrocrystalline and microcrystalline paraffin waxes in the temperature range below their melting points depends on the lattice structure, on the forces between the molecules forming the lattice and on the chemical composition defining the former. Thus, even in the case of identical origin, a given macrocrystalline or microcrystalline paraffin wax, at temperatures below its melting point, can behave as an elastic, viscoelastic or viscoplastic system, depending on crystallization conditions, especially on the cooling rate, moreover on the actual temperature, on the magnitude of the acting forces and on the mode of load. Since paraffin waxes are polycrystalline substances, no sharp boundaries between these deformation behaviour types depending on the above conditions can be drawn. Except for chemical uses, in almost all applications of macrocrystalline and microcrystalline paraffin waxes, definite rheological properties are required. It is noteworthy that none the less these properties had up to the present not yet been properly characterized and purposefully studied. Many wide-spread qualifying parameters, e.g. hardness, flexibility and tensile strength yield important pertinent information. In our research work in these directions we developed methods effectuating static and dynamic loads, corresponding to the crystal structure of paraffin waxes. In discussing the elastic and plastic deformation of crystalline substances, the following relationships are, to a greater or lesser extent, depending on conditions, also valid for paraffin waxes. (i) It is a general rule that the finer the crystal grains in a polycrystalline system, the higher its strength. The size of the crystal particles and the crystal structure can be modified by thermal and mechanical treatment resulting in recrystallization. The crystal structure can also be changed by adding a suitably selected additive. (ii) When a melt of a polycrystalline substance is being cooled, the system will in most cases assume an oriented structure below the melting point. In the direction of the highest temperature gradient during cooling, coarser particles will be formed than in the other directions. (iii) In the case of elastic deformation, the atoms, ions or molecules forming the crystal lattice will be shifted to a small extent against one another. The field of intermolecular forces or the field of atomic and ionic forces will be thereby disturbed, and the system will accumulate such an amount of potential energy as to keep equilibrium with external forces. When the external load ceases, internal stresses will return molecules, atoms or ions to their original places, and the initial lattice structure will instantaneously be re-established. (iv) If structural elements acquire higher energies than characteristic for their potential trough, they will pass the potential barrier and arrive into a neighbouring potential trough. If this process is successively repeated, it will manifest itself macroscopically in reaching the yield point, i.e. in plastic deformation of the
108
I. PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
system. In test specimens made of polycrystalline substances plastic deformation in various parts of the specimen will appear at different loads, indicating that although macroscopically the deformation appears elastic, plastic deformation may already have taken place in some parts. (v) Except in the case of ideal elastic deformation, the internal stresses caused by deformation relax with time. In crystalline systems, this relaxation is accompanied by the shift of numerous atoms or molecules along definite crystallographic planes. (vi) In polycrystalline systems, in addition to simultaneous elastic and plastic deformation and to relaxation of internal stresses, the so-called elastic post-effect usually also appears. This manifests itself in hysteresis of the stress-strain curves, i.e. these curves differ when stress is repeatedly applied. The fatigue phenomenon of polycrystalline systems is related to elastic hysteresis. Fatigue means that periodically changing loads, after a certain number of cycles, result in creep or break of the test specimen at loads lower than the load corresponding to the yield point. For evaluation of the rheological properties of crystalline substances, including paraffin waxes, testing methods belonging essentially to three groups can be considered :
(i) strength tests, (ii) hardness tests, (iii) fatigue tests. Strength tests include tensile, compression, bending, torsion and impact-bending tests. Hardness is the resistance against the penetration of a body (needle, or cone, or plunger rod) under a defined load, this body being made of a harder material than the substance being tested. To measure the hardness of paraffin waxes, penetration tests are widely accepted. It is a common feature of strength and hardness tests that the test specimens are subjected to short-time stresses. In addition to the characteristics that are obtained in this manner, long-period fatigue tests yield important information. For all solids a fatigue limit exists: this is the stress below which the substance is able to resist an infinite number of fatigue cycles without breaking. For paraffin waxes the fatigue phenomenon is of greatest interest in wax-plastics compounds containing relatively high amounts of plastics. The most wide-spread strength test for paraffin waxes is tensile testing. We investigated the tensile strength of macro- and microcrystalline paraffin waxes in great detail. Our results indicated that tensile strength of both macroand microcrystalline waxes in the temperature range from -20 "C to +25 "C increases with the speed of stretching. This finding demonstrates that waxes behave in this temperature range as viscoelastic systems. A great number of tests has confirmed that tensile strength can vary greatly even within relatively narrow melting point and oil content ranges, and between macrocrystalline paraffin waxes from the same origin, but chosen from different production batches.
(D) PHYSICAL PROPERTIES OF PARAFFIN WAXES
109
The limiting values measured with macrocrystalline paraffin waxes obtained from Romashkino crude, having a melting range of 52-54 "C and an oil content of 0.5-1.03 wt-%' are presented as an example in Table 1-51. Table 1-51. Maximum and minimum tensile strength values of macrocrystallineparaffin waxes from Romashkino crude (melting range 52-54 "C, oil content 0.5-1.03 wt- %) -~
Temperature,
~
O C
at 50 mrnlrnin
-20
+ +
Tensile strength, N/cm*
-49.0 9.8-58.8 45.1-78.4 -39.2
0 25 30
1
at 500 mmlmin
-
196.0 14.7-1 86.2 65.7-107.8 -39.2
According to our investigations, tensile strength values as listed in Table 1-52 should be expected from macrocrystalline paraffin waxes with good tensile properties. (The values are valid for stretching rates of 500 mmlmin and for test specimens as used by us.) Table I-52. Tensile strength values for macrocrystalline paraffin waxes specified as "good tensile" (Testing speed : 500 mmlmin) "C
- 20 0 25 30
+ +
Tensile strength, N/cm'
196.0-215.6 176.4-186.2 78.4-107.8 39.2-49.0
It may be seen from Tables 1-51 and 1-52 that tensile strength increases with lower temperatures (at least within the temperature range from - 20 "Cto +30 "C). This is valid for both macrocrystalline and microcrystalfine waxes. Tensile strength also reacts sensitively to oil content: it decreases with higher oil content, particularly at low temperatures. A comparison of tensile strengths of macro- and microcrystalline waxes does not allow the establishment of an unambiguous and generally valid relationship. Apparently the effect of other factors on tensile strength, e.g. oil content and temperature, is greater than the effect of macro- or microcrystalline crystal structure. Blends of macro- and microcrystalline paraffin waxes have tensile strengths which, when plotted against composition of the blend, yield curves exhibiting
110
I. PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
maxima. Figure 1-41 represents tensile strength versus composition of blends prepared from a macrocrystalline wax (melting point 52 "C, oil content 1.0 wt-%) and a microcrystalline wax (melting point 69 "C, oil content 13.0 wt-x), measured at different stretching rates at 0 "C. Compressive stresses and deformations are similar, apart from the sign, to those of tensile tests. In compression, the length of the circular or quadratic cross-sectional test specimen will decrease, and its specific value yields the deforniation corresponding to the given stress conditions. We developed a method for measuring compressive deformation in which we utilized test specimens with 1 cm2 circular cross-sections and 8.21 mm length. Temperatures are variable between -20 "C and +40 "C, compressive stresses between 2.45 N/cm2 and 981 N/cm2. After stress removal, also as a function of time, elastic recovery can be studied. The measured results can be evaluated based on the specific characteristics and functional relationships summarized in Table 1-53. Deformation and elastic recovery as a function of time, after removing the compressive stress, for a macrocrystalline paraffin wax (drop melting point 53 "C, oil content 0.18 wt-%) at
I
I
Microcryst. wax, w t - % L
100
l
~
i
l
l
l
80 60 40 20 Macrocryst. wax, wt-%
~
l
l
l
0
Fig. 1-41. Tensile strength versus composition for blends of a macrocrystalline and a microcrystalline paraffin wax. at 0 O C (v = stretching rate, mm/min)
111
(D) PHYSICAL PROPERTIES OF PARAFFIN WAXES
Table I-53. Specific characteristics and functional relationships for characterizing isothermal compressive deformation Symbols
height of the initial test specimen, mm height of the deformed test specimen, mm height of the test specimen after recovery, mm acorn,, compressive stress, N/cm* tR time of recovery, min tD time of deformation, min T temperature, OC
h0 h h,
Definitions ho- h D=deformation ratio related to the initial height of the test specimen (specific deho formation) h,- h recovery ratio related to the initial height of the test specimen, R =h0 D,= (D- R) permanent deformation
h,- h R’ = -ratio of recovery and deformation ho-h Functional relationships t D = const. aCOlllDI = f ( O ) R = f (tR) acomDr = const. a,,,,, = const. D~ = f ( t R ) %om,, = f(R’) tD = const.
t D = const. t R = const.
Table 1-54 Compression characteristics of a macrocrystalline paraffin wax at 25 “C (drop melting point 53 OC, oil content 0.18 wt-%)
I Characteristics
Initial height of test specimen ho, mm Height of the deformed specimen h, mm Height of the test specimen after recovery h,, mm ho-h D = -h0 h,- h R =h0 D,= D - R
h,- h R’ = _ _ ho- h
Compressive stress, Nlcm’
-l
I
29.4
I
49.0
58.8
Time of deformation, min
8.21
8.02
8.04
7.98
7.93
8.33
8.11
7.85
7.89
1.73
7.16
8.03
8.17
7.91
7.97
7.82
7.85
8.13
0.012
0.021
0.020
0.031
0.021
0.036
0.007
0.007
0.010
0.011
0.011
0.012
0.005
0.014
0.010
0.020
0.010
0.024
0.60
0.35
0.53
0.36
0.53
0.33
(D) PWSICAL PROPERTIES OF PARAFFIN WAXES
113
will be characterized by its compressive strength, that is, by the ratio of the force resulting in break and the initial cross-sectional area of the test specimen. Since the deformation of paraffin waxes is viscoelastic or plastoelastic, their compressive strength can unequivocally be determined only when conditions for the loading time are also defined. Compressive strength was defined by us as the compression force acting on a surface of 1 cm2 that leads to the break of the test specimen within 5 seconds. According to these tests, the compressive strength of macrocrystalline paraffin waxes at ambient temperature is higher than that of microcrystalline waxes. Oil content always reduces the value of the compressive strength. In Fig. 1-43 the compressive strength of two macrocrystalline and two microcrystalline waxes differing in oil content is plotted against temperature. An unambiguous relationship also exists between crystal structure, chemical composition and compressive strength. Compressive strength values for microcrystalline paraffin waxes obtained by fractional crystallization are summarized in Table 1-55. The starting material was a refined residual oil petrolatum from Romashkino crude. Its compressive strength could not be measured at 25 and 0 "C, since it underwent plastic deformation and did not break. Information on the behaviour of paraffin waxes to dynamic stresses is obtained from impact-bending tests. We developed a method for the evaluation of the toughness of paraffin waxes based on the use oethe Charpy pendulum. Without going into details of the method, it shall be noted that impact-bending strength Lfis defined as the ratio of the energy L required to break the test specimen and
350 300
250
200 150 100
,Macrocrystalline
waxes
50
,Microcrystalline
waxes
0 -
1 -20 -10
0
+I0 +20 + 10
Temperature, "C
Fig. 1-43. Compressive strength versus temperature for macrocrystallineand microcrystalline paraffin waxes 8
112
I. PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
25 "C is shown in Table 1-54. The values for elastic recovery always relate to a recovery time of 10 minutes. Numerous measurements have confirmed that the deformation of paraffin waxes resulting from a given compressive stress is, over the temperature range in question, i.e. -20 to f40 "C, a function of the loading time. After removal of the load, deformation will partly or totally disappear as a function of time. This finding also indicates that paraffin waxes that are crystalline at ambient temperature behave as vkcoelastic systems in this temperature range. Compressive deformation properties depend not only on external conditions, but also on crystal structure. Figure 1-42 represents compressive stresses leading to D = 0.02 specific deformation in a 3-min loading time against composition of blends prepared from a macrocrystalline wax (drop melting point 51 "C, oil content 1.0 wt-%) and a microcrystalline wax (drop melting point 69 "C, oil content 13 wt-%). By increasing compressive stress in crystalline substances, the yield point will be reached at a given value, and subsequent deformation will be plastic flow. However, under certain external conditions the test specimens will break before reaching the yield point. In such cases the rheological behaviour of the substance
l
I
I
f
l
l
l
l
l
l
l
100 90 80 70 60 50 LO 30 20 10 0 Macrocryst. wax, wt-"10 Fig. 1-42. Compressive stress resulting in 0.02 specific deformation versus composition for blends of a macrocrystalline and a microcrystalline wax (loading time 3 min)
114
I. PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
Table Z-55.Compressive strength values at different temperatures, for microcrystalline paraffin waxes obtained by fractional crystallization of a petrolatum from a refined residual oil
I
Tested material
Compressive strength, N/cm*
Petrolatum Two-stage fractionation: Stage I: Fraction of components having melting points above 20 "C
+
323.4
588.0
910.2
Stage 11: Fraction of components having melting points between 20 and 0O C
166.6
539.0
744.8
Fraction of components having melting points above 5 O C
214.4
431.2
901.6
+
+
the cross-sectional area F of the specimen :
L,=-L [J/cm21
(1-24)
The impact-bending strength of paraffin waxes depends on the dimensions of the test specimen and on test conditions. In our method we use test specimens having 16 mm diam. circular cross-sections and 110 mm lengths. The results obtained indicate that impact-bending strength of paraffin waxes increases with temperature and reaches a maximum value at a given temperature. From this temperature on, plastic flow appears and the test specimen does not break in the impact-bending test. Figure 1-44 shows impact-bending strength against temperature for macrocrystalline paraffin waxes, each having drop melting points around 50 "C, but differing in oil content. The test was carried out using a striker with an energy maximum of 3.92 J. This must be mentioned, since, particularly in dynamic tests, the viscoelastic or plastoelastic nature of paraffin waxes must be taken into account. It follows from this fact that the value of impact-bending strength will, under otherwise equal conditions, depend on the kinetic energy of the striker in the moment when it strikes the specimen, i.e. on the speed of deformation at that moment. Increasing speeds result in increasingly elastic behaviour : the wax becomes tougher, and finally, with increase from a given speed of deformation, it will behave as a brittle system. Figure 1-45 represents impact-bending strength against composition of blends prepared from macro- and microcrystalline paraffin waxes and measured with 0.98 and 3.92 J strikers at 0 and 25 "C. The figure demonstrates how sensitively impact-bending strength reacts to changes of the crystal structure. It should be noted that in the test at 25 "C using the 0.98 J striker, the blends containing 50 to 80 wt- % macrocrystalline paraffin wax did not break, but were only bent. However,
(D) PHYSICAL PROPERTIES OF PARAFFIN WAXES
115
0.40
0.35 Oil content, wt-%
0.30
6 .
T - 1.0 - 4.2 - 6.2 - 9.1 H - 11.4
a b c
7
L-
5 0.25 c
:
c
Ln
0
0.2c
C ._
U
C a,
J?
c U
0.1E
0
Q
E
-
0.1c
0.0:
c
-20
-10
0 10 20 Temperature,
"c
30
40
50
Fig. 1-44. Impact-bending strength versus temperature for macrocrystalline paraffin waxes differing in oil content
the blends containing less than 50 wt-% macrocrystalline wax, and the pure macrocrystalline wax itself exhibited well-defined breaks. On theother hand, the blends containing 50 to 80 wt-% macrocrystalline wax, when using the 3.92 J striker, also had defined impact-blending strength values. Hence, it may be assumed that the crystallite systems formed over the 50 to 80 wt- % macrocrystalline wax range show plastic flow at deformation speeds attainable with the 0.98 J striker, while a t the higher speeds realized with the 3.92 J striker, they behave as tough systems, and show some elasticity. Among methods and characteristics to be considered for the evaluation of strength properties of paraffin waxes, there is the Fraass breaking point used for the specification control of bituminous materials. We found that this method can also be applied for paraffin waxes : the breaking point satisfactorily characterizes low-temperature flexibility of waxes, i.e. the temperature limit where brittleness follows. Table 1-56 contains the Fraass breaking point of two-stage fractional crystallization products obtained from a refined residual oil petrolatum of Romashkino origin. In the first stage of fractionation, hard paraffin wax was separated at 30 and 10°C. In the second crystallization, soft microcrystalline 8*
116
I. PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES 1.01
0.1 I 100
I
I
I
I
I
I
I
I
80 60 40 20 Macrocryst. wax, wt-%
I
0
20 40 60 80 Microcryst. wax, w t - %
I
100
Fig. 1-45. Impact-bending strength versus composition for blends of a macrocrystalline and
a microcrystalline paraffin wax
Table 1-56. Fraass breaking point for paraffin waxes obtained by two-stage fractional crystallization of petrolatum from refined residual oil Fractiolu
Stage Z
Fraction obtained at Fraction obtained at
+ 30 + 10 OC
O C
Stage I1 Fractions from the filtrate of stage I at 30 OC Fraction obtained at -20 OC Fraction obtained at - 10 OC Fraction obtained at 0 OC Fractions from the fdtrate of stage I at 10 O C Fraction obtained at -20 O C Fraction obtained at 0 "C
I
Bredti% point,
++2525 -30 -30 -26 -30
-30
(D) PHYSICAL PROPERTIES OF PARAFFIN WAXES
117
wax fractions were separated at 0, - 10 and -20 "C. It may be seen from the data in the table that the second crystallization of the filtrate obtained at + 30 "C yielded, at 0 and - 10 "C,products plastic and flexible at low temperatures, while the products obtained in the first fractionation stage were already brittle at ambient temperature. Penetration measurement is the most wide-spread method for determining the hardness of paraffin waxes. Penetration measurements carried out at different temperatures are suitable to characterize the thermal sensitivity of paraffin waxes. Our investigations showed that in the temperature range below the solidification point the penetration of macrocrystalline waxes changes to a greater extent with temperature than that of microcrystalline waxes. An increase in oil content results in increased penetration values for both macro- and microcrystalline waxes. Besides these factors the penetration also depends to a great extent on the modscation of the crystalline structure. Figure 1-46 shows the penetration values against composition of blends prepared from macro- and microcrystalline waxes, measured at 0 "C and 25 "C. The tests were carried out with the needle specified in the ASTM standard. The macrocrystalline paraffin wax used had a drop melting point of 53 "C and an oil content of 0.6 wt-%. The corresponding values of the microcrystalline wax were 70 "C and 10.0 wt-%. 100 1
I
' 2b
I
!
I
I
40 60 '
8'0 'Id0
Macrocryst. wax, wt-"lo I I I I I I I I I ' A 100 80 60 40 20 0 Microcryst. wax, wt-"b
Fig. 1-46. Needle penetration versus composition for blends of a macrocrystalline and a
microcrystalline paraffin wax
118
I. PROPERTIES OF LIQUID PARAFFINS A N D PARAFFIN WAXES
5. Thermal properties A knowledge of specific heat is almost always necessary in engineering calculations. A value of 2.1 kJ/kg "C is being generally accepted for the specific heat of C2?-C40alkanes, both in the solid and liquid state. This value is in fact acceptable in many cases for industrial practice. It must, however, be remembered that it is only an approximate value. The specific heat of alkanes depends, in addition to temperature, on molecular weight, and in the solid state on crystal structure. According to Cragoe the specific heat of oils with high paraffin content can be calculated by using the following formula :
4.2 c = -(0.388-O.OOO45t)
d
(1-25)
where c is specific heat, kJ/kg * "C, d density at 15.6115.6 "C, and t the temperature in OF. This empirical formula is also suitable for calculating the specific heat of alkanes liquid at ambient temperature. The specific heat against temperature curves for some n-alkanes in the C,o-C,5 range are shown in Fig. 1-47. The figure demonstrates that the 2.1 kJ/kg * "C value is acceptable as an approach only in the C25
Fig. 1-47. Specific heat versus temperature for solid-state n-alkanes in the CI,-C,, range
119
(D) PHYSICAL PROPERTIES OF PARAFFIN WAXES
to C,, range, and even in this range only at temperatures between 30°C and 50°C. This, as well as the effect of crystal structure, are shown in Table 1-57. The temperature ranges indicated in the table include the temperature of the structural change taking place in the solid phase. It can also be stated from these data that specific heat changes over a very wide range with temperature. The specific heat of the crystalline modification stable above the a + /? transition temperature is substantially higher in all cases than that of the modification stable below the transition point, and also than that of the liquid phase. For alkanes which have no solid-phase transition, e.g. n-C,H,, and n-CUHs8, specific heat monotonouslyincreases up to themelting point. The specific heat of the liquid phase Tuble 1-57. Specific heat values of some n-alkanes over different temperature ranges n-Alkanes
C,,H,, n-Heneicosane
40.30-40.40
32.8
15-21 21-32 34-39 45-55
1.89 1.97 5.70 2.39
Cg4H,, n-Tetracosane
50.70-50.80
47.0
25-35 35-45 45-50 52-61
1.80 2.01 4.06 2.43
C30D61n-Triacontane
65.80-65.95
59.2
25-35 35-45 45-57 60-65 67-77
1.97 2.18 2.51 4.11 2.56
C36H74n-Hexatriacontane
75.80-75.85
73.5
25-35 35-45 45-55 65-72 74-75 77-86
1.80 2.01 2.35 3.10 3.77 5.12 2.56
55-65
C,,H,, n-Tetracontane
81.35-81.45
-
30-40 40-50 50-60 60-70 70-80 82-90
1.72 1.89 2.23 3.35 4.11 2.51
C,,H,, n-Tritetracontane
85.25-85.35
-
43-50 50-60 60-70 70-76 76-83 86-91
2.09 2.35 2.60 3.10 3.75 2.64
120
I. PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
is smaller in these cases too than the specific heat of the solid phase close to the melting point. The average heat of fusion of n-alkanes occurring in paraffin waxes is 167.6 kJ/kg. For hydrocarbons that have two crystal modifications in the solid phase, the thermal effect of a + p phase transition is around 83.8 kJ/kg. In macrocrystalline paraffin waxes both phase transition and melting take place over a broad temperature range, and these ranges may overlap, due to the numerous hydrocarbon constituents. Hence a separate determination of heat of fusion and heat of phase transition would meet with difficulties. The total thermal effect of the transformation from the liquid phase to the solid phase stable at the lower temperature is, according to the above-mentioned data, 230.5 to 251.4 kJ/kg. Heat of fusion and heat of transition values for some n-alkanes occurring in macrocrystalline paraffin waxes have been discussed in the foregoing chapter and are listed in Tables 1-33 and 1-34. The true heat of fusion varies between 159.2 and 167.6 kJ/kg. Heat of transformation, for even-numbered alkanes, is around 92.2 kJ/kg, i.e. a substantial fraction of total heat of fusion. In Table 1-58, heat of fusion values for the crystal modification stable at ambient temperature of macrocrystalline paraffin waxes having different melting points are listed. It should be noted from the data that heat of fusion values of macrocrystalline waxes are substantially lower than those of individual n-alkanes. The figures in the table
Table 1-58. Heat of fusion values for macrocrystalline paraffin waxes Melting Point,
"C
51.7 52.2 52.4 65.3
Heat of fusion for the crystal modification stable at ambient temperature, kJ/kg
168.86 163.00 147.07 183.52
do not exceed 184 kJ/kg, whereas the values for the total heat of fusion, relative to the crystal structure stable at ambient temperature for n-alkanes having closely similar melting points, are around 247 kJ/kg. Some authors explain this difference by assuming that in parafin waxes that are composed of hydrocarbon mixtures, the n-alkanes retain the crystal structure stable at the higher temperature, and no solid-phase transition occurs. Another explanation would involve the presence of signscant amounts of soft paraffin wax components in the tested macrocrystalline paraffin waxes, these components reduce the heat of fusion. Similar results were obtained by Further, Parks and Todd with three highly refined macrocrystalline waxes that are shown in Table 1-59.
(D) PHYSICAL PROPERTIES OF PARAFFIN WAXES
121
Table 1-59. Heat of fusion values for various average molecular mass macrocrystalline paraffin waxes Average number of Melting carbon point, "C atoms
20 25 33
36.4 53.3 71.1
Heat o f fusion for the crystal modification stable at the lower temperature, Mfkg
217.88 224.58 226.26
For microcrystalline paraffin waxes, owing to the total or partial absence of solid-phase transition, the values of heat of fusion vary between 146 and 168 kJ/kg. According to Trouton's rule, the molar entropy of evaporation at lo5Pa pressure approaches to a constant value for all substances: Mrs s, = = const = 21
Ts
(1-26)
where M is the molecular weight, r, the heat of evaporation in kcal/kg, and T, the boiling point in K. For C,+, alkanes, the value of the constant varies between 20 and 22. Kistiakowsky replaced the Trouton constant by the following function:
Mrs - - 8.82 + 4.575 lg T, Ts
(1-27)
for hydrocarbon mixtures. Heat of evaporation depends on external pressure according to the ClausiusClapeyron equation : dP r, = AT(V" - v') (1-28)
dr
where rs is the heat of evaporation in kcal/kg, T the boiling point in K, v" the specific volume of the vapour in m3/kg, uf the specific volume of the liquid in m3/kg,-dP the slope of the vapour pressure curve in kgf/m2 * K, and A is 11427
dT
kcal/m * kgf. To calculate the heat of evaporation for hydrocarbons at pressures differing from 1 bar (lo5 Pa), Schumacher introduced the following equation: MrS - -
T
8.82 + 4.575 lg- T V,
(1-29)
122
I. PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
where 0, is the so-called apparent molar volume of the liquid. Its value is 1.2 for n-alkanes, 1.1 for iso-alkanes and 0.9 for naphthenes and their derivatives. These us values are, however, valid only at 1 bar (lo5 Pa) pressure. For other pressures Mr, T -= 8.82 + 4.575 lg(1-30) T V,(P>” where the value of s depends on evaporation temperature. For n-alkanes the following function is valid : s =
0.685 lg T - 0.8
(1-31)
105
84
0
. E
x
7
63 C“
.c
0
2
0 Q
9 a,
-
Lc
0
0
42
aJ
I
21
0 Temperature, “C Fig. 1-48. Molar heat of evaporation versus temperature for n-alkanes liquid and solid at ambient temperature
(D) PHYSICAL PROPERTIES OF PARAFFIN WAXES
123
The evaporation process of alkane mixtures proceeds, of course, at successively changing temperatures at constant pressure, and at successively changing pressures at constant temperature. For this reason engineering calculations apply average boiling points. After determining the average boiling point, calculations are carried out with the individual hydrocarbon having the same boiling point as the average boiling point of the mixture. Figure 1-48 represents molar heat of evaporation of a number of n-alkanes liquid or solid at ambient temperature against temperature at different pressures. A further thermal property of paraffin waxes to be mentioned is thermal conductivity. This can be calculated for macrocrystalline paraffin waxes having melting points in the 50 to 54 "C range, over the temperature range from - 180 "C to +30 "C, using the following empirical relationship:
1 = 0.005 . (1
- 0.0016t)
(1-32)
-
where I is thermal conductivity in Jim "C * s, and f is temperature in "C. The above relationship is acceptable as an approach for microcrystalline waxes and for paraffLns liquid at ambient temperature.
6. Solubility Petroleum waxes are obtained, following the usual manufacturing processes, by crystallization, in the presence of various solvents, from pafaffinic distillates and refined paraffinic lubricant oil fractions. In some applications paraffin waxes are used in solution, and in many cases they come into contact with solvents during their service life. Thus solubility is a very important physical characteristic of paraffin waxes. The solubility values of macrocrystalline paraffin waxes, having 50-55 "C melting ranges, in solvents significant from the view of both manufacture and application are listed in Table 1-60. The data should be considered as average values, since, at identical melting points, the chemical composition of macrocrystalline waxes from different origins can vary, and hence their solubilities in a given solvent under given conditions will also vary. Figure 1-49 represents solubility against temperature data for a refined p a r a f i wax (melting point 51 "C) in various solvents. Figure 1-50 shows solubility versus melting point data for different paraffin waxes, measured at 20 "C, in various solvents. As a general rule it can be stated that solubility increases in all solvents with decreasing melting point. Solubility values of paraffin waxes in different boiling-range petroleum distillates can be determined by using the nomogram presented in Fig. 1-5 l . The lefthand scale of the nomogram represents the average boiling point of the solvent, the right-hand scale the difference between the melting point of the paraffin wax and the temperature of dissolution.
L
Table 1-60. Solubility of macrocrystallineparaffin waxes in various solvents (g wax/100 cms solvent)
I
Solvent
1 1 1 1 -15
Propane n-Pentane n-Hexane n-Heptane n-Octane n-Decane Naphtha (boiling range 96-146 "C) Kerosene (boiling range
0.18
0.27
178-271 "C) Methanol Ethanol n-Propanol Isopropanol n-Butanol Iso-butanol Acetone Methyl ethyl ketone Methyl propyl ketone Methyl butyl ketone Methyl isobutyl ketone Dichloroethane Benzene Toluene 30 % acetone- 35 % benzene- 35 % toluene
-10
0.011 0.024 0.045 0.034
-5
0.30
0
0.95
2.77 1.37 0.99
3.69 2.18 1.69 0.94
0.93
1.70
0.28
0.50
0.89
0.13
0.045 0.095 0.180 0.14 0.29
5
0.55
0.52
0.023 0.048 0.089 0.067
I
0.018 0.087 0.188 0.333 0.253 0.078
1
Temperature, "C 10
5.11 4.81 3.55 2.90 1.44
1
15
~
6.94 6.07 5.06 4.24 2.74
20
1
9.53 8.31 7.18 5.93 4.98
25
1
30
35
h,
P
1
40
1
45 ~
17.16 16.23 14.36 11.66 9.17
6C 8
1.60
0.037 0.366 0.666 0.488
0.024 0.096 0.063 0.18 0.185 0.063 0.202 0.775
0.032 0.145 0.11 0.31 0.315 0.095 0.306
0.047 0.21 0.18 0.54 0.543 0.135 0.650
0.008 0.08 0.44 0.33 0.94 0.97 0.258 1.31
0.024 0.17 0.71 0.61 1.86 2.14 0.52 2.53
0.063 0.318 1.35 1.23 3.60 4.03 1.07 7.48
0.103 0.55 2.65 2.36 7.05 9.60 2.30
0.16 0.97 4.95 4.63 16.7 30.0
E
52
0.62
0.8 1.4
0.29 1.90 3.05
0.40 4.4 6.6
0.91 10.5 14.5
2.24 24.5 32.0
5.10 56.0 69.0
0.07
-0.15
0.34
0.8
1.8
4.0
9.0
135
8
(D) PHYSICAL PROPERTIES OF PARAFFIN WAXES
0.11 I I ' I ! I 1 -18 -16 -14 -12 -10 -8-6 -4 -2
125
' ' '
' " I I I I 0 +2 +4 +6 t 8 +I0 +12 +14+16 +I8
Temperature, "C
Fig. I-49. Solubility versus temperature for a refined macrocrystalline paraffin wax (melting point 51 "C). I cyclohexane, 2 methylcyclohexane, 3 95-150 "C boiling-range petroleum distillate, 4 160-200 "C boiling-range petroleum distillate, 5 180-270 "C boiling-range petroleum distillate, 6 toluene, 7 propane, 8 mixture of 65 wt- % benzene and 35 wt- % acetone
Melting point,
O C
Fig. I-50. Solubility, of paraffin waxes versus melting point in various solvents at 20°C. I nitrobenzene, 2 ethylene dichloride, 3 paraffinic distillate, 4 naphtha
126
I. PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
24 Fig. I-51. Solubility of paraffin waxes in petroleum distillates having different average boiling points. Instruction f o r the use of the nomogram: identical sides of the solubility scale and the right-hand scale must be used together. Example: average boiling point 200 OC, temperature difference 19 'C. Then solubility is 47 g/100 cm3
(D) PHYSICAL PROPERTIES OF PARAFFIN WAXES
127
Several authors developed equations for calculating the solubility of paraffin waxes. Berne and Allen found the following relationship for hydrocarbon solvents, particularly for non-aromatic distillation fractions : C = (1120 - 2.97Y) 1.357"-")
(1-33)
where C is the solubility of the paraffin wax in g/100 cm'; Y , in "C, is the average of the temperatures at which yields of distillation of the solvent carried out according to ASTM standard are 10, 30, 50, 70 and 90%, respectively; m is the melting point of the wax in "C, and t is the temperature of the solution in "C. The equation is strictly valid only for solvents boiling between 60 and 300 "C, for waxes with melting points between 45 and 70 "C, and for solution temperatures between 0 and (m - 10) "C. Pool and his co-workers found that the solubility of paraffin waxes can be described by the following empirical equation : lg W = A (lg T - K)
(1-34)
where W is the solubility of the wax in g/100 g; T the temperature of the solution in K; A is a constant depending on the properties of the wax, and K is a constant depending on the properties of the solvent. The dependence of the solubility of solids on temperature can also be described by utilizing the Clausius-Clapeyron equation. Regarding the molar fraction of the solute, the following relationship can be derived : lgxi = - -.H F 4.575
HF T 4- 4.575Tf 1
-
(1-35)
where xi is the molar fraction of the solute; HF is the molar heat of fusion of the solute, in cal/mol; T is the saturation temperature of the solution in K, and Tf is the melting point of the solid, in K. The solution power of solvents is particularly important in solvent dewaxing processes. The requirement to the solvent is that it dissolve the wax only to a very slight extent or not at all at the operating temperature, while dissolving the oil readily. Solution power is usually varied by utilizing mixed solvents. We studied the solubilities of a macrocrystalline wax having a melting point of 53 "C and of the fractions obtained from the former by fractional crystallization. The solvents used were mixtures of acetone, benzene and toluene. The acetone content varied between 15 and 45 vol-%. Figure 1-52 shows the dependence of solubility on temperature for the original macrocrystalline wax in the pure individual solvents. The wax concentration is plotted on a logarithmic scale against the reciprocal of the absolute temperature. This mode of presentai ion corresponds to the Clausius-Clapeyron equation, with the difference that the unit of concentration is g/100 cn1' instead of molar fraction. Figure 1-53 represents the solubility of the same wax in mixed solvents containing 15, 30 and 45 vol-% acetone, respectively, the rest of the solvent being a 1 : 1 mixture of benzene and
128
I. PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
c
$ 30
m 0,
10 8 6 4
0 0
z 2 a"
5
1
g
0.8 0.6
5
0.4
.-
c
C
a, V
c
0
0.2
V
;j 0.1 3 C .+ ..+.
2P
0.03
3.3 3.4 3.5 3.6 3.7 3.8
3
Reciprocal of cloud point, (l/K).103
Fig. 2-52. Solubility of a commercial macrocrystalline paraffin wax in pure solvents. 2 acetone, 2 benzene, 3 toluene
I
I
I
I
I
I
3.3 3 4 3.5 3.6 37 3.8 : 3 Reciprocal of cloud point, (l/K),103
Fig. 2-53.Solubility of the same wax as in Fig. 1-52 in mixed solvents containing 1 5 , 30 and 45 vol-x, resp., of acetone and made up to 100% with 1 : 1 benzene/toluene
(D) PHYSICAL PROPERTIES OF PARAFFIN WAXES
' i aJ
-> $
129
10 8
6 4
0,
0
.2
0
X
0
3 1 m 0.8 c- 0.6
--0,
0.4
$ C
02
P
c
U 0
g
01
3 &
+ 0
b 003 I I I I I I a 3.3 3.4 3.5 3.6 3.7 3.8 : 3 ReciDrocal of cloud point, (l/K).103
Fig. 1-54 Solubility of the same wax as in Fig. 1-52 and its fractions in a mixed solvent (30 vol- % acetone, 35 vol- % benzene, 35 vol- % toluene). I hard wax, 2 initial wax, 3 intermedier wax, 4 soft wax
oluene. Figure 1-54 represents the solubilities of the initial wax and of the fractions prepared from it, in a mixed solvent consisting of 30 vol-% acetone, 35 vol-% benzene and 35 vol- % toluene. The melting points of the fractions were 56 "C for the hard wax, 50 "C for the intermedier wax and 46 "C for the soft wax. Many of the commercial paraffin waxes contain natural or synthetic waxes or other types of additives. It is, therefore, an important characteristic of their miscibility. In the molten state, petroleum waxes are normally well miscible with vegetable waxes, e.g. carnauba and candelilla wax. At melt temperatures only slightly above the melting point of the paraffin wax, however, solubility of vegetable waxes having higher melting points is rather poor. When such mixtures are stored in the temperature range between the melting points of the pure components, crystallization of the higher-melting component can occur. In the solid state of these systems two phases are present, the higher-melting vegetable wax crystals being uniformly distributed in the paraffin wax. This is presumably the reason for the significant rise in hardness of paraffin waxes even at small concentrations of vegetable wax. It has been observed that high-melting vegetable waxes readily soluble in lowermelting paraffin waxes cause smaller changes in properties than poorly soluble vegetable waxes. This is in agreement with the well-known fact that mixing of a low-melting and a high-melting paraffin wax, readily soluble in one another, 9
130
I. PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
causes only slight changes in properties, except for large concentrations of the higher-melting paraffin wax. The majority of natural resins are well miscible with paraffin waxes. However, the stability of such mixtures is not always satisfactory, because the resins sometimes separate already in the melt or become oxidized. Substantial property changes will take place again only if the solubility of the resin in the paraffin wax is poor. Miscibility of paraffin waxes with synthetic resins is a more complex question. Products containing substantial amounts of oxygen in the macromolecule are poorly soluble or insoluble, whereas polymers consisting essentially of hydrocarbon chains are, owing to their similarity of structure, well miscible with paraffin waxes.
7. Adhesive properties Two adhesive properties of paraffin waxes are sealing strength and blocking point. Laminated packaging materials consisting of two or more layers of usually different materials, e.g. paper, plastic films, metal foil, are frequently manufactured with paraffin wax as sealing agent. Both macro- and microcrystalline paraffin waxes, and products based on such waxes and containing various additives, are used for such purposes. Sealing strength is an important characteristic of laminates. It is numerically expressed by the force per unit length required to separate two bonded layers (paper-paper, paper-metal foil, etc.). The sealing strength of laminated packaging materials depends on the properties of the paraffin wax as well as on the amount of wax and on the laminating process. When laminating paper to paper, sealing strength will depend almost exclusively on the cohesion of the paraffin wax, since the latter readily penetrates into the pores of the paper and will be firmly anchored there. In paper to metal foil laminates, the strength of the bond will be chiefly determined by the adhesion of the wax to the metal, since the wax cannot penetrate into the metal layer. In metal to metal laminates, the bond strength will depend solely on the adhesion of the wax. In laboratory tests for measuring sealing strength, in addition to the above variables, testing conditions will affect results. The most significant testing conditions are angle of separation, speed of pulling the layers apart and the elapsed time between lamination and testing. In addition to suitable cohesive properties, flexibility is an important requirement with which laminating waxes must comply. As well as bonding, the wax film must also act as moisture barrier. To satisfy these various and partly contradictory requirements, laminating paraffin waxes contain various additives, e.g. polyisobutylene, ethylene-vinyl acetate copolymers, vegetable waxes, etc.
(D) PHYSICAL PROPERTIES OF PARAFFIN WAXES
Testing temperature, "C
Pulling speed, cmlmin
Paraffin wax load on paper, mN/mz
268.8 206.0 206.0 206.0 188.4 157.0 160.9
131
Sealing strength, mN/cm
14.7 13.7 12.8 11.8 10.6 10.1 10.1
Sealing strength of microcrystalline paraffin waxes usually greatly surpasses that of macrocrystalline refined waxes. Macrocrystalline waxes in the 360-420 molecular weight range and 5 M O "C melting range, and containing less than 1 wt-% of oil, are considered by many as not suitable for laminating, due to the low sealing strength. Among microcrystalline paraffin waxes, the harder types having higher melting points exhibit lower sealing strength values than the softer, plastic types with lower melting points. Table 1-61 lists the sealing strength of a macrocrystalline paraffin wax (melting point 62 "C)at different thicknesses of the paraffin wax film, i.e. mass of applied wax per unit surface area. The same results are also presented in Fig. 1-55. In the example referred to, it may be observed that above values of 157 mN/m2 sealing strength increases with the thickness of the wax film. However, this increase is presumably due to the fact that, upwards from a defined film thickness, the readings of the testing instrument will include the stiffness of the wax film-paper system in the sealing strength value.
E 2 Z E
15
5 cn
6
L
10
4 -
m
cn
-._0 C
0
rn
5 Wax load, mN/m2
Fig. I-55. Sealing strength versus paraffin wax load on paper
9'
132
I. PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
Table 2-62. Effect of waxing temperature on the sealing strength of macrocrystalline paraffin wax Testing temperature, "C
Waxing temperature,, "C
25 24 26
71 88 99
Paraffin wax load on paper, mN/ma
Sealing strength, mN/cm
Sealing strength of this paraffin wax, at film thicknesses around 157 mN/m2, changes little with temperature of waxing (Table 1-62). The effect of waxing temperature depends on the properties of the wax. Additives in the paraffin wax may result in increased dependence of the sealing strength on waxing temperature. Lamination temperature significantly affects sealing strength even when using relatively homogeneous waxes. Listed in Table 1-63 are sealing strength values, at different laminating temperatures, for the macrocrystalline wax having a melting point of 62 "C. Table 1-63. Effect of laminating temperature on the sealing strength of macrocrystalline paraffin wax Laminating temperature, O C
Sealing strength, mN/cm
93 120 150
10.1 10.5 13.7
In continuous film formation, sealing strength values increase with rising laminating temperatures, and decrease, at identical laminating temperatures, with rising final cooling temperatures. This effect is more significant with waxes containing additives. Table 1-64 lists sealing strengths at different laminating and Table I-64. Sealing strength of paraffin wax containing polyethylene wax at different laminating and final cooling temperatures Polyethylene wax, wt- %
1.1 1.1 1.1 1.1
Laminating temperature, "C
97 107 97 107
Final cooling temperature, OC
Sealing strength, mN/cm
(D) PHYSICAL PROPERTIES OF PARAFFIN WAXES
133
cooling temperatures for a macrocrystalline paraffin wax (melting point 60 "C) containing 1.1 wt- % polyethylene wax. Adhesion of microcrystalline paraffn waxes is substantially higher than that of macrocrystalline paraffin waxes. For this reason laminating waxes always contain microcrystalline paraffin waxes. Table 1-65 contains adhesion values for Table 1-65. Adhesion of micro- and macrocrystalline para& waxes
Sample
A
Drop melting point, "C (ASTM D 127)
Needle penetration at 25 "C, 0.1 mm (ASTM D 5)
Adhesion at 25 Oc9 mN'cma
J K
73 69 75 12 76 14 67 73 65 63 89
24 24 27 21 30 22 24 25 38 41
I
486.6 449.3 440.5 410.1 410.1 410.1 358.1 358.1 281.5 182.5 68.7
L
57
15
0.0
B
C D E F G H
Z
various microcrystalline paraffin waxes (samples A-K), and one macrocrystalline wax (sample L), having various drop melting points and needle penetration values. Adhesion is here defined as the force required to separate unit surface area bonded layers. The values refer to the separation of a cellophane film coated on both sides with wax and laminated on both sides with cellophane, i.e. to the separation of two laminations. The data in the table exhibit great differences between the adhesion of microcrystalline waxes having closely similar drop melting points or needle penetration values (e.g. samples A and H, samples A and F). Using this test method, the macrocrystalline refined wax L - owing to its largely differing crystal structure - yields an adhesion value of zero. Adhesion of the high drop melting point, hard microcrystalline wax K is also small. Another important adhesive property of paraffin waxes is the so-called blocking point, characterizing the sticking of waxed paper and self-sticking of waxes. The blocking point is defined, according to ASTM standard, as the lowest temperature at which waxed papers will stick together sufficiently to injure the surface films and performance properties. Since blocking may occur over a temperature range, a 50% blocking point is measured. For paraffin waxes having identical melting points, increased oil content substantially reduces the blocking point. Additives having lower melting points than the paraffin wax, if present in larger amounts, will also lead to low blocking points.
134
I. PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
With macrocrystalline paraffin waxes, a lower transition temperature also lowers the blocking point, since the crystal modification stable at the higher temperature is always softer than the modification stable at the lower temperature. In Table 1-66, blocking points for a number of low oil content macro- and microcrystalline paraffin waxes are shown, together with their melting points. The data indicate that the blocking temperature is usually lower by 10 to 20 "C than the melting point. Table 1-66. Melting and blocking points of paraffin waxes Difference be-
and blocking point, "C ~
A B C D E F G H I J K L M N 0
P R S T U V
51 50 51 52 54 55 55 56 55 56 58 59 59 58 59 61 62 64 67 71 84
35.6 32.2 32.2 33.9 33.9 37.2 36.7 36.1 39.1 36.7 39.7 43.0 41.9 42.4 43.0 44.1 45.2 52.9 54.0 53.4 63.9
15.4 17.8 18.8 18.1 20.1 17.8 18 3 19.9 15.9 19.3 18.3 16.0 17.1 15.6 16.0 16.9 16.8 11.1 13.0 17.6 20.1
Paraffin waxes are crystallized from a variety of solvents. The separation temperature of crystalline waxes is termed de-oiling temperature in the petroleum refining industry. From one and the same starting material, waxes differing in properties are obtained with different yields if the de-oiling operation is carried out a t different temperatures. Table 1-67 contains the blocking points of waxes obtained from a semirefined wax by crystallization from a mixture of methyl ethyl ketone and toluene, at de-oiling temperatures changing from -7 "C to 27 "C.Raising the de-oiling temperature results in paraffin waxes having higher blocking points. However, the temperature difference between the melting point and the blocking point decreases. At identical melting points, the blocking point of paraffin waxes largely depends on molecular weight distribution. A broader distribution results in lower blocking
+
135
(D) PHYSICAL PROPERTIES OF PARAFFIN WAXES
Table 1-67. Relationship between blocking point and temperature of de-oiling
1
~ f ~ ~ - ~ Paraffin ~ & wax f "C
yield, wt-%
-7 -1 4 16 21 27
1
Melting point,
"c
1
Blocking Point, "c
58
84 77 71 60 46 12
Difference between m.p. and blocking I Doint. "c ~
38.0 40.2 42.4 45.8 49.6 51.2
60 61 62 64 66
20.0 19.8 18.6 16.2 14.4 14.8
points. Table 1-68 presents blocking points for n-alkane mixtures. The data reveal that at identical melting points of the mixtures, the blocking point increases with narrower molecular weight distribution. At the same time, the difference between the melting point and the blocking point is lowered. Both changes improve the usefulness of the paraffin waxes. Table 2-68. Blocking points of n-alkane mixtures differing in molecular weight distribution
Components
1
I
I
Carbon atom number range
-
C25H52-C20H6CI
13 9 5
C2,H,,--C2sH,s
3
C27H56
1
C22H46-Ca4H70
C24HS0-cS2H66
58.0 58.5 58.0 58.0 59.0
I
I
Difference
I
1
point, "C
41.9 45.2 47.4 51.2 54.0
~-
16.1 13.3 10.6 6.8 5 .O
Lower-melting components substantially reduce the blocking point. In order to decide whether the blocking-point-reducing effect of iso-alkanes and naphthenes is due to their lower melting point or to their chemical structure, the blocking points of a commercial refined wax, its blend with an iso-alkane-naphthene mixture (melting point 45 "C, 28 wt- % iso-alkane, 66 wt- % monocycloalkane, 6 wt- % dicycloalkane), and its blend with an n-alkane mixture (melting point also 45 "C) were measured. The data are presented in Table 1-69, demonstrating that the effects of the added components were essentially the same in both cases, both with regard to blocking point and to the difference between blocking point and melting point. This points to the conclusion that the blocking point-reducing effect of hydrocarbons, other than n-alkanes, is mainly the result of their lower melting point. However, presumably this conclusion is not valid for paraffin wax products containing hydrocarbons other than n-alkanes in large amounts.
136
I. PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
Table 1-69. Effect of iso-alkanes and naphthenes on the blocking point of paraffin waxes
! '
Blocking point, "C
60.0
44.0
16.0
58.5
42.4
15.0
58.0
41.9
16.1
Melting point, "C
Materials
Difference between m.p. and blocking point, "C
~ _ _ _ _ _ _ _ _ _
-
Base paraffin wax (70 % n-alkanes, 24 % iso-alkanes, 6 % monocycloalkanes)
+
90 % base paraffin wax 10 % isoalkane-naphthene mixture melting at 45 O c
+
90% base paraffin wax 10% nalkane mixture melting at 45 "C
8. Water vapour permeability
In the manufacture of packaging materials, paraffin waxes are chiefly used to reduce water vapour permeability of paper. This is valid for both coating and laminating waxes, the latter being often applied for the sake of the low vapour permeability of the paraffin wax film. Water vapour permeability tests are usually carried out not with the wax itself, but with coated paper, carton etc., that is, with the prepared packaging material, since paraffin wax is used directly for coating only in exceptionalcases (e.g. fruits cheese). The water vapour permeability of waxed packaging materials is affected by a number of variables, including the properties of the paraffin wax, conditions of wax application, properties of the paper and mechanical stresses. No realistic picture can be obtained concerning permeability, if paper specimens treated under similar coating conditions, but using different macro- and microcrystalline paraffin waxes are compared. Instead, coating should be carried out under specific conditions for each paraffin wax, these being optimum conditions for the wax in question, and only such coated papers should be submitted to water vapour permeability testing. Permeability to water vapour of coated or laminated paper specimens, prepared under optimum conditions and measured prior to being subjected to mechanical stress, is essentially the same whether macro- or microcrystalline paraffin wax has been used, since, for unbroken films, these two wax types are equally resistant to water vapour. However, water vapour permeability measured prior to mechanical stress (folding) is insufficient to evaluate the quality of packaging materials. Papers coated or laminated with paraffin wax will, almost without exception, be subjected to various mechanical loads, especially to flexing, during their service life.
137
(D) PHYSICAL PROPERTIES OF PARAFFIN WAXES
As regards flexing, macrocrystalline and microcrystalline paraffin waxes behave quite differently. Refined paraffin waxes having macrocrystalline structures are brittle, easily cracking products. Under the effect of folding, the film coat will crack, the continuity of the film will be disrupted to a greater or smaller extent. Water vapour will readily permeate through the porous paper lying below the cracks. Hence, water vapour permeability will substantially increase under the effect of folding in a coating made with macrocrystalline paraffin wax. Among the great variety of microcrystalline paraffin waxes, coatings made of flexible products exhibit cracks to only a slight extent or not at all under the effect of folding, the continuity of the film remains largely undisrupted, and hence no significant change in vapour permeability will result. Plastic and flexible microcrystalline paraffin waxes would appear to be the most favourable for the manufacture of coatings and laminates with a low water vapour permeability. However, the tack of such soft microcrystalline waxes is too high, Table 1-70. Water vapour permeability values of paper coated with paraffin wax (sulphite paper, wax coating 25 wt- %)
Coating material
Melting OC
j
-
Water vapour permeability* g/m* 24 h
(<dore
folding
After folding
-
No coating
-
Refined macrocrystalline wax
54
0.20 0.45
12.4 16.2
Refined macrocrystalline wax
60
0.26 0.51
18.6 12.3
Plastic microcrystalline paraffin wax
67
0.27 0.39
3.9 4.8
* At
406.0
23 "C and 50% rei. humidity
their blocking point is low, their surface is dull and attracts much dust. For these reasons, they cannot be used in the pure state for coating, but are very suitable for blending to obtain low water vapour permeability coatings. Water vapour permeability values of paper coated with macro- and niicrocrystalline paraffin waxes, before and after folding, are presented in Table 1-70, 9. Water resistance
Water and aqueous solutions come into direct contact with waxed paperboard used for containers of deep-frozen food, milk cartons, paper cups, etc. Therefore, resistance to water is an important requirement in those applications where no water must be allowed to penetrate through the paraffin wax film.
I38
I. PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
Similarly to water vapour permeability tests, resistance to water is usually measured not with the pure wax, but with wax coated paperboard. Resistance to water of the composite material depends to a much greater extent on the properties of the paper substrate than in the case of water vapour permeability. When coating paper with a mottled surface (e.g. blotting paper), some of the wax will be absorbed between the fibres, but some fibres will protrude through the wax film to the surface. These fibres will then act as wicks in which moisture can easily penetrate through the wax film. Two types of water barrier tests are in use. In absorption tests, weighted waxcoated paper cups are filled with a 1 wt-% lactic acid solution coloured with methylene blue. The filled cups are then stored for 72 hours a t -4 "C or +20 "C, according to standard specification. Subsequently the cups are emptied and weighed. The amount of solution absorbed is determined from the weight increase. Simultaneously, the internal surfaces of the cups are visually checked for staining with methylene blue (location and magnitude of stained areas is observed). Resistance to water is considered satisfactory only if slight staining occurs, and that only at junctions and folds. The other test consists of a fatigue test. Waxed cartons, filled with water and sealed, are dropped at a rate of 144 per minute from a height of 9.6 mm, at 3 "C, by means of a suitable apparatus. The endurance of the waxed cartons is measured by the period before which 50% of the tested cartons (usually 24 specimens) exhibit cracks or break. In general, tests show that resistance to water of lower-melting microcrystalline paraffin waxes is superior to that of macrocrystalline refined waxes. This difference is presumably due to the denser crystal structure and higher flexibility of microcrystalline waxes. Blends of refined macrocrystalline and microcrystalline waxes are frequently used for waterproof coatings. 10. Electrical properties Owing to their relatively high dielectric strength, low water vapour permeability and good resistance to water, paraffin waxes, especially the higher-melting microcrystalline waxes, are used for insulating purposes in electrical engineering. Insulating coatings of paraffin wax provide efficient protection against both water vapour and water. The use of paper and textiles impregnated with paraffin wax for wire insulation has been known for a long time past. Paper impregnated with paraffin wax is used in capacitors as a dielectric; paper tubes coated with paraffin wax are placed inside the metal casing of dry cells to reduce desiccation of the cathode mixture. Pure paraffin wax or its blend with bitumen is frequently used in capacitors to keep components in place. Ceramic insulators are also frequently impregnated with paraffin wax to reduce water vapour permeability. The volume resistivity of paraffin waxes is in the order of 1016-5 . I d * ohm/cm3. The values normally decrease with rising temperature. However, in the solid-phase
139
(D) PHYSICAL PROPERTIES OF PARAFFIN WAXES
transition range of macrocrystalline paraffin waxes, this change is frequently inverse. Data found in the literature on the dielectric strength of paraffin waxes vary within very wide limits. The inordinately large differences are due to variations in chemical composition and purity, as well as to the different methods of measurement used by the various authors. Table 1-71 lists relative permittivity data for paraffin waxes and, for comparison, for some natural waxes. Table 1-72 contains relative permittivities and, by way of example, some dielectric strength values measured with two microcrystalline paraffin waxes differing in properties. Table 1-71.Relative permittivities of paraffin waxes and some natural waxes
Substance
Paraffin waxes Ceresins Candelilla wax Carnauba wax Beeswax
Initial value
After 6 months storage in 3.5 Wt-% NaCl solution
2.19-2.24 2.1 6-2.24 2.38-2.49 2.66-2.8 3 2.87-2.88
2.31-2.55 2.29-2.32 2.50-2.62 3.84-4.19 3.11-3.26
'
' 1
after repeated
2.24-2.30 2.28-2.29 2.45-2.56 2.82-2.83 2.84-2.90
Table 1-72. Dielectric properties of two microcrystalline paraffin waxes Properties
1
i
WaxA
i
88
Melting point, OC Needle penetration at 25'C, 0.1 mm Average molecular weight Oil content, wt- %
WaxB
2 890 0.6
84 7 804 10.4
I ~
Temperature, "C 80 60 40 20
Temperature, O C 20 40 60
2.46 2.37 2.31 2.16
2.30 2.39 2.25 2.09
2.38 2.42 2.56 2.62
2.47 2.44 2.44 2.45
2.49 2.53 2.74 2.79
Dielectric strength, kV/cm 82 1500 71 780 625 22
!
I
2.48 2.50 2.74 2.79
140
I. PROPERTIES OF LIQUID PARAFFINS AND PARAFFIN WAXES
Literature ASTM D 1465-57 T. ASTM D 1500-58 T. ASTM D 156-53 T. ASTM D 1321-61 T . ASTM D 937-58 T. ASTM D 1320-60 T. Berne-Allen: Ind. Engng. Chem., 30,806 (1938). Brooks, K. W., Oil Gas J., 58,89 (1960). Buchler-Graves: Ind. Engng. Chem., 19, 718 (1927). Davis, D. S., Ind. Engng. Chem., 32, 1293 (1940). Edwards, R. T., Petrol. Refiner, 36, 180 (1957). Eucken, A., Elektrochemie, 45, 126 (1939). Ferris-Cowles: Znd. Engng. Chem., 37, 1054 (1945). Gray, C. B., J. Inst. Petrol., 29, 236 (1943). Gruse-Stevens: Chemical Technology of Petroleum. McGraw-Hill Co., New York (1960). Hickel, A, E., Petrol. Refiner, 24, 207 (1945). Johnson, J. F., Ind. Engng. Chem., 46, 1046 (1954). Kinsel-Phillips: Znd. Engng. Chem., 17, 152 (1945). Kolvoort, E. C. H., J . Znst. Petrol., 24, 338 (1938). Lord, H. D., J. Inst. Petrol., 25, 263 (1939). Mazee, W. M., Red. Trav. chim. Pays-Bas, Belg., 67, 197 (1948). - : J. Znst. Petrol., 35, 97 (1949). M6zes-V8mos: Reoldgia 6s reometria. (Rheology and rheometry), Miiszaki Konyvkiad6, Budapest (1968). M6zes-Zsida-FBnyinB: MA-FKZ K6zI. (Report of the Hungarian Oil and Gas Research Institute), 9, 241 (1968). - : Chem. Tech. Berl., 20, 481 (1968). Miiller, A,, Proc. R . Soc., A 120, 437 (1928); A 127,417 (1930); A 138, 514 (1932). Padgett, F. W., Oil Gas J., 36, N o . 38, 30, 45 (1938). Padgett-Hefley-Hendrikson: Ind. Engng. Chem., 18, 832 (1926). Phillips, J., TAPPZ. Bull., 41, 291 (1958). - : Petrol. Refiner, 38, 193 (1959). Scott-Harley: J . Znst. Petrol., 25, 238 (1939). Seyer-Fordyce: J. Am. chem. SOC.,58,2029 (1936). Seyer-Morris: J. Am. chem. SOC.,61, 1114 (1939). Seyer-Patterson: J . Am. chem. Soc., 66, 179 (1944). Smith, A. E., J. chem. Phys., 21 2229 (1953). Templin, P. R., Znd. Engng. Chem., 48 154 (1956). Thorpe, T. C. G., J . Inst. Petrol, 37 275 (1951). Tiedje, J. L., Proceed. Fourth World Petroleum Congr., Section W/B, Preprint 1 (1955). Turner-Brown-Harrison: Ind. Engng. Chem., 47, 1219 (1955). Ubbelohde, A. R., Trans. Faraday Soc., 34, 282, 292 (1938). Van Vinkle, M., Petrol. Refiner, 27, 291 (1948). Warth, A. H., The Chemistry and Technology of Waxes. Reinhold Publishing Co., New York (1956). Watson, K. M.. Znd. Engng. Chem., 23, 360 (1931). West, C. D., J. Am. chem. Soc., 59 742 (1937). Wibaut-Langedijk: Red. Trav. chim. Pays-Bas, Belg., 59, 1220 (1940).
II. MANUFACTURE OF PARAFFIN WAXES AND CERESINS FROM PETROLEUM
An important operation in the production of lubricating oils is the dewaxing of the corresponding petroleum fractions and residues, since it is only possible to manufacture lubricating and industrial oils with low pour points and with viscosities, suitable for use at low temperatures, from crudes containing paraffin. The manufacture of petroleum waxes includes the following technological processes : - Production of slack waxes and petrolatums by dewaxing petroleum products. - De-oiling and fractional crystallization of slack waxes and petrolatums. - Purification of crude paraffin waxes. - Blending of paraffin waxes with additives. The manufacture of n-alkanes, liquid and solid at ambient temperatures, by processes based on urea adduct formation and use of molecular sieves also belongs to the complex of petroleum wax manufacture. n-Alkanes are important starting materials for the rapidly developing chemical industry. Depending on the field of application and corresponding to the standards valid in different countries, commercial petroleum waxes must be more or less resistant to light, only slightly coloured or white and, for most applications, odourless. Quality requirements for petroleum waxes are nowadays so manifold and regulations are so strict that some of them can only be satisfied by blending the waxes with suitable additives.
(A) The origins and development of dewaxing processes Dewaxing is important from two points of view: First, producing products with suitable pour points from waxy feedstock. However, this can be achieved only to a certain extent by reducing the wax content, since it is dependent chiefly on the average molecular weight of the feedstock. At low temperatures, below a limit characteristic of the material, the rheological properties of the oil cannot be improved by dewaxing, because the pour point of the oil in this range is no longer the property of the wax crystallizing from it, but of the inherent high viscosity of the oil.
142
11. MANUFACTURE OF PARAFFIN WAXES A N D CERESINS FROM PETROLEUM
The other important viewpoint is that, particularly in the case of higher average molecular weight petroleum distillates and distillation residues no sharp dividing line can be drawn between the hydrocarbons forming solid paraffins and those that cannot be considered as solid. Therefore, the yield of dewaxed oil obtainable from paraffinic feedstocks is in any case defined by the pour point required for the oil in question. If, for example, the objective is to manufacture very low-pourpoint products, most of the low-melting alkanes must also be removed. In the early days of petroleum processing, paraffin waxes contained in paraffinic crudes and their distillates were removed by simple cooling. The first method to be regarded as a true dewaxing process was to store paraffinic crudes or their lowboiling fractions in tanks for the winter period. By this method a part of the para& wax crystallized and was deposited at the bottom of the tank. The upper layer, relatively poor in wax, was pumped off and subjected to refining. This simple method could be applied to petroleum owing to the low-boiling, lowviscosity components. For the higher-boiling petroleum fractions, in many cases crystallization and crystal sedimentation did not take place at all. For this reason, the so-called cold sedimentation dewaxing was developed. In this process, the viscosity and density of the feedstock was reduced by dilution with gasoline, the amounts of the latter reaching values as high as 70 wt- % of the initial material. The diluted material was subsequently submitted to slow natural or artificial cooling, during which the crystallizing paraffin wax settled at the bottom of the tank. This process, however, was also very difficult to control, and a further development of the process of batch crystallization and sedimentation in tanks was continuous cooling and separation of the crystals by centrifuging. Meanwhile, experience demonstrated that paraffinic light fractions obtained by vacuum distillation of the residues of atmospheric distillation of paraffinic crudes contain, after cooling, significant amounts of macrocrystalline-structure paraffin wax that cannot be separated by simple sedimentation. This is due to a crystal web formed during cooling that spreads over the whole of the fraction, which will consequently solidify in its entirety. It was found that the liquid oil contained in this conglomerate can be separated from the wax crystals in filter presses by applying pressure. This process was called press dewaxing. At present filter presses are rarely in use in dewaxing technology. Direct separation of the oily fraction and the wax crystallizing after cooling from high average boiling-range distillates is not feasible. To reduce viscosity, dilution with gasoline or kerosine was applied. However, dilution raises difficulties in the manufacture of lubricating oils. Gasolines and kerosines are capable of dissolving relatively high amounts of paraffin waxes even at low temperatures. Therefore, if such solvents are used as diluents, lower cooling and pressing temperatures are needed to obtain the lubricating oil with the desired pour point than in the process without dilution, where the pour point of the dewaxed oil is close to the temperature of filter-pressing. In industrial practice, fractions with viscosities below 15-20 mm2/s at 38 "C were dewaxed without dilution, while those with viscosities of 20-50 mmZ/s at 38 "C were diluted, usually to 40-50 wt- %.
(A) THE ORIGINS AND DEVELOPMENT OF DEWAXMG PROCESSES
143
The first dewaxing process, which was equally suitable for various distillation fractions and residual oils, was developed in 1928 and called Weir process. Its essential feature is that kieselguhr was added as a filter aid to the gasoline diluent. This promotes build-up of the filter cake. Kieselguhr is subsequently recovered from the paraffin wax and recycled. However, the process did not become widely used. Neither did another attempt (known under the name of the Russian process) become a commercial success. This was characterized by adding a small amount of sulfuric acid before cooling to the oil diluted with gasoline. An acid resin is formed, and its particles act as crystalline iiuclei for paraffin wax crystals, promoting the growth of larger crystals. In the same period when these attempts were made, novel dewaxing processes were developed in which organic solvents were used for diluting the starting material. These so-called solvent-dewaxing processes then successively replaced all earlier methods. At present, solvent dewaxing is the exclusive process for new plants under construction.
Literature Burger-Combarnous: Revue Znst. f r . Petrole, 30, 551 (1975). Gerber, C., Freiberger ForschHft., A 283, 45 (1963). Ghublikian-Clapham-Dixon: Oil Gas J., 57, 83 (1959). Gipp-Heinze-Leibnitz: 1.prakt. Chem., 19, 74 (1963). Gruse-Stevens: Chemical Technology of Petroleum. McGraw-Hill Co., New York (1960). Kajdas-CzerwiecChodkiewicz: Tech. Smarownicza, 7 , Nos 5-6, 145 (1976). Kalichevsky-Kobe: Petroleum Refining wirh Chemicals. Elsevier Publ. C o . ,Amsterdam (1956). Lipovskaja-Rysakov: Chem. Tech. Berl., 19, 621 (1967). Nelson, W. L., Oil Gas J . , 64, 70 (1966). Rudakova-Sheremeta: Khimiya Tekhnol. Topl. Masel, 9, No. 4, 22 (1964). Teubel-Schneider-Schmiedel: Erddparafine. VEB Deutsch. Verl. fur Grundstoffindustrie, Leipzig (1965). Tiedje-McLeod: Petrol. Refiner, 34, 150 (1955). Wosnesenskaja-Griasnov-Sachsuvarova: Chem. Tech. Berl., 19, 61 7 (1967).
(B) The role of the crystal structure of paraffin waxes in the dewaxing process The size and shape of the paraffin wax crystals formed during cooling of paraffinic oils is an important factor in dewaxing .The factor was more important before the introduction of the solvent dewaxing processes. It is a general rule that large and well-developed so-called plate crystals can be readily pressed and filtered. The needle-shaped crystalline types can be easily sweated but cannot be separated by centrifuging. On the other hand, microcrystalline paraffin waxes cannot be separated (or only with great difficulties) by filter pressing, but are readily separated by centrifuging.
144
11. MANUFACTURE OF PARAFFIN WAXES AND CERESINS FROM PErROLEUM
With respect to earlier dewaxing processes, four types of paraffin waxes are distinguished : (i) Low-viscosity distillates are dewaxed by cooling and filter pressing. The product of this operation is termed slack wax, and de-oiled by sweating, which is essentially fractionation by pour point. (ii) When higher-viscosity distillates are subjected to cooling, paraffin waxes with an intermediate crystal structure are formed, for whose separation neither centrifuging nor filter pressing is applicable. (iii) In high-viscosity distillation fractions and residual oils, microcrystalline waxes can be found. These cannot be pressed, but readily separated by centrifuging after diluting with solvent. (iv) The high-melting so-called pipeline waxes are also unsuitable for filter pressing. This distinguishing between paraffin waxes suited for filter pressing, and intermediate and microcrystalline paraffin waxes that cannot be separated by means of filter presses, was of technological importance before solvent-dewaxing processes became wide-spread. The importance of such distinctions is due to the fact that the addition of only some tenths of 1 % of microcrystalline paraffin wax to macrocrystalline wax substantially deteriorates the filtering (by filter presses) and sweating properties of the latter. For this reason, it was attempted to distil the paraffinic crudes in such a manner as to achieve sharp separation of the distillates suitable for filter pressing from residual oils. The intermediate slop oil fraction was kept to the possible minimum amount. The formation of the paraffin wax crystals depends, in addition to boiling,range conditions, also on other factors. So that the separability of paraffinic distillates on filter presses can be improved by redistillation, distillation temperatures slightly exceeding the cracking temperature of the fraction are used. This operation also results in an increase of paraffin wax yield. It is probable that paraffin waxes present in the starting material will decompose to a certain extent and consequently the very complex structure of microcrystalline paraffin waxes will become simpler, and they will be converted to macrocrystalline waxes. The appearance of paraffin wax crystals is also affected by the conditions of crystallization, especially by the cooling rate and by the viscosity of the medium. By means of the modern solvent-dewaxing processes all types of lubricating oil fractions can be dewaxed, no distillation methods have to be used.
Literature Evans, E. B., Modern Petroleum Technology. The Institute of Petroleum, London (1962). Kalichevsky-Kobe: Petroleum Refining with Chemicals. Elsevier Publ. Co., Amsterdam (1956). Kobe-McKetta: Advances in Petroleum Chemistry and Refining. Vol. 10, Interscience Publ. Co., New York (1965).
(C) DEWAXING PROCESSES USING SOLVENTS
145
(C) Dewaxing processes using solvents In these processes, organic solvents are used as diluents which, at the temperature of filtering, dissolve parailin waxes only to a very slight extent, while they are good for dissolving the other components of lubricating oils. Rotary filters are mostly used to separate crystallized paraffin wax. Whichever process is examined, the requirements for the solvent are as follows: (i) It should dissolve paraffin wax only to a slight extent at the temperature of filtering, but be miscible with the oil within wide concentration limits. (ii) It should not be corrosive to the materials used in the construction of the equipment and should be non-toxic. (iii) Its boiling range should be so low as to be able to separate it readily from both the paraffin wax and the dewaxed oil. (iv) Its specific heat and heat of vaporization should be low. The first solvent-dewaxing plant was put into operation by the Indian Refining Company in 1927. At the start, the solvent used was a mixture of benzene and acetone. The process was further developed by the Texas Company. Centrifuges or rotary filters were used to separate paraffin wax. Subsequently the technology was modified by replacing acetone with methyl ethyl ketone, and benzene (partly or totally) with toluene. This is the most wide-spread process in the present time, and usually called the MEK process. In the U.S.A., 70% of dewaxing plants use this technology. Ketone solvents containing no aromatic component, e.g. methyl iso-butyl ketone, can be used alone for dewaxing. However, the disadvantage of this is that their capacity for dissolving high molecular weight feedstocks, e.g. refined residues, particularly for manufacturing low pour-point lubricating oils, is unsatisfactory. Hence a segregation of valuable paraffinic lubricating oil components takes place, reducing the yield of lubricating oil and impairing its properties. It is, therefore, expedient, particularly in the case of higher molecular weight ketones, to use a so-called dissolving component, e.g. benzene, in the solvent. Chlorinated hydrocarbons were, in earlier times, widely used for dewaxing purposes. These solvents facilitated centrifuging of slack waxes and petrolatums. By using chlorinated solvents of high specific gravity the wax portion, containing little oil and solvent and having a high setting point, can be removed from the central part of the centrifuge, in contrast to dewaxing with benzene, when paraffin wax is removed from the perimeter area. The so-called Bari-Sol process was developed in the 'thirties and is still in use. The solvent applied is a mixture of dichloroethane and benzene, the latter being sometimes replaced by toluene, chloroform or carbon tetrachloride. A solvent-dewaxing process using a mixture of sulfur dioxide and benzene has also been put into practice. Sulfur dioxide is used in the Edeleanu solvent-refining process for lubricating oils. In this process, by using a mixture of sulfur dioxide and benzene, the dewaxing and oil-refining operations are combined. However, the process did not spread, chiefly owing to the corrosive action of sulfur dioxide. 10
146
11. MANUFACTURE OF PARAFFIN WAXES AND CERESINS FROM PETROLEUM
Dewaxing with propane is relatively a much used process. The first plant of this type was put into operation by Standard Oil of Indiana in Wood River in 1932. The process was subsequently further developed by several refiners and engineering companies, e.g. Kellog Co. Crystal structure of the paraffin wax is of great importance in commercial processes due to the importance of rapid filtration rate, particularly when rotary filters are used for separating the liquid and solid phases. For a distillate with a given viscosity, crystal size and the consequent filtration rate depends on various factors. The principal factors are the boiling range width of the distillation fraction, previous treatment of the feedstock (e.g. solvent refining or deasphalting), the method of dilution with solvent and the cooling rate. A technology using electrical precipitation for dewaxing is fairly independent of the crystal structure of the wax. The process consists in subjecting the cooled solution, in propane, gasoline or other solvent, to the continuous effect of an electric field. The process is in operation in a pilot plant of Union Oil Co. Solvent-dewaxing processes cause crystallization of paraffin waxes by cooling the diluted solutions, and are hence the highest cost operations in the manufacture of lubricating oils. Attempts to develop processes that eliminate the costly cooling are, therefore, very welcome. In one of these attempts, p a r a f i wax is separated from the material diluted with solvent at temperatures above the melting point of the wax, and whilst still in the liquid phase. The operating temperature is below the critical temperature of miscibility of the wax and the solvent, so that the process is essentially an extraction, similar to solvent-refining of lubricating oils. However, up to the present the extent of selectivity achieved has not been such that could ensure economical operation of the process on a commercial scale. In the most wide-spread solvent dewaxing processes ketones (especially methyl ethyl ketone), propane and mixtures of dichloroethane with benzene are in use. A relatively recent process uses a mixture of propylene and acetone. Another novel approach is the Dilchill dewaxing process. 1. Methyl ethyl ketone dewaxing
Before considering the process in detail the physico-chemical and technological aspects of major importance in solvent dewaxing can be summarized: (i) composition of the solvent, (ii) extent of the dilution of the feed, (iii) size, morphology and aggregation of paraffin wax crystals in the slurry to be filtered, (iv) efficiency of solid-liquid separation at filtration. The respective relationships are generally valid, but have been developed in greatest detail for the most widely used process, i.e. that using methyl ethyl ketone. As regards solvents, acetone has been replaced in the ketone processes by
(C) DEWAXING PROCESSES USING SOLVENTS
147
methyl ethyl ketone, which has a higher boiling point and hence reduces solvent losses. Another trend to be observed is that instead of two-component solvents, three-component solvents are increasingly being used. About 30-50 vol- % of the benzene filling the role of the dissolving component in the mixture is being replaced by toluene. This is justified, because in addition its lower toxicity, toluene reduces the freezing point of the mixture, so that crystallization of benzene can be avoided in the manufacture of low-pour-point lubricating oils. The dewaxing solvent is suitable, if at the temperature of filtration it does not, or only slightly dissolves the paraffin wax, while it is miscible in any ratio with the component in the liquid phase. This requirement can be approached most easily by using a solvent mixture that contains a selective component in which paraffin wax is almost insoluble, and a dissolving component miscible in all ratios with the oily part. The selective component reduces the wax dissolving capacity of the mixture, while the dissolving component enables dissolution of the oily part at the temperature of filtration. In the absence of a selective component the spread value, that is, the difference between the temperature of filtration and the pour point of the dewaxed oil is high, the wax crystals are small and hence difficult to filter. Figure 11-1 shows the changes in filtrability against the composition of the solvent and temperature of filtration. The pour point of the dewaxed oil versus composition of the solvent and spread value is presented in Fig. 11-2. M. P. Kalshina and co-workers investigated how the composition of the solvent affects the main technological parameters of dewaxing, in the cases of transformer oil and light industrial oil manufacture from a paraffin and sulfur-containing crude. For transformer oils, the composition of the solvent mixtures (in vol-%) was (i) 39 acetone, 9.5 benzene, 51.5 toluene, and (ii) 56 methyl ethyl ketone, 10.4 acetone, 3.0 benzene, 30.6 toluene. The pour point of the dewaxed oil obtained 1400 1200 m
-
a;
-2
1000
800
Y
600
: 400 7
E
Q
200
u 1.0 2.0 3.0 4.0 5.0
'0
Filtration time, min Fig. ZZ-I. Filtrability versus composition of the solvent (feed: paraffinic refined fraction for
lubricating oil). I 61 wt-% MEK, 39 wt-% toluene, -21 O C ; 2 61 wt-% MEK, 39 wt-% toluene, -23 OC; 3 47 wt-% MEK, 5 3 wt-% toluene, -23 O C
10*
148
11. MANUFACTURE OF PARAFFIN WAXES AND CERESINS FROM PETROLEUM
+7,
Spread,
"C
Fig. 11-2. Pour point of dewaxed oil versus spread value and different solvent compositions. Feed and solvent composition: I refined distillate (61 wt-% MEK, 39 wt-% toluene); 2 refined distillate (47 wt- % MEK, 53 wt- % toluene), 3 refined distillation residue (47 wt- % MEK, 53 wt-% toluene)
with both solvent mixtures was -45 "C. For light industrial oil, compositions (in vol-%) were (i) 37 acetone, 7.4 benzene, 55.6 toluene, and (ii) 46 methyl ethyl ketone, 8.6 acetone, 3.0 benzene, 42.4 toluene. The pour points of the dewaxed products obtained using these solvents were - 30 and - 32 "C, respectively. The results of these authors showed that the use of methyl ethyl ketone in the solvent mixture proved advantageous from more than one respect. To ensure the desired pour points of the dewaxed products, the temperature of the feed +isolvent mixture and that of the wash solvent did not have to be so low when MEK was present than in the case of solvent containing no MEK. Hence, as compared to the 10-1 1 "C spread characterizing the solvents containing no MEK, only spread values of 2-5 "C were found with the MEK-containing solvents. This resulted in some percentage of power economy. In addition, less solvent was required for dilution and wash in the case of the MEK-containing solvent, reducing solvent recovery costs. Filtration rate was increased by more ;than lo%, raising the capacity of the equipment, and simultaneously there was an increase by some percentage in the yield of the dewaxed products. In our opinion, the favourable results obtained with a solvent containing methyl ethyl ketone should not be ascribed only, or even primarily, to the use of MEK. As the data presented by the authors reveal, the total ketone content of the solvents containing MEK, that is, the concentration of the selective components was substantially higher than that of the solvents consisting of acetone, benzene and toluene. This was the main reason leading to the more favourable technological parameters. In the choice of the concentration of the selective component in the solvent mixture, the following, in addition to the above, must also be considered. At a given temperature a phase separation of the oil-solvent mixture always takes place, the temperature being dependent on the characteristics of the oil, the solvent
(C) DEWAXING PROCESSES USING SOLVENTS
149
and on their ratio. A solvent-rich phase and a solvent-poor, the so-called oil phase, will be present side by side. The oil phase, although from its characteristics, e.g. viscosity index, belongs to the dewaxed oil, remains in the slack wax at filtration. Hence, while filtration rate sharply increases when the abovementioned separation takes place, the yield of dewaxed oil will be reduced significantly and its properties will deteriorate. For a given oil and a given solvent mixture, the temperature of the oil beginning to separate out, the so-called phase point, is increased by higher ratios of the selective component in the solvent mixture. Therefore, the composition of the solvent mixture must be chosen so as to ensure maximum filtration rate achievable under the given conditions, and, on the other hand, dewaxing should take place close to the phase point, but somewhat above this temperature. In this case the value of spread will also be the most favourable. In the manufacture of oils with pour points around - 15 "C the highest permissible MEK content in the solvent mixture varies between 50 and 75 vol-x, depending on the properties of the feed. An optimum exists in the relationship filtering capacity (related to feed) versus extent of dilution. In dewaxing, more solvent used for diluting the feed reduces oil concentration in the filtrate, hence its viscosity decreases. Lower viscosity of the filtrate will lead to higher filtration rates. On the other hand, lower oil content is equivalent to a lower amount of oil in a given volume of filtrate. As a result of these two changes in opposite directions, the amount of solvent-free oil obtained during a given filtration period will reach a maximum depending on the amount of diluting solvent. Tausz and co-workers, as well as Reeves, found that the following relationship is valid between the viscosity of the filtrate and its solvent content, if the solvent concentration in the filtrate exceeds 50 wt-%: p = BF"
or l g p = mlg F
(11-1)
+ lgp
(11-2)
where p is the dynamic viscosity of the filtrate, p the dynamic viscosity of the solvent, m a constant characterizing the oil, and F the concentration of the solvent in the filtrate, expressed in fractions by volume. From Kozeny's basic filtration equation and Eq. (11-1), the filtration rate of the solvent-free oil changes according to the following equation, at constant pressure and an incompressible filter cake:
(11-3) where R is the filtration rate of the solvent-free oil, V, the volume of the solventfree oil, A the filter area, A p the pressure drop in the filter cake, r the resistivity of the filter cake, v the filter cake volume relative to the unit volume of the filtrate, and V the volume of the filtrate.
150
11. MANUFACTURE OF PARAFFIN WAXES AND CERESINS FROM PETROLEUM
The derivative of the function R with respect to F, assuming a constant pressure drop, changes its sign from positive to negative at the point m Fop, = -m-1
(11-4)
thus the function has a maximum in this point. This calculation method is valid if the further simplifying assumption is true that the value of the product ruV, at constant filtration time, does not change with the amount of diluting solvent. Studies were carried out in the Hungarian Oil and Gas Research Institute to compare optimum dilution ratios established directly by laboratory filtrations and those obtained by computation. The feed used in the experiments was a residual oil with a viscosity of 23 mm2/s at 100 "C. Dewaxing and filtration, respectively, were carried out at - 25 "C using a solvent containing 30 vol- % acetone, 35 vol- % benzene and 35 vol- % toluene. The pressure drop during filtration was 66.65 kPa. Figure 11-3 presents the amount of solvent-free oil versus solvent content, in wt-%, of the slurry. With the applied laboratory filtration method, optimum dilution ratio was independent of the filtration time chosen for the computation. The weight fraction value of 0.775 of solvent in the slurry is equivalent to a dilution of 345 wt-% related to the paraffinic feed. The optimum diIution ratio was then computed using the above method. The viscosities of the filtrates obtained with different dilution ratios were determined, and, knowing the solvent content of the filtrates, the slope of the line lg viscosity versus lg concentration was established (Fig. IJ-4). Optimum dilution from this computation gave a weight fraction value of 0.79 for the solvent in the slurry, corresponding to dilution of
a
90 1
80
I
-
.- - 70 0
0,
FiI tr at i on
D
100 s
time
60-
@
c
'80s
; ; 50 -c
0
50 s
7 403
0
5
30
-~
,
177.5
,
I
85 95 Solvent content of slurry, w t - % 75
Fig. 11-3. Amount of solvent-free dewaxed oil versus solvent content of the slurry, at different filtration times. Filtration temperature: - 25 OC, feed : distillation residue from Romashkino crude, viscosity: 23 mm*/s at 100 "C
152
11. MANUFACTURE OF PARAFFIN WAXES AND CERESINS FROM PETROLEUM
Table If-I.Characteristics of paraffinic residual oils refined to different extents with phenol
1
Characteristics
Refined products 1
/
2
/
3
/
4 ~
Viscosity at 100 "C, mm2/s Density at 20 "C Pour point, 'C Aniline point, "C Conradson number, wt- % Group composition,* wt- % - alkanes naphthenes - aromatics with one or few rings - polycyclic aromatics - resins
14.91 0.8864 51.0 120 0.3
+
17.61 0.8965 50.0 115 0.6
17.64 0.8985 48.5 113 0.7
-
72.3
-
15.4 8.1 1.8
-
~~
18.86 0.9071 47.5 109 0.9
62.9
57.1
18.2 14.6 2.6
20.3 19.1 3.5
* Group composition was determined by chromatography, using silica gel support
The pour point of the dewaxed oil decreases with increasing Conradson numbers. It is of interest to note that in the case of solvent containing more than 60 wt-% MEK, products with pour points some "C lower than the temperature of filtration were obtained. The oil content of petrolatums shows a substantial decrease with increasing Conradson numbers. The cited authors confirmed by electron microscopic studies that the above relationships are the results of the size and extent of aggregation of the wax crystals formed in the slurry. They found that in feeds for the dewaxing operation with resin contents. that is Conradson numbers. between certain limits (in the 100 90 80 -
S
70-
c
-d a,
60-
F 50
-
40 -
30 20
I
0
I
I
I
I
I
I
1
0.1 0.2 0.3 0.4 0.5 0.6 0.7
I
I
0.8 0.9
1.0
,
Conrodson number, w t - % Fig. ZZ-5. Dewaxed oil yield versus Conradson number. 1 Acetone : toluene = 30 : 70; 2 Acetone : toluene = 40 : 60; 3 Acetone : toluene = 50 : 50; 4 MEK : toluene = 40 : 60
(C) DEWAXING PROCESSES USING SOLVENTS
20
151
7-
u
'10
20 30 50 70 100 Solvent content of filtrate, w t - %
Fig. 11-4. Viscosity of filtrateversus solvent concentration of filtrate (feed : paraffinic distillation residue)
376 wt-% related to the feed. Thus the difference between the computed and measured values did not exceed 10%. Establishment of the optimum dilution ratio by computation has the advantage that it only requires the measurement of the viscosities of filtrates with various solvent contents at the temperature of filtration; such filtrates can be obtained by dewaxing experiments or by diluting oils obtained in the former experiments, that is, by preparing model filtrates. Filtration rate, yield and pour point of the dewaxed oil, ahd oil content of the slack wax are all largely affected, under otherwise identical conditions, by the sue, morphology and extent of aggregation of the paraffin wax crystals contained in the slurry to be filtered. These characteristics of the crystals, for a given origin of the crude and given conditions, are modified by the concentration of resinous and asphaltene substances present in the oil. M. Fauzi, B. N. Kartinin and N. Y. Chernozhukov, among others, studied this problem, using residual oils originating from the same crude, but refined t o different extents with phenol and hence having different Conradson numbers. Some characteristics of these oils are listed in Table 11-1. Two-component solvents were used for dewaxing, namely mixtures of acetone and toluene and methyl ethyl ketone and toluene, in various ratios. The ratio of feed to solvent was 1 : 4, the cooling rate of the slurry before filtering was 1 "C/min, and filtering temperature -25 "C.The experimental results are presented in Figs 11-5-11-8. The conclusions based on the experimental results were as follows: The yield of dewaxed oil increases with increasing resin content and parallels to increasing Conradson number, in spite of decreasing pour point, that is, decreasing spread. Filtration rate, independently of the nature of the solvent, increases up to Conradson numbers of 0.5 wt-% corresponding to about 2 wt-% resin, and subsequently rapidly decreases.
(C) DEWAXING PRO ESSES USING SOLVENTS
1
153
240 220 200
/
-
180
160 ul
a- 140
-
.-E
'1
120
I
-2
1
2o00
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9-' Conradson number, w t - %
Fig. 11-6.Filtration time versus Conradson number of the dewaxed oil. I Acetone : toluene = 30 : 70; 2 Acetone : toluene = 40 : 60; 3 Acetone : toluene = 50 : 50; 4 MEK : toluene = 40 : 60; 5 MEK : toluene = 50 : 5 0 ; 6 MEK : toluene = 60 : 40
case of the oils studied, resin contents from 1.8 to 2.5 wt-%, that is Conradson numbers from 0.3 to 0.6 wt-x), larger and more agglomerated crystals were present in the slurry than in feeds with resin contents, that is Conradson numbers, beyond these limits. This finding demonstrates that the resin components of the refined oils have a favourable effect up to a certain concentration. The presence of resin amounts exceeding this limit, however, impedes growth and agglomeration of the crystals presumably owing to the adsorption of the resins on the surfaces of the paraffin wax crystals. Filtration of slurries containing satisfactorily large and agglomerated crystals results in porous filter cakes ensuring high filtration rates, ready wash of the cake and sharp separation of the oil and slack wax phases. A. M. Shevtsov investigated the relationship between filtration rate and cooling rate of the slurry. In dewaxing experiments carried out with a paraffinic residual oil having a viscosity of 19 mm2/s at 100 "C and a solvent mixture of 35 wt-% acetone and 65 wt- % toluene he stated that, under otherwise identical conditions, the rate of filtration is maximum when the cooling rate is 150 "C/h. However, at such cooling rates the yield of the dewaxed oil is very low. At higher cooling rates, up to 400 "C/h, oil yield increases, whereas at lower cooling rates only medium yields are obtained. The author attributed this phenomenon to the differences in
154
11. MANUFACTURE OF PARAFFIN WAXES AND CERESINS FROM PJZTROLEUM
-28
-
I
=
l
!
I
/
1
1
/ I 1 '0
01
0 2 0.3 04 0'5 016 d.7 d 8 0'9 1.0 Conrodson number, w t - %
Fig. 11-8. Oil percentage in petrolatums versus Conradson number. I Acetone : toluene = 30 : 70; 2 Acetone : toluene = 40 : 60; 3 MEK : toluene = 50 : 50
size and morphology of the paraffin wax crystals formed in the course of cooling. He concluded that it is expedient to apply different cooling rates in successive cooling stages. In the temperature range where the bulk of the wax present in the slurry crystallizes (in his case this was the range from - 5 to - 15 "C), it will pay to increase the cooling rate up to values of 300-400 "C/h, while in the ranges above and below (from + 10 to -5 "C, and - 15 to -30 "C,respectively, in the given case), a cooling rate of 150 "C/h is satisfactory.
(C) DEWAXING PROCESSES USING SOLVENTS
155
Regarding these experimental results it should be noted, however, that a cooling rate of 300 to 400 'Cjh is inordinately high for present industrial practice. Efficient separation of the liquid and solid phases in filtration is of great importance from the point of view of the yield of dewaxed oil, but it is even more so for the properties of the slack wax. After filtration, an oil-containing filtrate is retained in the pores of the filter cake. This is removed, at least partially, by washing with pure solvent. In the wash operation on the one hand the filtrate is displaced by the pure solvent, and on the other hand the retained oil is removed by diffusion. The retained oil indicates the amount of substance dissolved in the diluting solvent, this amount being dependent on the equilibrium conditions at the temperature of filtration. The efficiency of oil removal is obviously dependent on the amount of washing solvent applied. In the case of continuously operated rotary filters this amount cannot, however, be chosen arbitrarily. The relationship between the amount of solvent that can be used for the wash of a unit volume of the filter cake on the one hand, and conditions of the filtration operation and properties of the feed is a basic question on the other hand. Assuming that the filter cake is incompressible and the pressure drop within the cake is constant,
(11-5) where x is the thickness of the cake in the moment t, dx the change of the thickness during the period dt, Ap the pressure drop in the cake thickness x , and dp the pressure drop in the cake thickness dx, (11-6)
where dq is the volume of the filtrate passing through the unit area of the filter during the period dt. The term unit area here indicates an infinitesimally narrow and infinitely long filter element parallel to the axis of the filter. p1 is the dynamic viscosity of the filtrate, and Kl is the filter constant. The change dx of the thickness of the filter cake is proportional to the change of the volume of the filtrate. In the case of unit cake area, dx
=
sdq
(11-7)
where s is cake volume relative to unit filtrate volume. Its value depends, in the case of constant ratio of voids-volume in the cake, on the amount of solid matter in the feed. Taking into account Eqs (11-5)-(11-7): dxsdt
_ _Kl_ . _Ap_ p,
x
(11-8)
156
11. MANUFACTURE OF PARAFFIN WAXES AND CERESINS FROM PETROLEUM
or (11-9)
where x, is the thickness of the cake at the end of filtration (when the filter area element leaves the filtering section), t, is time of filtration (the residence time of the filter area element in the filtering section during one rotation of the drum). In continuously operated rotary filters x = 0 at the moment t = 0 (at the start of filtration), and x = x, at the moment t, (at the end of filtration). Integration of Eq. (11-9) yields
(I I- 10) Filtration time, i.e. the residence time of one filter area element in the filtering section during one rotation of the drum is defined by the speed of the drum and by the immersion angle of the filtering section. Considering drum speed as variable, t = -K2 n
(11-11)
where K2 is a constant characterizing the immersion angle of the filtering section, and n is the speed of the filter drum. From Eqs (11-10) and (11-11)
-xz_ - sKlK2Ap 2
(11- 12)
Pln
Among feasible wash conditions let us examine the case when washing solvent is in excess, i.e. the cake is flooded with solvent during the washing operation. Let us further assume that the value of Ap is identical in the filtering and washing stages. Then (11-13) where q t is the volume of washing solvent passed through unit area of the cake during unit time, K3 is the filter constant in the wash operation and py is the viscosity of the washing solvent. Total volume of solvent passing through unit area of the cake in the washing operation, taking residence time into account, can be written in the following form: (11-14) where qw is total volume of solvent passing through a portion of the cake with unit area, and hence with a volume of x,, during the washing operation, K4 is
(C) DEWAXING PROCESSES USING SOLVENTS
157
a constant characterizing the immersion angle in the washing section, and K J n is the residence time of the filter area element in the washing operation for single rotation. The total amount of solvent applicable for washing the unit volume of cake is then expressed by
(11-15)
(11-16) Equation (11-16)indicates that the amount of wash solvent applicable for washing the unit volume of cake, i.e. the effectiveness of wash is independent of the speed of the drum if the resistance of the filtering medium is negligible and solvent is present in excess. Hence, higher drum speeds increase filtering capacity at constant yield as long as the cake does not become excessively thin or the filtering medium does not clog. Equation (11-16)demonstrates that recycling of the filtrate to the slurry reduces the value of s and thereby improves the effectiveness of the wash operation. The extent of filtrate recycling is limited only by the dimensions of the equipment (e.g. surface area of the chillers). In reality the resistance of the filtering medium, that is, its change after wash with warm solvent cannot be neglected. According to studies of Mondria and co-workers the effectiveness of wash qv,in the case of significarit medium resistance, increases slightly with increasing speed of the drum. Relative wash effectiveness in a wash section flooded with solvent and for incompressible cake is related to drum speed as follows:
[
w=--[ a+l a+2
+
&
-&
+ a(a + 2)
I’al
(11- 17)
where a is the ratio of cake resistance and filtering medium resistance in the wash section, E is the ratio of the actual speed and a chosen reference speed ( E = n/n,), and W is the effectiveness of wash, W = qO(n)/qO(n,),where qO(n)and q0 (n,) are effectiveness values at the speeds n and n,, respectively. If, for instance, the resistance of the cake is twice as high as that of the filtering medium, doubling of speed will increase the wash effectiveness related to unit cake volume by about 8.5%. Equation (11-16)defines the maximum value of solvent applicable for wash. Actual consumption may be lower; in this case reduced speed of the filter improves wash effectiveness by reducing filtration rate. For the case of washing thin cake layers with larger amounts of solvent, the effectiveness of wash is given by the following equation: lgx, = - c--
vm vo
+ lg
(1.1 -
(II- 18)
I58
11. MANUFACTURE OF PARAFFIN WAXES AND CERESINS FROM PETROLEUM
where xR is the dissolved substance (related to the initial amount) retained in the cake after wash, V , is the volume of the wash solvent, V, the liquid content of the cake before washing and C is a reduced constant. The ratio V,/Vo = N , is termed wash ratio. With these symbols, the effectiveness of the washing operation is expressed by (11- 19)
that is, by the difference, in percentage, of total soluble component (oil) and soluble component retained, related to unit wash ratio. When choosing the amount of solvent for wash, in addition to what was said above, the changes in oil concentration in the wash liquid effluent must also be considered. The breakthrough curve of the wash solvent flattens in the diffusion section, and here the oil content of the slack wax changes only slightly with increasing amounts of wash solvent. Figure 11-9 presents a breakthrough curve taken from investigations of this type carried out in the Hungarian Oil and Gas Research Institute. This curve refers to the dewaxing of a residual oil at -25 "C. As can be seen, decrease of oil concentration in the wash liquid effluent, that is
Wash effluent volume/cake volume, cm3/cm3 I
l
l
l
l
l
~
i
l
l
I
0 051 103 155 2 0 8 2 6 2 3.15 4 2 4 4 7 6 530 Wash solvent volume/feed mass, cm3/g Fig. If-9. Oil percentage in wash effluent versus amount of wash solvent applied
(C) DEWAXING PROCESSES USING SOLVENTS
159
breakthrough of the solvent, takes place at a value of 0.6-0.7 cm3 solvent per cm3 cake volume. The two closely linear portions of the curve intersect at a specific wash solvent value of 1.22 cm3/cm3. This corresponds to employing about 200 wt- % solvent relative to feed. After the point of intersection it is not effective to further increase the amount of wash solvent in the case of a single filtration stage. In the given example the oil content of the slack wax was reduced, in agreement with the course of the breakthrough curve, up to using specific wash solvent values of 1.2-1.3 cm3/cm3. The methyl ethyl ketone dewaxing process is equally suitable for any boilingrange lubricating oil, both before or after solvent refining of the oil, with or without the use of filter aids. The feed is usually diluted with twice to four times its amount of solvent, then cooled and crystallized in continuously operated crystallizers. The slurry is then separated in rotary filters into filtrate and solvent-containing slack wax. Solvent is recovered from both filtrate and slack wax by distillation. Advantages of the methyl ethyl ketone process against propane dewaxing are : (i) For a given filtration temperature the MEK process yields oils with lower pour points, since lower spread values can be obtained. (ii) Substances modifying crystallization, and eventually present in the feed, interfere less than in the propane dewaxing process. For this reason, filter aids are usually unnecessary. (iii) Methyl ethyl ketone dewaxing and de-oiling processes can be combined, while this in not feasible in the propane process, since propane is less suited for de-oiling owing to the higher temperatures necessary in this operation (filtration difficulties, high vapour pressure, equipment construction problems etc.). Disadvantages of the methyl ethyl ketone process against propane dewaxing are : ( i ) The properties of the filter cakes obtained from residual oils by propane dewaxing are better. (ii) Relatively expensive coolers and crystallizers equipped with scrapers, socalled chillers, are necessary for the methyl ethyl ketone process. For these reasons, a view exists that it is preferable to carry out dewaxing of distillates by the methyl ethyl ketone and that of distillation residues by the propane process, respectively. In practice, however, it is uneconomic, for plants processing various distillates and residues to use more than one type of dewaxing process. Figure 11-10 presents the flow diagram of a methyl ethyl ketone dewaxing plant. The feed is heated, after dilution, to a temperature exceeding the cloud point of the mixture by 5 to 10 "C, and subsequently cooled in water coolers to the cloud point. Further cooling takes place at an average rate of 1 "C/min in continuously operated scraped-surface crystallizers, so-called chillers. About 60 % of the cooling energy required is obtained by heat exchange with the filtrate coming from the filters and the rest by evaporation of some refrigerant, e.g. propane or ammonia in the shell of the scraped-surface crystallizers. The slurry is cooled to a temperature about 5 to 12 "C lower than the desired pour point. The solvent is usually added
160
11. MANUFAC-fURE OF PARAFFIN WAXES AND CERESINS FROM PETROLEUM
Dilution solvent
Dilution solvent
Dilution solvent
Wash solvent
7
Paraffinic feed
I(\
t
1
Steam Cooling water Dilution solvent
Refrigerant
Vacuum Dewaxed oil
Slack wax, petrolatum
II LQ--
-74 Filtrate
Fig. 11-10. Flow diagram of a MEK dewaxing plant. I Heater, 2 Cooler, 3 Scraped-surface cooler, 4 Scraped-surface crystallizer, 5 Delivery tank for rotary filter, 6 Rotary filter, 7 Filtrate tank
to the feed in two or three stages at different temperatures. Wash solvents from the filters and the filtrate of the second stage are also used for dilution. The slurry, cooled to the filtration temperature, passes into the feed tank of the rotary filter?, and flows continuously from the tank through the troughs of the filters. Enclosed rotary filters are used to separate wax from filtrate, filtration is carried out under vacuum. The solvent is subsequently recovered by distillation from the filtrate and the slack wax. It is important to previously remove water contained in the slack wax by sedimentation in tanks.
2. The propane dewaxing process
Dewaxing with propane is a versatile and economic refining process. The main point in its introduction was the applicability of one and the same solvent for deasphalting the residue of vacuum distillation of crudes and dewaxing the deasphalted oil residue. The common solvent allows substantial simplification in solvent recovery operations and pretreatment. The flow diagram of a propane dewaxing plant is shown in Fig. 11-1 1. The main stages of the dewaxing process are as follows: (i) heating the solution of the oil in propane above the mixing temperature, (ii) direct cooling of the solution by evaporation of propane, (iii) filtration under pressure, usually in rotary filters, and wash of the filter cake with cold propane,
(C) DEWAXING PROCESSES USING SOLVENTS
161
xed oil
fin
wax
Fig, 11-11.Flow diagram of a propane dewaxing plant. 1 Propane tank, 2 Oil-propane solution tank, 3 Crystallizer, 4 Delivery tank for rotary filter, 5 Rotary filter, 6 Filtrate tank, 7 Propane evaporizers for filtrate, 8 Stripper for oil, 9 Cold propane tank, 10 Propane evaporizers for slack wax, I 1 Stripper for slack wax, 12 Water condenser, 13 Spray catcher, 14 Propane compressor
(iv) evaporation of the solvent, usually carried out in two or more stages, the first being flash distillation, and the final solvent recovery stage the removal of propane traces by stripping with steam, (v) removal of water traces in the dewaxed oil by vacuum drying (heating of the oil at reduced pressure). Preparation of the slurry starts with dilution of the liquid paraffinic feed. The ratio of solvent to feed varies usually between 1 : 1 and 4 : 1. Similarly to other solvent dewaxing processes, increased specific amounts of solvent improve the yield of dewaxed oil, while decreased amounts raise plant output. The feed-solvent mixture is heated to a temperature at which all waxes and additives promoting crystal formation will be completely dissolved, this being the precondition for reliable control and, if necessary, modification of the crystallization process. The slurry is cooled to the cloud point by water cooling in shell-and-tube heat exchangers, and is subsequently led for further cooling into the evaporator-crystallizer. This is essentially a well-insulated horizontal tank. Propane vapours are then compressed and subsequently condensed in a water-cooled heat exchanger. Condensed propane is recycled into the process or pumped into a storage tank. Heat of vaporization of propane at 0 "C is around 377 kJ/kg. Thus, to cool 1 kg of slurry by 20"C, about 0.03 kg of propane, and to crystallize 1 kg of paraffin wax, about 0.4 kg of propane must be evaporized. 11
162
11. MANUFACTURE OF PARAFFIN WAXES AND CERESINS FROM PETROLEUM
Dilution in batch crystallkers is usually controlled by the liquid level. Propane added to the slurry during crystallization is cooled in heat exchangers with cold filtrate or cold repulped wax. Cooling rate is usually controlled by the compressor performance. Growth of the crystals takes place under controlled conditions. Longer periods of crystallization (slow cooling) or higher solvent ratios generally result in slurries that can more readily be filtered. In the propane dewaxing process the liquid and solid phases are separated in rotary filters operated under pressure. The filter cake is washed in the filter with cold propane for better removal of its oil content. Final oil yield and oil content of the paraffin wax largely depend on the effectiveness of the wash operation. The amount of solvent used for wash cannot be chosen arbitrarily. Its upper limit is defined by the operating conditions of filtration. Wash solvent per unit cake volume is independent of drum speed when the resistance of the filtering medium is negligible. Hence the output of the filter will increase with increasing speed up to the point where the cake becomes excessively thin or the filtering medium clogs. Advantages of the propane dewaxing process are: (i) The solvent is available in most petroleum-processing plants, it is cheap, non-corrosive and, under the given conditions, miscible in all proportions with lubricating oil fractions. (ii) Cooling by direct evaporation of a part of the propane allows the elimination (at least partly) of expensive scraped-surface heat exchangers and chillers. (iii) In bright stock manufacture, the first stage is deasphalting of vacuum distillation residues with propane. The oil-containing propane from this operation can then be directly dewaxed, so that removal of propane by distillation after deasphalting is eliminated. If, however, the oil requires solvent refining, this succession of operations is not profitable. In this case, refining should directly follow deasphalting, since in this way the amount of feed for dewaxing will be reduced substantially by refining losses, so that only this reduced amount has to be submitted to dewaxing, thereby resulting in reduced operating cost. Besides these listed advantages of the process, its disadvantages should, however, be also considered: (i) Propane is a relatively good solvent for paraffin waxes, therefore,lower filtration temperatures are required for manufacturing dewaxed oil with a desired pour point than in the case of ketone dewaxing. For instance, to manufacture oil with a pour point of - 15 "C, filtration temperatures of - 30 to - 35 "C are required, so that the advantage originating from direct cooling will partly be lost. ~ji>Y~%+m a%%rn%i$-c~&~hb%i b -a-=-~%%xbmmbmiik%aX\ bj-mix. b (iii) It is much more difficult to obtain easily-filterable paraffin wax crystals than in ketone processes. This is particularly true when dewaxing distillates. Filter aids are therefore usually necessary in propane dewaxing processes. Also, refining operations like deasphalting with propane, solvent extraction, hydrogenation, etc., frequently remove natural substances originally present in the feed, thereby
163
(C) DEWAXING PROCESSES USING SOLVENTS
modifying the crystal structure of the paraffin wax. This also impairs filtration. Such effects are less noticeable in ketone processes. In propane dewaxing too, previously non-refined oils show better filtration properties than refined residues. Filter aids, since these are also used in other solvent dewaxing processes, will be discussed separately in Section 6 . 3. Dewaxing with a mixture of propylene and acetone
As mentioned earlier, spread values are high for propane dewaxing, so that the process is only suited for manufacturing oils with pour points of - 15 to - 18 "C. For many applications, however, oils with lower pour point are required. To eliminate this disadvantage, experiments were made at Exxon Research and Engineering Company with mixtures of propane and various selective solvents (ketones, sulfur dioxide, alcohols, amines). The maximum concentration of the selective solvents at which oil and solvent mixture do not separate and the selective solvent is fully miscible with propane at the filtration temperature was also determined. However, in contrast to expectations, spread values could not be substantially reduced by applying these selective solvents. The studies were continued by replacing propane with propylene. Mixtures of propylene with various selective solvents gave significantly better results : miscibility of the oils and solvents was improved and spread was reduced. In addition, the required amount of filter aid was also less. The results of dewaxing with solvents of different compositions are summarized in Tables 11-2 and 11-3. Table 11-2. Filtration temperatures for dewaxing a feed oil having a viscosity 32 mmz/s at 37.8 "C to a pour point of - 17.8 O C using various solvents (Dilution: solvent to feed 1.5 : 1 vol/vol) Solvents
-___ -
Propane Propylene
- 38.8 - 36.6
Selective component
1
SO,
- 37.7 -28.9
I
Alcohol
-31.7 -31.7
j
Acetone
- 36.1 - 29.5
Table 11-3. Filtration rates attainable with acetone-propane and acetone-propylene solvent mixtures (Feed: 32 mmz/s at 37.8 "C viscosity distillate. Dilution: solvent to feed 1.5 : 1 vol/vol) Process conditions
Propane
Filtration temperature for a pour point of - 17.8 OC of the product, OC Relative rate of filtration
* The acetone concentration 11*
- 38.8
1.o
Propylene
-36.6 1.2
Propaneacetone*
Prowleneacetone'
-36.1
-29.5
1.5
1.5
in the solvent mixture is so high that no liquid-liquid separation takes place.
164
11. MANUFACTURE OF PARAFFIN WAXES AND CERESINS FROM PETROLEUM
* Dilution solvent
7
Feed
Batch chilling on 'Dewaxed automatic control 011 filtration on rotary pressure filters Dilution
Dewaxed
I
Filter Decanter
recovery
Fig. 11-12. Flow diagram of the Exxon propylene-acetone dewaxing plant
The mixture yielding the best results was found to be that of propylene and acetone. Exxon Research and Engineering Co., therefore, developed a commercial process for this solvent. The flow diagram of the process is shown in Fig., 11-12. In practice this dewaxing process allowed the manufacture of oils with pour points of - 15 to -26 " C , depending on the composition of the solvent, on the amount of solvent applied and on the properties of the feed. Spread values obtained varied within the range of 6-12 "C. 4. Dewaxing with chlorinated hydrocarbons
Literature data and patents indicate that numerous chlorinated hydrocarbons are suitable for dewaxing. Owing to the high density of these solvents, centrifuging is expedient for the separation of slack wax and filtrate. This does not, however, exclude the feasibility of using filters. Among the processes using chlorinated hydrocarbons, the Bari-Sol process was put into practice on a commercial scale. In this process, trichloroethylene or a mixture of dichloroethane with benzene is used, in the latter case the dichloroethane content of the solvent varies between 75 and 80 vol- %. The composition of the solvent depends above all on the properties of the feed. Benzene increases the oil-dissolving capacity of the solvent. Pure dichloroethane tends to precipitate high-viscosity index paraffinic components. Usual operating conditions include the dilution of the waxy feed with a solvent mixture about three times its volume. This mixture is then homogenized in con-
(C) DEWAXINO PROCESSES USING SOLVENTS
165
tinuously operated mixer tanks or columns at about 45 "C and subsequently cooled to the dewaxing temperature, first in aqueous heat exchangers and then in chillers using ammonia as refrigerant. Cooling rates above 0 "C are 4-5 "C/min, below 0 "C 7-8 "C/min. In this process spread is very satisfactory, as low as 3-5 "C. The solvent-containing wax phase is separated from the filtrate by centrifuging. Low solvent-content slack wax or petrolatum are removed from the interior of the centrifuges with scrapers, and the solvent-diluted dewaxed oil is the efluent of the centrifuge. In order to reduce the oil content of the waxy part (slack wax or petrolatum) dewaxing is carried out in two stages. The fraction obtained in the first stage, containing more solvent and having a higher melting point, is subjected to repeated centrifuging after previous dilution with solvent to a ratio of 8 : 1. The temperature of the second centrifuging stage is usually lower by 1-3 "C than that of the first stage. The low oil-content filtrate from the second stage is mixed with fresh solvent and used for feed dilution. As a result of great density differences and special centrifuge construction the centrifuges are operated at speeds of 8OOO9000 rpm. The products are won from the filtrate by distillation of the first stage and from the solvent-containing slack wax or petrolatum of the second stage. Among more recent processes we wish to mention the process developed by the Edeleanu Gesellschaft, called Di-Me. A mixture of dichloroethane and dichloromethane is used as solvent, the first being the selective, the second the oildissolving component. The mixture usually contains 50-70 volume parts of dichloroethane. Its composition is chosen so as to ensure that no separation of the oil takes place at the dewaxing temperature. If it is chosen correctly, the spread, according to literature data, is as low as 1-4 "C.For low-viscosity oils the amount of diluting solvent is around 300 vol-%, for high-viscosity oils it varies from 400 to 500 vol-%. The main advantage of the process is that very low oil-content slack waxes (2-6 wt-%, depending on wash ratio) can be obtained in a single filter stage. In addition, the process is only slightly sensitive to changes in solvent ratio, maintaining low spread values. 5. Dilchill dewaxing process To eliminate the numerous drawbacks of dewaxing based on indirect cooling (breakage of crystals, secondary nucleus formation, wide crystal size distribution) a novel dewaxing concept applying direct cooling has been developed. The essential feature of the Dilchill process is that the homogeneous feed is heated to a temperature higher than its cloud point, and introduced into a specially constructed crystallizer provided with mechanical agitation. The diluting solvent, cooled to an appropriately low temperature, is injected directly into the feed. During this operation, intensive agitation is provided, particularly in the area of the point
166
11. MANUFACTURE OF PARAFFIN WAXES AND CERkSINS FROM PETROLEUM
of injection. In this method cooling of the feed close to filtration temperature and crystallization of the bulk of the wax takes place in a single equipment, the Dilchill crystallizer. The temperature of the cold solvent is so chosen as to yield a temperature in the crystallizer closely approaching the desired filtration temperature. For final cooling to this temperature one or a few scraped-surface chillers are applied. For example, if the filtration temperature is -23 "C, the solvent is cooled to about - 4 5 "C at solvent to feed ratios of 2 : 1-5 : 1. Spread varies between 3 and 6 "C,depending on solvent composition and properties of the waxy feed. Usual solvents, e.g. mixtures of MEK and toluene are used. Since the solvent is cooled in this process, only dry solvent can be used, otherwise ice crystals would be formed on the solvent coolers. Experiences have demonstrated that in spite of shock cooling, the individual crystals formed in the specially constructed crystallizer are larger, approximately spherical in shape and their size distribution range is narrow. As a result of this crystal build-up, filtration rate is increased by approximately 50 % as compared to conventional processes, drier filter cakes are formed, and the oil content of slack wax obatined in one-stage filtration is 3-15 wt- %. The Dilchill process allows the manufacture of dewaxed oils down to pour points of -30 "C. 6. Filter aids
In the first section of this chapter we discussed the importance of the size and morphology of the wax crystals to be filtered in the dewaxing process. To influence these factors favourably, the use of filter aids has become increasingly wide-spread in the past 10 to 15 years. By their use, filtration rate is increased, the oil content of the slack wax is reduced, while higher yields of dewaxed oil are achieved, solvent requirement decreases and finally, the crystallization process is less affected by the cooling rate. In general, the advantages resulting from filter aids can be expressed by the following data: yield increase 3 to 5%, filtration rate increase 15 to 20%, oil content reduction in slack wax around 50%. The action mechanism of filter aids is explained variously. The most plausible explanation for the action of filter aids soluble in oil and crystallizing together with the waxes during cooling, or separating from the diluted solution before crystallization of the waxes is their modifying effect on the crystalline structure of the paraffin waxes. In the place of plate-shaped crystals, the crystals formed are branched, tree-shaped dendrites that are not entrapped in other crystal lattices, but remain separated in solution. In this manner a less compact filter cake with a more homogeneous crystalline structure is formed, allowing higher filtration rates and retaining less oil. Among the numerous oil-soluble filter aids, the most frequently used are condensation products of chloroalkanes and phenol, polymethacrylates with different molecular weights, chloroalkylated benzene and toluene products, polyethylene
(C) DEWAXING PROCESSES USING SOLVENTS
167
waxes, butadiene-styrene copolymers, vinyl ester polymers and alkylated polystyrenes. The amount of filter aid used usually varies from 0.03 wt- % to 2 wt- %, depending on the feed and on the type of the filter aid. In some cases only one, in others more, generally two, types of filter aids are used to modify the crystalline structure of paraffin waxes. When using combinations of filter aids, it was found that their effectiveness is greatly increased by adding them in a number of stages in the course of cooling. In one-stage addition the additive should be added to the oil-solvent mixture before crystallization of the wax starts. In multistage addition, the filter aid portions are added to the slurry as it cools, at successively decreasing temperatures, in the ranges where the effectiveness of the filter aid is highest.
Literature Adams-Mertens-Godino: Petrol. Refiner, 40, 189 (1961). Asinger, F., Chemie und Technofogie der Parafin-Kohlenwasserstoffe.Akademie-Verlag, Berlin (1956). Bushnell-Eagen: Oil Gas J., 73, No. 42, 80 (1975). Chesnokov, A. A., Neftepererab. Neftekhim., No. 10, 18 (1964). Deen-Williges: Hydrocarb. Process. Petrol. Refin., 42, No. 9, 43 (1963). Di-Me solvent dewaxing and wax deoiling. Hydrocarb. Process., 53, No. 9, 169 (1974). Eagen-Gudelis-Shaw-Walker: Ninth World Petroleum Congress. Vol. 5. Processing and Storage. Applied Science Publ. Ltd., London (1975). Fadeev-Pereverzev: Neftepererab. Neftekhim. Slantsepererab., No. 1, 20 (1976). Fauzi-Kartinin: Neft’ i Gaz, 6, No. 8. 61 (1963). Gerber, C., Freiberger ForschHft., A 283, 45 (1963). Gipp-Heinze-Leibnitz: J. prakt. Clzem., 19, 74 (1963). Gipp-Heinze: Chem. Tech. Berl., 15, 133 (1963). Glazov-Falkovich-Chernozhukov: Neftepererab. Neftekhim., No. 3, 7 (1964). Glazov-Unksova-Falkovich: Khimiya Tekhnol. Topl. Muse/, 9, No. 4, 16 (1964). Gruse-Stevens: Chemical Technology of Petroleum. McGraw-Hill Co., New York (1960). Gudelis-Eagen-Bushnell: Hydrocarb. Process., 52, No. 9. 141 (1973) Kacvinska, V., Ropa Uhlie, 19, No. 11. 641 (1977). Kalichevsky-Kobe: Petroleum Refining with Chemicals. Elsevier Publ. Co., Amsterdam (1956). Kalsina-Kushnir: Neftepererab. Neftekhim., No. 7, 61 (1976). Kazakova-Gundyrev: Khimiya Tekhnol. Topl. Masel, 21, No. 10, 18 (1976). King, E. P., Oil Gas J., 51, 122 (1953). Kobe-McKetta: Advances in Petroleum Chemistry and Refining. Vol. 10, Interscience Publ. Co., New York (1956). Korsakov, N. M., Neftepererab. Neftekhim., No. 3, 17 (1970). Leonidov-Pereverzev : Neftepererab. Neftekhim., No. 12, 13 (1975). Movsumzade-Bleybutova: Neff’ i Gaz, 8, No. 1, 55 (1965); 6, No. 6, 73 (1963). Olkov-Sharafutdinov: Neftepererab. Neftekhim. No. 9, 7 (1964). Petrol. Refiner, 41, 235 (1962). Petrol. Refiner, 43, 220 (1964). Propylene acetone dewaxing. Hydrocurb. Process., 53, No. 9. 183 (1974). Reeves, E. J., Petrol. Refiner, 27, 80 (1948). -: Ind. Engng. Chem., 39, 203 (1947).
168
II. MANUFACTURE OF PARAFFIN WAXES AND CERESINS FROM PETROLEUM
Rudakova-Sheremeta-Ostrovskaya-Khamolina-Sereda: Neft’ i Gaz, No. 4, 40 (1968). Schneider, N., Petrol. Refiner, 42, 104 (1963). Shevtsov, M., Neftepererab. Neftekhim. Slantsepererab., No. 1, 16 (1976). - : Nefrepererab. Neftekhim. Slantsepererab., No. 2, 12 (1976). Szadkowszki, K., Nafta, Krakow, No. 8 , 216 (1958). Tiedje-McLead: Petrol. Refiner, 34, 150 (1955). U.S. Pat. 2 223 939.
U.S.Pat. 3 458 430. U.S. Pat. 3 475 321. U.S. Pat. 3 576 735.
Vamos-Zakar-Mozes-Keszthelyi: Acta Chim. Hung., 31, 267 (1962). Weinstabl-Elkes: Erdd Erdgas Z . , 93, 193 (1977).
(D) De-oiling and fractional crystallization of slack waxes and petrolatums Slack waxes and petrolatums formed in the dewaxing process contain substantial amounts of oil, usually 1@30 wt- %. “Oil” in this sense is a mixture of the components dissolved in the solvent at the filtration temperature, and seriously impairs some properties of the wax important for its use. Wax fractions already crystalline at the temperature of dewaxing, but having relatively low melting points and consisting mainly of iso-alkanes have similarly detrimental properties. For this reason, these substances, that is, oil and low-melting fractions must be removed from the slack wax. The process is called de-oiling. De-oiling is fractional crystallization of slack or paraffin waxes by their melting point. If the product obtained still has a wide melting range, it is necessary in some cases to subject it to repeated fractional crystallization, in order to obtain paraffin waxes with narrow melting ranges. In this sense, de-oiling and fractional crystallization are essentially several stages of one and the same operation. Slack waxes obtained from light distillates by cooling and pressing were formerly de-oiled exclusively by a process called sweating. This consisted essentially of the separation, by fractional melting, into fractions with narrower melting ranges. By slowly raising the temperature of the solid slack wax, first the oily parts with the lowest melting point will be removed (slack oil I). These are followed by fractions with successively higher melting ranges and lower oil content, but richer and richer in wax (slack oil 11, semiparaffin wax etc.). When the sweating operation is completed, the residue consists of the solid paraffin wax with the desired melting point and oil content. Sweating is carried out in sweating pans placed in heated sweating chambers. At one third or half of the height of the pan, wire gauze is fitted across horizontally. Frequently coils of pipe, for circulating cold and warm water, are installed above the sieve. The molten slack wax is led into the sweating pan and its temperature, in the upper part of the pan, is allowed to drop below its melting point. During
(D) DE-OILING AND FRACTIONAL CRYSTALLIZATION
169
the introduction and cooling of the molten slack wax the space below the gauze is filled with water that can be circulated if required. In this manner, the slack wax solidifies on the gauze and in the space above the sieve and forms a layer of 10-18 cm thick. After solidification of the slack wax the water is drained from the space under the sieve, and sweating begins. The temperature in the chamber is raised a t a rate of 0.5-1 .O"C/h, so that successively higher-melting fractions Will drip through the sieve. By way of example, the results of sweating a slack wax with a melting point of 44 "C and an oil content of 35 wt-% at various rates of temperature increase, are presented in Table 11-4. Table 11-4. Sweating of a 35 wt- % oil-content slack wax (melting point 44 "C) Rate of
Sweated paraffin wax
increase, "C/h
0.6 1.5 3.0 5.6 0.6 1.5 3.0 5.6
wt-%
20 20 20 20 15 19 22 25
54.0 53.5 53.0 52.5 53.4 53.4 53.4 53.4
0.15 0.39 0.63 1 .oo 0.10 0.38 0.80 1 .so
Selectivity of sweating is unsatisfactory. Desired grade products can be obtained in this manner only with relatively low yields. Also, sweating is an extremely slow process, one cycle taking as much as, or more, than 50 hours. A further disadvantage is that the process is only suited for de-oiling slack waxes yielding well-developed, macrocrystalline, preferably needle-shaped paraffin wax crystals. Small amounts of microcrystalline paraffin waxes already present impair sweatability of slacks. Waxes obtained from heavy paraffinic distillates and distillation residues cannot be de-oiled by sweating. For this reason, and owing to the listed disadvantages of the sweating process, solvent de-oiling processes are being increasingly adopted. In its principles solvent de-oiling is essentially identical with solvent dewaxing. Conditions of commercial-scale solvent de-oiling differ from dewaxing conditions in filtration temperature and amount of solvent used. De-oiling temperature varies between - 5 and + 5 "C,depending on the desired properties of the end product. The amount of solvent used for dilution and wash of the filter cake may be as high as 12 times the amount of the feed. De-oiling is usually carried out in two stages, the filtration temperature of the second stage being higher by 0-5 "C than that of the first stage. All solvents suitable for solvent dewaxing lend themselves for this purpose too. Similarly to dewaxing, the solvent most used currently is methyl ethyl ketone.
170
11. MANUFACTURE OF PARAFFIN WAXES AND CERESINS FROM PETROLEUM
Y. M. Fadeev and co-workers investigated the effect of the nature of the solvent on relative rates of filtration and on the yield and properties of the de-oiled product. The studied solvents were mixtures of acetone and toluene with various acetone contents, mixtures of MEK and toluene with various MEK contents, diethyl ketone, a mixture of dichloroethane and dichloromethane, and a mixture of 80 % dichloroethane and 20 % benzene. They found that mixtures of MEK and toluene are the most effective solvents, ensuring the highest extent of de-oiling and best filtration rates. The mixture of dichloroethane and dichloromethane gave the poorest results. With MEK-toluene mixtures, the MEK content can be increased up to 100% without a substantial decrease of the melting point and increase of the oil content of the wax product. In contrast, in the case of acetonetoluene mixtures, the acetone content must not exceed 30% to avoid a high oil content and low melting point for the paraffin wax obtained. Solvent dewaxing and de-oiling can be combined in one plant. The dewaxing and de-oiling plant in the Tulsa refinery of DX Sunray Oil Co. can be considered as an example. A simplified flow diagram of this three-stage plant is shown in Fig. 11-13. In the first stage dewaxing of the feed (lubricating oil distillates or distillation residues) takes place. The slack wax obtained is then diluted with the filtrate of the third stage and de-oiled in the second stage at a filtration temperature higher than that of the first stage. The product of the second stage is soft wax. The filter residue of the second stage is again subjected, after dilution with solvent, to de-oiling, using, however, an even higher temperature than that of the second stage. Its product is a harder wax. The solvent is a mixture of methyl ethyl ketone and toluene, dewaxing is carried out at temperatures below - 10 "C, de-oiling a t -7 to 18 "C. The plant processes 800 to 1500 tons of feed per day, depending on the viscosity of the oil charge. Another way of combining dewaxing and de-oiling consists in using the higher filtration temperature in the first stage, this stage thus corresponding to the deoiling operation and yielding a higher-melting hard wax. The filtrate of this stage is cooled to the dewaxing temperature and subjected to the second filter stage where dewaxed oil and lower-melting soft wax are separated. The hard wax from the first stage is frequently subjected to further de-oiling a t a lower temperature. Dewaxing and de-oiling within one plant also is feasible with the previously discussed Dilchill process. The slack wax from the last, usually second, filter stage is mixed with warm solvent, and the slurry heated to the temperature of de-oiling is separated in one or two filter stages into de-oiled wax and "foots oil". In this manner the oil content of the de-oiled wax will not exceed 0.5 wt-%. The flow diagram of this combined process is shown in Fig. 11-14. Fractional crystallization is of primary importance in processing petrolatunis with wide melting range obtained from distillation residues : with this operation microcrystalline paraffin waxes differing largely in properties can be produced. Detailed studies were carried out in the Hungarian Oil and Gas Research Institute concerning the fractional crystallization of petrolatums from Romashkino crude distillation residues.
+
Chillers Exchangers
Oil charge
Dewaxing filter
Surge tank
Chillers
Prirnarg irczt Chlllers filter
Repulp f i x : filter
S ,rgo tank
172
11. MANUFACTURE OF PARAFFIN WAXES AND CERESlNS FROM PETROLEUM
Rotary vacuum filters (1 or 2 dewaxing
Wash solvent I
Cold wash
Cold dilution solvent recovery
1
"Footsoil" De-oiled wax to hydrofining
Dewaxed oil
Fig. 11-14. Flow diagram of the Dilchill dewaxing and de-oiling process
Table ZZ-5. First stage of a laboratory two-stage fractional crystallization of a petrolatum from residual oil Preparation of hard microcrystalline paraffin waxes: Exuerimental conditions: Separation temperature, O c Solvent composition v01-x MEK Benzene Diluting solvent, wt- % Washing solvent, wt-%
I
Products and characteristics
'
Residual oil petrolatum (startingmaterial)
Hard microcrystalline paraffin wax
+ 30 OC and + 10 OC + 30 and + 10, resp.
at
70 30 700 400 Oil and soft microcrystalline paraffin wax
obtained at +30"C
Yield related to starting material (petrolatum), wt- % Density, d:O Viscosity at 100 OC, nirnz/s Melting point, OC Drop melting point, "C Penetration at 25 OC, 0.1 mm (Hung. Standard MSZ 13162) Oil content, wt-% (ASTM) Breaking point (Fraass), OC
100 0.8264 12.43 65.5 67 144 23.78 -29
22.1 0.7953 10.18 78.2 78
9 1.o above +22
77.9 0.8360 13.52 45
Hard microcrystalline paraffin wax
1
Oil and soft microcrystalline paraffin wax
obtained at + l O T
55.0 0.8065 10.50 70.5 70.7
33 6.65
above +22
45.0 0.8535 16.92 22
173
(D) DE-OILING AND FRACTIONAL CRYSTALLIZATION
Table 11-6. Second stage of a laboratory two-stage fractional crystallization of a petrolatum from residual oil Preparation of soft microcrystalline paraffin waxes from the oil filtrate obtained in the f i s t stage at 30°C Experimental conditions : Separation temperature, "C -20, -10andO Solvent composition, vol- % MEK 70 Toluene 30 Diluting solvent, wt- % 400 Washing solvent, wt- % 700 Soft microcrystalline paraffin wax Products and characteristics
_.
I
a t - ~ ~ o ~
Yield related to starting material (petrolatum), wt-% Density, di0 Viscosity at 100 "C, mmZ/s Melting point, O C Drop melting point, "C Penetration a t 25 "C, 0.1 mm (Hung. Standard MSZ 13162) Oil content, wt- % (ASTM) Breaking point (Fraass), O C
43.5 0.8174 10.62 50.4 50.2 96 5.18 below -30
__
at-100~
1
37.0 0.8128 10.38 52.5 51.8 57 1.30 - 30
31.1 0.8106 10.12 53.2 53.0 33 0.51 - 26
Table 11-7. Second stage of a laboratory two-stage fractional crystallization of a petrolatum from residual oil Preparation of soft microcrystalline paraffin waxes from the oil filtrate obtained in the first stage at 10 "C Experimental conditions: -20 and 0 Separation temperature, "C Solvent composition, vol-% MEK 70 Toluene 30 Diluting solvent, wt-% 400 Washing solvent, wt-% 700 Products and characteristics
Yield related to starting material (petrolatum) wt- % Density, dQo Viscosity at 100 O C , mmz/s Melting point, O C Drop melting point, O C Penetration at 25 "C, 0.1 mm (Hung. Standard MSZ 13162) Oil content, wt- % (ASTM) Breaking point (Fraass), "C
I
soft microcrystalline paraffin wax
12.6 0.8212 10.43 52.3 55.8 124 5.58 below -30
6.0 0.8160 9.89 55.4 59.0 75 1.66 below -30
at00~
174
11. MANUFACTURE OF PARAFFIN WAXES A N D CERESINS FROM PETROLEUM
Fractionation was carried out in two stages. In the first stage hard microcrystalline waxes were separated from the petrolatum at 30 and 10 "C. In the second stage soft microcrystalline waxes were separated at 0, - 10 and -20 "C from the above oily filtrates. The solvent used in the first stage was a mixture of 70 vol-% methyl ethyl ketone and 30 vol- % benzene. In the second stage, owing to the lower temperatures, benzene was replaced by toluene. The total amount of solvent was identical in both stages. In the second stage the ratio of wash solvent was increased, because the cake was more difficult to wash and for microcrystalline waxes a low oil content is required. The conditions of the first stage of fractional crystallization and the main characteristics of the petrolatum and of the products are listed in Table 11-5. The results indicate that at +30 and 10 "C, at an oil content of 1-7 wt-%, hard microcrystalline paraffin waxes are obtained with drop melting points of 70-80 "C and needle penetrations in the range of 1@35 * lo-' mm a t 25 "C (depending on oil content). It is noteworthy that the increase of the drop melting point by 10 "C, as compared to that of the feed, was accompanied by a mass loss of about 80 wt- %. This loss also encourages the production of further types of paraffin wax from the oily filtrate obtained in the high-temperature separation. Data concerning the soft microcrystalline paraffin waxes obtained from the oily filtrates by separation at 0, - 10 and -20 "Care presented in Tables 11-6 and 11-7. These data provide evidence that the products obtained at 0 and - 10 "C, from the oily filtrate separated at +30 "C, are greatly plastic even a t low temperatures. Their breaking point is - 26 and - 30 "C, respectively. Their oil content is 0.51.5 wt- % and their penetration does not exceed the values permitted in the respective standards. Including the yield of the hard microcrystalline wax a t the first stage, 52-60 wt-% of the petrolatum can thus be processed to valuable microcrystalline paraffin waxes possessing specific properties. The products separated at -20 "C from the oily filtrate obtained at +30 "C, as well as the products separated at 0 and -20 "C from the oily filtrate obtained at 10 "C are also plastic, their breaking point is below -30 "C. However, due to high penetration values, their use without additives is limited. Summing up the results of the studies, it may be stated that in contrast to conventional de-oiling processes, which are unsuited to manufacture special paraffin waxes flexible at low temperatures, fractional crystallization produces high dropmelting-point low-penetration microcrystalline paraffin waxes. In addition, using the same system, soft microcrystalline waxes flexible at low temperatures are produced.
+
+
+
+
Literature Abdullin, R. A , , Khimiya Tekhnol. Topl. Masel, 8, No. 10, 34 (1963). Adams-Mertens-Godino: Petrol. Refiner, 40, 189 (1961); 42, 104 (1963). Bowman-Burk: ind. Engng. Chem., 41,2008 (1949). Freund-Keszthelyi-M6zes: Chem. Tech. B e d , 17, 582 (1965).
(E) MANUFACI'URE OF I1-ALKANES
175
Freund-Keszthelyi-Csikbs-Mbzes: Chem. Tech. Berl., 19, 688 (1967). Gerber, C., Freiberger ForschHft., A 283, 45 (1963). Ghubikian-Clapham-Dixon: Oil Gas f.,57, 83 (1959); Petrol. Refiner, 38, 192 (1959). Gipp-Heinze: Acta Chim. Hung., 31, 85 (1962). Gipp-Heinze-Leibnitz: J . prakt. Chem., 19, 74 (1963). Greber, W., Chem. Tech. Berl., 8, 571 (1956). Lipovskaya-Voznesenkaya: Khimiya Tekhnol. Topt. Masel, 7, No. 12, 15 (1962). Mahrwald, R., Freiberger ForschHft., A 283, 35 (1963). Makare-Lezhnev: Khimiya Tekhnol. Topl. Masel, 20, No. 7, 28 (1975). McLaren, F. H., TAPPZ. Bull., 34, 462 (1951). Meyer, E., White Mineral Oil and Petrolatum. Chemical Publ. Co., New York (1968). Nelson, W. L., Oil Gas J., 60, 19 (1962). Petrol. Refiner, 33, 234 (1954). Scheianu-Cristoloveanu: Mine, Petrol Gaze, 14, 571 (1963). Schneider-Teubel-Schmiedel: Chem. Tech. Berl., 17, 577 (1965). Teubel-Schneider-Schmiedel: Chem. Tech. Berl., 15, 601 (1963); 16,427 (1964). - : Erdolparufine. VEB Deutsch. Verl. fur Grundstoffindustrie, Leipzig (1965). Triems-Leibnitz-Heinz: Freiberger ForschHfc., A 299, 55 (1963). Vlasenko-Gorgeev-Pereverzev: Neftepererab. Neftekhim., No. 5, 14 (1976). Wax Fractionation. Hydrocarb. Process. Petrol. Refin., 53, No. 9, 195 (1974). Wax Deoiling. Hydrocarb. Process. Petrol. Refin., 53, No. 9, 179 (1974).
(E) Manufacture of n-alkanes n-Alkanes are used in large amounts by the detergent industry. There is a steadily increasing demand for n-alkanes in the manufacture of various additives, phenylalkane-type plasticizers for plastics, as well as in the a-olefin based petrochemical industry. A relatively recent field of application is the manufacture of proteincontaining animal food from n-alkanes by niicrobiological conversion. Two types of processes have been developed in recent decades to manufacture n-alkanes from paraffinic petroleum products : one based on crystalline adduct formation of n-alkanes with urea, the other on adsorption, using molecular sieves.
1. n-Alkane manufacture based on adduct formation with urea The discovery of adduct formation with urea is linked with Bengen's name, who, after his first results, systematically studied numerous alcohols, aldehydes, ketones, acids and esters with respect to their capacity for adduct formation. He found that in addition to hydrocarbons, these compounds also form urea adducts, if their carbon chain is not branched, but a straight alkyl chain. Research has confirmed that only non-branched compounds form adducts, with the exception of compounds possessing only a slight branching as compared to the length of the carbon chain. Adduct formation is affected by the length of the chain. For example, in the n-alkane series, n-hexane forms an adduct, but n-pentane not. In the ketone series, acetone is already capable of adduct formation.
176
11. MANUFACTURE OF PARAFFIN WAXES A N D CERESINS FROM PETROLEUM
For various organic compounds, the type of the functional group also affects the possibility of adduct formation. Manufacture of n-alkanes by means of urea is composed of four stages: (a) adduct formation, (b) adduct separation, (c) adduct decomposition, (d) post-treatment. Feedstocks to be considered for n-alkane manufacture by urea adduct formation include atmospheric and vacuum distillates of petroleum in the boiling ranges corresponding to C , to C,, n-alkanes. Before adduct formation the feed is usually mixed with so-called wetting agents (activators) in order to eliminate the effect of impurities interfering with adduct formation. Since the suspension obtained in the course of adduct formation has a very high viscosity, the feed is usually diluted with a suitable solvent or with the wetting agent. The diluted feed is brought into contact with the solid or dissolved urea in stirred tanks. The suspension passes into rotary filters or centrifuges. The separated adduct is usually washed with the solvent used as wetting agent. The washed adduct is then transferred to the decomposer, where it is decomposed by thermal treatment and aqueous dilution. Subsequently, separation of the n-alkanes and the urea solution follows in a separator. A single-stage urea extraction is sufficiently selective, under suitable conditions, to yield a practically pure n-alkane extract, and a fraction free of n-alkanes from the paraffinic petroleum distillates. Table 11-8. Extraction of gas oil by urea adduct formation --
Period of experiment,
Urea, wt-%
h
Starting material and products
Yield, wt-%
Density at 20°C
Aniline point, “C
20 “ C
Diesel index
Cetane Cetene numnumber ber I
~
24
10.0
48
25.0
48
40.0
48
60.0
1.4740
-13
79.6
1.4610 1.4760
+7 -16
84.8 69.0
1.4608 1.4786
+5
-24
84.5 65.6
1.4630 1.4786
-1 -24
1.4684 1.4812
-7 -35
61.16 53.87
57.8 57.8
66.1
-
-
57.8
66.1
78.4 65.6
49.58 49.58
76.5 63.2
-
-
-
46.50
53.0
60.6
66.1
-
-
-
57.8
66.1
Experimental studies carried out with kerosines in the Hungarian Oil and Gas Research Institute demonstrated that the n-alkanes removed from kerosines by extractive crystallization yield satisfactory grades of primary material for the chem-
(E) MANUFACTURE OF n-ALKANES
177
ical industry. Some results of studies considering gas oil are summarized in Table 11-8. Extractive crystallization can obviously be applied for other purposes too, e.g. for the manufacture of feed for low-pour-point transformer oil. Adduct formation can also be used to manufacture high drop melting point, hard ceresins from petrolatums. (a) Mechanism of adduct formation, factors aflecting adduct formation, structure of adducts
When urea is brought into contact with n-alkanes, a reaction starts between the n-alkane and the small amount of urea dissolved in the hydrocarbon phase. The rate of reaction increases in the presence of activators. Presumably the equilibria established in the course of the reaction are (11-20) urea (solid) e urea (dissolved) (11-21) n-alkane (liquid) e n-alkane (dissolved) (11-22) urea (dissolved)+ n-alkane (dissolved) S adduct (dissolved) (11-23) adduct (dissolved) e adduct (solid) The equilibrium controlling adduct formation is expressed by Eq. (11-22) The equilibrium constant for this equation is (11-24) where aA is the equilibrium activity of the adduct, ap the equilibrium activity of the n-alkane, a, the equilibrium activity of the urea and m the molar ratio of nalkane to urea in the adduct. The dissociation constant is the reciprocal of K: (11-25) If the decomposition of the adduct is caused by an aqueous urea solution, the adduct forms a solid phase, and n-alkane is immiscible with the decomposing solution, then aA = 1 and ap = 1, and hence: KD = a?
(11-26)
Using this equation it is possible to calculate, with a knowledge of m and of the equilibrium urea concentration of the aqueous urea solution, the dissociation constant for the adducts of individual n-alkanes. Or, knowing the dissociation constant, the equilibrium concentration of the urea solution can be calculated. A linear relationship exists between the logarithm of the dissociation constant and the molar ratio m for the individual members of the homologous series forming the adduct. According to Redlich, the following relationship is valid : lg K D = 2.20 - 0 . 4 0 3 0 ~ 12
(11-27)
178
11. MANUFACTURE OF PARAFFIN WAXES AND CERESINS FROM PETROLEUM
Figure 11-15 presents Redlich's data, lg KD values plotted versus the reciprocal of the thermodynamical temperature. The stability of urea adducts is proportional (under otherwise equal conditions) to the molecular weight of the addition compounds. In homologous series the equilibrium expressed by Eq. (11-22) will shift towards the right-hand side with growing molecular weight, that is, the tendency of the adduct to dissociation will decrease. Thus, 0.01 mol of heptane adduct will dissociate completely in 1 mol of benzene, whereas the cetane adduct will dissociate, at identical concentrations, only to an extent of 3.3%. Adducts formed with C,, or higher hydrocarbons are fully stable. Schlenk and co-workers found that for each group of adduct-forming compounds a maximum chain length exists where adduct formation still takes place. The solution in benzene of synthetically prepared n-C,,H,,, gave no adduct. Hydrocarbon solvents added to the reactants shift the equilibrium (11-22) towards the left-hand side. This is an important aspect both from the analytical and the technological point of view, since, if too much solvent is used to wash the adduct, the latter will partially decompose. It is, therefore, important to carry out the wash operation at subambient temperatures, applying optimum amounts of a solvent that is inert to urea. Solvents should be differentiated depending on whether they dissolve the organic component or the urea of the adduct or both. The dissociating effect acted on the adducts by solvents dissolving the organic components is the result of their associating effect on the organic part of the adduct. With such solvents it is to be expected that simultaneously with evolving of heat of admixture a partial dissociation of the adduct will appear.
37
36
r
35
10'IT 33 32
34.
31
30
29
- 0.; - 0.4 0.6 -1.2 -1.4 9 -1.6 -1.8 -2.0 -2.2 -2.4 -2.6 -2.8
3
t
-
-
-
-
-3.01
1
0
I
I
I
25 40 5 0 Temperature, "C
I
60
Fig. 11-15.Dissociation constant for urea adducts of n-alkanes versus temperature
(E)
MANUFACTURE! OF
n-ALKANES
Temperature,
179
"c
Fig. 11-16. Decomposition temperatures of urea adducts of n-alkane mixtures from petroleum.
I n-Kerosine, 2 n-Gas-oil, 3 n-Ceresin
One of the best solvents for urea is water. Hence small amounts Will be able to decompose the adduct practically completely. For example, an adduct consisting of 1 mol of cetane and 17 mols of urea will dissociate in 72 mols of water at 31 "C to an extent of 97.5%. Figure 11-16 shows decomposition temperature versus final concentration of decomposing solution for adducts of n-alkane mixtures from petroleum distillates; the decomposing solution was urea dissolved in water. The main properties of the n-alkane mixtures shown in Fig. 11-16 are listed in Table 11-9. The n-alkane content of the ceresin adduct involved in the study was 23 %, that of the gas oil adduct 15.80% and that of the kerosine adduct 12.80%. Table ZZ-9. Characteristics of n-alkane mixtures from petroleum Characteristics
Density, di0 Refractive index, n$' Pour point and melting point, resp. Average molecular weight Carbon atom number per molecule corresponding to average molecular weight n-Alkane content in the mixture, wt- %
0.7617 1.4278 +9 182
0.7782 1.4365 +I4 227
G$
C15
94
92
0.7868
-
+73 564 CUJ
85
In temperatures above 25 "C most urea complexes dissociate, and the equilibrium (11-22) is shifted towards the left-hand side. The adducts do not possess welldefined melting points. Their dissociation usually starts before the crystals begin to melt, and the organic component vaporizes. The residual urea then melts at 132.7 "C. Some dissociation temperatures measured by Rosenberg and co-workers are listed in Table 11-10. Krichevsky and co-workers disproved the assertion that maximum decomposition temperature of urea adducts is identical with the melting 12'
180
11. MANUFACTURE OF PARAFFIN WAXES AND CERESINS FROM PETROLEUM
Table IZ-10. Dissociation temperature of some adducts measured by DTA n-Alkane component of the adduct
Dissociation temperature, O
C
106-109 116-117 120-122 121-123 123-124 126-1 29 130-131 130-132
point of urea. They found that some ceresin adducts decompose at temperatures exceeding 132.7 "C. Detailed studies regarding the mechanism of adduct formation of n-alkanes with urea were carried out by Rosenberg and Genekh. They concluded that, especially for kerosine fractions, the optimum temperature for complex formation is 20-22 "C, and the amount of methyl alcohol required for wetting is 15-18 wt-% of urea applied. In their analytical investigations they determined the molar ratios corresponding to complete adduct formation, using mixtures prepared from urea with individual n-alkanes. Their results were : 1 : 9.0 for C12H2s 1 : 10.5 for G3H28 1 : 11.0 for C14H3, 1 : 12.5 for C15H32 1 : 13.0 for C16H34 The adducts of the C,-C,, n-alkane range, as well as those of C12H26,C20H42, C2,H,, and C2,H,, were investigated by Schlenk; his results are presented in Fig. C
0
n
24 .
Chain length of hydrccarbon molecule,
1
A
Fig. 11-17. Number of urea mols required to bind one mol of hydrocarbonversus chain length
(E) MANUFACWRE OF n-ALKANES
181
11-17. Chain length in A of the n-alkanes studied is plotted against the number of urea mols required to bind one mol of the n-alkane. This figure again shows clearly that molar ratios between urea and n-alkanes are well-defined values for individual compounds, but not whole numbers. According to Redlich and co-workers the relationship between the molar ratio of urea to n-alkane and carbon atom number of the alkane is
m = 0.653n + 1.51 if 6 < n < 17
(11-28)
where n is the number of carbon atoms in the alkane molecule. Based on x-ray analysis, Smith established the following relationship :
m = 0.692% + 1.49
(11-29)
The mass of urea per unit volume of n-alkane is almost a constant: for n-alkanes in the C,-C,, range this value is around 2.48 g urea/cm3 n-alkane. Urea adducts are crystalline. The length of the crystals is in the millimetre range, but sometimes crystals several centimetres long have been observed. Since the composition of the adducts are not stoichiometric, but the amount of urea bound per molecule varies with the molecular weight of the organic component, it may be assumed that spatial relations are of decisive importance in the structure of the crystals. On the other hand, the fact that the composition of the adducts is independent of the chemical character of the organic component leads to the conclusion that adducts containing different organic components are similar in structure. This was confirmed by Schlenk who found that adducts crystallize in well-developed, long, hexagonal prisms. His Debye diagrams demonstrated that the interference pattern is not changed by varying the organic component of the urea adduct. The crystal model for urea adducts was created by Hermann. According to this model, the urea molecules form regular hexagonal prisms. The centres of the oxygen atoms are located on the edge of the prism. The distance along the edge is 4.8 A and the distance between two superposed urea molecules is 3.7 A. The elementary cell consists of six urea molecules and its volume is 650.66 A3. From x-ray studies and density determinations of adducts, the elementary cell of tetragonal urea consists of two urea molecules, and the cell has a volume of 156.5 A3. The transition of tetragonal urea crystals into hexagonal adduct crystals is accompanied by a volume expansion of about 38% relative to the initial volume. Both theory and practice indicate that adduct formation does not take place if more space is necessary for incorporation than is available, as calculated from the urea structure. In fact, if the calculated space is too small, adduct formation will not take place, or only reluctantly. Adduct formation is an exothermic process. The forces between the n-alkane and urea molecules are of the order of magnitude of van der Waals forces. X-ray and IR spectrography of the adducts indicate that no bonds resulting from chemi-
182
11. MANUFACTURE OF PARAFFIN WAXES AND CERESINS FROM PETROLEUM
cal reactions are present in the adducts. The heat evolved in the formation of various adducts was measured by Schlenk, Zimmerschied, Redlich and co-workers. They found that the heat of formation is the sum of three components: (i) Heat absorbed when the molecules of the organic component, associated in the liquid state, are isolated into individual molecules. (ii) Heat evolved when individual organic molecules and urea molecules combine to form the adduct. fiii) Heat evolved when the tetragonal crystals of urea are converted into the hexagonal crystals of the adduct. The first part of the heat evolved is approximately identical with the heat of vaporization. Calculations by Schlenk showed that lattice conversion energy had a value of 3.9 kJ/mol urea. However, heat of formation values measured for the adducts differ from the values calculated by this method. Tables 11-11 and 11-12 list the values of Schlenk, Redlich, Zimrnerschied and Terres for heat of formation of urea adducts and heat of combination of urea and organic component. The values reported for certain individual alkanes are limits indicating the extreme values of the scattered data disclosed by the different authors. Table ZZ-II. Heat of formation for urea adducts Organic component
mol urea
'
Heat of formation, J
mol organic component
4.23 4.61
n-Heptane n-Octane n-Nonane n-Decane n-Dodecane n-Hexadodecane Methyl ethyl ketone Diethyl ketone Dipropyl ketone n-Octanol n-Butyric acid Methyl n-butyrate
30.6-31.8 30.0-40.6 49.4 38.2-54.9 67.5 62.k95.1 18.0 23.0 30.9 22.7 22.8 23.4
-
5.20 4.49 4.91 5.15 3.39 5.72 4.33
Table 11-12. Heat of combination o f adduct formation
1
Group
=CHZ =co -OH - COOH
-coo
1
Heat of combination, J relative to 1 g
e
~
11.3 33.1 18.0 57.0 34.4
1
to
1 A length ~
9.0 26.4 12.6 23.0 14.2
~
~
f
(E) MANUFACTURE OF n-ALKANES
183
Zimmerschied and co-workers treated a kerosine distillate, consisting of C,,-C,, hydrocarbons, with methanol-wetted urea. They washed the filtered adduct with iso-pentane and decomposed it with water. The n-alkanes thus obtained were repeatedly treated with urea, but adduct formation did not take place. When, however, these same n-alkanes were previously subjected to treatment with silica gel, adduct formation proceeded smoothly. It was thus demonstrated experimentally that substances exist which inhibit adduct formation, namely sulfur compounds, peroxides and other similar substances. The inhibitory effect is presumably caused by the adsorption of the inhibitor on the surface of urea, thereby preventing the penetration of the n-alkane chains into the structure of the urea crystal. T. A. Smolina and co-workers experimentally confirmed that the inhibitors do not always originate from the feedstock, but may also be hydrolysis products of the heated urea solution. An aqueous urea solution, saturated at 25 "C,was heattreated at 80 and 90°C, and ammonium hydrogen carbonate and biuret were found as a result of hydrolysis. When these solutions were added to a mixture of hexadecane and decalin, the induction period of complex formation increased with the period of heat treatment of the urea solution (Fig. 11-18). The cited authors also proved that ammonium hydrogen carbonate and biuret are capable of reacting with certain components of the feed, and their reaction products also act as inhibitors. Urea complexes were prepared from the above model mixture of hexadecane and decalin, using urea solutions to one of which was added biuret and to the other ammonium hydrogen carbonate, and urea solutions previously treated with fresh, unrefined diesel fuel and also to one of which biuret was addedand
Time of heat treaiment, t i
Fig. ZZ-18. Induction period of adduct formation versus time of heat treatment of the urea solution at different temperatures. 1 Temperature of heat treatment 80 OC, 2 Temperature of heat treatment 90 O C
184
11. MANUFACT’URE OF PARAFFIN WAXES AND CERESINS FROM PETROLEUM
60
50 C
*c
40
d .-0 bQ 30 C
.-0 c
20 -0
C -
10
0
I
I
I
2
4
6
Simulated heat treatment, h Fig. II-19. Induction period of adduct formation versus “simulated” heat treatment of the urea solution, i.e. reduced activity by additives. I Fresh solution with biuret additive, 2 Fresh solution with ammonium hydrogen carbonate additive, 3 Solution previously treated with diesel fuel and with biuret additive, 4 Solution previously treated with diesel fuel and with ammonium hydrogen carbonate additive
ammonium hydrogen carbonate to the other. The induction periods of complex formation are shown in Fig. 11-19. On the other hand, the presence of some solvents facilitates and speeds up the adduct formation. The solvent used most widely for this purpose is methanol, but other alcohols, ethers, ketones and esters are also suitable. Water is also of use, but less effective. Such solvents are termed activators. n-Alkanes in petroleum fractions usually do not form adducts without the presence of an activator. In contrast, pure n-alkanes react with urea in the absence of an activator. According to experiments carried out in the Hungarian Oil and Gas Research Institute the amount of wetting agent necessary is less than the generally used amount of 10 wt-% relative to urea, namely 2-5 wt-%. With these lower concentrations complex formation takes place as readily as with 10wt- % wetting agent. The advantage of using less methanol is better consistency of the adduct, and hence easier handling. According to Zimmerschied the action of activators (wetting agents) is explained by their acting as solvents of urea. They thereby ensure the purity of the surface ofthe urea crystals and hence the penetration of the n-alkane chains into the crystals.
185
(E) MANUFACTURE OF Il-ALKANES
(b) Technology of adduct formation The first pilot pIanr putting extractive crystallization with urea into practice was reported by Bailey and co-workers.The plant processed 300 litres of feedstock per day, and the results achieved allowed the process to be industrialized. With the exception of low-boiling distillates, n-alkanes could be separated from almost all petroleum distillates in the pilot plant, and the purity of the products exceeded 95 wt-%. Earlier, Redlich and co-workers had described the use of water and alcohol as solvents in adduct formation with urea. Their studies concerning the rate of reaction and ease of crystallization led to the recognition that significant advantages can be achieved by using low molecular weight ketones together with water in adduct formation. Based on these findings methyl iso-butyl ketone + water were used in the pilot plant. Methyl iso-butyl ketone and water dissolve one another to a small extent only. Urea is readily soluble in water, and hydrocarbons, including the fractions from naphtha to lubricating oils, in methyl iso-butyl ketone. The ketone also acts as wetting agent, reducing the reaction barrier between the aqueous urea phase and the oil phase. Thus a rapid reaction can be achieved between the saturated aqueous urea solution and the solution of the hydrocarbons in methyl iso-butyl ketone. The adduct crystals obtained when using this solvent readily lend themselves to filtration and wash.
Feed
Urea solution
Water
Urea solution
T n-Alkanes,
I
Fig. 11-20. Flow diagram of first pilot plant for extractive crystallization with urea. I Reactor, 2 Filter, 3 Separator, 4 Wash tower, 5 Heat exchanger, 6 Decomposer, 7 Wash tower, 8 Wash
tower, 9 Solvent recovery
186
11. MANUFACTURE OF PARAFFINWAXES AND CERESINS FROM PETROLEUM
The simplified flow diagram of the pilot plant is presented in Fig. 11-20. The hydrocarbon stock, the ketone solvent and the aqueous urea solution were fed into the reactor 1. Taking advantage of the high temperature coefficient of solubility of urea in water, the aqueous phase was permanently kept at the saturation level of urea. The reactor was divided into four sections, corresponding, according to experimental data, to two separate equilibrium stages. The crystalline adduct was then separated in a rotary filter 2 or in a centrifuge, in some cases by simple sedimentation. The adducts were washed with fresh ketone solvent, and the wash liquid was used in the next stage as solvent. An inert gas atmosphere was maintained within the enclosed rotary filter, the gas sucked through the filter by the vacuum pump being recycled to the filter. The aqueous urea solution from the separator 3 was washed in the tank 4 with fresh solvent to remove residual traces of hydrocarbon. The washed solution was then added to the washed adduct and the temperature was increased, by passing the slurry through the heat exchanger 5, to a temperature 20-40 "C above that of the reaction. As a result of increased temperature and decreased percentage of urea, the complex dissociated in the decomposer 6, and the oil phase consisting of n-alkanes was separated from the aqueous urea solution. The extract was washed with water and passed to solvent recovery, while the urea solution was recycled into the process. It was found that the optimum ratio of solvent to feed varies with the composition of the feedstock. Choosing the correct ratio is of great importance from the viewpoint of rate of reaction, size of crystals formed and ready washability of the adduct. Under suitable conditions the slurry obtained lends itself well to filtration and the crystals are 0.1 mm long, needle-shaped particles. Hydrolysis of urea proceeds rapidly at the temperatures used in the process: the rate of hydrolysis doubles with each temperature rise of 5.5 "C. Ammonium carbonate formed during the hydrolysis was found not to interfere with the process. Under the listed conditions, purity of 95% for the n-alkanes was readily achieved. Purity depends greatly on efficient washing of the precipitate. It was found that in fractions containing higher molecular weight compounds, slightly branched compounds also react with urea: extracts above C,,contained appreciable amounts of iso-alkanes. Results that the cited authors obtained with kerosine, light and heavy household fuel oil from a Los Angeles crude are listed in Table 11-13. The essential features of the technology based on dilution and wash with gasoline, developed in the Hungarian Oil and Gas Research Institute are shown in the flow diagram Fig. 11-21. The gas oil feedstock is diluted with gasoline in the tank 1 and fed into the reactor 2, where it comes into contact with the urea containing a few percentage of water. Adduct formation starts here and is completed in the chiller 4. By controlling the size of adduct crystals a precipitate that is easy to filter and wash is obtained. Filtration and washing with gasoline takes place in continuously operated centrifuges 5. The washed adduct is heated, together with an aqueous urea solution saturated at 20 "C, in the decomposer 6. n-Alkanes are separated from the
Table 11-13. Characteristics of the feedstocks and the products extracted with urea (fractions of a Los Angeles crude) 1
Light household fuel
Kerosine
Characteristics Feed
1
I
~ ~ : ~ ~ : ~ Residue s l
Feed
[z'::ts1
1
Heavy household fuel Residue
Feed
I [z::::;,1
Residue
n
-3
z
188
11. MANUFACTURE OF PARAFFIN WAXES A N D CERESINS FROM PETROLEUM
Wash gasoline
f-
Gas oil
=
IF-
Gasoline
4 ;m-
I
t
I
I
I
Iso-qas
011
o o
0 0
7
Fig. 11-21. Flow diagram of the Hungarian Oil and Gas Research Institute process for manufacture of n-alkanes with urea. I Mixing tank, 2 Reactor, 3 Urea tank, 4 Chillers, 5 Filter centrifuges, 6 Decomposer, 7 Separator, 8 Solvent recovery, 9 Chillers, 10 Filter
centrifuges, I1 Solvent recovery
aqueous urea solution in the separator 7, washed with water and subsequently freed from solvent in solvent recovery 8, and finally treated with a few percentage of sulfuric acid and activated clay. The aqueous urea solution from the separator is cooled to 20 "C in the chiller 9, the crystallized urea is Separated in the centrifuge 10 and recycled to use again in adduct formation. Part of the isogas oil leaves the system, after aqueous wash and freeing from solvent, as end product, while the rest is used for dilution. The main stages of adduct formation technology with aqueous urea solution in the presence of acetone, as developed by the Hungarian Oil and Gas Research Institute, are as follows: (i) Adduct formation is carried out at 50 "C with a urea solution saturated at 35 "C and containing 30 w t - x of acetone. (ii) After adduct formation has started, the mixture is cooled, under slow agitation, to 20 "C. (iii) When adduct formation is completed, the precipitate must immediately be filtered off. (iv) The dried precipitate is washed four times with 50 wt- % acetone. (v) The adduct is decomposed by heating in the aqueous urea solution (previously separated from the is0 part of the feed) to 70-80 "C. The temperature of adduct formation is of great importance for the quality of the precipitate. Adducts formed at lower temperatures are usually inconvenient for handling and unsuitable for filtration. Since the quality of the precipitate depends, above all, on the size of the adduct crystals, it is adviseable to apply low rates of cooling and relatively mild agitation.
(E) MANUFACTURE OF n-ALKANES
189
Experiments were carried out in the Hungarian Oil and Gas Research Institute to suppress the oleophilic nature of the surface of the precipitate by using alkyl sulfates simultaneously with ammonium chloride as additives. It was to be expected that alkyl sulfates, by wetting the surface of the adduct particles, will make them hydrophilic, and thereby remove adsorbed oily compounds. Alkyl sulfate being not only a wetting agent, but also a detergent, it will hence form an oil emulsion. To decompose this emulsion, and also to prevent its formation, an electrolyte, namely ammonium chloride was added. As expected, these additives proved efficient. The experiments of R. B. Alieva and co-workers demonstrated that the addition of 25 wt-% (relative to urea) of quartz sand or sodium chloride improves the yield and purity of n-alkanes. This amount of additive is the optimum concentration for a gas oil feedstock boiling between 200 and 330 "C, containing 8.2 wt-% aromatics, 18.9 wt-% naphthenes, and 72.9 wt-% paraffins including 28.5 wt-% of compounds forming adducts with urea. The amount of urea relative to the amount of feed is an important technological parameter. The experiments of the Hungarian Oil and Gas Research Institute indicated that 60-80 wt-% of urea relative to gas oil feed is sufficient to recover nalkanes, and their purity cannot be increased substantially by using higher amounts of urea. In contrast, the pour point of the is0 gas oil obtained in the adduct formation process is closely related to the percentage of urea applied. For example, under identical conditions of temperature, the is0 gas oil extracted with 60 wt- % of urea has a pour point of -26 "C, whereas the pour point of is0 gas oil extracted by applying 200 wt-% of urea is as low as -70 "C. Adduct formation with urea is also suitable for the manufacture of so-called normal ceresin from petrolatum. Two variants of a technology for this purpose have been developed by the Hungarian Oil and Gas Research Institute, one using water, and the other acetone as wetting agent. For the development of the latter process, a 45 wt-% solution in gasoline of a 60 "C melting point petrolatum originating from a paraffinic heavy oil distillate was chosen. When 10 wt-% urea relative to solid petrolatum was used, no ceresin was obtained. By increasing the percentage of urea, the yield of ceresin relative to petrolatum at first rapidly increased. When the amount of urea reached 110120 wt-% relative to solid petrolatum, the rate of increase slowed, and finally, from a urea percentage of about 2W220 wt- %, no futher increase in ceresin yield could be achieved (Curve I in Fig. 11-22). On the other hand, a distinct maximum is observable in the curve ceresin yield relative to urea versus urea percentage relative to petrolatum (Curve 2 in Fig. 11-22). Hence optimum urea utilization occurs at about 100-120 wt-%, while at this percentage, ceresin yield is still far from the maximum achievable value. It is, therefore, expedient to choose urea percentages of 230-240 wt- %. The melting point of the ceresins obtained with the described process at first slightly decreases with increasing amount of urea used, and subsequently, after passing through a minimum, increases. The increase rate, however, decreases
(E) MANUFACTURE OF
n-ALKANES
191
It is, therefore, advisable to use acetone as a wetting agent and 230-240 wt-% of urea for the petrolatum solution in gasoline containing 45 wt- % solids. Under these conditions, the ceresin yield is close to the maximum, while urea utilization is not substantially below the optimum, the density of the normal ceresin end product is close to the minimum, and its melting point is maximum. In this technology, ceresin adducts are decomposed with aqueous urea solutions saturated at 20-25 "C. These solutions must, therefore, be heated to a higher temperature to become unsaturated and to be able to dissolve the urea formed in the decomposition of the adduct. A definite degree of unsaturation of the urea solution is necessary to decompose the adduct, the decomposition taking place at lower than thermal decomposition temperatures only up to the defined urea concentration of the equilibrium, which differs from saturation to a degree depending on temperature, or is identical to saturation. Figure 11-24 presents the decomposition temperature of ceresin adducts versus final concentration of the decomposing solution. The adduct used in these experiments contained 23 wt- % of ceresin. Clay treatment of the petrolatum, previous to adduct formation, reduces the induction period. The character and extent of the effects achievable by such pretreatment obviously depend largely on the grade of the activated clay used. The major characteristics of n-ceresin, iso-ceresin and iso-oil obtained by using the acetone-wetting process are listed in Table 11-14. The products C1, C,, C, and C, belong together: the first urea treatment yielded C,, the part forming no adduct was C,, so-called iso-ceresin. By repeated urea treatment of C , yielded C,, a so-called semi-normal ceresin, and C , is iso-oil obtained from the filtrate by dewaxing with methyl iso-butyl ketone. In ceresin manufacture using acetone as wetting agent, low-loss solvent recovery causes difficulties. It, therefore, appeared reasonable to study the feasibility of replacing acetone with water. The results demonstrated that nearly maximum urea utilization and maximum ceresin yield can be attained with 19&200 wt-% urea. Up to this percentage of urea, the melting point of the ceresin decreases continuously and then remains almost constant with further increases of urea.
'i; 751
I
63 64
I
65
I
66
I
67
I
68
I
I
69 70 Final concentration of urea solution, w t - %
71
Fig. 11-24 Decomposition temperature of ceresin adducts versus concentration of the
decomposing solution
190
11. MANUFACTURE OF PARAFFlN WAXES AND CERESINS FROM PETROLEUM
s
20
- 18 sJ- 16
.!- 3 6 3 E- '32 -
'-
Percentage of urea re(ative to petrolatum, w t - %
Fig. 11-22. Ceresin yield versus percentage of urea. Feed: 45 wt-% solution of petrolatum (melting point 60 "C) in gasoline
gradually from urea percentages of 230-240 wt- % upwards, and finally becomes zero (Curve I in Fig. 11-23). The relationship between the density of n-ceresins and the amount of urea applied is shown in Curve 2 of Fig. 11-23: density first rapidly
-
0.7960 -
70
0.7920 -
69
0.7900 -
68
0.7880 -
67.
0.7940
0
.-mn
y c
c
n 0.7860
0
-
66
a,
65
0.7820 -
54
0.7800
5
5
-
0.7840
.E
Q
c
I
l
l
l
l
0 20 40 60 80100
l
l
140
l
l
180
l
l
220
l
l
260
l
l
300
l
l
340
l
l
380
63
Fig. 11-23. Melting point and density of ceresin versus percentage of urea. Feed: 45 wt-% solution of petrolatum (melting point 60 "C) in gasoline
192
11. MANUFACTURE
OF PARAFFINWAXES AND CERESINS FROM PETROLEUM
Table 11-14. Characteristics of ceresin obtained by adduct formation Characteristics ma1 ceresin
Oil content, wt- % Density, d:," Refractive index, ng Penetration at 25 OC, 0.1 mm Viscosity at 100 Oc, mmz/s Melting point, OC (after Zhukov) Drop melting point, O C Molecular weight
1.34 0.7790 1.4404 16 6.99
72.1
-
1.21 0.7798 1.4379
2.55 0.7854 1.4367
0.53 0.8131 1.4497
1.70 0.7966 1.4421
14 6.99
14 6.85
32 9.98
31 7.78
-
67.9 -
49.6
62.2
69.8
-
-
-
-
iso-oil
0.8895
-
17.05 -
420
Preconditions for this process are satisfactory pretreatment of the feedstock to remove substances inhibiting adduct formation, the presence of a few percentage of water in the crystalline urea, and a few adduct crystals added to serve as nuclei for adduct formation. Recrystallized urea leads to higher rates of reaction and higher yields than technical-grade urea. The induction period of adduct formation can be reduced even more efficiently, down to values of about 20 minutes, if clay clarification is preceded by a treatment with sulfuric acid. The following processes, amongst others, have been commercialized for the manufacture of n-alkanes : - the process applied in the Ufa Petroleum Refinery, - the Edeleanu process, - the Gulf process, - the Nippon Mining process. In the Ufa refinery, gas oil is processed to manufacture low pour-point gas oil and normal gas oil. The feedstock is mixed with iso-propyl alcohol. Urea is added in the form of an aqueous-iso-propanolic solution. The initial temperature in the adduct-forming reactor is 55 O C , the end temperature 35 "C. The adduct is then washed with iso-propanol in a countercurrent-operated, agitated tower. The washed adduct outlet is at the bottom of the tower. The adduct passes into the decomposer. Normal gas oil from the decomposer and is0 gas oil from the separator are led, after washing with water, into columns for solvent removal. In the Edeleanu process, methylene chloride is used as solvent, and urea is introduced into the reactor in the form of a saturated aqueous solution. A part of the methylene chloride (b.p. 41 "C) distills over from the reactor, heat of vaporization being provided by the heat of reaction of adduct formation. The adduct is washed in rotary filters under pressure and then washed with methylene chloride. The adduct is then suspended in methylene chloride, and the suspension is again subjected to filtration. The pure adduct obtained in this manner is decomposed with steam. A simplified flow diagram of the process is shown in Fig. 11-25.
(E) MANUFACTURE OF
193
n-ALKANES
?
c
n-Hydrocarbons
iso-Hydro carbons
Fig. 11-25. Flow diagram of the Edeleanu process. 1 Reactor, 2 Filter, 3 Repuddle, 4 Urea recovery, 5 Decomposer, 6 Separator, 7 Distillation column
As reported by the Edeleanu Co., the purity of Ci,-C15 n-alkanes manufactured by this process is 96 %, that of C,,-C2, n-alkanes 95 %, and that of C25-C40 n-alkanes 94-95 %. No detailed technological and economical data on the Gulf and on the Nippon M ining processes have been made public. However, both processes are commercially applied, the plants built on their basis have annual outputs between 40,000 and 60,000 tons. 2. Manufacture of n-alkanes using molecular sieves
Certain minerals, like various zeolites, mordenites, montmorillonites, etc. are capable of selective adsorption of various molecules. Their capacity for selective adsorption is connected with their crystalline structure. Such materials are called molecular sieves, and can also be prepared synthetically. Molecular sieves are in commercial use for various purposes, including for example the separation of n-alkanes from hydrocarbon mixtures, drying of gases, vapours and liquids (e.g. cracking gases, acetone, transformer oils), removal of hydrogen sulfide and low mercaptans from hydrocarbon mixtures, removal of oxygen from argon, etc.
13
194
11. MANUFACTURE OF PARAFFIN WAXES AND CERESINS FROM PETROLEUM
(a) Composition, structure and adsorption properties of synthetic molecular sieves Synthetic molecular sieves are crystalline sodium and calcium aluminium silicates. They are graded and classified on the basis of their average pore diameter. Marks like 4A, 5A, 1OX and 13X indicate pore diameters of 4, 5, 10 and 13 A, respectively. The pore diameter is dependent on the composition, basically on the ratio of alkali oxides, alkali earth oxides and alumina to silica. A1 to Si ratio varies between 1 : 1 and 1 : 5 for different types of molecular sieves. According to Barrer and co-workers, molecular sieves of the 4A and 5A grades have cubic crystal lattices, while 13X grades have tetrahedral crystal lattices. The lattices include cavities with diameters of 10-30 i% and channels with diameters of 4, 5, 10 and 13 A, connecting the cavities. At the activation of molecular sieves, water present in the channels is removed and an uninterrupted system of cavities and ducts is created. The size of the crystals varies between 0.1 and 100 pm, depending on type. The volume of the. cavities makes up about 45% of the total volume, the internal specific surface area of the cavities is as high as 700-800 m2/g, while the specific area of the external surface of the crystals in only about 1 to 3 m2ig. Adsorption takes place internally, on the surfaces of the cavities. In the case of mixtures consisting of molecules differing in size, only those molecules whose size allows them to pass through the channels will be able to enter the cavities. Thus, the channels act as filters. In the case where several components are capable of passing through the channels, separation within the cavity will take place, owing to the different extents of their adsorption, so that adsorption equilibria will be established. However, when selecting the most appropriate molecular sieve, one should always aim at the predominance of the sieve effect. The major factor in the separation capability of molecular sieves is hence the size of the molecules. In the case of mixtures of molecules similar in size, their polarity (for hydrocarbons, unsatnration) will be of importance. The laws for common polar adsorbents are also valid for the adsorption behaviour of molecular sieves: (i) The amount of the adsorbed substance increases with the partial pressure or concentration, and decreases with increasing temperature. In continuous operation the amount of adsorbed substance decreases with increasing flow rate. (ii) At a given partial pressure and temperature, the amount of the adsorbed substance increases with molecular weight. (iii) The rate of adsorption is controlled by the rate of diffusion of the substance towards the surface of the adsorbent and within the channels. These processes are subjected to Fick's law. The rate of adsorption decreases with increasing temperature and with the approach to the adsorption equilibrium. (iv) Increasing temperatures and decreasing partial pressures will accelerate desorption. The rate of desorption also depends on the nature of the inert component present.
(E) MANUFACTURE OF n-ALKANES
195
(b) Manufacture of n-alkanes using molecular sieve processes Among n-alkanes, iso-alkanes, naphthenes and aromatics present in petroleum, the diameters of n-alkanes are smallest: 4.9 A in average. Hence molecular sieves with pore diameters around 5 A are capable of adsorbing them, and such molecular sieves are used for the recovery of n-alkanes from petroleum products. The composition of these molecular sieves is
-
1 2 ~ ~ ~ ~ 2 ~ 1 2 1 Na3Ca4.5~ ~ ~ ~ ~ 2 ~ nH2O Feedstocks for n-alkane manufacture are petroleum distillates with boiling ranges corresponding to the desired carbon atom number products. Composition requirements for the feedstocks vary with the process and the objective, but it is a general requirement that n-alkane content be 15-30 wt-%, maximurn sulfur content 300-600 p.p.m. and maximum nitrogen content 20 p.p.m. To eliminate polymerization in the course of adsorption, maximum permissible olefin content in the feedstock is limited to 1-2 wt-%. To meet these requirements, it is often necessary to subject the feedstock to preliminary refining. Processes developed up to the present are operated batchwise, with stationary beds. Owing to the low mechanical strength of molecular sieves, continuous, moving-bed operation could not yet be achieved. The technological process consists essentially of four stages : - adsorption, - flushing, - desorption, - periodical regeneration of the adsorbent. Adsorption is carried out in most processes in the vapour phase. However, liquid-phase operation is also feasible. Adsorption is usually not continued to total saturation of the adsorption column. Adsorption capacity of molecular sieves at 300-400 "C is 5 to 10 wt-%, the value decreasing with higher temperatures. The adsorption isotherms of lower n-alkanes are more readily controlled by pressure changes in the course of adsorption than those of higher alkanes. The length of the adsorption zone in the column depends on many factors, including temperature, pressure, nature of the adsorbent, its pore diameter and particle size, flow rate, molecular weight of the n-alkanes to be adsorbed and their concentration in the feedstock. First, n-alkanes with smaller molecular weight and higher rate of diffusion will be adsorbed in the pores of the adsorbent, subsequently these will be displaced by those with higher molecular weights, and hence breakthrough will occur at different moments for each individual component present. Flushing is carried out with some nonadsorbable gas or with the solvent used in desorption, eventually applying vacuum. This operation has the purpose of removing substances other than n-alkanes deposited on the surface of the molecular sieve particles and in the spaces between the particles. Flushing conditions must be such that no desorption of n-alkanes take place during flushing.
13*
196
II. MANUFACTURE OF PARAFFIN WAXES AND CERESINS FROM PETROLEUM
The next operation, desorption of n-alkanes, is always carried out in the vapour phase. This can be achieved in different manners: ( i ) The temperature of the column is raised above that of adsorption. The disadvantages of this technique are, on the one hand, that the temperature is limited by the thermal sensitivity of the n-alkanes, and on the other hand, cycle time is substantially longer, owing to heating-up and subsequent cooling of the column. (ii) Pressure in the column is reduced to a value lower than the pressure during adsorption. This method is best suited for the manufacture of low molecular weight n-alkanes, that is, for processing gasoline fractions. Time requirement is significantly lower than in the previous method, but it has the disadvantage that utilization of adsorbent capacity is low. (iii) Large amounts of an inert gas, e.g. nitrogen or methane are passed through the column at low pressure, high temperature and high flow rate. After separating the n-alkanes from the desorbate, the gas is recycled into the system. (iv) Desorption can be achieved by the displacement of the n-alkanes to be recovered, using lower molecular weight n-alkanes (C,-C,) or compounds greatly liable to adsorption, e.g. carbon dioxide or ammonia. When gasolines are being processed, the pressure-reducing method is primarily used, while the displacement desorption method is the most wide-spread for manufacturing higher n-alkanes (from kerosine and gas oil fractions). In the latter case, n-alkanes lower than those to be recovered are mainly used for displacement. The periodical regeneration of the column is carried out by ignition methods. In the following, some commercial processes for n-alkane manufacture using molecular sieves will be discussed in more detail. The application field of the Texaco Selective Finishing (TSF) process is wide, it is equally suitable for light and heavy distillates and products of catalytic reforming (gasolines, kerosines, gas oils). The adsorbent used is molecular sieve grade 5A. The process is carried out in the vapour phase, batchwise, in a stationary bed. The time of the desorption operation is reduced by simultaneous use of the pressure-reduction and displacement methods. n-Alkanes lower than those to be recovered as product are used as desorbents, namely n-pentane, n-hexane or n-heptane. Desorption temperature is above the critical temperature of the desorbent. In a pilot plant of Texaco Co., one model mixture used consisted of 26.3 wt-% n-hexane and 73.7 wt-% iso-hexane. A two-bed construction was used. The feed was introduced into the adsorber at 163 "C, and the column was heated by the heat of adsorption of n-hexane. At the start of adsorption the gauge pressure was 136 kPa. Feed was continued without any product Ieaving until the gauge pressure in the column attained 680 Ha. Only then was effluent taken off. The adsorption period took 20 minutes. Subsequently the feed inlet was switched over to the second adsorber where desorption had just been completed. For desorption, the pressure in the saturated column was reduced to 136 kPa gauge pressure and desorption carried out by passing iso-pentane through the column. The time
(E) MANUFACTURE OF n-ALKANES
197
required for desorption was also 20 minutes, the temperature of the iso-pentane influent was 427 "C,providing the heat required for desorption. Iso-pentane was then stripped from the desorbate. A simplified flow diagram of the process is shown in Fig. 11-26. A plant applying the Texaco process, with an output of 68,000 tons per year of C,,-C,, n-alkanes, was built in Pointe Pierre (Trinidad) in 1965. The feedstock is kerosine and gas oil, and the products are used mainly in the detergent and plastics industries. The purity of the products exceeds 99 wt-%, and the activity of the adsorbent remains satisfactory up to more than 200 cycles. The Molex process was developed by Universal Oil Products Co. It applies isothermal, stationary-bed displacement desorption. The adsorbent is a special molecular sieve with 20-40 mesh particle size, equally useable in the liquid or vapour phase. When processing gasolines, adsorption is carried out in the vapour phase at about 300 "C,at a maximum pressure of 1000 kPa, while for processing kerosines and gas oils, the temperature is 150-200°C, pressure 3000 kPa, and adsorption takes place in the liquid phase. Only feedstocks with maximum 200 p.p.m. sulfur and 20 p.p.m. nitrogen are processed. The most characteristic feature of the process is that it uses only a single adsorber. The adsorbent is placed on 10 to 16 trays centrally interconnected with tubes filled with molecular sieves. Three to four of the trays always operate in the same stage. The feedstock and the desorbent (n-pentane, n-hexane or n-heptane) simultaneouslyenter the column, and the so-called raffinate and the so-called extract also leave the system simultaneously. The raffinate consists mainly of branched compounds and aromatics from the feed, but always contains some desorbent, too. The extract contains the n-alkanes displaced by the desorbent, and
7
I
-1
I Fig. 11-26. Flow diagram of the Texaco process. I - Adsorber. Dimensions: 2 . 4 21.4 ~ m. Average temperature 260 'C, gauge pressure 780 kPa, operation time 20 min.; 2 - Desorber. Dimensions: 2 . 4 21.4 ~ m. Average temperature 304 "C, gauge pressure 240 kPa, operation ~ m, number of plates 30, time 20 min.; 3 - Distillation column. Dimensions: 1 . 8 27.0 head temperature 45 'C, pressure 2000 kPa. Adsorbent packing: 54.4 t/column
198
11. MANUFACTURE OF PARAFFIN WAXES AND CERESINS FROM PETROLEUM
obviously, desorbent, too. Therefore, both effluents must be rectified to remove the desorbent. If, for example, the column contains 11 trays, and the feed is introduced at the 9th tray counted from the bottom, the desorbent will be introduced at the third tray from the bottom. n-Alkanes will become adsorbed on the 10th tray, and nonadsorbed branched and aromatic compounds will pass to the 1 ltli tray, flushing the desorbent still present there. One part of this stream will leave the column as raffinate, while the other part is recycled to the 11th tray as so-called secondary reflux. The desorbent introduced into the column at the third tray will pass, together with the displaced n-alkanes, through the two or three trays above it (trays 4,5 and 6), and subsequently its major part will leave the column as extract, a smaller part, the so-called primary reflux, will pass to the next trays 7, 8 and 9, where it will flush raffinate retained on the surfaces and interspaces of the molecular sieve particles to prevent contamination of the product. This cycle takes only 2 to 5 minutes; subsequently all streams are switched over by means of a rotation-system valve control to the trays above those operated previously. Thus taking the adsorber as a whole, the operation is continuous. The flow scheme is presented in Fig. 11-27. The average output of the plants built on the basis of this process is 40,000 to 50,000 tons per year. The Isosiv process was developed by Union Carbide Corp. It is a vapour-phase, isothermal, stationary-bed process, developed in two versions, one for light distillates (gasoline and naphtha) which is often combined with plants used for
r
Raffinate
-
v
W Fig. 11-27. Flow diagram of the Molex process
(E) MANUFACTURE OF n-ALKANES
199
aromatics extraction and reforming, the other for processing kerosines and gas oils to manufacture n-alkanes. The maximum admissible sulfur content in the feedstock is 300 to 600 p.p.ni., that of nitrogen in bases 5 to 20 p.p.m., olefin content 1 wt- %, aromatics content 15 to 20 wt-%. According to information given by Union Carbide the service life of the molecular sieve is 5 years at a sulfur content of 300 p.p.m., but only 1 year at 2000 p.p.m. The n-alkane content of the products is 86 to 97 wt-% when light distillates are being processed, and even as high as 99 wt-% for kerosine processing. The raffinates, on the other hand, contain less than 1 wt-% of n-alkanes. The version for light distillate processing is based on pressure change, the version for kerosines and gas oils uses displacement for desorption. In one Union Carbide plant, a light distillate containing 45 vol- % n-alkanes is processed to yield a practically pure mixture of n-alkanes and a high-octanenumber isomer mixture. n-Alkanes are transferred into a hydroisomerizing plant. The stabilized isomerized product, mixed with fresh feed, is again introduced into the adsorber, where non-transformed n-alkanes are again separated. A carbon-containing residue successively builds up on the surface of the adsorbent. This is periodically removed in regeneration plants by ignition. . As an example, 55.3 kmol/h n-pentane and 43.0 kmol/h n-hexane are preheated and united with the liquid product from the stabilizer of the hydroisomerizing plant. This stream is heated to 300-320 "C at 540 kPa gauge pressure and evaporated. The vapours are introduced into the adsorber at a gauge pressure of about 400 kPa. The adsorber is filled with 36 tons of 5A grade molecular sieve. During adsorption the temperature rises to about 330 "C. Non-adsorbed branched and cyclic compounds, together with small amounts of n-pentane, are cooled and condensed. Since n-hexane is more readily adsorbed than n-pentane, adsorption is continued up to the breakthrough point of n-pentane, and subsequently the column is switched over to desorption. At its start, pressure is reduced to atmospheric pressure and then to 20 kPa gauge pressure, and following this, vacuum is applied to the column. The n-alkanes desorbed pass to a condenser and then to storage, or are directly transferred into the isomerizing unit. After desorption is complete, the pressure in the column is as low as 6.67 kPa. Three adsorbers connected in parallel are in operation in this plant, so that the process can be regarded as practically continuous. During adsorption the gas flow direction is upwards, and during desorption it is downwards. At the start of the process, the operation periods of the adsorbent are 14 days, followed by regeneration. Ageing of the adsorbent results in successively shorter operation periods, falling to as low as 5 to 6 days after 2-year's use. Regeneration consists in heating the adsorbent to 450 "C in nitrogen gas and in subsequent ignition of the deposits. The process is suitable for processing catalytic reformates, alkylates, products of isomerizing plants and gasoline-type light distillates. For the manufacture of n-alkanes from kerosines and gas oil the displacement alternative is used. In this
200
11. MANUFACTURE OF
PARAFFIN WAXES AND CERESINS FROM PETROLEUM
case systems with 4 or 5 columns are operated to shorten cycle time, and in such a manner that desorption occurs simultaneously in two or three of the adsorbers. n-Hexane is used as desorbent, and no flushing is applied. 8 to 10 plants based on the Isosiv process have been built up to the present time in the U.S.A., in West Germany and in Japan, with outputs varying between 20,000 and 85,000 tons per year. The British Petroleum process was developed with the objective of being equally suited for processing gasoline, kerosine and gas oil. The process operates in the vapour phase under isothermal and isobaric conditions, at temperatures of 350 to 400 "C and pressures of 1000 to 1800 kPa. The system consists of several stationary-bed columns, 5 to 6 being specified in recent BP patents, including 3 or 4 operating as desorbers, one for flushing and one for adsorption. During the adsorption stage nitrogen is introduced together with the feed, with the purpose, on the one hand, to reduce n-alkane concentration in the feed, and on the other hand, to suppress cracking reactions. Lower n-alkane concentration is of importance because it facilitates the control of the ratio of adsorption to desorption time. Nitrogen or C,C, hydrocarbons are used for flushing. Desorption is carried out with n-pentane or n-heptane. The advantage of isothermal operation is that adsorbers can be installed in one block, resulting in better heat economics. The advantage of high pressure is acceleration and improvement of n-alkane adsorption, while their desorption in the flash operation is suppressed. The essential features of the process are shown in Fig. 11-28. The preheated feed and nitrogen are introduced into the adsorption column. The product freed
c -
Fig. 11-28. Flow diagram of the British Petroleum process. 1 Feed preheater, 2 Pentane preheater, 3 Nitrogen preheater, 4 Adsorber columns, 5 N, compressor, 6 N, tank, 7 Column
for N, separation, 8-Pentane tank
20 1
(E) MANUFACTURE OF 11-ALKANES
from n-alkanes passes, together with the nitrogen carrier gas and n-pentane left over from the previous adsorption operation, into the separator column. Nitrogen used for flushing is also fed into this column, and the nitrogen effluent of the separator column is recycled, whereas the n-alkane-free product passes into a stripper where n-pentane is separated. After flushing with nitrogen, the n-alkanes in the adsorber are desorbed with n-pentane. The desorbate passes into a stripper to remove n-pentane. British Petroleum reports that the adsorbent need only be regenerated after 500 hours of operation, on condition that the sulfur, olefin and nitrogen content of the feedstock is low. Plants using this process, with outputs of 30,000-50,000tons per year, have been built in West Germany and in England. The Ensorb process developed by Esso is characterized by vapour phase, isothermal and isobaric operation. Desorption is carried out with ammonia which is readily separable from n-alkanes, stable to heat and has a high adsorption capacity. Owing to the high rate of adsorption of ammonia, there is no need for more desorption columns. The system is composed of two columns with stationary beds. Operating pressure is relatively low, 150-400 kPa. Temperature varies, depending on the feedstock, between 260 and 370 "C. It is an interesting feature of the process that ammonia is introduced together with the feed in order to reduce the catalytic cracking activity of the adsorbent. An Esso plant in Texas manufactures C&,, n-alkanes with this process. A pilot plant produced n-alkanes up to C33. The Parex process operates under vapour phase, isothermal, isobaric conditions, in stationary-bed equipment. In this process too, desorption is carried out with ammonia, a t pressures of 500-IOOO kPa, at 400 "C.Hydrogen is introduced together with the feed into the adsorber filled with a special-type molecular sieve that contains 1 wt-% of nickel in its crystal lattice. Owing to the nickel content, hydrogenation takes place, olefins will be saturated, cracking and polymerization reactions will be suppressed, so that the adsorbent can be operated for 6000-8000 hours without need for regeneration. Hydrogen and ammonia are removed from the product with water in wash towers, and ammonia is recovered from the aqueous ammonia solution. Table ZZ-15. Characteristics of the products obtained from a 240-320 OC boiling-range gas oil by the Parex process Characteristics
Density, d y n-Alkane content, wt- % Aromatics content, wt- % Olefin content, wt- % Sulfur content, wt- % Pour point, Oc
!
Feed
n-Alkanes
0.817
0.170 99.0 0.01 1.0 0.004 +8
21.3 21 .o 2.0 0.010 -22
Gas oil free of n-alkanes
0.828
4.0 25.0 2.3 0.013
-60
202
XI. MANUFACTURE OF PARAFFIN WAXES AND CERESINS FROM PETROLEUM
The characteristics of the products obtained by the Parex process from a 240320 "C boiling-range gas oil are listed in Table 11-15. The n-alkane product figuring in the table is a post-treated product.
Literature Adams, O., VDJ Zeitschr., 98, 1055 (1956). Alieva-Kuliev: Nefkpererub. Neftekhim., No. 11, 19 (1974). - : Neftepererub. Neftekhim. Sluntsepererub., No. 1, 28 (1976). Andreas, F., Chem. Tech. Berl., 16,449 (1964). Asher-Campbell: Hydrocurb. Process., 48, 134 (1 969). Avery-Lee: Oil Gus J., 60, 121 (1962). -: Erdd, Kohle, 15, 356 (1962). Bailey-Bannerot-Fetterley-Smith: Znd. Engng. Chem., 43, 2125 (1951). Bailey, W.A,, Proceedings of the Third World Petroleum Congress. Section 111, 160 (1951). Barrer, R. M., Brennst. Chem., 35, 325 (1954). - : Nature, Lond., 181, 176 (1958). Barrer-Brook: Trans. Furaduy SOC.,49, 940 (1953). Barrer-Bultitude-Sutherland: Trans. Furuduy SOC.,55, 1111 (1959). Barrer-McKenzie: J . phys. Chem., 58, 560, 568 (1954). Barrer-Meier: Helu. chim. Actu, 29, 229 (1956). - : Trans. Furuday Soc., 54, 1074 (1958). Barrer-Rees: Trans. Furuduy Soc., 50, 989 (1954). Barrer-Robins: Trans. Faruduy SOC.,49, 807 (1953). : Trans. Faruduy Soc., 49, 929 (1953). Bithory, J., MAFKZ kiuduany (Report of the Hungarian Oil and Gas Research Institute), No. 25 (1952). -: MAFKZ kiadudny (Report of the Hungarian Oil and Gas Research Institute), No. 87 (1954). -: MA-FKZ kiadudny (Report of the Hungarian Oil and Gas Research Institute), No. 93 (1 955). - : MAFKZ kiadudny (Report of the Hungarian Oil and Gas Research Institute), No. 114 (1955). -: MdFKZ kiadudny (Report of the Hungarian Oil and Gas Research Institute), No. 190 (1959). Bathory-Freund : MAFKZ kiududny (Report of the Hungarian Oil and Gas Research Institute), No. 322 (1965). Bathory-Orszag : MA-FKZ kiuduany (Report of the Hungarian Oil and Gas Research Institute), No. 163 (1958). Bhthory-Orszag: MdFKZ kiududny (Report of the Hungarian Oil and Gas Research Institute), No. 301 (1964). - : MAFKZkiudvuny (Report of the Hungarian Oil and Gas Research Institute), No. 302 (1966). Bathory-Orszag-Balogh: MA'FKZ kiadudny (Report of the Hungarian Oil and Gas Research Institute), No. 191 (1959). - : MA-FKZ kiududny (Report of the Hungarian Oil and Gas Research Institute), No. 227 (1 960). Bengen, F., Angew. Chem., 63, 207 (1951). Breck-Eversole-Milton: J . Am. chem. SOC.,78, 2338 (1956). Brit. Put., 776 467. Brit. Pat., 777 232. Brit. Pat., 996 393., 1055 363. Broughton,O. B., Chem. Engng. Prog., 64, 60 (1968).
-
(E) MANUFACTURE OF n-ALKANES
203
Broughton-Carson: Oil Gas J., 57, 112 (1959). Brown-Rightmire-Strecker: Fifth World Petroleum Congress. Section 111, Paper 23 (1959). - : Oil Gas J., 57, 189 (1959). Calderbank-Nikolov: J. phys. Chem., 60, 1 (1956). Cannon, P., J. Am. chem. Soc., 80, 1766 (1958). Carson-Broughton: Petrol. Refiner, 38, 130 (1959). Cooper-Grieswold-Lewis-Stokeld: Chem. Engng. Prog., 62, 69 (1966). FoldvAri, I.: MAFKZkiadua'ny (Report of the Hungarian Oil and Gas Research Institute), No. 265 (1962). Franz-Christensen-May-Hess: Petrol. Refiner, 38, 125 (1959). Griesner-Rhodes-Kiyonaga: Erdd, Kohle, 13, 650 (1960). -: Petrol. Refiner, 39, 125 (1960). Guyer-Theichen: Helv. chim. Acta, 40, 1603 (1957). Hermann-Lennk: Nafurwissenschuften, 39, 234 (1952). Hessler-Meinhardt: Fetfe, Seifen, 55, 7 (1953). Hoot-Azarnoosh-McKetta: Petrol. Refiner, 36, 255 (1957). Jeo-Mather-Gilbert-Baker: Sixth World Petroleum Congress. Section IV, Paper 15 (1963). Justice-Lamberti: Chem. Engng. Prog., 60, 35 (1964). Kington-Laing: Truns. Furuday Soc., 51,287 (1955). Klopp-Gorog-Sipos: Magy. Kim. Lap., 21, 607 (1966). Knight-Witnauer-Coleman: Analyt. Chem., 24, 106 (1952). Kohe, K. A., Petrol. Refiner, 31, 106 (1952). Laurent-Bonnetain: Znd. chim., 31, 461 (1966). Leithe, W., Analyt. Chem., 23,493 (1951). Lindner, R., Seifendle-Fefte- Wachse, 94, No. 5 , 110 (1968). Lozin-Manovyan : Neffepererab. Neftekhim. Slantsepererab., No. 1, 21 (1976). Martirosov-Filatov: Nefepererab. Neffekhim., No. 10, 37 (1975). Martirosov-Filatov-Pereverzev: Neffepererab. Neffekhim., No. 10, 37 (1975). Newey-Shokal-Mueller-Bradley-Fetterly : Znd. Engng. Chem., 42, 2238 (1950). Nikolina-Neymark: Usp. Khim., 29, 1088 (1960). Oil Gus J., 56, 115 (1958). Oil Gus J., 57, 116 (1959). Oil Gas J., 61, 46 (1963). Orszig, I. : MdFKZ kiaduciny (Report o f the Hungarian Oil and Gas Research Institute), No. 276 (1962). n-Paraffins. Hydrocarb. Process., 54, No. 11, 167 (1975). Redlich-Gable-Dunlop-Millar: J . Am. chem. Soc., 72, 4153 (1950). Redlich-Gable-Beason-Millar: J . Am. chem. SOC.,72,4161 (1950). Ryazantsev-Kurnoskina: Khimiya Tekhnol. Topl. IMasel, 21, No. 1, 18 (1976). Scott, K., Petrol. Refiner, 43, 97 (1964). Schiessler, R. W., J. Am. chem. SOC.,74, 1738 (1952). Schlenk, W., Angew. Chem., 62, 299 (1950). : Fortschr. chem. Forsch., 2, 92 (1951). Schlenk-Holman: Science, N.Y. 112, 19 (1950). -: J. Am. chem. SOC.,72, 5001 (1950). Shaburo-Fominykh-Setannikov: Neftekhimiya, 16, N o . 1, 154 (1976). Sherwood, P. W., Brennst. Chem., 40, 354 (1959). Smith, A. E.,J. chern. Phys., 18, 150 (1950). : Acta crystallogr., 5, 224 (1952). Smolina-Chegodaev: Khimiya Tekhnol. Topl. Masel, 20, No. 9, 28 (1975). -: Neftepererab. Neftekhim., No. 10, 7 (1974). Sterba, M. J., Hydrocarb. Process., 44, 151 (1965). Swern, D., J. Am. chem. SOC.,74, 1738 (1952). -: J. Am. chem. SOC.,74, 1655 (1952).
-
-
204
11. MANUFACTURE OF PARAFFIN WAXES AND CERESINS FROM PETROLEUM
Topchiev-Rosenberg-Nechitalyo-Terentera: Dokl. Akad. Nauk SSSR., 98, 223 (1954). Urea Dewaxing. Hydrocarb. Process., 53, No. 9. 194 (1974).
US.Pat., 2 442 191. US.Pat., 2 606 140. US.Pat., 2 818 449. U.S. Pat., 2 841 471. U.S.Pat., 2 847 280. U.S. Pat., 2 859 256. U.S.Pat., 2 886 509. Wehner-Kaufmann-Seidel: Chem. Tech. B e d , 19, 385 (1 967). Wendt-Ried: Angew. Chem., 63, 218 (1951). Zimmerschmied-Dinerstein-Weitkamp-Marschner: Znd. Engng. Chem., 42, 1300 (1950).
(F) Purification of paraffin waxes The purity of paraffin waxes is an important aspect in their grading. The required extent of purity, obviously, depends on the type of the field of application. Paraffin waxes used for candle manufacture, for instance, must be white and stable to colour changes. Paraffin waxes applied in food conservation and packaging must be odourless and free from compounds damaging the human organism, above all from polycyclic aromatic substances. Similar, but even more strict specifications are applied for paraffin products to be used for medical purposes. Purity criteria, including whiteness and colour stability, call for refinement of paraffin products. De-oiling, discussed in the previous chapter, in addition to improving the mechanical properties of paraffin waxes, is also a refining process, since to meet the above-mentioned purity requirements, a correspondingly low oil content is essential. However, white colour, stability of colour to atmospheric oxygen, higher temperatures and light, aromatics content satisfactorily low or completely absent etc. can only be attained by satisfactory purification operations. The complete purification of macro- and microcrystalline paraffin waxes and paraffins liquid at ambient temperature is hence equivalent to the removal of impurities, usually present in small concentrations, like unsaturated compounds, mono-, bi- and polycyclic aromatics, hydrocarbon derivatives containing sulfur, nitrogen and oxygen atoms, heterocyclic compounds, while n-alkane, branched alkane and naphthene compounds should as far as possible remain intact. Owing to the manifold and wide-spread applications of paraffin waxes and products manufactured from them, as well as to the great variety in the composition of the feedstocks used, a large number of purification processes have been developed. According to Landa and Mostecky, up to the year 1952, in the U.S.A. alone, 1430 patents for paraffin wax purification have been issued. Of these, 778 patents used acids and alkalis and 224 patents used adsorbents. At present, both traditional and modern processes are being applied on a world-wide basis. These can be classified essentially into three groups : purification processes based on (i) treatment with chemicals, (ii) adsorption, (iii) hydrogenation.
205
(F) PURIFICATION OF PARAFFIN WAXES
1. By treatment with chemicals
It is a common feature of all chemical purification processes that to achieve the desired grade, rather vigorous conditions have to be used. The agents include potassium hydroxide, sodium hydroxide, sodium carbonate, ammonia, alkaline solution of magnesia, zinc oxide. Other patents advocate extraction with alcoholic alkali solution, aeration of the product to be purified in the presence of bleaching earth at 120-200 "C,treatment of microcrystalline p a r a h waxes with hydrogen peroxide or with sodium metal. Both macro- and microcrystalline paraffin waxes have also been subjected to purification with aluminium chloride, followed by neutralization and final clarification. The most wide-spread method is purification with sulfuric acid. In this process, among many other intermediate reactions, oxidation, condensation, polymerization, sulfonation and resin-forming take place. The final effect of the purification depends on the composition of the initial product, sulfuric acid concentration and amount used, temperature of operation, contact time and manner of execution. In purification with sulfuric acid, only those alkanes that contain tertiary carbon atoms will react, and naphthenes also are reluctant to react with sulfuric acid. On the other hand, aromatics will be sulfonated, unsaturated hydrocarbons yield polymerized products, and neutral esters and resinous components are converted, via polymerization and oxidation reactions, into asphaltenes. Microcrystalline paraffin waxes, owing to their composition, react much more readily than macrocrystalline paraffin waxes. Oleum is also suitable for purifying paraffin waxes; however, operating temperature must be very carefully chosen. Table II-16. Conditions for the de-aromatizing process of liquid p a r a h
1 Conditions
Sulfuric acid consumption relative to liquid paraffin single charge successive charge Temperature of contact, settling, neutralization and washing, OC Contact time, min Speed of agitator (laboratory scale), rpm, minimum Settling time of acid resin, h, minimum NaOH consumption relative to liquid paraffin, wt-%
1
Concentration, % of 98.6% sulfuricacid
4 3 45-60
1
1
Of Oleurn
3 2
45-60
60
60
900
900 2
2
0.16-0.20
0.16-0.20
206
11. MANUFACI'URE OF PARAFFIN WAXES AND CERESINS FROM PETROLEUM
In sulfuric acid purification of macrocrystalline paraffin waxes it is usually satisfactory to treat the initial product with 5 wt- % sulfuric acid in one stage, and subsequently with 5 wt- % bleaching earth. For microcrystalline paraffin waxes, however, multistage acid and clarification operations are frequently needed. The yield in the purification of macrocrystalline waxes is around 90 to 95 wt- %, while the value for microcrystalline waxes may be as low as 50 wt-%. Final purification with sulfuric acid is sometimes used in the manufacture of n-alkanes by urea adduct formation. Although the latter process allows the formation, under suitable conditions, of n-alkanes containing less than 0.5 wt- % aromatics, final purification is needed if the specified aromatics content may not exceed 0.01 wt-%. As an example, some experimental work by A. G.Ismaylov and co-workers can be cited. They studied sulfuric acid purification of a liquid paraffin oil with a boiling range of 270-370 "C obtained by urea adduct formation from diesel fuel. The aromatics content, initially 0.4 wt- %, could be reduced, by acid treatment under optimum conditions, to practically zero. Conditions of the de-aromatizing process are shown in Table 11-16, the major characteristics of the liquid paraffin oil before and after purification are listed in Table 11-17. The flow diagram of the sulfuric acid purification plant in the Novo-Kuybishev Petroleum Refinery is presented in Fig. 11-29. The product subjected to continuous purification in this plant is a liquid paraffin oil with 95-97 wt-% urea-adductforming hydrocarbons and 1.5-2.5 wt- % aromatics content. An interesting feaTable 11-17. Changes in composition and characteristics of liquid paraffin due to purification ~
~
Liquid paraffins
Character istics
__________
-
cation
Boiling range, "C Start 10 % 50 % 90 % 95 % Density, d p Refractive index, nio Molecular weight Viscosity at 50 "C, mm2/s Melting point, OC Aromatics content, wtaccording to GOST 9437-60 by UV spectroscopy Composition, wt- % sulfur content complex-forminghydrocarbons n-alkanes determined by chromatography
273 284 309 350 365 0.7918 1.4400 234 3.36 25
+
0.4 0.39
tion
274 285 309.5 351 366 0.7924 1.4431 245 3.45 28
+
none 0.004
0.02 93.7
none 94.0
97.58
98.42
(F) PURIFICATION OF PARAFFIN WAXES
207
70 -.
l1
T-*
Fig. 11-29. Flow diagram of the process for purification of liquid paraffins with sulfuric acid. Z Separator, 2 Acid treatment in agitated tank, 3 Settler for acid resin, 4 Separator, 5 Alkali wash and separator, 6 Aqueous wash and settler, 7 Separator for drying the liquid paraffin, 8 Pump for water recycling, 9 Agitators in the pipeline, I 0 Check valves, I 1 pH-measuring
instrument, I Paraffin feed, IZ Sulfuric acid or oleum, IZI Acid resin, IY Recycled alkali solution, V Fresh alkali solution, VI Water, VII Products of neutralization and aqueous wash, VIII Purified liquid paraffin
ture of the process is the d.c. electric field applied for the acceleration and improvement of sedimentation in the acid treatment, neutralization and aqueous wash stages. Some parameters of the operation are: sulfuric acid or oleum consumption 7-10 wt-% relative to feed, temperature of acid treatment 50-6OoC, voltage in the separator 4 15-20 kV, alkali concentration 3 4 wt- %, neutralization and aqueous wash temperature 50-60 “C, wash water consumption relative to feed SO-lOO%, voltage in the separators 5 and 7 10-15 kV. Under these conditions the initial aromatics content of 1.5-2.5 wt-% is reduced to 0.2-0.4 wt-%. Sulfuric acid and adsorption purification are often compared. If the comparison is related to identical amounts of adsorbent and sulfuric acid, an undeniable advantage of sulfuric acid purification is the higher degree of purification achievable. Also, sulfuric acid is less expensive than adsorbents. None the less, continuous adsorption processes, the so-called percolation operations are keen competitors of sulfuric acid purification, since no corrosion problems due to sulfur dioxide and sulfur trioxide arise, purification losses are lower, and no acid resin waste product is formed, creating problems of disposal. 2. By adsorption processes
The simplest process, essentially purification by adsorption, is by mixing with bleaching earth. After a satisfactory contact time, i.e. after equilibrium has been established, the paraffin wax is separated by filtration and the used bleaching earth is discarded. Various types of fuller’s earth (e.g. Tonsil, Montana, Terrana etc.), activated carbon, silica gel, bauxites, bentonites, natural or synthetic aluminium silicates are suitable adsorbents.
208
II.MANUFACTURE OF PARAFFIN WAXES AND CERESINS FROM PETROLEUM
Treatment with bleaching earth at 70-80 "C is mostly used as a final operation after treatment with chemicals, especially with sulfuric acid. It improves the colour of macro- and microcrystalline paraffin waxes. Studies carried out in the Hungarian Oil and Gas Research Institute demonstrated that even food industry grades can be obtained from low oil-content macrocrystalline paraffin wax with suitable activated bentonites by contacting for 3 hours at 100 "C. The purification of petrolatums is effective only at substantially higher temperatures, around 200 "C. However, when speaking of adsorption purification, it is not so much the batchwise one-stage equilibrium contacting that is considered, but rather processes based on adsorption chromatography. Chromatography is a generic term for all processes where a liquid-phase material to be purified flows through a solid phase with a large specific surface area and in this process some distribution between the two phases is established for each individual component of the liquid-phase feed. This distribution is obviously equivalent to the separation, to a given extent, of the components. There exist four basic methods of chromatography: - development chromatography, - frontal chromatography, - elution chromatography, - displacement chromatography. Development chromatography consists in developing a chromatogram on the adsorption column, that is, the individual components are localized in sharply confined superposed bands. To obtain individual components, the colunln must be taken apart to separate the individual bands. This method is unsuited for purification of paraffin waxes. In frontal chromatography the multicomponent mixture is introduced onto the column without solvent or with a solvent only slightly adsorbed by the packing. Feed is continuous, thus the component most strongly adsorbed will fis t be bound on the top part of the column, and only when this part is saturated with the component, will it gradually move downwards, displacing before its front the less strongly adsorbed components. Thus, the individual components will appear at the bottom of the column successively in the order of their liability to adsorption. The most strongly adsorbed component will be the last to leave the column. If the concentrations of the components successively leaving the column are plotted against the volume of the eluate, the individual components will appear on the chromatogram in the shape of sharp steps termed chromatographic fronts or breakthrough points. Frontal chromatography is successfully used to remove impurities present in small amounts, and, therefore, suitable for the purification of paraffin waxes. Elution chromatography is in fact, a refined form of development chromatography. Here, when separation of the components in the form of bands in the column is completed, a solvent, or a series of solvents is admitted to the column. These solvents are preferentially adsorbed by the column and the components
(F) PURIFICATION OF PARAFFIN WAXES
209
to be separated are successively eluted from the column. The industrial application of this method has the disadvantage that the individual components must be freed from the solvent after separation. In displacement chromatography the mixture to be separated is first admitted to the column in an amount smaller than the adsorption capacity of the column. The mixture is then washed through the column with a solvent capable of displacing all components, this taking place obviously in the order of their strength of adsorption. Components with higher retention will desorb and displace the components with lower retention. In this manner, component bands closely following one another will be formed and will successively leave the column. In this method, in contrast to frontal chromatography, the steps on the chromatogram correspond to pure components. The height of the step depends on the property and measuring unit used to express the concentration of the individual component, while the length of the step is proportional to the concentration of the component in question relative to the initial mixture. Combinations of these methods are usually used in industrial practice. The most frequent process is to purify the product by frontal chromatography and subsequently elute the impurities from the column. One of the oldest and most wide-spread chromatographic techniques in petroleum refining, used both for lubricating oils and paraffin waxes, is the percolation process. Its principles were developed by Engler and Bohm, and subsequently by Engler and Albrecht. The technology used at present is based on the research work of Gurvich, in 1917-1925. Two alternative methods of percolation purification are known : the stationarybed method, essentially identical with frontal chromatography, and the movingbed method. Stationary-bed processes are more wide-spread on a commercial scale, especially in the petroleum industry of the U.S.A. In this process several adsorption columns connected in series are used. The spent adsorbent is washed and regenerated, and often a semi-purified product is recycled. The two main operations are the adsorption purification and treatment of the spent adsorbent. In one of the columns connected in series, regeneration or change of the adsorbent takes place, while the other columns are operated in the purification stage. From the last of these columns, a completely de-aromatized product is obtained at the start. Subsequently, after the breakthrough of aromatics, the grade of the product will successively become worse, and finally this column is spent for purification purposes. Then the freshly filled column is connected in the place of the first adsorber, the last column is changed over for regeneration, and the feed is introduced into the column that stood in the second place in the previous cycle. When the column now standing in the last place is spent, permutation of the columns is repeated. In this manner percolation purification can be regarded as continuous. Before regenerating the spent column, the paraffin wax held back between the particles of the adsorbent, although it does not satisfy the requirements of the end product, it is higher-grade than the unpurified feed, is displaced by an inert gas 14
2 10
11. MANUFACTURE OF PARAFFIN WAXES A N D CERESINS FROM PETROLEUM
or by steam. This so-called displaced wax is recycled or burnt as fuel. Subsequently, the paraffin wax particles adsorbed by or mechanically adhering to the surface of the spent adsorbent are eluted with a solvent, e.g. gasoline. After stripping to remove the solvent, this so-called washed-off wax is added to fuel oil. The solvent traces retained on the surface of the adsorbent and between its particles are removed by superheated steam. The spent adsorbent is regenerated by air flow in stationary-bed furnaces or fluid-bed equipment. Subsequently it is refilled into the column and reconnected into the process. Wash of the adsorbent can be dispensed with, in this case the adsorbent is discarded or regenerated by ignition. By discarding, purification losses will obviously increase. If the adsorbent is regenerated by ignition, the heat demand of ignition is only partly covered by external sources, the heat of combustion of the hydrocarbons providing for the rest. The disadvantage of stationary-bed percolation is that part of the equipment is constantly unutilized for purification, and hence investment cost relative to purification capacity is rather high. For this reason endeavours are being made to
Adsorbent
Oil level -
r
1
Purified oil
Oil
Fig. 11-30. Continuously operated, controlled-flow adsorber. 1 Adsorbent vessel, 2 Elevator drive, 3 Filter press, 4 Collector drive
21 1
(F) PURIFICATION OF PARAFFIN WAXES
develop continuous countercurrent moving-bed processes, in which not only the feed, but also the adsorbent is in continuous countercurrent motion. Since the adsorbent leaving the equipment has been is contact with fresh feed, adsorbent utilization is better than in stationary-bed equipment. One process that has been put into operation on a pilot-plant scale is shown in Fig. 11-30. Particle size of the adsorbent moving downwards is so chosen that the equipment operates below the fluidization limit of the adsorbent. The feed enters the equipment a t the bottom and flows upwards. The product is tapped at the required height. The adsorbent arriving a t the bottom is scraped off in a thin layer by a suitable device and leaves the column by means of a screw conveyor. It is then washed, stripped and regenerated by ignition. After regeneration it is recycled into the process. Another alternative for moving-bed percolation is shown in Fig. 11-31. The feed enters the adsorber column at the bottom after passing through a preheater and a distributor, and flows upwards, in countercurrent to the adsorbent moving downwards. The end product leaves the column at the top. The adsorbent enters the column at the top, through a distributor system, and leaves at the bottom. The product entrained with the adsorbent is washed off in a second smaller column with gasoline, and the solvent is subsequently removed by stripping. The washed adsorbent is treated with superheated steam and regenerated in a continuously operated fluidized-bed furnace. The regenerated adsorbent is then raised above the level of the percolator into a distributor tank, where it cools and is recycled
Final product
r@--
-
Feed
Addition of adsorbent
Steam
Fig. 11-31. Countercurrent percolation plant. I Thermophor ignition furnace, 2 Elevator, 3 Adsorbent distributor, 4 Percolator, 5 Stripper, 6 Separator, 7 Filter press 14*
2 12
11. MANUFACTURE OF PARAFFIN WAXES A N D CERESINS FROM PETROLEUM
into the process. Dust produced from the adsorbent is entrained with the feed stream and will thus be included in the purified product, from which it is subsequently removed by filter presses. In one purification plant a stripping column has been inserted after the percolator to deodorize the purified paraffin wax. A more complex continuous percolation process was developed in the Soviet Union by Zherdeva and co-workers for manufacturing high-grade paraffin wax. The adsorbent used was < 1 mm particle size aluminium silicate. The principle of the process is shown in Fig. 11-32. The unpurified paraffin wax is dissolved in the diaphragm agitator 4 in aromatics-free gasoline at 90-140 "C and enters zone I of the adsorption column. Regenerated adsorbent is introduced at the top of the column. In zone 1 the paraffin wax flows upwards, countercurrent to the adsorbent moving downwards. In this zone the temperature is relatively low. Zone 2 of the column is fed with solvent; this zone acts as hydraulic seal to prevent the refined product flowing downwards. The purified product leaves the column at the top end of zone I and passes through the filter 6 to remove entrained adsorbent particles. The adsorbent containing the aromatics from the feed passes through the hydraulic seal 2 to enter the desorption zone 3. Here, at temperatures around 100 "C, aromatics with non-condensed structures will be desorbed, and the desorbate leaves the system at the top of the zone through the filter 6a. Desorp-
c
4
Solvent
pzT! Fig. 1Z-32. Moving-bed percolation plant for paraffin wax. I, 2, 3 Zones of adsorption column, 4 Diaphragm agitator, 5 Nozzle, 6 and 6u Filters, 7 Stripper, 8 Regenerator of adsorbent, 9 Cooling chamber, 10 Adsorbent tank, I 1 Still for solvent, 12 Furnace to produce hot air, 13 Stripper, 14 Collector of final product, 15 Solvent tank, 16 Stripper, 17 Cooler, 18 Semi-purified product
(F) PURIFICATION OF PARAFFIN WAXES
21 3
tion in zone 3 is due to the solvent fed into the bottom part of the column through its conical end-piece fitted with the nozzle 5. Superheated solvent vapour from the still 11 is blown through the nozzle, partly to heat up the adsorbent, and partly to transport it pneumatically into the solvent stripper 7. Solvent is here removed from the fluidized adsorbent and passes, together with steam, through the cooler 17, to be collected in the solvent tank 15. The adsorbent is regenerated in the ignition chamber 8 by means of air heated to 550-600 "C in the furnace 12. The regenerated adsorbent is transferred back to the adsorption column through the cooling chamber 9 by pneumatic transport using flue gas. Adsorbent losses due to dust formation are replaced by fresh adsorbent from the storage tank 10. Solvent is removed from the de-aromatized paraffin wax in the distillation system 13, the solvent passing to tank Z5, while the final product is collected in the receiver tank 14. The semi-purified product from zone 3 is freed from solvent in the column 16, bottoms are collected in tank 18, heads pass to the solvent tank. The Hungarian Oil and Gas Research Institute also studied paraffin wax purification by percolation, and developed a process using activated bauxite on a large laboratory scale. The characteristics of the type of bauxite suitable for the process are summarized in Table 11-18. This adsorbent can, according to the experiments, be ignited fifty times without a significant loss in adsorption activity. The preparation of the adsorbent includes crushing the crude bauxite, drying, milling, screening and activation by ignition a t 400-600 "C. Table 11-18. Characteristics of bauxite adsorbent suitable for purification by percolation of p a r a h waxes Screen fraction, mni wt- %
Specific surface area (BET), mz/g Average pore radius, A Density measured in benzene, g/cm3
0.25-0.50 85-90
minimum 160 35-45 maximum 3.6
The Hungarian Oil and Gas Research Institute also developed and put into use, on a pilot-plant scale, a process for the purification of liquid paraffins and macrocrystalline paraffin waxes, including the regeneration of the adsorbent. The process is essentially based on frontal chromatography and uses silica gel as adsorbent. The main features of the process are: The unpurified product is fed without solvent into the adsorption column packed with previously dried, narrow-pore silica gel. The feed temperature of rnacrocrystalline paraffin wax is 70-75 "C. Feed is continued until the product leaving the column satisfies the requirements for purified grade. Subsequently feed is stopped and the column is washed in the reverse direction with a solvent composed of acetone, toluene and benzene. In this operation the extract, composed mainly of aromatics, is displaced from the column. The silica gel adsorbent is regenerated
'
I
r' I
1
---3 13
-1
II
I
f
Fig. 11-33. Continuously operated adsorption plant for the purification of macrocrystalline paraffin wax. -Paraffin wax, - o - Solvent, - x - Extract, - - - - Air, - . - . - Steam. I Adsorber; 2 Air heater; 3, 4 , s Feed; 6, 7, 11, 12 Final product; 8, 9 Solvent; 10, 15, Extract; 13 Compressor; 14 Pump station; 16 Distillation; 17 Tank car
(F) PURIFICATION OF PARAFFIN WAXES
215
by blowing superheated steam, followed by hot air through the column, which is then ready to repeat a purification cycle. In an alternative process the feed of the unpurified material is not stopped when the product leaving the column no longer satisfies the purified-grade specifications, but is continued to obtain technical-grade liquid paraffin or paraffin wax. These can then be marketed as final products, or refed into the column at the start of the next cycle as semi-refined feed, to raise the yield of purified product per unit adsorbent. The flow diagram of the pilot plant is shown in Fig. 11-33. A shell-and-tube type adsorber is used. The pilot-plant adsorber contains 85 tubes, 36 mm in inner diameter and 5000 mm high, within the welded tubular top and bottom parts of the shell of the cylindrical adsorber. The adsorber is heated with superheated steam introduced into the space between the tubes and the cylindrical shell. Experiments demonstrated that the optimum screen fraction of the narrow-pore silica gel is 0.2-0.5 mm. Drying of the fresh packing is carried out at 110-120 "C, solvent wash at 75-80 "C. The disadvantage of using a single adsorber is also true for this process, namely that only a relatively small fraction of total cycle time is utilized for actual purification, while the rest is used for obtaining the secondary product and for regeneration of the adsorbent. Analyses of the economics of the process demonstrated that the indispensable condition for rentability is the effectuation of a technology operating with several adsorbers. The process yields practically aromatics-free, odourless purified liquid paraffins and paraffin waxes possessing high colour stability. Purification also results in a reduction of the oil content of paraffin waxes by 0.3-0.4 absolute wt-%.
3. By hydrogenation
Up to the 'fifties, hydrogenation was not much in use in the petroleum refineries, owing to the expensiveness of hydrogen. However, with increasing demand for high-octane number gasolines, petroleum refineries were compelled to build a large number of catalytic reforming plants, yielding hydrogen 75-80 mob% pure as by-product. The cost of this by-product is only one tenth of the price of hydrogen manufactured in hydrogen plants. In the meantime, hydrogen manufacture from methane and steam also reduced the cost of direct hydrogen production. Hence, within a very short time hydrogenation refining operations became economical in comparison to other refining processes. On the other hand, from those years onwards petroleum refineries were forced to process ever increasing amounts of crudes containing sulfur and high percentages of asphaltenes, and at the same time the quality requirements of fuels, lubricating oils and paraffin waxes became much higher. Hence it became increasingly difficult to manufacture such products from the crudes available. All these factors contributed to the rapid world-wide
2 16
11. MANUFACTURE OF PARAFFIN WAXES A N D CERESJNS PROM PETROLEUM
spread of hydro$enation, from the end of the 'fifties, for refining a variety of petroleum products. Hydrogenation processes can essentially be classified into two groups : - those significantly changing the physical and chemical properties of the feedstock, and - those whose objective is final purification of the products, only partly changing, and then only to a slight extent, the chemical and physical properties of these products. The feedstocks for the processes belonging to the first group are not so much the crude paraffins, but rather lubricating oil fractions and distillation residues. In both cases macro- and microcrystalline paraffin waxes are obtained in distillation and dewaxing of the hydrogenated petroleum products. The paraffin waxes are then subjected to some post-treatment, e.g. claying. The processes belonging to the second group are widely used for various purposes, e.g. for refining the feedstocks of catalytic reforming to protect the platinum catalyst, for desulfurization of Diesel fuels, for pretreatment of heavy oil feedstocks prior to catalytic cracking, for improving combustion properties and colour stability of kerosines, for improving the colour and stability of lubricating oils. These processes are equally suitable both from the technological and economical view for the final purificaticn of liquid paraffins and parafin waxes. The essence of all refining hydrogenation processes can be summarized as follows : (i) A suitable mixture of the feedstock and hydrogen is heated to the required reaction temperature. (ii) The gas-phase or liquid-phase or gas-liquid phase reaction mixture enters the reactor packed with catalyst where the desired reactions and side reactions proceed. (iii) The contents of the reactor are cooled, the hydrogen-rich gas phase is separated in a high-pressure separator, hydrogen sulfide formed in the reactions is removed and the gas is recycled into the process. (iv) After reduction of pressure, the gases dissolved in the liquid reaction product are removed by flash distillation, hydrogen sulfide by washing with water, and finally the light components formed in hydrogenation by distillation. The desired primary reaction in hydrogenating the final purification stage is always the conversion of the sulfur, from sulfur compounds in the feed, to hydrogen sulfide, and removal of the latter. The usual sulfur compounds present in petroleum products, including paraffin waxes, being mercaptans, sulfides, disulfides, thiophen, benzothiophen derivatives, etc. Conversion of the sulfur into hydrogen sulfide proceeds according to the following reactions : R-SH H, + RH HZS
+
Rl-S-R,
Rl-S-S-R,
+ + 2 Hz + RIH + R,H + H,S + 3 H, -+ R,H + R,H + 2 HZS
(F) PURIFICATION OF PARAFFIN WAXES
217
Even these few reaction equations demonstrate that desulfurizing leads to the formation of compounds with a lower molecular weight as compared to the sulfur compound, and consequently having a lower boiling temperature. These compounds have to be removed from the purified product to eliminate their reducing effect on the flash point. By hydrogenation under suitable conditions, as much as 80 to 90 wt-% of the sulfur content in petroleum products can be removed. Purification by hydrogenation not only reduces the sulfur content, but also the oxygen content, and under suitable conditions also the nitrogen content. In addition, diolefins present are hydrogenated into alkanes, and polycyclic aromatics into naphthenes and aliphatic side-chain monoaromatics. Reactions leading to desulfurization do not proceed at appreciable rates at temperatures below 260 "C. On the other hand, reaction temperatures above 430 "C result in a considerable amount of undesirable side reactions, e.g. hydrocracking, and increasing carbon deposits. The sulfur content of the feed to be purified decreases proportionally not only to increasing temperature, but also to increasing partial pressure of hydrogen, the latter, however, making the process more expensive. Hence an optimum value for the hydrogen partial pressure is found. Usually higher reaction temperatures (above 430 " C ) and lower pressures (below 600 kPa) favour reforming reactions and carbon deposits, lower temperatures (around 300 "C) and higher pressures (around 6000 kPa) favour hydrogenation of aromatics to naphthenes. A great variety of hydrogenating catalysts are being used. In the beginning nickel and tungsten sulfides were used. At present the most wide-spread catalysts are mixtures of cobalt and molybdenum sulfides on y-alumina support. These catalysts have high mechanical strength and prolonged activity. Under appropriate technological conditions their activity does not decrease appreciably after an operating period of 12 months. The catalysts are regenerated at temperatures around 400 "C with steam or air mixed with an inert gas. With periodical regeneration their service life is prolonged indefinitely. We wish to mention that the use of nickel and tungsten catalysts is especially advisable when only partial hydrogenation is required. This is the case, for instance when diolefines and styrene present in gasolines from thermal cracking or naphtha pyrolysis are to be hydrogenated. Comparative studies of various hydrogenating catalysts were carried out by A. G. Martynenko and co-workers. The catalysts investigated were tungsten
2 18
11. MANUFACTURE OF PARAFFIN WAXES AND CERESINS FROM PETROLEUM
disulfide; a mixture of tungsten disulfide and nickel sulfide; the latter mixture on an alumina support; and a mixture of nickel and chromium. The model substance used was n-hexadecane. The experimental conditions were : 200-375 "C, 5000 kPa, 0.3 h-I flow rate and a ratio of 1000 m3 hydrogen to 1 m3 feedstock. They found that with tungsten sulfide and tungsten sulfide-nickel sulfide mixed catalysts, conversion, especially isomerization, of the feed becomes significant from temperatures around 300 "C, while at temperatures above 350 "C destruction reactions become predominant. With the tungsten disulfide-nickel sulfide catalyst on alumina support, a more significant amount of isomerization is observed only at 375 "C, whereas with the nickel-chromium catalyst, isomerization starts even at 230 "C. They concluded that in order to minimize isomerization reaction temperature must not exceed 280-300 "C for tungsten disulfide catalysts and 200-220 "C for nickel-chromium catalysts. Flow rate and the proportion of recycled gas are also important parameters of hydrogenation purification processes. Increased flow rates, under otherwise identical conditions, reduce the extent of desulfurization. Higher proportions of recycled gas, although increasing the service life of the catalyst, result in a higher energy demand for the process. Many hydrogenating processes for purification are now available, but essentially they do not differ much. Their operating conditions are usually: 250-430 "C, 600-9000 kPa, 0.5-10 h-I flow rate of liquid, recycle ratio 200-5000 m3/m3. One of the most wide-spread hydrogenating purification processes is the ferrorefining process developed by the British Petroleum Co. The process is characterized by a catalyst containing, as well as the conventional components, also iron oxide. A typical catalyst composition (in wt-%) is 10 molybdenum oxide, 3.3 cobalt oxide and 15 iron(I11) oxide on alumina support. The process not only reduces sulfur, nitrogen and oxygen content, but also ensures satisfactory colour and de-odorizing of the final product. Hence the ferro-refining process may be considered satisfactory for the manufacture of macro- and microcrystalline paraffin waxes used in the food and pharmaceutical industries. The de-aromatization by hydrogenation of a liquid paraffin (boiling range 270-360 OC, aromatics content 1.2 wt- %) prepared by urea adduct formation was studied by A. G. Martynenko and co-workers. Experimental conditions were: tungsten disulfide catalyst, 280 to 360 "C, 0.3 to 1.0 h-' flow rate. The results are shown in Fig. 11-34. The percentage hydrogenation of the aromatics initially present in the test substance are plotted on the left-hand ordinate, the percentage isomerization of the initial n-alkane components on the right-hand ordinate. The figure demonstrates that temperatures exceeding 300 "C are unfavourable to the grade of the final product, since the rate of isomerization reactions increases and aromatization processes start. Experiments carried out at 300 "C, varying the pressure (Fig. 11-35), demonstrated that the extent of de-aromatizing is largely susceptible to pressure. Also, the character of the relationship between flow rate and extent of de-aromatization is a function of temperature (Fig. 11-36). The properties of the purified products obtained from four different liquid paraffins
219
(F) PURIFICATION OF PARAFFIN WAXES
KX
100
P
'
2
I
I
80
80
m-
u
' a
a, C 0
I
F $
60
60
7 C
c
0
c
0
C
Q
%
C
40
540
0
a
.-N
01
t
2
U
2 20
20
sE
I
0
0
280
300 320 Temperature,
340
360
"C
Fig. 11-34. Hydrogenation of aromatic hydrocarbons and isomerization of n-alkanes versus temperature. I Flow rate 0.3 h-l, 2 Flow rate 0.5 h-l, 3 Flow rate 1.0 h-'
by hydrogenation at 300°C, 5000 kPa pressure and 0.3 h-l flow rate are listed in Table 11-19. A second hydrogenation of these products, using a nickel-chromium catalyst susceptible to poisoning resulted in final products with an aromatics content below 0.01 wt- % and sulfur contents below 0.0004 wt- %. Experiments with the objective of finding out whether food-grade paraffin waxes could be manufactured from the de-oiled paraffin waxes obtained from
sp
100
m.-u #
E
0,
90
0 c
0 C 0
=0
80
srn 2
73
n
1
70
fi 5
I 10
I
15 Pressure, MPa
I 20
Fig. 11-35. Hydrogenation of aromatic hydrocarbons versus pressure. I Flow rate 0.3 h-l, 2 Flow rate 0.5 h-l, 3 Flow rate 1.0 h-l
220
11. MANUFACTURE OF PARAFFIN WAXES AND CERESINS FROM PETROLEUM
Flow rote, h-' Fig. 11-36. Hydrogenation of aromatic hydrocarbons versus flow rate. I Temperature 300 O C , 2 Temperature 280 O C , 3 Temperature 350 O C
1
point,
Sulfur
Aromatics
0.0040 0.0009
1.2 0.08
97.2 95.2
-_______
n-Alkanes
.-
Paraffin A from urea treatment Paraffin A after hydrogenation Paraffin B from paraffin A after vacuum distillation Paraffin B after hydrogenation Paraffin C separated with zeolithes in pilot plant Paraffin C after hydrogenation Paraffin D obtained by urea treatment in pilot plant Paraffin D after hydrogenation
0.793 0.792
291 271
360 360
+25 24.5
0.772 0.772
264 258
311 309
+13 13
-
2.2 0.19
97.0 95.4
0.761 0.761
215 206
292 290
-7 -7.8
-
1.1 0.28
97.1 95.0
0.792 0.791
278 271
360 360
+25 +24.5
0.026 0.001
3.0 0.3
95.9 93.9
+
+
vacuum distillation of sulfur-containing West-Siberian paraffin crudes were carried out by K. s. Lipovskaya and co-workers. They found that this could be achieved by hydrogenation of the paraffin waxes containing 0.3 wt- % oil, in the presence of aluminium-platinum or aluminum-cobalt catalysts at 250-300 "C and 4000 kPa. They used feed flow rates of 0.5-1 h-' and hydrogen recycling ratios of 600 m3/m3. The purified product of the paraffin wax obtained from the 360400 "C boiling-range fraction had a melting point of 54 "C, that from the 400490 "C boiling-range fraction a melting point of 58 "C. Both products were fully satisfactory for food industry requirements regarding colour, colour stability
22 1
(F) PURIFICATION OF PARAFFIN WAXES
and carcinogen content. Their n-alkane content, determined by urea adduct formation, was 95 wt-%, their oil content 0.3"/,. Other Soviet researchers, K. M. Badyshtova, 0. P. Ushatinskaya and T. N. Shabalina prepared purified products by hydrogenation of a paraffin wax, melting point 55.8 "C, oil content 0.2 wt-%, originating from a sulfur-containing crude. Hydrogenation conditions were: aluminium-platinum catalyst, temperatures 250, 275, 300 and 325 "C, pressure 4000 kPa, flow rate 0.5 h-l, hydrogen recycling ratio 800 m3/m3.The characteristics of the purified products are listed in Table 11-20. Badyshtova reports final hydrogenating purification of hard paraffin waxes originating from high-sulfur content crudes. She obtained yields of 99 wt-%. The same author also carried out comparative technological and economical analyses for hydrofinishing, aluminium silicate percolation and purification with sulfuric acid and bleaching earth. The results demonstrated hydrofinishing occupying the first place, owing to high yield, continuous operation and ready accomodation to the composition of the feedstock available. Final hydrogenation purification is especially useful for microcrystalline paraffin waxes, since their purification with sulfuric acid frequently results in yields as low as SO%, owing to the attack, by sulfuric acid or oleum, on groups containing tertiary carbon atoms. Landa and Mostecky studied the hydrogenation purification of petrolatums, under the following conditions : tungsten disulfide catalyst, 340 "C, 28 MPa, ratio of gas to product 1875 l/kg. Table 11-20. Physico-chemical properties of paraffin waxes obtained from sulfur-containing crude, refined at different temperatures by hydrogenation in the presence of an aluminium-platinum catalyst ~
Characteristics
Unrefined paraffin wax
Odour Melting point, O C Oil content, wt- % Colour stability, days a-Benzopyrene content
,~~~~
i
325 "C
Paraffin wax refined by hydrogenation at ~
~
-
- -
300°C
55.8 0.20
55.8 0.48 I detectable
56.0 0.29 7
none
1
__
275 "C
~
,
250°C
1
~
200°C
none 56.0 0.20 7 none
56.0 0.20 I none
56.0 0.20 I none
Hydrocarbons complexforming with urea Yield on paraffin wax, wt- % Melting point, "C Refractive index, n g
91.5 56.4 1.4322
98.5 56.4 1.4358
98.0 56.6 1.4348
98.0 56.6 1.4348
97.5 56.2 1.4324
97.5 56.4 1.4326
Hydrocarbons forming no complex with urea Yield on paraffin wax, wt- % Melting point, 'C Refractive index, n p
2.5 42.8 1.4412
1.5 41.8 1.4436
2.0 42.4 1.4416
2.0 42.0 1.4414
2.5 41.2 1.4418
2.5 40.4 1.4400
222
11. MANUFACTURE OF PARAFFIN WAXES A N D CERESINS FROM PETROLEUM
The Shell paraffin wax plant in Stanlow (England) uses hydrogenation for purification. The hydrogenation plant was put into operation in 1963 with a performance of 100 tpd. To manufacture macrocrystalline paraffin waxes, they start with a broad slack wax fraction which is separated by vacuum distillation into three paraffin wax fractions, a light heads product and a heavy residue. The feedstock for microcrystalline paraffin waxes is petrolatum from heavy oil. The three paraffin wax fractions and the heavy oil petrolatum are subjected to two-stage solvent de-oiling. The six macrocrystalline and two microcrystalline paraffin waxes obtained in this manner are then purified by hydrogenation, at a pressure of 12 MPa and a temperature of 300-315 "C, in the presence of a nickel sulfidetungsten sulfide-alumina catalyst. By vacuum stripping of the products complete de-odorization is attained. The company markets six types of macrocrystalline paraffin waxes with melting points ranging from 52 to 68 "C, one plastic ceresin and a high-melting hard ceresin.
Literature Adams-Mertens-Godino : Hydrocarb. Process. Petrol. Refiner, 40, No. 9, 189 (1961). Badyshtova-Skibenko: Neftepererab. Neftekhim., No. 10, 15 (1975). Badyshtova-Ushatinskaya: Neftepererab. Neftekhim. Slantsepererab., No. 2, 18 (1976). Badyshtova, K. M., Khimiya Tekhnol. Topl. Masel, 6, No. 21 (1961). Brit. Pat. 851 969. Brit. Pat. 911 813. Chernykh-Sedunov: Nejiepererab. Neftekhim., No. 7, 21 (1974). De Henau, G., Bull. Ass. Techns. Pdtrole, 158, 177 (1963). Evans-Magin-Savaca-Shea: Petrol. Refiner, 32, 117 (1953). Gurevits-Shardanashvili: Khimiya Tekhnol. Topl. Masel, 4, No. 10, 1 (1959). Ismaylov-Terteryan: Khimiya Tekhnol. Topl. Masel, 20, No. 12, 6 (1975). Kreuder, W., Seifen-Ole-Fette- Wachse, 84, 665, 699, 735, 773, 849 (1958); 85, 19, 41, 67, 93 (1959). Landa-Mostecky: Chemickij Prum., 7, 393 (1957). -: Chem. Tech. Berl., 15, 129 (1963). Lipovskaya-Agafonov: Neftepererab. Neftekhim., No. 3, 23 (1976). Martynenko-Goncharenko: Khimiya Tekhnol. Topl. Masel, 20, No. 4, 19 (1975). Presting-Keil: Pharmazie, 8, 16 (1953). Presting-Boenke: Pharmarie, 9, 562 (1954). Reitz-Kohrt: Erdd, Kohle, 11, 18 (1958). Schmiedel-Schneider-Teubel: Chem. Tech. Berl., 16, 37 (1964). Schneider-Teubel-Schmiedel: Chem. Tech. Berl., 17, 577 (1965). - : Chem. Tech. Berl., 17, 467 (1965). Schneider-Teubel-Schmiedel-Heymer : Chem. Tech. Bed, 15, 138 (1963). Sherwood, P. W., Brennst. Chem., 40, 354 (1959). -: Brennst. Chem., 42, 220 (1961). -: Fette, Seifen, 65, 521 (1963). Teubel-Schneider-Schmiedel: Erddparaffine. VEB Deutsch. Verl. fur Grundstoffindustrie, Leipzig (1965). U S . Pat. 2 985 579.
(G) BLENDING OF PARAFFIN WAXES
223
U.S. Pat. 2 998 377. U.S. Pat. 3 089 841. U.S. Pat. 3 119 762. Vamos, E., Zpari adszorpcids kromatografia (Industrial Adsorption Chromatography). Miiszaki Konyvkiad6, Budapest (1964). Wolf-Kahlert-Berg : Erdol & Kohle Erdgas Petrochem. Ver. Brennst-chem., 24, No. 3, 153 (1971). Zerbe, C. : Mineralole u. verwandte Produkte. Berlin-Gottingen-Heidelberg, Springer (1952).
(G) Blending of paraffin waxes Paraffin waxes and liquid paraffins in their various fields of application require many different specifications. These can only partly be satisfied by a suitable choice of feedstock and the above-discussed manufacturing processes, or even by some modifications of these processes. In order to fully meet the great variety of demands, and to further increase the assortment of paraffin wax grades, manufacturers resort to blending. This operation involves blending of brittle, fragile, low tensile strength, friable macrocrystalline slab waxes, having relatively poor adhesion properties, with microcrystalline paraffin waxes, polymers and other additives. In this manner certain properties important for the application field in question can be improved, while other properties disadvantageous in this context are suppressed or minimized. The two groups used as additives to macrocrystalline paraffin waxes are (i) microcrystalline paraffin waxes (petrolatums, ceresins, ozokerite, etc.), and (ii) polymers, e.g. polyethylene, polyisobutylene, ethylene-vinyl acetate copolymers, ethylene-ethyl acrylate copolymers, ethylene-isobutyl acrylate copolymers, fatty acid amides, natural and synthetic resins, etc. An important criteria in the manufacture of paraffin wax products having special properties is the choice of the paraffin wax to be blended. The effect of the additives can be enhanced if the properties which require improvement are already present in the starting material. Thus, for example, products flexible at low temperatures can only be obtained, using a little additive, from starting materials containing microcrystalline paraffin waxes. Paraffin waxes possessing particular properties are usually manufactured from mixtures of macro- and microcrystalline paraffin waxes, possessing different melting points, instead of starting from a single paraffin wax product. The proportions of the individual components in the mixture depend on the desired grade of the final product and on the properties of the additives to be used.
224
II. MANUFACTURE
OF PARAFFIN WAXES AND CERESINS FROM PETROLEUM
1. Blending with microcrystalline paraffin waxes
Microcrystalline petrolatums possess high flexibility at low temperatures and low permeability to water vapour. By using them as additives to blend paraffin slab waxes, high-grade products can be obtained, e.g. for the impregnation of packaging material for deep-frozen goods. High melting-point, low oil-content microcrystalline ceresins promote gloss and high resistance to mechanical impact and solvents when added to macrocrystalline slab waxes. Table 11-21 lists data obtained by Teubel and co-workers concerning the effect achieved by the addition of several microcrystalline waxes, in concentrations of 20 wt- %, on the melting point, break point and penetration of a macrocrystalline slab wax initially melting a t 56 "C. The data show that the microcrystalline petrolatum (melting at 69 "C) practically does not, at such concentrations, affect the melting point, while the two ceresins have quite a substantial effect on the melting point. On the other hand, the petrolatum, as shown by the breaking points, significantly improves flexibility, whereas the ceresins increase hardness and result in a better temperature coefficient of penetration. Table II-21. Characteristics of macrocrystalline slab wax blended with microcrystalline paraffin waxes
.
Macrocrystalline slab wax
56
+20
11
14
65
20 wt- % petrolatum (melting point 69 "C) 80 wt- % slab wax
58
-6
9
11
36
20 wt- % ceresin (melting point 81 "C) 80 wt- % slab wax
65
-2
7
10
23
71
+I
7
9
26
+
+ 20 wt- % ceresin (melting point 88 "C) + 80 wt- % slab wax
Studies were carried out in the Hungarian Oil and Gas Research Institute to investigate how and to what extent the rheological properties of macrocrystalline paraffin waxes can be changed by blending with microcrystalline paraffin waxes. The results, among others, indicated that maxima appear in the plots tensile strength, compressive strength and impact strength versus composition of the blend (see Figures 1-41, 1-42 and 1-45 on pages 1 1 0, 112 and 1 16).
225
(G) BLENDING OF PARAFFIN WAXES
2. Blending with polymers
Technologically, blending of paraffin waxes involves melting and mixing or rubbing. Hence the softening and melting ranges of the polymer additive, and the variation of viscosity with the temperature of the melt, must be considered in thechoiceof the polymer. To avoid deterioration paraffin waxes should not be heated to temperatures exceeding 14&180 "C. The viscosity of polymers is a function of their average molecular weight, and the viscosity of high molecular weight polymers is rather high even at such relatively high temperatures. Therefore, polymers with lower degrees of polymerization are usually considered for blending. The most wide-spread additives are polyethylenes and polykobutylenes. Polyethylene melts with an average molecular weight of up to values around 9000 can be blended by simple mixing. Polyethylenes with molecular weights exceeding 12,000 are rarely used as additives. However, the molecular weight of polyisobutylenes used for blending varies between 5000 and 100,000. Investigations in the Hungarian Oil and Gas Research Institute frequently indicated that difficulties occurred when blending paraffin waxes with polyisobutylenes, owing to poor miscibility. Blending macrocrystalline paraffin waxes with polyethylene waxes rakes the melting point, increases hardness and, to a lesser degree, flexibility, and thereby reduces permeability to water vapour. The viscosity of the paraffin wax increases with the molecular weight and concentration of the additive. Small amounts of low molecular weight polyethylene wax raises the melt viscosity of the wax blend to a slight extent only, but substantially improves the gloss. Table 11-22 lists the properties of products obtained by blending slab paraffin wax with a 2000 average molecular weight polyethylene wax. The structural viscosity of the polyethylene measured at 120 "C varied between 1300 and 1700 Table 11-22. Major characteristics of macrocrystalline paraffin wax with polyethylene additive (Average molecular weight of PE: 2000) Ratio of additive'
Slab wax without additive 0.5 1.5 5 10 20 50 70
at 25 O
52 54 54 56 60 82 89 94
53 53 53 53 52 53
3.09 3.45 3.87 5.71 9.13 22.38 181.91
-
C
19 17 15 15 13 11 7 6
* Additive ratios are additive mass amounts added to 100 mass units of paraffin wax 15
226
u.
MANUFACTURE OF PARAFFIN WAXES AND CERESINS FROM PETROLEUM
mm2/s, depending on shear stress. Its drop melting point was 104"C, and its melting point was 92"C, as measured in the Hungarian Oil and Gas Research Institute. Among the characteristics of the products, the logarithm of viscosity measured at 100 "C increases linearly with polyethylene concentration. The melting point (rotating thermometer) increases substantially up to additive concentrations of 20 wt-%, higher concentrations affecting it only to a slight extent. Tensile strength versus additive concentration is shown in Fig. 11-37. After a sharp rise in the additive concentration range of 0-5 wt- %, the curve flattens, but again becomes steeper from 70-80 wt- % on. Impact strength values of the same products measured at -20, 0 and $25 "C are shown in Fig. 11-38. Compression behaviour of paraffin waxes blended with polyethylene are also of interest: some deformation values measured at 0 and +25 "C are listed in Table 11-23. Deforma280 260 240 220 N
200
E . z 180 V
5-
160
P 5 140
-.-am
c 120 a
k
100
ao 60 40 20
I
L
I
1
60 80 1( Polyet hy tene, w t - 'lo
20
40
I
I
I
I
I
1
100
80
60
40
20
0
Macrocrystalline wax, wt - %
Fig. 11-37. Tensile strength of macrocrystalline paraffin wax blended with polyethylene versus additive concentration. Temperature 25 O C , u = pull velocity, mm/min
(G) BLENDING
2.0
221
OF PARAFFIN WAXES
c
1.5 -
. E V
c Polyet hy lene, w tI
I
I
1
I
I
60 40 20 0 Mocrocrystolline wox, w t - % 100 80
Fig. 11-38. Impact strength of macrocrystalline paraffin wax versus concentration of the polyethylene additive, measured at different temperatures
Table 11-23. Compressive deformation and recovery of macrocrystallineparaffin waxes containing polyethylene additive at 0 "C and 25 OC
+
at 0 "C Additive concentration, wt-%
Compressive stress, N/cmz
Deformation D during 3 minutes
__ h, - h R' = h, h deformation time:
-
u tes
15+
Compressive stress, N/cm*
at +25"C
I
Deformation D during 3 minutes
-h R* = h, h. - h deformation time: 3 minutes
228
11. MANUFACTURE OF PARAFFIN WAXES AND CERESINS FROM PETROLEUM
bility increases at 0 "C, and, in contrast, decreases at +25 "C with increasing additive concentration. Thus, polyethylene wax retards the deformability caused by rising temperature in paraffin waxes. This result, together with the results for impact strength, leads to the conclusion that blending with polyethylene wax yields products more plastic at low temperatures, but less plastic at higher temperatures, than macrocrystalline slab wax. The data also demonstrate that elastic recovery (after relieving compressive stress) increases with polyethylene concentration within the temperature range 0 to 25 "C. Polyethylene also substantially increases compressive strength of paraffin waxes in the temperature range -20 to +30 "C (Fig. 11-39). The outstanding property of polyisobutylenes is their high adhesion strength, this property also appearing in parafib waxes blended with these polymers. Their flexibility-increasing effect is especially significant at lower temperatures. From these viewpoints, polyisobutylenes are more effective than polyethylenes. On the other hand, they have the disadvantage of substantially raising the melt viscosity of the paraffin waxes, while their effect on melting point and hardness is insignificant. Some data concerning blends of a 55°C melting-point paraffin wax and a 40,000 average molecular weight polyisobutylene, that are characteristic of the effect of this additive, are listed in Table 11-24. Apart from the polymer additives previously discussed, an ethylene-vinyl acetate copolymer with the trade name Elvax became widely accepted. This additive 1000 1
-
0
-30 -20 -10
0
10 20 30 40 !
Temperature,
"C
Fig. 11-39. Compressive strength of macrocrystalline paraffi wax versus temperature, at different concentrations of the polyethylene additive. a 0.5 wt-% additive, b 1.5 wt-% additive, c 20 wt- % additive, d 70 wt- % additive
229
(G) BLENDING OF PARAFFIN WAXES
Table 11-24. Changes in the properties of 55 "C melting-point macrocrystalline paraffin wax by adding polyisobutylene (average molecular weight of polyisobutylene: 40,rn)
*
~ wt- %
1
0.0 0.5 I .O 2.0 3.0
I
~
Melting point oc
viscosity~at
100 OC, rnm*/s
55 55 56 56 56
*'~
~
Peactraat 0.1 mm
4.14 5.50 7.50 12.00 20.00
-
24 23 24 24 25
particularly increases flexibility, and is, therefore, used mainly with paraffin waxes intended for coating waterproof paper. It improves blocking properties and gloss. Products containing 40-70 wt-% of this additive tend to lose their paraffin wax nature and behave like plastics. Studies concerning the effects achievable with this additive were carried out in the Hungarian Oil and Gas Research Institute. Table 11-25 lists the properties Table 11-25. Properties of a macrocrystalline slab wax and a microcrystalline petrolatum I
Characteristics
Melting point, "C Drop melting point, O C Viscosity, mm*/s at l W e C at 14OoC Oil content, wt-% Penetration at 25 OC, 0.1 mm (ASTM) Impact strength (with the 0.98 J striker), J/cme at o0C at +25 "C Tensile strength, N/cm* (pull velocity 50 mm/min) at 0°C at +25 OC
'
;
Macrocrystai- Microcrystalline slab wax line petrolatum
53 -
65 70
3.07 1.85 0.75 12
12.05 5.85 8.0 66
0.05 0.15
0.40
I1 45
-
85 24
of the macrocrystalline paraffin wax and the petrolatum involved in the studies. The properties of a mixture of these two waxes are presented in Table 11-26. This product was blended subsequently with three polyethylene types and two ethylenevinyl acetate copolymers. The characteristics of these additives are shown in Table 11-27, those of the products obtained by their addition in Table 11-28.
230
11. MANUFACTURE
OF PARAFFIN WAXES AND CERESINS FROM PETROLEUM
Table 11-26. Characteristics of a blend of the macrocrystalline slab wax and microcrystalline petrolatum figuring in Table 11-25
Drop melting point, OC Viscosity, mmys at loooc at 140°C Oil content, wt- % Penetration, 0.1 mm (ASTM) at O°C at 15 "C at +25 "C at +35 O C Impact strength at 0 O C (with the 0.98 J striker), J/cm2 Tensile strength at 0 "C, N/cm2 (pull velocity 50 mm/min) Break point (Fraass), O C
60 5.65 3.22 4.3 6 12
+
21
109 0.11 207 -8
Table 11-27. Characteristics of paraffin wax additives ~~
Characteristics A
Melting point, "C Drop melting point, OC Viscosity at 140 "C, mmz/s Penetration at 25 O C , 0.1 mm (ASTM needle) Intrinsic viscosity at 30 OC, mmz/s (0.25 g/100 cm3 toluene) Softening point, OC (ASTM) Hardness, 10 s (Shore)
I
96
B
103
l
~
Ethylene-vinyl acetate copolymers
Polyethylene waxes C
97
D
~
-
-
-
106 48
114 448
107
-
1029
-
-
7
1
2
-
-
-
-
-
-
-
0.78
0.54
115
99
67
83
Viscosities measured at 140 "C versus additive concentration are plotted in Fig. 11-40. The relationship is exponential. The slope of the line obtained by plotting the logarithms of viscosity versus concentration depends on the properties of the additive. Figure 11-41 represents the relationship between drop melting point and additive concentration, demonstrating that although the two copolymers substantially increase the melt viscosity of the paraffin wax, they affect its drop melting point only slightly. Figure 11-42 indicates the relatively important decrease in penetration resulting from addition of the copolymers. A comparison of the melt viscosity of products with identical penetrations shows that among the additives in question,
E
23 1
(G) BLENDING OF PARAFFIN WAXES
Table 11-28. Characteristics of three-component systems consisting of macro- and microcrystalline parafin wax and various additives Additive
Polyethylene wax A
1 3 6 10
Polyethylene wax B
1 3
6 10
Polyethylene wax C
1 3 6
so
71 76 80 82
3.30 3.58 4.08 4.54
23 21 19 18
104 97 90 78
86 90 92 95
3.46 3.92 5.00 6.81
21 20 17 14
105 94 82 64
76 80 83 85
3.52 4.22 5.22 7.59
23 20 18 16
100
93 81 69 53
Ethylene-vinyl acetate copolymer D
1 3 6 10
64 66 68 69
4.06 6.43 12.50 31.79
21 20 19 16
Ethylene-vinyl acetate copolymer E
1 3 6 10
65 67 69 70
4.01 6.48 11.92 26.34
23 21 16 13
96 86 74
89 73
49 37
Note: The characteristics of the mixture of macro- and microcrystalline paraffin wax are shown in Table 11-26. those of the additives in Table 11-27
40 30
I
0
2
I
I
4
6
1
8
10
1
Additive concentrotion, wt-%
Fig. 11-40. Viscosity measured at 140 OC versus additive concentration. I , 2 Copolymers E and D;:3, 4, S,!Polyethylene waxes A , B and C
233
(G) BLENDING OF PARAFFIN WAXES Polyethylene wax 100 %
WO x
Fig. 11-43. Viscosity of three-component systems measured at 140 “C, mmZ/s
the polyethylenes and the copolymer E yield lower melt viscosity products than the copolymer D. From the previous tables and figures it may be concluded that by changing the composition of “three-component’’ blends consisting of macro- and microcrystalline paraffin waxes and polymers, quite a series of products with various properties can be obtained. The relationships between the different properties and composition are preferably represented in the form of triangle diagrams. By way of example, Fig. 11-43 represents the viscosities, measured at 140 “C, of the three-component systems consisting of the macro- and microcrystalline paraffin waxes described in Table 11-25 and the polyethylene wax C described in Table 11-27. The straight lines in the diagram connect the compositions corresponding to identical viscosities. The numbers above these lines indicate the viscosity, in mm2/s. The position of these ‘%oviScosity” lines indicates that viscosity increases more than linearly with increasing polyethylene content. The triangle diagram shown in Fig. 11-44 represents the penetration values measured at 0 “Cfor systems composed of the same components as in the preceding figure. Frequently several and, to a certain extent, contradictory quality demands are simultaneously required from blended paraffin wax products, depending on the field of application. Such simultaneous demands may for instance be some maximum or minimum limit value of penetration measured at 25 “C and vkcosity
232
11. M A N U F A ~ U R EOF PARAFFIN WAXES AND CERESINS FROM PETROLEUM
0
6
3
1
10
Additive concentration, wt-% Fig. 12-41. Drop melting point versus additive concentration. I , 2 Copolymers E and 3, 4, 5 Polyethylene waxes A, B and C
D:
120
110 100 E E
-.
O C
75
0
c
0,
c
a,
d
50
40 30
2c
I-L_ --; -' 1
3
6
1
10
Additive conceptration, w t - o / o
Fig. 11-42. Penetration measured at 35 *C versus additive concentration. I , 2 Copolymers E and D ; 3, 4, 5 Polyethylene waxes A , B and C
234
11. MANUFACTUREOF PARAFFIN WAXES AND CERESINS FROM PETROLEUM
Polyethylene wax 100
Macrocrystalline paraffin wax
Microcrystalline paraffin wax
Fig. 11-44. Penetration of three-component systems measured at 0 "C,0.1 mm
measured at 140 "C.To manufacture such a product, the changes of the properties in question must obviously be considered simultaneously. Figure 11-45 represents the composition curves corresponding to identical viscosity values at 140 "C and penetration values at 25 "C for the above-discussed systems. It may be noticed that the various penetration values at 25 "C can be assigned to identical viscosities at 140 "C by preparing three-component systems having suitable compositions. Figure 11-46 represents tensile strength at 25 "C and melt viscosity at 140 "C, demonstrating that, for unchanged polyethylene content, increased percentages of microcrystalline wax result in simultaneous decrease of tensile strength and increase of melt viscosity. When, on the other hand, microcrystalline wax content is unchanged and polyethylene wax percentage is increased at the expense of macrocrystalline wax content, both tensile strength and viscosity Will increase. The same situation is attained by increasing polyethylene percentage at the expense of microcrystalline wax, leaving macrocrystalline wax content unchanged. If, for some reason, macrocrystalline wax content must be reduced without a change occurring in the desired tensile strength, this can be achieved by an increase of microcrystalline wax accompanied by a relatively large increase in polyethylene wax content.
(G) BLENDING OF PARAFFIN WAXES
235
Polyethylene wox 100 %
100 OI.3 Macrocrystollrne paroffln wax
% Microcrystalline poraffin wox
Fig. 11-45. Penetration measured at 25 "C and viscosity measured at 140 "C of three-componen Penetration, 0.1 mm; Viscosity, mmys systems.
-
------
Figure 11-47 shows the relationships between tensile strength measured at 25 "C and penetration. Penetration decreases with tensile strength increase, that is, the product becomes harder. The proportion of these two properties to one another can, however, be varied within certain limits by suitable variation of composition. As previously mentioned, Bogdanov and co-workers studied the effect of using small percentages of various polymers on the properties of macrocrystalline paraffin waxes. The properties of the starting wax are listed in Table 11-29. The additives' properties are shown in Table 11-30.The concentration of the additives (low-density polyethylene, polyethylene wax and ethylene-vinyl acetate copolymer) varied between 2 and 10 wt-%. Figures 11-48 and 11-49 represent the melting point, viscosity and penetration versus additive concentration. The increase of the melting point was highest With low-density polyethylene: 4 wt- % of this additive gave a melting point of 75 "C, whereas 8 wt- % of polyethylene wax was required to reach this value. If, however, higher-melting products were desired, e.g. in the 75-85 "C range, polyethylene wax appeared more suitable, since low-density polyethylene's effect does not
236
11. MANUFACTURE OF PARAFFIN WAXES AND CERESINS FROM PETROLEUM
Polyethylene wax 100 'Jo
100 Macr-0crystalline paraffin wax
100 'Ja Microcrystalline paraffin wax
Fig. 11-46. Tensile strength measured at 25 OC and viscosity measured at 140 O C of three-component systems. - Tensile strength (pull velocity 50 mmlmin), N/cma; - - - - - - Viscosity, mm*/s
Tubfe11-29. Characteristics of the macrocrystalline paraffin wax used in blending1experiments Melting point, OC Oil content, wt- % Penetration, 0.1 mm at 25 OC at 3OoC at 40°C Viscosity at 100 O c , mm*/s
56.5 0.3 12 17 104 3.05
Table 11-30. Characteristics of the polymer additives Characteristics
Melting point, "C Molecular weight Density, di0 Tensile strength, N/cmz Elongation at break, % Colour
Low-density polyethylene
PoIyethyIene wax
110-120 18,000-25,OOO 0.92-0.93 1200-1600 380
95-100 3500 0.93-0.94 1000-1300 240
White
White
Ethylene-vinyl acetate copolymer
100-102
-
0.94 900 590
Transparent
237
(G) BLENDING OF PARAFFIN WAXES Polyethylene wax 100 %
100 OIo Macrocrystalline paraffin wax
100
Microcrystalline paraffin wax
Fig. 11-47. Tensile strength and penetration of three-component systems measured at 25 "C.
Penetration, 0.1 mm; - - - - - - Tensile strength (pull velocity 50 mm/min), N/cme
significantly change at concentrations exceeding 4 wt- %. Ethylene-vinyl acetate proved far less effective for increasing the melting point; even percentages as high as 10 wt-% only attain 70-75 "C. The figures demonstrate that the highest viscosity increases result from blending with low-density polyethylene; however, the effect of the copolymer is almost as good, while polyethylene wax is worst in this respect. Penetration of the blends is decreased by all three additives, most of all by lowdensity polyethylene. It is of interest that penetration decrease is significant both at 35 and 40 "C. The cited authors developed a method for measuring flexural rigidity. A barshaped test specimen is subjected to flexural stress, and deformation at 30, 35 and 40 "C is recorded in mm. The results were that flexural rigidity of the blends obtained in all three cases investigated is lower compared to the initial paraffin wax. Increase in tensile strength could be attained especially by adding low-density polyethylene; the 135 N/cmZvalue of the initial wax was increased to 198 N/cm2 by the effect of 2 wt-% of low-density polyethylene. Similar concentrations of
238
11. MANUFACTURE OF PARAFFIN WAXES AND CERESINS FROM PETROLEUM
100 r
LO
1
-
0
2
4
6
8
Polymer content, w t - %
90
7-
80 70
10
E 6o
E
50 c
0 ._
2
40
c
a
20
" Polymer content, wt-"h
1-
at 25 "C
2
4
6
8
:-
Polymer content, w t - %
Fig. 11-48. Characteristics of blended paraffin waxes versus additive concentration.
0 Polyethylene wax,
A Low-density polyethylene, x Ethylene-vinyl acetate copolymer
polyethylene wax and ethylene-vinyl acetate copolymer increased tensile strength by only a slight amount. Water vapour permeation of packaging materials coated with the blends was reduced by 25-40%, using any of the three additives in concentrations of 2 wt- %. The cited examples clearly show the wide potential of blending. In this way, paraffin wax manufacturers are capable of meeting widely varying requirements. Obviously, further prospects can be opened up by the appropriate variation of the properties of macro- and microcrystalline waxes used as the starting material, and by developing four- or even five-component systems simultaneously containing two or three types of polymer.
( G ) BLENDING OF PARAFFIN WAXES 90
239
r
Fig. ZI-49. Penetration of blended paraffin waxes measured at different temperatures versus additive concentration. Curves I , 2, 3: 25 ' C ; 4, 5, 6: 30 'C; 7,8,9 : 35 OC; 10, 11, 12: 40 "C. 0 Polyethylene wax, A Low-density polyethylene, X Ethylene-vinyl acetate copolymer
Literature Bogdanov-Parfenova: Khimiya Tekhnol. Topl. Masel, 21, No. 1, 7 (1976). Brit. Pat. 1 039 989. Brit. Pat. 1 066 415. Brotz, W., Fette, Seijen, Ansfr-Miftel,62, 31 (1960). Markaryan-Kazakova: Neftepererab. Neftekhim., No. 3, 3 (1970). M6zes-Zsida-M. FBnyi: Znt. Chem. Engng., 8 , Process Inds., 268 (1968). Nagrodsky, J. R., Neftepererab. Neftekhim., No. 10, 38 (1964). Sterk, B. J., Adhusion, 7, 277 (1963). Teubel-Schneider-Schmiedel-Peper : Chem. Tech. Berl., 16, 427 (1964). Turov-Geshman-Kushnir-Marintseva: Neftepererab. Neftekhim., No. 6, 25 (1969). rr
P
D-,
u.0. I
q o o c cnc1
U L . L 772 JVO.
111. APPLICATIONS OF PARAFFIN WAXES AND LIQUID PARAFFINS
By means of the various technologies discussed in the previous chapter, a wide assortment of paraffin waxes, paraffin-derivatives and products containing such waxes, showing a great variety of chemical composition and properties, can be manufactured in the course of processing paraffin crudes, or by complementary operations. At the present time, choosing the most appropriate and economical use for paraffin waxes and liquid paraffins has already become an important problem in the processing of paraffin crudes. The potential uses of liquid paraffins and paraffin waxes are large and very diverse. Essentially they can be classified into three main groups: (i) utilization without any chemical transformation, (ii) utilization as feedstock for the chemical industry, (iii) manufacture of proteins and other products by the biological transformation of paraffins. The present chapter will deal with the uses of petroleum paraffins under the above headings.
(A) Direct applications of paraffin waxes and liquid paraffins The areas of direct application of macro- and microcrystalline paraffin waxes and liquid paraffins will be discussed under the following headings : 1. Applications in the paper industry. 2. Applications in household chemicals (polishes, creams, candles, etc.). 3. Application in cosmetics. 4. Applications in the food industry and in agriculture (cheese-coating, poultry processing, fruit preservation, etc.). 5. Miscellaneous applications (matches, textiles, electrical industry, pyrotechnics, pencil manufacture, precision casting, wax emulsions for building construction, etc.).
(A) DIRECT APPLICATIONS
24 1
Literature Bennett, H., Commercial Waxes. Chemical Publishing Co., New York (1956). Bennett, H., Zndustriul Waxes. Chemical Publishing Co., New York (1975). Guthrie, V. B. (Ed.), Petroleum Products Handbook. McGraw-Hill Book Co., New York (1960). Inzelt, I., Vegyi receptek (Chemical Formulations). Miiszaki Konyvkiad6, Budapest (1967). Warth, A. H., The Chemistry and Technology of Waxes. Reinhold Publishing Co., New York (1956).
1. Paraffin waxes in the paper industry
Although the use of plastics steadily increases in packaging, cellulose-based papers, cardboard and corrugated paperboard still remain the most important packaging materials. Besides other additives, paraffin waxes and wax-containing auxiliary products are largely used for improving the properties of paper, cardboard and corrugated paperboard. The packaging industry is one of the most important consumers for direct applications of paraffin wax. This is due mainly to the following factors: - paraffin waxes are inexpensive, - they are available in practically unlimited quantities, - their grades do not vary. In fields where the paraffin waxes themselves are not capable of meeting the necessary requirements, their functional properties can readily be improved by the addition of natural or synthetic waxes or polymers. Such products can be utilized in the paper industry using simple and rapid operations. Paraffin waxes, with suitably selected plastics additives, have favourable properties :good adhesion, permanent gloss, impermeability to water and water vapour, broad ranges within which viscosity, plasticity and mechanical strength may be varied. Para& waxes are used in the paper industry especially for impregnation, coating and laminating. In addition, paraffin waxes are used as additives to paper sues.
(a) Paraf i n waxes for impregnation Impregnation is used both during paper manufacture and for the finishing of the paper. Paper has a capillary structure which causes it to absorb moisture. This property is often inconvenient and can be mitigated by impregnation with various additives, e.g. paraffin waxes. The formed paper web can also be impregnated by leading it, by means of guide rolls, through the solution or melt of the impregnating material. Shaped paper products, such as containers, etc., can also be subjected to impregnation. Various methods have been developed for the impregnation of paper webs, either by dipping the web into the impregnating bath and subsequently leading it between heated pressure rollers, or by spraying the impregnating material onto 16
242
111. APPLICATIONS OF PARAFFIN WAXES AND LIQUID PARAFFINS
the web before the heated rollers. The excess impregnating material is squeezed out by the pressure rollers. The uptake of impregnating material depends on the edge pressure of the roller pair, on the absorptivity of the paper, on the concentration of the impregnating solution or on the temperature of the melt, on the temperature of the web entering the impregnating material and on its speed. If a solution is used for impregnation, the operation is followed by drying to remove the water or organic solvent. In the case of melt impregnation, the impregnated paper web is cooled to ambient temperature before winding up. Depending on the type of operation, impregnated papers are water-repellent or impermeable to water. The impregnating substance uptake is defined by the above-cited conditions. It usually varies between 3 to 35 g/m2. The substances suitable for impregnation are macro- and microcrystalline paraffin waxes, their blends, and modified low melt-viscosity paraffin waxes containing a maximum of 10 wt-% polymer. The polymers used for this purpose are polyethylene, polyisobutylene, ethylene-vinyl acetate copolymer, butyl rubber, etc. Table ZZI-1. Characteristics of the product Paraffin-60 used for the impregnation of paper and paperboard ~~
~
Density at 100 OC (TGL 14812)
0.758-0.762
Congealing point, OC (TGL 0-51556)
55-65
Penetration at 25 'C,1/10 mm (TGL 12622)
40-60
Neutralization value, mg KOH/g (TGL 0-51558)
0.10-0.20
Ash, wt-% (TGL 0-51768) Oil content, wt- %
0 -7
Table 111-1 lists the characteristics of a product (trade name Paraffin-60) manufactured in the German Democratic Republic for the impregnation of paperboard and paper. It consists of C,-C, paraffin hydrocarbons.
(b) Parafin waxes in coatings In coating, a film is formed directly on the surface of the paper, without applying an adhesive between the film and the paper. In addition, the film is an unbroken, glossy, flexible, smooth layer, it is waterproofing and impermeable to water vapour. Also, it protects the legibility of print applied before coating. Coating is generally carried out with liquid film-forming material. Exceptions are metal coats, applied in the form of vapour sprays, and films polymerizing on the surface from the gas phase. However, these procedures have not yet been
(A) DIRECT APPLICATIONS
243
introduced widely into industrial practice. Liquid film-forming materials are applied as melts, solutions or dispersions. The advantage of using melts is the absence of the solvent removal operation, with attendant economies in energy and solvent. However, the procedure can only be applied, if - the melt of the coating material behaves as a low-viscosity liquid and its viscosity is constant at a given temperature; - the coating material is not heat-sensitive, i.e. its composition, molecular weight, colour, odour, etc. does not change under the effect of heat; - the temperature at which the viscosity of the melt is satisfactorily low does not exceed 60 to 140 "C. The equipment developed for melt-coating is based on rollers, discharge devices or nozzles. For high-viscosity hot-melt coating special discharge slots, so-called curtain-coating equipment has been developed, forming a film curtain under which the shaped products pass and become coated. The melt uptake is controlled according to the viscosity of the melt and the porosity of the paper material; 10 to 20 g/m2 paraffin wax application yields a continuous layer. Three types of melt are used for coating : - paraffin waxes with a maximum 10 wt-% polymer content, with melting points only slightly higher than that of the paraffin wax, and with low melt viscosities ; - waxes and paraffin waxes with 20 to 35 wt-% polymer content (so-called hot-melts), having higher melting points than those of the former type, and medium melt viscosity values ; - extrusion coating materials with high melting points and high melt viscosities. For coating with paraffin wax products it is expedient to use suitable blends of macro- and microcrystalline waxes. The macrocrystalline waxes lend gloss, light colour, stiffness and transparency to the coating, the microcrystalline waxes provide low permeability to water vapour and fatty substances, adhesion and high flexibility. The particularly important duty of the microcrystalline wax components is to preserve impermeability to water vapour of packaging materials (corrugated paperboard for machines, instruments, food, containers, cups, etc.) under the effect of mechanical loads. The difference in water vapour permeability between macro- and microcrystalline paraffin waxes is scarcely detectable. However, the papers coated with these waxes show significant differences, since microcrystalline waxes, owing to their higher flexibility, form layers more resistant to mechanical effects. For this reason, paraffin wax products for the paper industry always contain microcrystalline waxes. According to whether their function is coating or increase of hardness, Rumberger stipulated the requirements listed in Table 111-2 for microcrystalline paraffin waxes. Waxes for coating originate from residual oils, and improve the melting 16*
244
III. APPLICATIONS OF PARAFFIN WAXES AND LIQUID PARAFFINS
Table 111-2.Properties of microcrystalline paraffin waxes suitable for coating and improvement of hardness
'
Microcrystalline waxes
Properties
Hardness-
Melting point, OC
60-75
75-100
Penetration at 25 O C 0.1 mm
18-28
<5
Oil content, wt- % n-Alkane content by the urea method, wt-%
0.5-2.0
0.0-0.1
20-40
50-90
point and the vapourproofing properties of the macrocrystalline waxes. Microcrystalline waxes for improving the hardness and melting point of macrocrystalline waxes are products obtained from tank waxes or petrolatum by de-oiling. The surface gloss obtained with paraffin wax products can be increased with hard waxes as additives. The further advantages of these components consist (a) in their anti-blocking property, i.e. surfaces placed one on one another do not stick together; and (b) in their flexibility, ensuring that the film does not crack during use. Table 111-3 sums up the characteristics of a paraffin wax product suitable both for coating and impregnating paper. The product ensures good mechanical strength for the raw paper. It improves resistance of the papers to cracking, and reduces their permeability to water and water vapour. Owing to the optimum oil Table 111-3.Characteristics of a paraffin wax product suitable for the impregnation and coating of paper
Colour Structure Melting point, OC (DIN 51556)
Yellow to light brown Fine crystals 65-68
Drop melting point, OC (DIN 51801)
Penetration at 25 OC, 0.1 mm (DIN 51579) Viscosity at 90 OC. mmx/s (DIN 51562) Oil content, wt- % (DIN 51571) Neutralization value, rng KOH/100 g (DIN 51558) Density at 90 O C (DIN 51757)
74-77 2540 7 3-5 0
0.7665-0.7675
(A)
245
DIRECX APPLICATIONS
content, the wax layer has a high flexibility and smooth surface. Due to the high drop melting point, packaging paper treated with the product can also be used in warm climates. The low viscosity of the melt allows simple processing. Among polymers containing p a r a h wax products, the three-component products consisting of polyethylene, macrocrystalline p a r a h wax and microcrystalline paraffin wax are prominently good. Coatings made with such products are glossy, impermeable and do not tend to block. Polyethylene waxes for such three-component systems have the following properties: molecular weight -2000, viscosity at 120 "C 1300 to 1700 mmz/s, melting point 90 to 95 "C; slightly soluble at ambient temperature in alcohols, esters, ketones ; readily soluble in warm benzene, toluene, xylene, turpentine; insoluble in water. Such polyethylene waxes mix readily with paraffin waxes at temperatures around 110-120 "C, and only slightly increase the melt viscosity of the paraffin waxes. Increased gloss can be observed with percentages of the additive as low as 2 wt-x, and the blocking temperature is also higher. To achieve the gloss, melting point, blocking temperature, abrasion resistance and flexibility required in specifications, 3 to 5 wt-% of the polyethylene additive must be used. Still higher gloss is obtained by 6 to 10 wt-%. In Table 111-4, the properties of a product manufactured from macro- and microcrystalline paraffin waxes and a suitably chosen polyethylene wax are presented. This product worked well for the safe sealing of flasks and containers used to pack goods sensitive to air and moisture. TabIe 111-4. Properties of a product intended for vacuum sealing and moistureproofing of containers (Trade mark: PB XII; manufacturer: VEB Hydrierwerk Zeitz) Colour Structure Melting point, "C (DIN 51556) Drop melting point, "C (DIN51801) Penetration at 25 ' C , 0.1 mm (DIN51579) Viscosity at 90 "C, mm*/s (DIN51562) Fraass breaking point, "C Neutralization value, mg KOH/100 g (DIN51558) Density at 90 "C (DIN 51757)
White to paleyellow Microcrystalline 52-56 55-59 20-35 7-9
0 0.767-0.112
246
111. APPLICATIONS OF PARAFFIN WAXES AND LIQUID PARAFFINS
Milk cartons, butter and ice-cream cartons, containers for deep-frozen food, etc. require coatings allowing the filling of the containers at higher temperatures, and, therefore, higher melting points of the product used for coating. The characteristics of such products, also used for coating packaging materials for bread, meat, candies, etc., are listed in Table 111-5. The paraffin wax products contain polyethylene wax. Table 111-5. Characteristics of paraffin wax products suitable for coating and impregnating paper and paperboard for food packaging -
~~~
I
Characteristics
d ~-
Melting point, OC
__
--
73-77
68-72
57-61
~
-
Penetration at 25 "C, 0.1 mm
12
11
10
10
Viscosity at 100 OC, mmp/s
5-1
5-7
6-8
7-9
Neutralization value, mg KOH/g Sulfuric acid test
__
76-80
0
0
0
0
negative
negative
negative
negative
0
0
0
0
Polycyclic aromatics content, wt-
%
In curtain coating the composition of the coating material, especially its additive content, may be varied within a wide range. The viscosity of these hot-melts may be as high as 10 to 12 Pa * s at the temperature of coating. In Table 111-6 the viscosity values and coating speed for some hot-melts used in curtain coating are summarized. Table 111-6. Viscosity of hot-melts for curtain coating, versus the coating rates and the coating temperatures in practice
__
Viscosity of product, Pa.s Codemark
1
~~
1 5 6 10
/----
at the tempera-1 ture of coat- I ing
at 120°C
2.21 3.55 7.00 6.00
3.44 7.40 60.00 39.00
1
1 co$Kpiqte,
I I
___
305 305 365 230
I I
Coating temperature, "C
135 143 191 182
Table 111-7 lists the significant properties of some hot-melts and the functional properties of corrugated paperboard coated with them. The data in this table were obtained with coating materials resulting from Hungarian pilot-scale manufacture. A special field of application for wax-coated papers arises from the possibility of sealing prepackaged goods by short-time heating under pressure. These applications require specialized hot-sealable paraffin wax products. The seals obtained
247
(A) DIRECT APPLICATIONS
Table 111-7.Properties of hot-melts prepared with high-melting microcrystalline paraffin wax, and of coated products Properties
~
PHM-52
i
Melt index of additive, g/10 min Viscosity, mmz/s at 120 O C at 14OoC Penetration, 0.1 mm (ASTM, 100 g/5 s at 25 O C at 35 Oc Drop melting point, O C (ASTM D-
PHM-54
I
PHM-55
16 3150 1790
6 1400 8 20
6 3800 2190
11 15
12 19
10 17
75
127)
Fraass breaking point, "C Tensile strength, N/cmZat 25 "C, draw rate 50 mm/min Water vapour permeability, g H20/m2,24 h flat corrugated Fat resistance, h, flat corrugated Air permeability, cma/s * cm2 Frost resistance, "C Fuchsine test Gloss number (Richter)
1
- 26
77
- 25
76
-28
245
2.4 10.5 48
-
0.02 -25
-
2.88
2.1 19.6 48 12 0.04 -45 10-15 2.08
3.0 4.7 48 25 0.02 -45 15-20 2.06
with plastics products are stronger than those obtained with paraffin wax-based products. However, in many cases the latter are preferable for this very reason, because the lower seal strengths allow the package to be opened without also destroying the whole packaging material. This is an important advantage when the content of the package is not consumed all at once, e.g. for bread packages. The strength of the seal depends both on the adhesion forces between the paper and the wax, and on the cohesion forces within the paper and the wax. These forces can be controlled by the temperature and time of the sealing operation, by the amount of wax applied, by the cooling speed after hot sealing, by the composition of the wax product and by the grade of the paper. (c) Parafin waxes for lamination
Lamination is the bonding operation of two or more webs, films or foils made of the same or of different materials (paper, metal foils, plastics films, etc.). Lamination allows the combination of the advantages of different types of packaging materials and the minimizing of their disadavantages. The number of combinations is practically unlimited ;however, the most wide-spread combination is that of aluminium foil and paper, especially for packaging butter, margarine, creams, bread, sweets and soaps. Laminates of cellophane to cellophane
248
111. APPLICATIONS OF PARAFFIN WAXES AND LIQUID PARAFFINS
should also be mentioned. They are suited for strong, transparent packaging materials impermeable to fatty substances, gases and aromas. The main laminating processes are: - wet lamination using aqueous adhesives (silicates, starches, resin emulsions, latices, aqueous glues); - so-called dry lamination using adhesives in organic solvents. The adhesives are varnish resins, rubbers, etc.; - hot-melt lamination eliminating any use of solvents. The adhesives are paraffin waxes, microcrystalline waxes, paraffin waxes with polymer additives. The adhesive is applied from a heated tank onto one web, which is then joined with the other web, and finally the adhesive is solidified by passing over cooling rollers. This lamination procedure allows high speeds. Excellent packaging materials for e.g. macaroni, biscuits, cakes can be manufactured; - so-called stretch-lamination, in which paper is laminated with heat-plasticized, considerably stretched plastics film. Among hot-melt adhesives, waxes and paraffin waxes alone yield only low bond strengths, but this can substantially be improved by adding synthetic thermoplastic adhesives. The viscosity of the melt is controlled by temperature. Compositions whose viscosities are suitable within the 120 to 200 "C temperature range lend themselves readily to processing. The most widely used laminates manufactured by the hot-melt process are combinations of paper with aluminium foil, paper with cellophane and paper with plastics films. The grade of the microcrystalline paraffin waxes used as components of hotmelt adhesives depends on the area of application. For instance, if porous layers are to be bonded, microcrystalline wax with good cohesive properties is required, with low oil content and no low-melting fractions. Such wax will not cause stains on the surface of the packaging material, and the low-melting fractions will not exude. According to Rumberger, the microcrystalline paraffin waxes best suited as the adhesive components for various purposes should possess the following characteristics: melting point 54-58 "C,penetration at 25 "C 20 to 35 10-1mm, oil content 1 to 15 wt-%, n-alkane content determined by the urea method 20 to 35 wt-%. (d) ParafiE waxes as additives to paper sizes Paraffin waxes are used for sizing to reduce the moisture absorption of paper. Paraffin waxes or their emulsions used as additives promote the uniform distribution of the size in the fibrous structure of the paper, since the wax particles separate the resin adhesive particles from one another, thus preventing their agglomeration. Another advantage of adding paraffin wax is that it compensates the effect of the resin adhesives to mix with the various pigments. Thereby printability is improved and efficiency of printing is increased. Also, the addition of 1 to 5 wt-% paraffin wax results in a substantial moisture repellent effect, owing to an increase of the surface tension of the adhesive. It is preferable to introduce the paraffin waxes into the system as emulsions containing usually 35 to 50 wt-%
(A) DIRECT APPLICATIONS
249
of solids. Particle size in the emulsion varies between 0.5 and 5 pm. Microcrystalline paraffin waxes or blends of micro- and macrocrystalline waxes with melting points between 50 and 65 "C are used for these emulsions.
Literature Arabian, K. G., TAPPI Bull., 41, 275 (1958 June). Brown-Turner-Snith: TAPPI Bull., 41,295 (1958 June). Butterworth, J. F., TAPPI Bull., 43, Suppl. 26A (1960 June). Coating, 7, No. 11, 333 (1974). Clary, B. H., Paper Film Foil Convert., (1955 Sept). - :Paper 2nd. Paper, 27, 1679 (1945). Feldmann, J., Coating, 8, No. 5, 126 (1975). Fox, R. C., TAPPI Bull., 41, No. 6, 283 (1958). Freund-Keszthelyi-Mc5zes: Chem. Tech. Berl., 582 (1965). Gabriel, F., Wbl. PapFabr., 104, No. 2, 71 (1976). Helyes-Keszthelyi-Kbnya-Knerczer : Anyagmozgatas-csomagolds, 15,264 (1970). Hughes-Walker: TAPPI Bull., 41, No. 6, 280 (1958). Keszthelyi-Mbzes: Comm. of the Hungarian Oil and Gas Research Institute, 9 , 185 (1968). Keszthelyi-Mbzes-Szirbek: Ropa Uhlie, 13, No. 1, 27 (1971). Macomber, L. H., TAPPI Bull., 40, No. 11, 174 (1957). Matscholl, G., Fette, Seifen, Anstr-Mittel, 64, No. 2, 153 (1962). MelzerovB, M., Papir Celul., 24, No. 7 (1969). Muhlemann, M., Celuloza Hirt., 18, No. 4, 173 (1969). Proceedings of the Seminar on What's New in Equipment: Waxes and Hot Melt, Chicago (1968). Seubert-Andrews: TAPPI Bull., 36, No. 6, 174 (1953). Sterk, B. J., TAPPI Bull., 45, No. 11, 179 (1962). Thorpe, T. C. G., J . Inst. Petrol., 37, No. 330, 275 (1951). Tuttle, J. B., Encyclopedia of Chemical Technology. Vol. 10. Interscience Publ. Co., New York (1953). Yates, W. J., Paper Film Foil Convert, No. 3,41 (1956).
2. Application of parafin waxes in household chemicals Various grades of macro- and microcrystalline paraffin waxes are used in household chemicals. The main consumers for p a r a f i waxes are polishes and candles. Paraffin waxes are used as additives in many polishes, and a substantial part of candle material is paraffin wax.
(a) Polishes wilh parafin wax as an additive Polishes are materials which, on the one hand, increase the gloss of the treated surface or restore its initial gloss, and on the other hand, protect the surfaces against mechanical and chemical effects, and thus prolong the service life of the object. Solvent-containing, liquid polishes have a cleaning effect, too.
2 50
111. APPLICATIONS OF PARAFFIN WAXES AND LIQUID PARAFFINS
Satisfactory polishes form uniform, glossy films free from cracks, ensuring protection against mechanical effects for a long time. Other requirements are good storability and ease of application to the surface to be treated. These properties depend on the solid components of the polish, and on the properties and amount of solvent. Polishes containing considerable amounts of paraffin waxes include floor, furniture, shoe and automobile polishes. Polishes usually contain several kinds of natural and synthetic waxes, paraffin waxes, resins, solvents, auxiliary agents and water. As well as the requirements of the consumer, cost of the components is an important factor in the formulations. This is one of the reasons for the tendency to replace a part of the relatively expensive natural and synthetic waxes by less expensive paraffin waxes. The two basic types of polishes are the emulsions products and the solventbased products. The water or organic solvent evaporates in the course of application, and a polishable film, or a glossy film needing no further polishing, is left behind on the treated surface. The consistency of solvent-containing polishes greatly varies with their solids content. Solid polishes usually contain more than 35 wt-% of solids, paste-like products less than 35 wt-%, and liquid products less than 15 wt-%. The basic materials for polishes are partly natural waxes and their chemically and physically refined derivatives, and partly synthetic products. The origin of natural waxes is diversified: carnauba wax, for example, is obtained from a palm, bees-wax is produced by the insect, and crude montan wax is extracted from lignite. Refined montan wax, chemically transformed into acid esters or partly hydrolyzed, is widely used. The synthetic waxes include products obtained by esterification of fatty acid fractions from the oxidation of macro- and microcrystalline paraffin waxes, as well as polyethylenes with average molecular weights below 10,OOO, polyethylene oxides and esters, etc. Waxes of vegetable origin, montan wax and montan-based waxes are used in relatively high quantities for household chemicals. They have the advantage of forming stable emulsions with non-ionic emulsifying agents, while polyethylene waxes are more difficult to emulsify. Polyethylene oxides and esters are easier to emulsify. The solvent absorption and retention capacity of the solid components are important factors in the manufacture of polishes. The solvent absorption capacity of ceresins, macrocrystalline parafin waxes and ozokerite is low as compared to that of, say, carnauba wax or candelilla wax. It is a general rule that the solvent absorption capacity decreases with increasing melting points. Exceptions to this rule exist, however. Bees-wax absorbs substantially less solvent, and bleached montan wax substantially more than predicted by their melting point. Retention of the solvent also varies with different waxes. For example, evaporation of the solvent from ozokerite pastes is accompanied by a uniform contraction of the whole mass, while solvent evaporates mainly from the surface layer of pastes made from paraffin waxes. The solvent retention capacity of microcrystalline paraffin waxes is relatively high. Evidently, solvent absorption and
(A) DIRECT APPLICATIONS
25 1
retention capacity of pastes prepared from waxes and paraffin waxes depends both on temperature and on the boiling point of the solvent. If the solvent evaporates too rapidly from the paste during its application, uniform thickness of polish will not be achieved. High-boiling solvents facilitate application of the paste, but in such cases the film might be too thin, impairing both surface gloss, and durability of the film. Storability, ready applicability and good film quality also depend on the properties of the solid components of the polish. At low temperatures, or reduced water or solvent content, the wax components will precipitate, depending on their chemical composition, in a crystalline or gel structure. This again affects such properties as storability without sedimentation, solvent retention, uniformness of film formation, etc. For this reason, the ratio of crystallizing and gel-forming waxes must be chosen to conform with the proposed uses of the product in question. Application becomes difficult if the product contains sticky waxes. For instance, bees-wax in itself is disadvantageous from this point of view, owing to its high plasticity. Carnauba and candelilla waxes yield glossy surfaces, but to achieve uniform application, they must be blended with montan wax or ceresin, and to ensure satisfactory plasticity of the film, bees-wax must be added. Suitably selected paraffin waxes improve gloss, but greater amounts may result in an opaque surface. Another important factor in the choice of the solid components and their ratios is the requirement to form a mechanically resistant film. Bees-wax, for instance, increases the toughness of the film. Certain soaps, e.g. calcium stearate, improve toughness and add abrasion resistance. The boiling point of the solvent and the melting points of the solid components also affect durability of the film. From this point of view, excessively high-boiling solvents and excessively lowmelting solids are detrimental. For certain fields of application, it is of importance that polish components should be chosen which will not melt when exposed to solar radiation. The solids content of emulsion preparations consisting of the above-mentioned waxes and paraffin waxes varies between 15 and 30 wt- %. Their main constituent is water. Tn addition to the emulsifying agent, some products also contain some organic solvent, improving the cleansing effect of the polish. The emulsions are either of the water-in-oil or of the oil-in-water type. Their consistency depends above all on their solids content, and varies from creams to free-flowing liquids. Both non-ionic and ionic emulsifying agents, as well as their mixtures may be used. Ethoxylated fatty alcohols and alkylphenols are widely used non-ionic emulsifiers for polishes. For ionic emulsifying agents, an interesting process can be mentioned; waxes with high acid values are reacted with polyfunctional amines. The resulting amine soaps ensure that stable emulsions Will be formed.
252
111. APPLICATIONS OF PARAFFIN WAXES AND LIQUID PARAFFlNS
Floor polishes
Floor polish coatings serve the purpose of preventing water, vapour and air penetrating into the floor and protecting the flooring against wear. Wood floors are usually coated first with a priming wax layer, and subsequently, if necessary, with a liquid polish. After evaporation of the solvent, the film remaining is rubbed to produce a gloss. Solid floor polishes are pastes or solventless polishes. Liquid polishes yield either surfaces requiring rubbing for gloss formation, or yield directly glossy surfaces after drying. Solid floor polishes
Floor pastes are usually manufactured from carnauba or some corresponding wax, montan wax, macrocrystalline paraffin wax and ceresin. Total solids content is about 30 wt-%. The solvent is usually a mixture of white spirit (boiling range 130-200 "C) and turpentine oil (boiling range 150-180 "C). Carnauba or corresponding waxes and montan wax serve to provide the gloss and hardness of the coat. The paraffin waxes, which are softer than the former waxes, ensure proper consistency of the paste and increase solvent retention capacity. The carnauba wax content seldom exceeds 12 wt-%. Since wood absorbs paraffin waxes readily, their content is kept around 10 wt-%. Within these general ranges the formulations for floor pastes vary widely. To increase flexibility of the film, bees-wax is often added. This, as well as high-melting ceresins and esterified waxes promote smoothness of the coatings. A typical floor polish formulation is presented in Table 111-8. Table 111-8. An example of floor polish formulation -_ Component
Carnauba wax Refined montan wax Ceresin 54 O c melting-point macrocrystalline paraffin wax White spirit Turpentine oil
Percentage,
1
wt-%
12 5 3
11 60 9
An important characteristic of polishes is solvent uptake. Table 111-9 lists the solvent uptake capacity of some natural waxes and paraffin waxes, indicating the amount of turpentine oil required to yield identical penetration. Even if the structure of the product after manufacture is a perfect gel, crack$ may be formed in the course of storage, and the spreading properties of the wax may deteriorate. This is the result of poor solvent retention of the waxes. 'This
253
(A) DIRECT APPLICATIONS
Amount of turpentine oil rsquiredto
Solid3
100 g of the
Mltrid. 8
disadvantage may be avoided by using waxes with less adhesion and solvents with slower evaporation. Softer waxes and paraffin waxes also lessen desiccation. The solvent retention capacity can be measured by the weight loss under defined conditions. Table 111-10 presents the weight losses that occur in various gelstructure pastes owing to solvent evaporation. 4 cm3 of turpentine oil was mixed with 2 g solids in the manufacture of these pastes. Esterified synthetic waxes, based mainly on montan wax and containing calcium soaps are frequently used for solid floor polishes. These components increase the Table IZZ-10. Solvent retention of a paste prepared from various waxes, paraffin waxes, calcium stearate and stearic acid (Testing conditions: at 25 'C, in uncovered glass vessels)
____
Evaporation loss, wt- % after
Solids ~-
24h
..
_ _ _ _ _ _ _ _ _ ~
Macrocrystalline paraffin wax Microcrystalline paraffin wax (ceresin) Carnauba wax Candelilla wax Esparto wax Montan-base, partly saponified wax Japan wax Calcium stearate Stearic acid
j
48h
1
72h
1
7days
0
0
7.3 9.2 1.8 7.3
9.0 16.5 3.7 11.0
18.0 34.9 5.5 23.4
7.3 12.6 14.7 1.8
14.7 20.0 23.5 3.6
39.7 32.5 45.2 9.0
0
0
3.6 5.5 0.5 3.6 0.5 5.5 7.3 0.9
254
111. APPLICATIONS OF
PARAFFIN WAXES AND LIQUID PARAFFINS
hardness of the paraffin constituents and significantly improve gel formation even in small amounts. With turpentine oil, the synthetic waxes yield lustrous surfaces. Synthetic, acid or esterified waxes based on montan wax possess high solvent uptake capacities, but relatively low solvent retention, and, therefore, cracks may appear in the pastes if these waxes are present in exceedingly high concentrations. In turn, solvent uptake of paraffin waxes is low, but solvent retention is excellent. Thus, relatively high amounts of paraffin wax combined with small amounts of montan wax-based synthetic waxes yield readily gelling pastes with good solvent retention. The carnauba wax content can be thereby reduced without impairing the grade, resulting in lower cost polish. Table 111-11 contains such a formulation, with only 4 wt- % carnauba wax in a total of about 29 wt-% solids. Tabte 111-II.Composition of a floor polish containing high percentages of paraffin wax and small amounts of natural and synthetic waxes Components
Macrocrystalline paraffin wax Microcrystalline paraffin wax (ceresin) Montan wax Carnauba wax Bees-wax Japan wax Montan-based, partly saponified wax Turpentine oil White spirit
12.1 7.5 1 .o 4.0
2.0 2.0 0.5 25.2 45.7
Solventless floor polishes consist of macro- and microcrystalline paraffin waxes, bees-wax and montan wax. Inorganic materials such as talcum, and calcium, zinc and aluminium stearate additives are also used. Liquid floor polishes
With liquid floor polishes a gloss is obtained by rubbing the film formed after applying the polish. The components of the polishes are the same as those of pastes, the only difference being the solvent content. The solids content of liquid floor polishes varies between 8 and 15 wt-%. The most widely used components of floor polish emulsions are bees-wax, carnauba wax, candelilla wax, japan wax, and macro- and microcrystalline paraffin waxes. An example of a formulation for a liquid emulsion floor. polish of the oil-inwater type, but also containing organic solvent, is shown in Table 111-12.
255
(A) DIRECT APPLICATIONS
Table 111-12. Composition of a liquid floor polish emulsion containing organic solvent Components
__..-_____
Refined carnauba wax Montan wax base ester wax Macrocrystalline paraffin wax White spirit Alkylphenol (15-20 ethox) Alkylphenol (3-6 ethox) Water
1
j
_
Percentage, wt-%
_
~
5 2 9 25 4 1 54
Recently, plastics floorings of various types have been gaining more and more ground. It is obvious that polishes containing organic solvents are not suited for such floorings. Therefore, emulsions whose liquid component is water only have become of great significance in the course of the past 10 to 15 years. After application, these polishes yield high-gloss surfaces by slight rubbing or no rubbing Table 111-13. Emulsion for cleaning plastics surfaces Components
Emulsion containing 25 wt- % montan-based wax Paraffin sulfonate Fatty alcohol (15-22 ethox) Butyl glycol 25 % ammonia solution Water
Percentage, wt- %
70 8 4 10 3 5
at all. For cleaning plastics surfaces, products have also been developed that consist essentially of wax emulsions and detergents, e.g. paraffin sulfonates. An example for such a formulation is presented in Table 111-13. Furniture polishes
The duty of furniture polishes is to remove dust and other dirt from the surface of the furniture and to increase its gloss. The requirements for the composition of the polish are that it must not remove the initial coating (e.g. varnish), nor cause a sticky or greasy feel, but yield a smooth, lustrous surface. The five large groups of furniture polishes are furniture oils, oil-in-water type emulsions, wax emulsions, furniture pastes and silicone-containing furniture polishes. Paraffin waxes are used in two of these groups, in wax emulsions and in furniture pastes.
256
111. APPLICATIONS OF PARAFFIN WAXES AND LIQUID PARAFFINS
The most widely used solid components of wax emulsions are carnauba wax, beeswax, macro- and microcrystalline paraffin waxes, stearic acid and various estersed synthetic waxes. A wax emulsion furniture polish formulation is presented in Table 111-14. Table 111-14. Composition of a high carnauba wax content furniture polish emulsion Componects
Microcrystalline paraffin wax Carnauba wax Bees-wax Stearic acid Turpentine White spirit Triethylamine Water
8 16 8 4
14 13 2 35
Furniture pastes are non-aqueous preparations with paste-like consistencies. Their components are essentially the same as those of wax emulsions. As well as white spirit and turpentine oil, tetralin and hexalin are also frequently used solvents. The composition of a furniture paste is presented in Table 111-15. Table 111-15. Formulation of a furniture paste containing candelilla wax Components
Macrocrystalline paraffin wax 100 OC Synthetic wax, m.p. Candelilla wax White spirit Tetralin Hexalin N
30.0 23.0 2.0 39.0 1.5 4.5
Automobile polishes
The duties of automobile polishes are manifold: they cleanse the car body and the metal decorating elements from dirt, e.g. dust, oil spots, etc., they restore the initial gloss and smoothness of the varnish, and form a thin continuous film that will protect the varnish coat against weathering for some time. In addition to the usual %axes, paraffin waxes, plasticizers, emulsifiers and solvents, automobile polishes also contain abrasive powders, which remove dust particles adhering strongly to the surface and cause roughness. Such strong adhesion is the result of paint and varnish softening by the heat of sun radiation or by the heat of the motor.
257
(A) DIRECT APPLICATIONS
The abrasives most widely used for this purpose are fuller’s earth, silica, diatomaceous earth and tripoli. Automobile liquid polishes are usually aqueous emulsions with an organic solvent content to increase the cleaning effect. The abrasives are maintained in suspension in the polishes, the total solids content usually exceeding 25 wt-%. Table 111-16 presents the composition of a liquid emulsion polish containing two different abrasives. Table 111-16. Composition of an automobile liquid polish containing two different abrasives Percentage, wt- %
Components
Macrocrystalline paraffin wax Carnauba wax Bees-wax Tripoli earth Bentonite Glycerol oieate Triethanolamine stearate White spirit Kerosine Water
1.5 2.5 1.5 12.0 2.5
3.5 5.0
33.0 2.5
36.0
Table IZZ-17. Composition of an automobile polish paste containing no abrasive Components
Microcrystalline paraffin wax Ozokerite Carnauba wax Candelilla wax Kerosine White spirit
I
Percentage, wt-%
6.0 1.5 6.0 16.5 10.0 60.0
Table 111-18. Composition of an automobile polish paste containing abrasive Components
Montan wax based ester wax E Montan wax based ester wax F Montan wax based acid wax Macrocrystalline paraffin wax Silicone oil Neuburg chalk White spirit 17
Percentage wt- %
I 1 3
1 3 5 80
258
111. APPLICATIONS
OF PARAFFIN WAXES AND LIQUID PARAFFINS
The composition of automobile liquid polishes containing no abrasives are similar to furniture polishes. Some are non-aqueous. Paste-like automobile polishes yield films that have a more durable gloss. Their application, however, is much more cumbersome than that of liquid polishes. Sometimes pastes prepared with abrasives are used as precleaning treatments before applying the final non-abrasive liquid polish. Tables 111-17 and 111-18 present paste compositions without and with abrasive, respectively. Shoe polishes
Shoe polishes are required to protect and shine the leather. They form flexible, glossy wax films resistant to water, dust and the effects of weather. As well as various natural waxes, paraffin waxes are also being used in the manufacture of shoe polishes. An accepted terminology is hard and soft shoe polishes. However, these attributes do not refer directly to the hardness of the waxes or paraffin waxes present, but to other properties, such as solvent uptake, solvent retention, consistency, film-forming properties, drying time, etc. All these properties are of equally great significance in the manufacture, storage and application of shoe creams. The attribute “hard” refers, in this respect, to waxes such as carnauba wax, hard macrocrystalline paraffin waxes and ceresins, candelilla wax, while “soft” applies to waxes such as crude montan wax, bees-wax, japan wax and various microcrystalline paraffin waxes. As a substitute for natural waxes, many synthetic waxes are being used at present. In the formulation of shoe creams the proper proportion of hard and soft materials is of particular importance. Hard materials jn themselves are unsuitable for manufacturing shoe creams having paste-like consistencies. The soft waxes act as binders for the hard waxes and also as a binder between the paraffin waxes and solvent. On the other hand, hard waxes and hard paraffin waxes are imperative from the viewpoint of shine. In addition to the above solids, shoe creams that are aqueous emulsions contain oleic acid, stearic acid, borax and triethanolamine as well as sodium and potassium soaps. Table ZII-19. Shoe cream formulation containing microcrystalline paraflin wax Components .~ . _
Crude montan wax Carnauba wax Stearic acid Microcrystalline paraffin wax Nigrosin colorant Turpentine
Percentage. wt- %
4.6 4.6 1.7 12.6 1.0 75.5
239
(A) DIRECT APPLICATIONS
The most widely used solvent is turpentine. In addition, other solvents, mainly hydrocarbons in the 110-200 "C boiling range, e.g. white spirit, are used. Shoe creams contain about 15 wt-% hard waxes and hard paraffin wax, and about 10 wt-% soft waxes and microcrystalline p a r a f i wax. Their solvent content varies between 60 to 70 wt-%. Colorants - with the exception of leather dyes - do not exceed 5 wt-%. Table 111-19 shows the formulation of a shoe cream based on microcrystalline paraffin wax. Emulsion cream formulations are found in Tables 111-20-111-22. Table 111-20. Formulation of a shoe cream emulsion Percentage, wt- %
Components
10 3 10 3 15 12 47
Carnauba wax Bees-wax Macrocrystalline paraffin wax Potassium soap Turpentine Naphtha Water
Table 111-21. Formulation of a shoe cream emulsion containing a non-ionic emulsifier Percentage, wt-%
Components
3 6 18 2 3 1 37 30
Montan wax based ester wax Crude montan wax Macrocrystalline paraffin wax Colorant Fatty alcohol (18-22 ethox) Fatty acid (3-7 ethox) White spirit Water
Table 111-22. Formulation of a shoe cream emulsion containing ionic and non-ionic emulsifiers Components
Montan wax based acid wax Montan wax based ester wax Macrocrystalline paraffin wax Colorant Fatty alcohol (18-22 ethox) 3-Methoxypropylamine White spirit Water 17,
1
Percentage, wt-%
4 3 12 2 3 1 40 35
260
111. APPLICATIONS OF PARAFFIN WAXES AND LIQUID PARAFFINS
Shoemaker’s waxes are manufactured from bees-wax, japan wax, carnauba wax, paraffin waxes and ceresins, sometimes with small amounts of turpentine, together with oil-soluble colorants. The composition of a shoemaker’s wax is listed in Table 111-23. Table 111-23. Formulation of a shoemaker’s wax ___ Components
Percentage, Wt%
Resin Ester gum Montan wax Macrocrystalline paraffin wax Stearic acid pitch Bees-wax
8 2 30 45 10 5
(b) Candles One of the oldest fields of application for paraffin waxes is in the manufacture of candles. Paraffin waxes were first used for this purpose in the middle of the last century. The composition of candles is defined by their intended use, by climatic factors and by the specific demands of the consumers. The manufacturing process corresponds to the composition and type of the candle. The most important processes are :mechanized moulding using cylindrical moulds, dipping and pouring. The illumination power of pure paraffin wax candles per mass unit is higher, owing to the pure hydrocarbon composition, than that of candles containing other components besides paraffin waxes. However, pure paraffin wax candles have several disadvantages. Their low melt viscosity causes excessively high amounts of melt being picked up by the capillaries of the wick, and consequently the flame tends to soot. Candles made of macrocrystalline paraffin waxes with low softening points may bend and adhere to one another under the effect of their own weight. Candles made of higher softening point waxes, on the other hand, will be difficult to light in cold weather, the flame will tend to blow out, and repeated lighting will again be difficult, because the heat of the igniting flame will not be satisfactory for easy melting of the candle material. For this reason, the majority of candles are manufactured from blends of macrocrystalline paraffin waxes and stearic acid. Also, bees-wax, microcrystalline paraffin waxes (ceresins), vegetable and synthetic waxes are used. Macrocrystalline paraffin waxes having melting point between 48 and 54 “C are suitable for candle manufacture. So-called composite candles made of paraffin wax and stearic acid contain 5 to 15 wt- % stearic acid, which can, however, be substantially higher in candles manufactured for hot climates. Even candles made of pure stearic acid are being manufactured.
26 1
(A) DIRECT APPLICATIONS
The melting point of composite candles is around 50 "C. The melting point of commercial stearic acid is 55 to 60 "C. The melting point of the blend is lower over the total concentration range than that of the individual constituents. The melting point minimum is around the 50/50 wt- % ratio of the constituents and is lower by 6 to 9 "C than that of the pure paraffin wax. However, softening starts at a higher temperature than that of the pure paraffin wax. Table 111-24 presents a formulation for a composite candle. Table 111-24. Formulation of a composite candle Components
Macrocrystalline paraffin wax Stearic acid Carnauba wax
Percentage, wt- %
79.0 19.5 1.5
Church candles, in contrast to other candle types, contain a higher share of bees-wax, sometimes exceeding 50 wt-%. A candle material with high bees-wax content is presented in Table 111-25. Table 111-25. Formulation of a church candle Components
Macrocrystalline paraffin wax Bees-wax Stearic acid
Percentage, wt- "/.
50.0 40.0
10.0
Literature Allen, D., Candles and Night Lights (Ed: A. E. Dunstan): The Science of Petroleum, Vol. 4. Oxford University Press, New York (1938). John, D. W., Modern Polishes and Specialties. Chemical Publ., Brooklyn (1946). Kroner, A., Soap sanit. Chem., 27, No. 3, 1 1 1 (1951). Lesser, M. A., Modern Chemical Specialties. McNair-Dorland, Publ. Co. New York (1950). Nowak, G. A., Soap sanit. Chem., 33, No. 8, 155 (1957). Summary of Information on Waxes and Candles. U.S. Department of Commerce, April (1968). Treffler, A., Soap Janit. Chem., 28, No. 4, 147 (1952). U.S.Pat., 251 904 (1950). U.S.Pat., 2 126 096. US.Pat. 2 153 161. U.S. Pat., 2 188 887. US.Pat., 2 199 193. William, D. J., Modern Industrial Polishes and Specialties. Johns Ltd., London (1946).
262
111. APPLICATIONS OF PARAFFIN WAXES AND LIQUID PARAFFINS
3. Application of paraffin waxes in the cosmetics industry The manufacture and the mechanism of action of cosmetic preparations will not be discussed in this book, we only wish - by presenting some formulations to draw attention towards the potentials of paraffin wax applications in this field. These formulations are only variants among the many possible combinations, even in the case of a given type of product. Initially raw materials of vegetable or animal origin were solely used for such purposes. Only later did petroleum products make their entrance into the cosmetics industry and find general acceptance. This was, however, accompanied by many debates. Objections were made that petroleum products clog the pores of the skin, impede exudation and irritate the skin. On the other hand, they were found to have many advantages: they improve the consistency of creams, they are not absorbed by the skin, they keep perfumes dissolved so that the latter will not be absorbed and cause skin irritations. The problem of clogging pores can be solved by choosing suitable formulations. An absolutely indispensable requirement for petroleum products used for cosmetic purposes is their complete freedom from unsaturated and aromatic compounds. A wide assortment of waxes, fats, oils, petroleum products and perfumes is used for cosmetic products of different types, and manufactured for various purposes. Among vegetable waxes, the most important are carnauba wax and candelilla wax. Among vegetable fats and oils, those most widely used are cocoa butter, peanut oil, coconut oil, linseed oil and castor oil. The animal materials used in cosmetics are tallow, whale oil, lanolin and bees-wax. Among synthetic waxes, those based on montan wax are the most important; fatty alcohols used are cetyl alcohol, stearyl alcohol and various mixtures of fatty alcohols; among fatty acids stearic acid and lauric acid are in use. The most widely used acid derivatives in cosmetics are stearates and the glycol esters of fatty acids. The following petroleum products are in use for cosmetic purposes : vaseline oil, vaseline, macro- and microcrystalline paraffin waxes. Macro- and microcrystalline paraffin waxes make a significant difference to the resistance to mechanical impact, hardness and softening point properties of cosmetic preparations. Microcrystalline paraffin waxes are tougher than macrocrystalline waxes, they exhibit plastic flow under the effect of compression, while macrocrystalline waxes have higher compressive strength. Since the solvent and oil uptake capacity of microcrystalline paraffin waxes are very high, increasing oil content usually results in higher plasticity. But with macrocrystalline waxes increasing the oil content yields friable, low-strength products. Hence the oil content in microcrystalline waxes may be varied among wider limits, and may reach values as high as 10 to 12 wt- % in cosmetic products. Microcrystalline paraffin waxes are capable of partly replacing natural and synthetic waxes.
263
(A) D I R E a APPLICATIONS
Vaselines are important constituents in a large sector of cosmetic products. With regard to their origin, vaselines are natural vaselines, so-called slack wax vaselines or artificial vaselines. Natural vaselines are obtained from the distillation residues of petroleum by direct treatment with bleaching earth, or by refining with sulfuric acid and bleaching earth. Alternative processes are deasphalting of the residue followed by bleaching, or refining with sulfuric acid and bleaching. Slack wax vaselines are manufactured from paraffin slack waxes or petrolatums. Artificial vaselines are blends of vaseline oils and macro- or microcrystalline paraffin waxes. It is a common characteristic of all vaselines that they contain, besides cycloalkanes and alkyl-aromatic hydrocarbons, substantial amounts, in the range of 20 to 40 wt-%, of n- and iso-alkanes. The use of vaselines can be regarded as an indirect use of macrocrystalline, and, especially intermediate and microcrystalline paraffin waxes. (a) Solid perfumes Solid perfumes are used to scent the surface of the skin. Those having a higher alcohol content also have a refreshing effect that can be increased by menthol. The two main types of solid perfumes are fatty and alcoholic perfumes, the latter containing more than 75 wt- % alcohol. Paraffin waxes are used in the manufacture of fatty solid perfumes. A formulation for such a product is shown in Table 111-26. Table 111-26. Composition of a solid perfume containing macro- and microcrystalline paraffin waxes Components
j
Macrocrystalline paraffin wax Microcrystalline paraffin wax Vaseline oil G&,, fatty alcohols Perfume additive
Penrentape, wt-%
44 30 5 6 15
(b) Cosmetic creams Cosmetic creams are paste-like preparations used for skin care of the face and hands. The types discussed in the following are so-called dry, semi-fatty and fatty creams. Dry creams are emulsions of the oil-in-water type with a high water content. The most important requirement for these creams is that they be fully absorbed after application. They are usually prepared on a stearate base. In addition to stearic acid derivatives they contain relatively high amounts of petroleum products
2 64
111. APPLICATIONS OF PARAFFIN WAXES AND LIQUID PARAFFINS
(vaseline, vaseline oil), fatty alcohols (e.g. cetyl alcohol) and multifunctional alcohols (e.g. glycerol). Fatty creams contain less water and more fatty substances, waxes, fatty alcohols and petroleum products. After their application a fatty layer remains on the surface of the skin. Water-in-oil emulsions are frequent among these creams, but anhydrous preparations are also being manufactured. Special summer and winter varieties of these creams also exist: within a given formulation these varieties are prepared by changing the oil content (e.g. vaseline oil) and the content of solid or semi-solid components (e.g. vaseline, paraffin wax). Semi-fatty creams are transitions between dry and fatty creams. Cleansing creams belong to the group of fatty creams. They are primarily intended for persons with sensitive skins, to cleanse the facial skin. Anhydrous cleansing creams contain higher amounts of paraffin waxes, vaseline and vaseline oil. Homogeneous creams can be prepared best by using microcrystalline paraffin waxes, since they retain oil at the temperature of application. Cold creams belong to the fatty or semi-fatty type, depending on fat content. These are aqueous emulsions with a cooling effect on the skin. Of the petroleum products, cold creams use greater quantities of vaseline oil and vaseline, but lesser amounts of paraffin waxes. Semi-fatty cold creams are usually based on glycerol monostearate or diglycol stearate, with a substantially higher water content than that of the fatty creams. In contrast to fatty creams they do not leave behind an oily, fatty film on the skin. They can readily be removed from the skin with pure water. A formulation for a semi-fatty cold cream is presented in Table 111-27. Table 111-27. Composition of a semi-fatty cold cream containing glycerol monostearate Components
Glycerol monostearate Macrocrystalline paraffin wax White vaseline Vaseline oil Glycerol Water Odour additive and stabilizer
Percentage, wt-
%
12.0 6.0 9.0 14.0 3 .O 55.0 0.5
So-called conditioning creams contain, in addition to the usual components, substances of nutritive value for the skin, e.g. cholesterol, vitamins, hormones. Petroleum products for such creams are primarily vaseline and vaseline oil. The composition of a skin-conditioning cream is listed in Table 111-28. So-called massage creams also belong to the group of fatty creams. Tbey contain from petroleum products mainly vaseline and vaseline oil. Nutritive substances, e.g. cholesterol and lecithin are also often included. A formulation is shown in Table 111-29.
265
(A) DIRECI' APPLICATIONS
Table 111-28. Formulation of a skin-conditioning cream, containing cholesterol Components
i'
Percentage, wt-%
Macrocrystalline paraffin wax White vaseline Vaseline oil Cholesterol Lanolin Bees-wax Water
7 17 4
2 5 10 55
Table 111-29. Emulsified massage cream containing paraffin wax unperfumed I
Components
Macrocrystalline paraffin wax Vaseline oil Spermaceti Lecithin Cholesterol Borax Water
j
Percentage, wt-x
15 45 10 1.5
0.5
1.o
30.0
Baby creams also contain substantial amounts of vaseline and vaseline oil. Their composition resembles that of cleansing creams. Sport creams belong to the semi-fatty group. They are aqueous emulsions containing substantial amounts of petroleum products. A formulation is presented in Table 111-30. Table Ill-30. Sport cream containing paraffin wax Components
Hard microcrystalline paraffin wax White vaseline Vaseline oil Lanolin Cetyl alcohol Glycerol Water
Percentage, wt- %
5.0 10.8 17.7
2.4 4.8 3.0
56.3
The so-called acid creams are slightly acidic, owing to their lactic acid, citric acid or benzoic acid content (pH value 4 to 5). These aqueous emulsions, containing larger amounts of vaseline, have an antiseptic effect.
266
111. APPLICATIONS OF PARAFFIN WAXES AND LIQUID PARAFFINS
(c) Beauty masks The main objective of beauty masks is to relax the tissues of the face and enhance blood circulation. A formulation for a paraffin wax beauty mask is listed in Table 111-3 1. Table 111-31. Formulation of a beauty mask based on paraffin wax .
Components
Macrocrystalline paraffin wax Bees-wax Cocoa butter Lanolin Camphor Benzoic acid
-~
~
Percentage, wt- %
51.8 34.4 8.6 3.6 0.5 1 .o
(d) Protective creams for industrial workers Protective creams are being used in many branches of industry, especially to protect the skin on the hands and arms of the workers against harm caused by various chemical and physical effects. Protective creams form a thin, continuous layer on the surface of the skin. No universal protective cream exists, since potential dangers are largely diversified. A suitable formulation must, therefore, be made up for every individual situation. Most of the protective creams are based on vaseline, but some of them also contain macrocrystalline paraffin waxes. (e) Facial care and beauty products
Cosmetic preparations for facial care, e.g. to soften dry, parched lips are made of natural and synthetic waxes, fats, fatty alcohols, vaseline and ceresin. Their melting point is in the range of 40 to 50 "C.A formulation for a lip pomade is given in Table 111-32. The most important starting materials for the manufacture of lipsticks are various natural and synthetic waxes, fats, fatty alcohols, vaselines, paraffin waxes and dyes. Mechanical strength of the lipstick is achieved by using waxes and Table 111-32. Composition of a lip pomade, unperfumed Components
Microcrystalline paraffin wax White vaseline Bees-wax Lanolin
Percentage, wt- %
10 75 10 5
267
(A) DIRECT APPLICATIONS
microcrystalline paraffin waxes with higher melting points. Among natural waxes, bees-wax is typical of the kind used in almost all types of lipstick, owing to its plasticity. Its content varies in the range of 5 to 50 wt-%. However, higher concentrations cause granular structure and stickiness. The gloss of the lipstick is achieved by carnauba and candelilla waxes, which also add strength and hardness. Carnauba wax content usually does not exceed 10 wt-%. Lanolin is an excellent plasticizer, readily mixing with the other constituents and enhancing the compatibility of the latter. It thus reduces exudation of the fatty substances and prevents cracking. Excessive amounts of this plasticizing material, however, cause stickiness. Cetyl alcohol, stearyl alcohol and whale wax are not used in amounts exceeding 4 to 5 wt- %, since they impair gloss and have a friable crystalline structure. The spreading property is defined by the proportion of fats and synthetic fatty substances, e.g. iso-propyl myristate, stearate and palmitate. Among these substances the particular advantage of cocoa butter is the low softening point combined with suitable hardness, and yields a uniform, homogeneous system. It has, however, the disadvantage that it tends to efflorescence on thesurface of the lipstick, and can, therefore, be used only in limited amounts. Castor oil is used for lipstick primarily due to its being a good solvent and dispersing agent for eosin. Among petroleum products, high-melting microcrystalline paraffin waxes raise the strength and softening point of the lipstick, but are rarely used in amounts exceeding 15 wt-%, because they tarnish the gloss of the surface. The use for macrocrystalline paraffin waxes is limited, due to their causing a granular structure. Vaseline increases gloss and is of importance for the consistency of the product. It is, however, easily wiped off from the lips. Vaseline is usually present in concentrations of 20 to 35 wt-%. The effect of vaseline oil is very similar to that of vaseline. In addition, it improves uniform spreading of the lipstick. Excess amounts of both vaseline and vaseline oil result in low-melting, soft lipsticks. The melting point of lipsticks varies between 45 and 65 "C. Lower-melting types spread better, while contours are easier to draw with the higher-melting lipsticks. Table 111-33 presents one of the many formulations found in the literature for lipsticks. This particular one is characterized by its high paraffin wax content. Face make-up is manufactured from the same raw materials as lipsticks. The main requirement is easy and uniform spreading, so that they contain higher Table 111-33.Formulation for a lipstick base material, without added colour or perfume Components
Microcrystalline paraffin wax White vaseline Bees-wax Castor oil Lanolin
Percentage,
wt- %
35 35 18
4.1 7.3
268
Ill. APPLICATIONS OF PARAFFIN WAXES AND LIQUID PARAFFINS
percentages of fatty substances, vaseline and vaseline oil. Their softening point is in the range of 35 to 45 "C. The composition of eyebrow pencils also shows the many uses of paraffin waxes, especially microcrystalline waxes, in make-up. Table 111-34 presents such a formulation. Table 111-34. Composition of an eyebrow pencil, unperfumed Components
1
Microcrystalline paraffin wax Vaseline Carnauba wax Colorant
Percentage, wt-
%
30 50 10 10
(f)Hair preparations Among cosmetic preparations for hair, solid brilliantine and hair pomades utilize significant amounts of paraffin waxes and vaseline, the higher percentages being found in the latter. Formulations for such products are presented in Tables 111-35 and 111-36. Table 111-35. Formulation of a solid brilliantine Components
Microcrystalline paraffin wax Vaseline Vaseline oil Spermaceti Perfume additives
Percentage, wt- %
8 45 41 5 1
Table 111-36. Composition of a hair pomade _______ Components
Macrocrystalline paraffin wax Vaseline oil Hardened soya oil Bees-wax Perfume additives and antioxidant
~~
Percentage, wt-%
40.0 29.4 20.0 10.0 0.6
( g ) Anti-perspirants
A perspiration-reducing and deodorant product containing relatively high percentages of paraffin wax and vaseline is presented in Table 111-37.
269
(A) DIRECT APPLICATIONS
Table 111-37. Formulation of an alcohol-free deodorant - -
Components
._
Percentage, wt %
~
Macrocrystalline paraffin wax Vaseline Bees-wax Lanolin Kaolin Cocoa butter Crystalline aluminium chloride
25 5 10 10 25 10 15
Literature Hajdb, J., A kozmetikai b a r ktzik5nyue. (Manual of the Cosmetics Industry), Mfiszaki Konyvkiad6, Budapest (1962). Hask6, L., Zsirok 6s olajok kkmidja 6s technoltjgihja. (Chemistry and Technology of Fats and Oils). filelmiszeripari 6s Begyujtesi Konyv- 6s Lapkiad6 VBllalat, Budapest (1954). Janistyn, J., Handbuch der Kosmetika und RiechJtofle. 3 . ed. Alfred Huethig Verlag, Heidelberg (1978). Jellinek, J. S., Kosmetikologie. 3. ed. Alfred Huethig Verlag, Heidelberg (1976). Meyer, E., Drug Cosmet. Ind., 49,270 (1941). NavarreMill: The Chemistry and Manufacture of CoJmetics. Van Nostrand, New York (1 941). Sagarin, E., Casmetics. J. Wiley Interscience Publ., New York (1972). Schrader, K., Grundlagen und Rezepturen der Kosmetika. Alfred Huethig Verlag, Heidelberg (1979). Thiele, F. A., Drug Cosmet. Ind., 53, 553 (1943). U . S . Pat., 1997 160. U . S . Pat., 1999 161. Walton, B., Coding, 9, No. 1, 13 (1976).
4. Application of paraffin waxes in the food industry and in agriculture
Paraffin wax usage in the food industry is partly implied in paper industry applications, since a major part of paper products coated or impregnated with paraffin wax, and also laminated films and foils using paraffin waxes as adhesives are manufactured for food packaging. These applications have been discussed earlier. Paraffin wax is widely used in the poultry-processing industry for the wax picking of poultry, mainly for ducks and geese. After depluming, the poultry is immersed in melted paraffin wax. When the wax coating has solidified, it is removed by a so-called whipping machine. The feather pins and small feathers left after depluming, embedded in the wax coat, will be removed together with it. Macroctystalline slab wax is unsuited for wax picking owing to its brittleness. The products used for this purpose consist of blends of macro- and microcrystalline
270
III. APPLICATIONS OF PARAFFIN WAXES AND LIQUID PARAFFINS
paraffin waxes, together with additives, e.g. polyethylene wax. The microcrystalline wax increases flexibility, the additives serve to improve adhesion and toughness. The major characteristics of a paraffin wax-based product for wax picking are listed in Table 111-38. Table ZZZ-38. Characteristics of a paraffin wax-based product for wax picking in the poultry-processing industry Drop melting point, 'C Viscosity at 100 O c , mmz/s Penetration at 25 "C, 0.1 mm
60-65 4.5-5.5 30-40
Paraffin wax products are frequently used for direct coating of food. The most important of such applications are coatings for cheese and fruit. The paraffin wax coat on the surface of the cheese prevents its desiccation, reduces loss in flavour substances, and protects the surface of the cheese from undesired moulding. The main requirements for paraffin waxes used for coating cheese are melting points between 55 and 75 "C, melt viscosities in the range of 5 to 15 mm2/s at 100°C, high flexibility and good adhesion. Flexibility is of importance from two viewpoints: it ensures that no cracking will occur under the effect of mechanical impact, and it allows the preparation of peelable coatings. Consequently macrocrystalline slab waxes cannot be used by themselves for cheese coating, the formulation must always contain substantial amounts (60 to 80 wt- %) of microcrystalline paraffin wax and polymer additives. Among the types of microcrystalline paraffin waxes, those with melting points of 55 to 60 "C, manufactured from residual oil or from the paraffin by-product of residual oil by fractional crystallization, are particularly suited for high-grade cheese waxes. The additives used are synthetic rubbers, polyisobutene, polyethylene waxes and various copolymers. To inhibit mould formation, propionic acid and stearic acid are added. The properties of such a product are listed in Table 111-39. Table 111-39. Characteristics of a paraffin wax-based product for coating of cheese Drop melting point, O C Viscosity at 100 OC, mm2/s Penetration at 25 OC, 0.1 mm Fraass breaking point, "C
70-75 7-8 30-40 below -10
Paraffin wax coatings are applied to fruit and other agricultural produces whose peel will not be consumed, and to those transported to long distances, for example to lemons, oranges, tangerines, melons, egg-fruit. In some countries apples, tomatoes and fodder beet are also being waxed. Fodder beet is waxed by immersion in melted paraffin wax a t 120 to 130°C. For citrus fruits, a widely used process is to spray the fruit, as it passes on a con-
(A) DIRECT APPLICATIONS
271
veyor belt, with a solution of paraffin wax in white oil. After coating, uniform thickness of the coat is achieved by brushing. In another process the wax is dissolved in gasoline and sprayed on the fruit. Melons, egg-fruit and tomatoes are coated by immersion in cold wax emulsions, after being washed with cold water. Main requirements for the emulsions are low surface tension, good wetting power and rapid drying after coating. The melting point of paraffin waxes used for emulsions is around 52 to 60 "C.The emulsifying agent is usually a soap-type product. For coating fruit and other agricultural produces, colourless, odourless and tasteless macrocrystalline slab waxes are preferred. In agriculture, saplings, shrubs and grafts are frequently protected during storage against desiccation and plant diseases by coating with paraffin wax. The coating is carried out by immersion in melted paraffin or by spraying with a paraffin emulsion. For these purposes, mainly for immersion, blends of macro- and microcrystalline paraffin waxes are used. Coating waxes made with microcrystalline paraffin waxes yield impact-resistant, flexible coatings.
Literature Coating, 9 , No. 5, 112 (1976). U.S.Pat. 2 052 423. US.Pat. 2 153 487. U.S.Pat. 2 181 134. U.S.Pat. 2 261 229. U.S.Pat. 2 266 700. US.Pat. 2 290 452. U.S.Pat. 2 292 323. U.S. Pat. 2 429 410.
5. Other fields of application for p a r a n waxes
In addition to the discussed fields of application, paraffin waxes are used in many branches of industry, such as the match industry, the rubber industry, PVC processing, precision casting of metals, manufacture of refractory ceramics, the electrical industry and building construction. Further consumers of para& waxes are the textile industry, dental profession, pencil manufacturers, pyrotechnic industry, etc.
(a) The match industry The match industry is one of the oldest consumers of paraffin waxes. Paraffin impregnation of the matches, usually made of wood, has the objective of ensuring rapid ignition of the matchwood after striking the matchhead. In addition, waxing improves adhesion of the matchhead to the matchwood and resistance to moisture. The latter is of particular importance for matches stored and used in high-moisture climates.
2 72
111. APPLICATIONS OF PARAFFIN WAXES AND LIQUID PARAFFINS
Previously, lower-melting macrocrystalline paraffin waxes (42 to 46 "C m.p.) were preferred for match impregnation. At present higher-melting waxes (m.p. 46 to 54 "C)are more wide-spread in use. Still higher-melting waxes could also be used, but are too expensive. The oil content of paraffin waxes for impregnation must not exceed 5 wt- %; the usual value is around 3 wt- %. Higher oil content leads to excessive flickering of the flame. Some match manufacturers use 1 to 2 wt- % paraffin wax in the matchhead, too, resulting in more uniform burning. (b) The rubber industry
The rubber industry is also one of the most important paraffin wax consumers, using it for a variety of purposes. Paraffin wax, when used as an additive to rubber increases the stiffness of the product. This is of major importance in press-moulded rubber products. If the paraffin wax content in rubber exceeds 1 to 2 wt-%, it migrates to the surface and forms a continuous thin layer. This phenomenon is called efflorescence. The thin layer bends, without cracking, with the rubber products. Experience has shown that the layer of wax effectively inhibits the oxidative ageing processes accelerated by light. If it is desired to obtain low-friction surfaces, 3 to 5 wt-% paraffin wax is added to the rubber compounds. Paraffin waxes are often used with painted rubber goods to prevent decolouration. In rubber latices various paraffin waxes (I to 2 wt-%) are used as plasticizers to reduce toughness. Almost all types of paraffin waxes are in use in the rubber industry. In the manufacture of air tubes, macrocrystalline paraffin waxes containing 2 to 5 wt- % oil are used to ease moulding and to achieve uniform surface resistance to abrasion in the tyre. Blends of macro- and microcrystalline paraffin waxes are used in the manufacture of sealing rings for preserve jars and other types of sealing rbgs. For industrial-purpose rubber goods, e.g. hose, where requirements of colour and odour are not so critical, less refined petrolatums of darker colour are used. (c) Precision casting
Precision casting is a useful process for the economical manufacture of metal components and tools in small batches. Although the process is also used for components of mass greater than 100 kg, its most important field of application is with smaller components, with mass of the order of a kilogramme. The process consists of the following steps : a die is made from a prototype, and wax is poured or pressed into the die. After cooling, the wax model is removed from the die, and a ceramic coating is applied onto the model. When the ceramic coating has solidified, the wax is melted and poured from the ceramic shell, which is subsequently baked in a kiln. The molten metal is usually cast into the ceramic moulds
273
(A) DIRECT APPLICATIONS
whilst the moulds are still hot. After solidification of the melt, the ceramic shell is broken to remove the casting. The most important components of casting waxes are lower-melting paraffin waxes, various natural waxes, e.g. carnauba wax, synthetic waxes, as well as highermelting fatty acids, e.g. stearic acid. Blends of around 50/50 wt-% macrocrystalline paraffin wax and stearic acid are frequently used. In addition, some casting waxes contain bitumen. Studies carried out in the Hungarian Oil and Gas Research Institute demonstrated that low-contraction casting waxes can be produced from partially oxidized niicrocrystalline paraffin waxes and microcrystalline paraffin waxes containing wax esters.
(d) The manufacture of refractory ceramics Paraffin wax casting of ceramics is a process being increasingly used in industry, mainly for porcelain, A1,0,, MgSiO,, ZnTiO,, TiO,, ZrO, and fireclay. Other materials for which the process has been used are CaO, MgO, MgA1,0,, Sic, MoSi,, Si,N,, Si, TiB,, TiN, ZrB, and other high-melting compounds. Clay cannot be used as binding material for shaping, since it reduces the melting point of refractories. Instead, the ground refractories are mixed with molten paraffin wax to yield a malleable mass, which is then cast into metal moulds or moulded at pressures of several hundred bars. Injection moulding is also used for mass production. The parts solidified in the water-cooled moulds are coated with a porous embedding material and introduced into the prefiring kiln. The temperature is slowly raised to 400-60O0C, whereupon paraffin wax diffuses out into the embedding material where it evaporates and burns away. Depending on the composition of the ceramic, prefiring is continued to 9001250°C. Subsequently the embedding material is removed and final firing at high temperature follows. Slab wax melting at 50-54 "C is used to prepare the slurry for casting. Surfaceactive additives simultaneously increase the viscosity of the paraffin melt, so that
Table 111-40. Composition of para& wax-based ceramic-casting slurries Ground ceramic material
Alumina prefired at 1450 OC Alumina prefired at 1700 OC Stabilized ZrOe Melted spinel Melted MgO MgO prefired at 1450 OC 18
23 14-15 15 18
16 26
3.4 5
5 4.4 5 6.6
274
111. APPLICATIONS OF PARAFFIN WAXES AND LIQUID PARAFFINS
the ground refractory will not agglomerate and sedimentate in the course of shaping. Suitable surface-active materials are oleic acid, ricinoleic acid, stearic acid, ,, fatty alcohols, etc. bees-wax, C-C The casting slurry is prepared at 60-70 "C. Before casting into the mould it must be carefully freed completely from air and moisture to avoid crack formation during firing. Some examples of suitable compositions for casting slurries, depending on the refractory starting material, are presented in Table 111-40. The process is also applicable for the manufacture of large-size ceramic products. ( e ) The electrical indusiry
The electrical industry uses large amounts of different types of paraffin waxes for insulation at ambient temperature. Obviously, paraffin waxes alone cannot be used at higher temperatures, only in blends with synthetic waxes. In addition to high relative permittivity, low dielectric loss and high resistivity values, important requirements for paraffin waxes to be used in the electrical industry are flexibility, ductility and low thermal expansion coefficients. Direct paraffin wax coating is frequently used for the insulation of Wires, cables, flat or irregular-shaped metal surfaces. For such purposes only microcrystalline paraffin waxes which are flexible, adhere well to metals, and have only a slightly shrinkage on cooling are useable. Paraffin wax impregnation of other insulating materials, e.g. paper, textiles, asbestos, wood, is also frequently used in order to improve their insulating properties and moisture resistance. Paraffin waxes and paraffin waxes with additives are much used for building up blocking layers, e.g. for capacitors, for cable terminals and couplings, for impregnating cable-insulation paper, for filling the space between cables and around the coupling. The zinc casings of dry cells can be sealed with paraffin wax or paraffin waximpregnated paper. This will efficiently reduce desiccation of the cell. Paraffin waxes used for insulation usually have melting points above 55 "C and oil contents below 1 wt-%. Paraffin waxes are used to reduce the viscosity of bitumen used for impregnating linen tape. For this purpose the oil content may be as high as 2 to 4 wt-%. To impregnate paper for paper-insulated capacitors, the oil content must not exceed 0.5 to 1 wt-%, and the melting point should exceed 55 "C. In roll-type cyclindric or flat capacitor elements encased in metal or paper the empty space is usually filled with paraffin wax. For paper casings, blends of highermelting microcrystalline paraffin waxes and various resins are used. The melting point of cable waxes is in the range of 55 to 65 "C. Requirements are non-stickiness and absence of components with boiling points below 180 "C.
276
111. APPLICATIONS OF PARAFFIN WAXES AND LIQUID PARAFFINS
Literature Davis-Blake: The Chemistry and Technology of Rubber. Reinhold Publ. Co., New York (1937). Dixson, W. H., The Match Industry: Its Origin and Development. Sir Isaac Pitman Sons Ltd, London (1937). Eberlin-Burgess: J . Ind. Engng. Chem., 19, 87 (1927). Kingery, W. D., Ceramic Fabrication Processes. J. Wiley Interscience Publ., New York (1958). LeeLowey: J. Ind. Engng. Chem., 19, 304 (1927). Tkrknyi, Gy., Parafinalapri kerdmiai 6nt6iszapok tanulmdnyorha (Study of Parafin WaxBased Ceramic Casting Slurries). Thesis (1969). U.S.Pat., 1 709 498. U.S. Pat., 2 050 428. Wiertelak-Czarnecki: J . Ind. Engng. Chem., 27, 543 (1935).
(B) Paraffin waxes and liquid paraffins as starting materials for the chemical industry As well as their direct application, paraffin waxes are also utilized as raw materials for the chemical industry. From this point of view, straight-chain paraffins and low oil-content macrocrystallineparaffin waxes are of greater importance. For certain applications, however, e.g. manufacture of wax-like esters by oxidation and esterification, microcrystalline waxes are also suitable. In this chapter chlorination, sulfochlorination, oxidation and thermal decomposition of paraffins and the areas of application of the products obtained will be discussed.
1. Manufacture and utilization of chlorinated paraffins
(a) The chlorination process Halogenation, including chlorination, of paraffins is a strongly exothermic substitution reaction. In industrial practice, one assumes the heat of reaction of 1508 kJ/kg chlorine. To dispose of the considerable amounts of heat evolved is one of the greatest problems in the technology of chlorination. Three types of chlorination processes are used industrially : catalytic, - thermal, - photochemical chlorination. Catalytic chlorination is used especially for gaseous hydrocarbons. It is carried out in a solvent, mainly carbon tetrachloride. The homogeneous-phase catalysts used for this purpose and also for the chlorination of hydrocarbons liquid at ambient temperature are substances that yield readily dissociating compounds with chlorine, e.g. iodine, phosphorus, sulfur, antimony chloride, iron chloride or zinc chloride.
-
275
(A) DIRECT APPLICATIONS
(f)Paraf i n wax emulsions in building construction Aqueous emulsions of paraffin waxes have found a wide range of applications in recent years. The emulsions prepared in the presence of emulsifying agents, at appropriate temperatures and stirring rates, are satisfactorily stable, mobile liquids at ambient temperature. They are oil-in-water type emulsions, that is, the continuous phase is water, the disperse phase is paraffin wax. The most important applications of paraffin wax emulsions (paper industry, household chemicals, food industry) have already been discussed in earlier chapters. Another, more recent potential for their application is in the field of building construction to protect the surface of green concrete structures. It is well known that green (uncured) concrete must continually be kept moist during the curing process. By coating the concrete surface with a paraffin wax emulsion half an hour after the concrete has been laid, the need for watering can be eliminated. When the water content of the emulsion has evaporated, the paraffin wax particles will seal the pores on the surface of the concrete and the capillaries leading to the surface. In this way, rapid decrease in the water content of the concrete can be prevented. Strength data of concretes coated with different emulsions, and, for comparison, of non-treated concrete are listed in Table 111-41. The data refer to the compression strength of concrete test specimens (20 x 20 x 20 cm) measured under standard conditions, after 28 days of ageing. Table 111-41. Compression strength of concretes treated with paraffin wax emulsions Treated with emulsion Codemark
1 2 114 114 215 215 316 317
in laboratory, N/cmz
3230
3050 2390 1990 2880
outdoors, N/crnz
3030 1840 2910 1390 2370 1930 1910 2190
__
Non-treated
in laboratory, Nlcrn'
3720 2560 3540 1570 2820 2510 2040 3340
Specified break value,
Nlcmz
Of
application
I
N/cmP
1490 2800 1250
,,
2800 2000 2000 2000
2000 2000 2000
2000
Brush Brush Spray Brush Brush Brush Spray Spray
The data confirm that water loss in concretes protected from drying out by coating with paraffin wax emulsions is in fact low, since the strength properties of the respective specimens are not worse than those of the traditionally cured concrete. The application of such emulsions might, therefore, lead to substantial economies in manpower and energy. Paraffin wax content of emulsions for concrete coating varies between 5 and 25 wt- %. The emulsifier concentration required is 2-4 wt- %.
(B) PARAFFIN WAXES AND LIQUID PARAFFINS AS STARTING MATERIALS
277
70 60 2
,
+
50
C
40
0
c
q
30
i
2
20
0
10 0 Number of chlorine atoms per molecule
Fig. ZIZ- 1. Chlorine content of chlorinated parafins versus chlorine atoms per molecule for
paraffins of various chain lengths
Several processes have been developed for the thermal chlorination of highparaffin petroleum fractions and parafin waxes melting in the 50 to 60 "C temperature range. Bond splitting in the chlorine molecule can also be achieved by radiation energy, i.e. photochemical initiation of the chain reaction is also feasible. The absorption range of chlorine is 2500-4500 A, it is thus capable of utilizing UV and UVypectrum of visible light. Maximum energy absorption takes place at 3400 A. Kinetics of paraffin chlorination reveal that the bond energies of the hydrogen atoms attached to the primary, secondary and tertiary carbon atoms in hydrocarbons decrease in this order, tertiary carbon atoms are chlorinated at the highest rates and primary carbon atoms at the lowest rates. Figure 111-1 shows the relationship between chlorine content, number of chlorine atoms per molecule and number of carbon atoms per molecule.
(b) Batchwise and continuous chlorination of parafins Chlorinated paraffins were prepared by Bolley as early as 1858. He found that they were oily, viscous liquids at ambient temperature. The highest chlorine content that he succeeded in achieving was 62 wt-%. Scharschmiedt and Thiele used paraffin slab wax for chlorination at 155-160°C. When the product was heated to 300 "C, chlorine was split off in the form of hydrochloric acid. Gardner and co-workers reported chlorination of a 55 "C melting point paraffin wax at 70 "C.
278
111. APPLICATIONS OF PARAFFIN WAXES AND LIQUID PARAFFINS
Groggins described a lead-lined reactor made of iron or a ceramic material for the photochemical chlorination of liquid paraffins. The feed was saturated with chlorine and recycled, by means of an impeller fitted at the bottom of the reactor, through a glass tube irradiated by a mercury vapour lamp. The hydrochloric acid formed in the reaction left the system through a reflux cooler. Chlorination was continued until the required chlorine content was attained. Studies to obtain chlorinated paraffins, to be used as PVC plasticizers, were carried out a t the Hungarian Oil and Gas Research Institute. The flow sheet of the batchwise pilot plant is presented in Fig. 111-2. The melted paraffin wax from the steam heated vessel 13 passed by gravity into the reactor 4, a 200-litre vessel lined with acid-proof enamel and jacketed for heating. Light energy was provided by a 40 W fluorescent lamp protected by the potassium glass casing 11. Chlorine gas was supplied by the liquid chlorine flask I. The gas was sprayed into the reactor through the porous glass distributor 3. The product was neutralized with lime in the heated and enameled stabilizer 14 equipped with agitator 19. The suspension obtained was filtered on the filter press 21 retaining solids, and passed to the filtrate collector 22 and the product outlet 23. During chlorination,
Fig.IIZ-2. Pilot plant for the batchwise chlorination of paraffins. I Chlorine bottle, 2 Copper pipe for chlorine, 3 Glass tube chlorine distributor, 4 Enameled reactor for photochlorination, 5 Jacket for heating or cooling, 6 Condensed steam outlet, 7 Cooling water inlet, 8 Steam inlet, 9 Cooling water outlet, 10 Waste gas outlet, 11 Protective glass casing of the light source, I 2 Electric power supply, 13 Vessel for paraffin melting, 14 Stabilizer, 15 Thermometer, 16 Product entry into stabilizer, 17 Inlet and outlet of tempering oil, 18 Lime hydrate charger, 19 Agitator, 20 Centrifugal pump, 21 Filter press, 22 Filtrate collector, 23 Product outlet
(B) PARAFFIN WAXES AND LIQUID PARAFFINS AS STARTING MATERIALS
279
the temperature in the reactor was held at 85-95 "C, and the same temperature was maintained in stabilization. The acid value of the product after stabilization was less then 0.5 mg KOH/g. Batchwise chlorination is disadvantageousfrom many respects. Chlorine utilization is low even when chlorine feed is uniform, since a substantial part of the chlorine is removed with the waste gas before the reaction has started, and later, when higher-chlorinated products are present, the utilization of chlorine will again decrease. Also, uniform quality of the product is difficult to achieve. For these reasons, most paraffin-chlorinating plants are continuously operated. The first continuous plant was started in 1945 in the U.S.A. The starting material (Kogasin) flows through nine lead-lined reactors coupled in series. The temperature, controlled by water cooling, is 90-100 "C. No mechanical agitation is required. Operation is counter-current, that is, the material to be chlorinated meets pure chlorine in the last reactor. Many suggestions have been made in the past years for the further development continuous reactors. Rosmer and Teubel experimented with packed reactors, assuming that the large contact area between the liquid and gas phase will improve the homogeneity of the product and a high mass transfer coefficient will be attained. Figure I113 shows the flow diagram of a continuous paraEn chlorinating plant. The feed is an average C,,-C,, paraffin wax, activation proceeds by a combined photochemical-thermal path. The reactor is made of glass. Chlorination is carried out in several stages. The hydrochloric acid content of the terminal gas is absorbed in water, yielding a 37 wt-% HCl solution. The liquid terminal product is freed from dissolved gases and stabilized. Details of the process are as described below. The starting material a enters the preheater 2 through the filter I . It then proceeds to the column 3, where it comes into contact with the unreacted chlorine from the preheater 6 and from the reactor 7 which are recycled into the column 3. The HC1 gas b is exhausted, and the intermediate product passes on to the cooler, 4, and further through the buffer vessel 5 and the preheater 6 into the reactor 7. Fresh chlorine c is introduced into the reactor. The reaction product passes into
Fig. 111-3. Flow diagram of a chlorinating plant for paraffin wax
2 80
111. APPLICATIONS OF PARAFFIN WAXES AND LIQUID PARAFFINS
the vessel 8, where air d is blown through to remove all dissolved gases, leaving the system together with the airf. The stabilizer e is added to the product in the storage vessel 9, and the stabilized final product g is transferred to storage 10. The plant produces three grades of chlorinated paraffins: 10 wt-%, 42 wt-% and 70 wt-% chlorine content products, the last being manufactured in the presence of a solvent. The total output of the plant is 2000 to 2500 tons per year. (c) Factors affecting the manufacture and grade of chlorinated parafins Previously paraffin slab waxes and paraffins originating from the FischerTropsch synthesis were used almost exclusively for chlorination. However, the rapid growth in the production of lower molecular weight normal paraffins brought methods for their chlorination into importance. Currently, both types of starting material are being used for chlorination. Some fields of application prefer chlorinated paraffins from liquid normal paraffins, others prefer those from paraffin waxes. Estimates for the future indicate more rapid growth for the chlorination of lower molecular weight paraffins, since plasticizer properties of the products are better than those of the products made from paraffin waxes, and their emulsions are also more stable. The grade of the chlorinated products depends greatly on the oil ccntent of the starting material. Results obtained in the Hungarian Oil and Gas Research Table III-42. Comparison of chlorinated paraffins manufactured from paraffin slab wax of varying oil content _~_
Code mark
Paraffin I Paraffin 11 Paraffin 111 Paraffin JV KP-1 KP-2 KP-3 KP-4 KP-5 KP-6 KP-7 KP-8
Oil content of paraffinic feed, wt- %
0.34 1.04 1.74 3.30
._
I ofaftertreatment,
rine content.’ wt-%
-
39.1 40.4 44.5 43.5 38.4 38.8 39.0 40.5
-
1.74
50 100 50 100 50 100
3.30
50 100
2.34 1.04
Refrac-
1
t
!lviscos-
Acid
___ Resistivity at 25
“C, 10” ohm
0.7726 0.7711 0.7704 0.7718 1.1003 1.1001 1.1183 1.1148 1.1029 1.1026 1.0987 1.0987
351 328
-
601
594 578 558
Schoeniger chlorine determination photometer, filter No. 8, layer thickness 5 mm
** Pulfrich
I
1
1.4308 1.4304 1.4302 1.4311 1.4832 1.4832 1.4852 1.4852 1.4832 1.4832 1.4832 1.4832
0.23 0.22 0.16 0.18 0.19 0.23 0.22 0.22
-
-
-
-
-
0.02 0.06 0.07 0.32 0.13 0.67 0.53 1.47
23.24 23.46 27.21 25.24 21.94 20.57 19.69 19.47
3.92 2.31
-
2.01 0.47
(B) PARAFFIN WAXES AND LIQUID PARAFFINS AS STARTING MATERIALS
28 1
,I 50
s-; c
40
z-30 3
a 0 ._ c 2 20
o'Q
z+ 0
0
10 0
0
1
2 3
4 5 6 7 8 9 Time of chlorination, h
1 0 1 1 12
Fig. 111-4. Chlorine content of chlorinated paraffin versus chlorination time, at different
temperatures
Institute from experiments carried out with slab waxes containing differing amounts of oil, in continuous and batchwise laboratory equipment, are listed in Table 111-42. The chlorine content of the products was around 40 wt-%. The data demonstrate a decrease in the density, average molecular weight, viscosity measured at 100 "C and resistivity measured at 25 "C, with increasing oil content of the feed. Tumarkina, Posvolsky and Platonov studied the rate-controlling factors of chlorination. They found that the rate of chlorination increases with increasing temperature. The chlorination process consists essentially of two stages, the absorption of chlorine, and the successive rapid substitution reactions. Hence the rate-controlling factor is the rate of diffusion. Since the viscosity of the reaction product increases substantially in the course of chlorination, an increase of temperature results in significant increases of diffusivity and thereby of the rate of chlorination. Figure 111-4 demonstrates that towards the end of chlorination, when the viscosity of the product is high, the effect of temperature increase is more important than at the start, when viscosity increase is not yet significant. The properties of chlorinated paraffins prepared from a given starting material vary greatly with chlorine content. Gardner and co-workers prepared the chlorinated paraffins listed in Table 111-43 from a 55 "C m.p. paraffin wax at 70 "C. Tumarkina, Posvolsky and Platonov studied the chlorination, at 70-80 "C, of a paraffin wax melting at 56 "C and having an average molecular weight of 350. They also stated that the melting point decreases until a chlorine content of 36 wt- % is reached, and subsequently increases. The authors explain this phenomenon by assuming that with the introduction of chlorine into the compounds, van der Waals forces become weaker, the crystalline structure slackens, up to a chlorine content of around 36-37 wt-%. Further chlorine uptake, however, results in the rapid increase of intramolecular forces that counterbalance the absence of crystal-forming capacity. The authors also found that branching in
282
111. APPLICATIONS OF PARAFFIN WAXES AND LIQUID PARAFFINS
Table 111-43. Physical properties of chlorinated paraffins (tabulated by Gardner) rine
Viscosity, Pa. s, at
Density, g/l, at ~~
content,
37.8 "C
20.0 34.0 37.0 39.0 44.0 45.4 48.7
1.040 1.070 1.100 1.125 1.216 1.238 1.287
1.ooo 1.023 1.054 1.079 1.157 1.180 1.239
37.8 "C
100 "C
0.132 0.467 0.590 0.630 13.500 31.600 200.000
0.015 0.029 0.031 0.037 0.087 0.107 0.277
dyn/cm
-1 - 16 - 18 - 16 +2 12 18
+ +
37.0 38.9 39.8 42.0 44.1 46.0 51.8
Table 111-44. Physical properties of chlorinated paraffins prepared from 1.04 wt- % oil-content paraffin ChIorine content,* wt-%
0.00 10.74 18.74 21.22 23.58 26.02 29.35 31.66 35.23 38.51 40.45 41.43 44.53
Refractive index,
ng
1
1.4305 1.408 1.4502 1.4530 1.4563 1.4600 1.4635 1.4678 1.4752 1.4794 1.4823 1.4848 1.4888
Density, d;o
0.7711 0.8343 0.8954 0.9159 0.9333 0.9566 0.9804 1.0047 1.0510 1.0787 1.0970 1.1110 1.1400
1
Acid value, mg KOH/g
0.05 0.08 0.09 0.09 0.09 0.09 0.08 0.12 0.08 0.12 0.11 0.12
Molecular weight
328 368 412 422 444 453 470 462 530 559 554 598
* Scboeniger chlorine determination
the cai ,on chain results in molecules containing chlorine atoms loosely ,ound to tertiary carbon atoms. Further characteristics of chlorinated paraffins are presented in Table 111-44. The data shows that for a given starting material there is a regular change in density, refractive index and viscosity with increasing chlorine content. According to the studies of the Hungarian Oil and Gas Research Institute, viscosity of chlorinated paraffins measured at 50 "C increases more rapidly than that measured at 100 "C with increasing chlorine content. Presumably this is due to a higher degree of association of molecules with increasing chlorine content, at least from chlorine contents exceeding 30 wt-%. These relationships are presented in Fig. 111-5 for products prepared from 55 "C melting point paraffin slab wax.
(B) PARAFFIN WAXES AND LIQUID PARAFFINS AS STARTING MATERIALS
283
.500 m
N
E
200
E 5 100' + -
6
U
50
r_?
20 I n"
1 I
0
10
20
I
I
30
40
50
Chloririe content, w t - %
Fig, Ill-5. Viscosity of chlorinated paraffins at 50 and 100 OC,versus chlorine content
I kinematic viscosity at 100 OC,2 kinematic viscosity at 50 'C
Chlorinated paraffins are usually soluble in petroleum, petroleum products and organic solvents. The solubility is dependent upon the chlorine content. Adequate stability of chlorinated paraffins is essential for their utilization. In some fields of application the temperature of the processing is high, in other fields the chlorinated paraffins come into contact with water or some other solvent. Should hydrochloric acid be split off in such cases, it would impair the quality of the product or might cause corrosion. For this reason, extensive research has been carried out to find inhibitors for dehydrochlorination and hydrolysis. Some stabilizersreported in the literature are various bases, e.g. tridhylamine, triethanolamjne, pyridine and pyridine-type cyclic compounds. Another mode of stabilization consists in passing superheated steam (120-130 "C) through the product in the presence of concentrated alkali. More recently, oxybromine compounds have been used to combine with the HCl and to prevent dehydrochlorination. Other authors report obtaining excellent results with dibasic lead phosphite (diphos) and with dibasic lead carbonate, regarding both dehydrochlorination and colour stability. Studies carried out in the Hungarian Oil and Gas Research Institute revealed that epichlorhydrin used as stabilizer for C,-C, chloroalkanes is successful also in stabilizing higher chlorinated paraffins.
(d) Applications of chlorinated parajins Monochloroparaffin is used for the alkylation of benzene, phenol and naphthaIene in the manufacture of detergents, lubricant additives (detergents, dispersing agents, oxidation inhibitors, antifrost agents) and textile finishing agents. Chlorinated paraffins are also used as intermediates for synthetic lubricating oils. In the presence of aluminium or zinc chloride catalysts they can be transformed into lubricant-like products by dehydrochlorination. The latter reaction is also used for producing olefins.
284
111. APPLICATIONS OF PARAFFIN WAXES AND LIQUID PARAFFINS
Chlorinated paraffins are also used in the manufacture of pesticides. The largest quantities of chlorinated paraffins are used in plastics processing. The most important characteristics of I.C.T. manufactured chlorinated paraffins, used as secondary PVC plasticizers, are listed in Table 111-45. The chlorinated Table 111-45. Characteristics of chlorinated paraffins manufactured by I.C.I. for use as PVC plasticizers Characteristics
Chlorine content, wt- % Average chain length Density at 25 OC, g/cm3 Viscosity at 25 'C, Pa.s Colour (Hazen units) Volatility, wt- %* Stability,** HCl wt- %
I
Ccreclor S-45
~
Cereclor S-52
42-45
50-52
c,,
c 1 . 5
1.15-1.17 0.15-0.25 50 2.8
0.15
1
1.23-1.26 0.9-1.9 60 1.4 0.15
Ccreclor 42
41-44 czs
1.15-1.18 1.5-3.0
250 0.4 0.15
* Percentage loss aher heating for 4 hours at 180 "C
** Heating at
175 " C ;N, flow rate 12 I/h
paraffin marketed under the trade mark Cereclor S-52 can also be used alone as a primary plasticizer in semirigid PVC compounds. In other cases it is combined with other plasticizers. Chlorinated paraffins substantially improve the resistance to cold of flexible PVC. At the temperature of injection moulding, it reduces the viscosity of the compound to an extent that allows an increased rate of processing. For improving the flame resistance of glass-fibre reinforced polyesters, polystyrene, phenolic and urea moulding powders, as well as synthetic rubber, chlorinated paraffins with a chlorine content of 70 wt-% are used. The characteristics of a solid chlorinated paraffin containing 70 wt- "/, chlorine, manufactured by Hoechst, are presented in Table 111-46. Table 111-46. Characteristics of Chlorparaffin Hoechst/70
Appearance White powder Chlorine content, wt- % 69-72 1.60-1.65 Density, di0 Viscosity** at 20 'C, Pa-s 0.01-0.03 Refractive index, n y 1.54-1.55 Melting point range,'C (DIN 53181) 65-80 1.o Volatility, wt-% (4 11, 150 "C) Stability,* HCI wt- % 0.1 Iodine colour number max. 5
* 20 g of the product +20
g paraffin oil in a 1 I/h nitrogen stream for 4 hours at 175 "C solution in toluene
** SO%
285
(B) PARAFFIN WAXES AND LIQUID PARAFFINS AS STARTING MATERIALS
Products with high chlorine content, in the range of 42 to 70 wt-%, are of excellent use as paint additives. They increase the resistance of the paint coat to water, chemicals and flame. Such paints are especially suitable for objects exposed to extremes of weather conditions. Lower chlorine-content chlorinated paraffins are used as binders and plasticizers. Chlorinated paraffin containing 70 wt-% chlorine is used as a binder. The chlorinated paraffins manufactured by I.C.T. for the paint industry are characterized in Table 111-47. Table 111-47. Chlorinated paraffins manufactured by I.C.I. for the paint industry I i
Characteristics
Cereclor 42
Cereclor 70
42 570 1.16 2.5 250 0.15
1I
Cereclor 65-L
Ccrcclor 70-L
70 1010 1.63
65 460 1.45
70 530
loo* 0.20
35.0 250 0.20
~-
Chlorine content, wt- % Molecular weight Density, d,25 Viscosity at 25 "C,Pa.s Colour (Hazen units) Thermal stability, g HC1/100 g
* 10 parts by weight Cereclor 70 + 100 parts by
-
1.55 2000.0 500 0.20
weight toluene
Chlorinated paraffin additives increase the pressure uptake capacity of gear oils and hypoid oils. Their use in cutting oils and boring oils substantially lengthens the service life of the machine tools. The setting point of fuel oil is reduced by 10 to 15 "C by adding a few tenths of 1% of chlorinated paraffin. Setting points of fuel oils with chlorinated paraffins as additives are presented in Table 111-48. Chlorinated paraffins are capable of replacing materials that are expensive or difficult to obtain in the leather, textile and paint industries. A blend of 25 wt- % polyvinylether with chlorinated paraffin containing 40 wt- % chlorine is a good substitute for fish tallow, whale oil, seal oil and tallow. Table 111-48. Setting point of fuel oils with chlorinated paraffin additives -
Chlorine content of additive, wt- %
-0.1 %~
I I -
_ 0.2 % _ -1 _
Fuel oil I1
- 12
.
- 15 -21 -3
0.2 %
0.1 %
additive
__ ___
4.75 11.4 15.0 Without additive
Setting point of fuel oil, "C
-
Fuel oil I
ad&tive
- 12
- 12 - 18 -21 -3
+
-9
- 12 - 18
-3
-18 -3
- 12
-I
I
~
__ Fuel oil I11
I
0.1%
-3 -6 -3 +3
Fuel oil I : 53 wt- % Sahara vacuum residue 47 wt- % Middle-East gas oil Fuel oil 11: 29.3 wt- % Sahara vacuum residue 22.1 wt-% MiddleEast vacuum residue Middle-East fuel oil Fuel oil 111: 30 wt- % Gabon vacuum residue 70 wt- % Gabon gas oil
+
+
0.2%
additive
- 21
- 18 - 18 +3
+ 48.6 wt-%
286
III. APPLICATIONS OF PARAFFIN WAXES AND LIQUID PARAFFINS
Large amounts of chlorinated paraffins with 40 wt-% chlorine content are used in the textile industry as willowing oil, shredding oil, carding oil and grease. Linseed oil varnish can also be replaced by chlorinated paraffins, with the advantage that the viscosity can be selected as desired by varying the chlorine content. In the food industry, chlorinated paraffins are used in the manufacture of packaging materials and fruit-preserving emulsions. Further uses are: impregnation of textiles, wood, paper and other materials to reduce flammability, manufacture of disinfectants, printing inks, dielectrics. One application that is gaining importance is in the area of flame-resistant plastics. In polyolefins, polyurethanes, etc., combinations of antimony trioxide and chlorinated paraffins are used as the basic additives to reduce flammability. In most formulations, it is endeavoured to produce a synergetic effect of the various additives in order to achieve good results. Japanese researchers found that if chlorinated paraffins, lead fluoride and antimony oxide are present as additives in the PVC compound, PVC-coated textiles are not only flame-resistant and waterproof, but protect, to a certain extent, against radioactive radiation. Chlorinated paraffins varying in chlorine content are also used to increase bond strength after vulcanization between nitrile rubber and neoprene, or natural rubber and ethylene-propylene copolymer elastomers. It is reported that without chlorinated paraffin, the bond strength is 80 N,km2, while the value, but when using chlorinated paraffin, is as high as 180 N/cm2.
Literature Asinger, F., Chemie und Technologie der Parafin-Kohlenwassersfof f e .Akademie-Verlag, Berlin (1957). Baird E., BIOS Rep. (Textile Auxiliary Products Manufactured by I. G. Farbenindustrie A. G. Ludwigshafen) No. 421 (1945). Bell-Fowler: Kunststoffe, 57, 671 (1967). Bell-McAdam: Kunststoffe, 57, 7 (1967). Bell-McAdam-Caesar: Gummi, Asbest, Kunstsoffe, 22, 803 (1969). Borzsonyi-Csiszar-Csik6s-Losonczy: MAFKZ KozlernCnyek (Comm. of the Hungarian Oil and Gas Research Institute), 15, 119 (1974). Csik6s-Losonczy-Borzsonyi-Csiszar : MAFKI K6zlemknyek (Comm. of the Hungarian Oil and Gas Research Institute). 12, 163 (1971). -: MA-FKZ K6zZernCnyek (Comm. of the Hungarian Oiland Gas Research Institute), 13, 113 (1972).
Eckhardt-Grimm: Farbe, Lacke, 73, No. 1, 36 (1967). Eckhardt-Teubel-Drescher : Freiberger ForschHft., A 194, 164 (1960). Fr. Pat., 774 128. Galina, R. S., Dokl. Akad. Nauk, SSSR, 88, 983 (1953). Galina-Nekrasov: Dokl. Akad. Nauk. SSSR, 100, 701 (1955). Gardner, F. T., Ind. Engng. Chem., 25, 1211 (1953). Ger. Pat. 673 332. Ger. Pat. 750 018.
(B) PARAFFINWAXESAND LIQUID PARAFFINS AS STARTING MATERIALS
287
Ger. Pat. 814 442. Ger. Pat. 2 200 985. Hendricks-Withe-Bolley : Ind. Engng. Chem., 42, 899 (1950). : Hoechst AG Prospekt. (Chlorparaffine). Hoyt, R., Synthetic Detergent and Washing Agents. BIOS Miscellaneous Rep., No. 11 (1945). Hiils Prospekt (Chlorparaffine in der Mineralol-, Textil-, Lederhilfsmittel-, Lack- u. Kautschuk-Industrie) (1968). I.C.I. Rep., No. 25, 437 (1947). I.C.I. Technical Service Note No. TS/B 2219. CERECLOR Chlorinated Paraffinic Hydrocarbons. Properties and Uses. I.C.Z. Technical Service Note No. TS/B 2224. CERECLOR Chlorinated Paraffinic Hydrocarbons. Properties and Uses. Z.C.Z. Technical Service Note No. TSlB 2226/1. CERECLOR Chlorinated Paraffinic Hydrocarbons. Properties and Uses. Jpn. Pat. 7 322 532. Jpn. Pat. I 390 397. Kolbel, H., Erdd, Kohle, 1, 308 (1948) Nekrasova, W. A., Doki. Akad. Nauk. SSSR, 88,475 (1953). Nekrasova-Shuykin: Vsp. Khim., 22, 179 (1953). -: Dokl. Akad. Nauk, SSSR, 97, 843 (1954). Losonczy, G., MdFKI jelentis (Final Report of the Hungarian Oil and Gas Research Institute), No. 5-121 (1969). Oltay-Gorognd-Egri: MA-FKI Kiaduciny (Report of the Hungarian Oil and Gas Research Institute), No. 67. (1953). Rhys, J. A,, Chem. Ind., 21, 187 (1969). Rosner-Teubel: Chem. Tech., B e d , 15, 662 (1963). Strauss, R., 01, Kohle, 11, 83 (1935). Teubel-Drescher: Freiberger ForschHft., A 194, 202 (1960). Teubel-Rosner-Leschner: Chem. Tech., Berf., 14, 320 (1962). Tumarkina-Posvolsky-Platonov: Zh. Prikl. Khim., Leningr., 23, 958 (1950). U.S. Pat. 2 025 024. US. Pat. 2 1I1 253. US.Pat. 3 914 513. Zach, M., Plaste Kautsch., 12, 11 (1976).
2. Sulfochlorination of paraffins and utilization of the products obtained The hydrocarbon feedstock for sulfochlorination is gas oil treated with oleum or normal hydrocarbon mixtures obtained from gas oil. To achieve odourless, white products, mixtures of normal hydrocarbons are required. A suitable starting material, as determined by gas chromatography, contains 99 wt-% normal hydrocarbons, has a melting point in the range of 0 to 5 "C, boils in the range of 230 to 320 "C, and has an average molecular weight around 210. Many researchers studied, in order to achieve optimum reaction conditions and products of higher grade by the pretreatment of the starting materials before sulfochlorination. For instance, Heinz recommended refining by adsorption, others suggested hydrogenation. Kiinster and Leuter introduce aqueous
288
111. APPLICATIONS OF PARAFFIN WAXES AND LIQUID PARAFFINS
ammonia solution into the system during sulfochlorination, since products treated with ammonia are lighter in colour and possess improved storability. Traditional batchwise sulfochlorination is similar to chlorination of paraffins, with the difference that sulfur dioxide and chlorine are introduced in suitable proportions. The reaction temperature is usually around 30 to 50 "C. Since the reaction is exothermic, the system must be cooled, so that double-wall reactors equipped with agitators are used. Riche and Weissenborn reported that in continuous operation there is a great risk of disulfochloride formation and chlorination. However, if the operation is carried out in several reactors coupled in series, these disadvantages can be partly or totally eliminated. Such systems consist of two or more cooled reactors fitted with agitators, and light sources protruding into the reactors. The inlet of the gar mixture and of the starting material is at the bottom of the reactors. The liquid phase leaving the individual reactors is led into the next reactor, while the hydrochloric acid formed passes through a spray catcher and leaves the system. Processes using gas recycling are also known. In the equipment developed by J. B. Roberts and co-workers the horizontal sections of a tubular reactor, fixed one above the other, are connected with elbow tubes. The gas mixture and the hydrocarbon feed continuously enters the system in the undermost horizontal section and flows upward. After leaving the tubular reactor it enters a gas-liquid separator which has an outlet for the hydrochloric acid gas in the upper part, and an outlet for the liquid product at the bottom. Cooling water flows downwards on to the horizontal sections of the reactor and is collected a t the bottom. Each section is irradiated separately by mercury vapour lamps. The residence time of the reactants in the reactor is 2 to 8 minutes. Lockwood describes a continuous vertical sulfochlorination equipment. It consists essentially of a vertical glass tube, the reaction taking place in its lower one third part. The inlet for the feed is at the top, that of the gas mixture at the bottom. The terminal gas leaves at the top, the product at the bottom of the reactor. The reactor is externally cooled with compressed air. Erlenbach and Sieglich found it expedient to introduce chlorine and sulfur dioxide under pressure, in the liquid state. Violent local reactions can thereby be eliminated and there is no need for cooling, since a substantial part of the heat of reaction is used up in vaporization of the liquid reactants. The products obtained by sulfochlorination of average CI5 normal paraffins can be used directly for tanning. Their effect is based on the reaction between the sulfochloride and the amino groups of the hide. Sodium alkyl sulfonates obtained by saponification of alkyl sulfochlorides are well-known, effective detergents. The reaction of alkyl sulfochlorides with sodium sulfide, in aqueous or alcoholic media, yields sodium alkyl thiosulfates :
R- S0,Cl
+ Na,S
+
R- S0,SNa
+ NaCl
These compounds are efficient wetting agents and detergents in neutral and alka-
(B) PARAFFIN WAXES AND LIQUID PARAFFINS AS STARTING MATERIALS
289
line media. Also, they are useful for preparing sulfur-containing ointments, detergents, etc. Alkyl sulfochlorides can be esterified, in the presence of ammonia, with aliphatic alcohols : R- SOlCl R’- OH + NH, -+ R - SO, - OR’ NHdCl
+
+
Among such esters, those prepared from C,-C,, alcohols are particularly good as plasticizers for PVC. Phenol esters obtained in the reaction between alkyl sulfochloride and phenolates are also suitable for plasticizing PVC: R-S02Cl
+ NaO-
0 0
-+R-SO,-O-
The C1 atom of the sulfochloride group readily reacts with ammonia and its derivatives, yielding alkyl sulfamides and their substituted derivatives:
+ NH&1 R - S02C1 + 2 NH@’ + R - SOZNHR‘ + R’NH,. HC1 R- SO&l+ 2 NHRS-+ R - SOZNR; + R;NH HCl R - S0,Cl
+ 2 NH,
-+
R- SO2NHz
*
These products are utilized as surface-active agents, and as plasticizers in the spinning bath for rayon fibres. C8-Cl8 alkyl sulfamides are efficient water-soluble detergents. Since they are susceptible to substitution reactiom on their amino groups, they form the basis for a number of further derivatives.
Literature Asinger, F., Chemie und Technologie der Parafin-Kohlenwassersto ffe. Akademie-Verlag. Berlin (1957). Kharasch-Brown: J . Am. chem. SOC.,61, 2142 (1939). -: J. Am. chem. SOC.,61, 3089 (1939). Kharasch-Chao-Brocon: J . Am. chem. SOC.,62, 2394 (1940). Ger. Pat. 742 927. Ger. Pat. 840 693. Ger. Pat. 881 794. Ger. Pat. 18 202. Ger. Pat. 18211. Ger. Pat. 20023. Sisk, G . F., Znd. Engng. Chem., 40, 1671 (1948). US.Pat. 2 197 800. U.S. Pat. 2 334 186. US.Pat. 2 665 305.
19
290
111. APPLICATIONS OF PARAFFIN WAXES AND LIQUID PARAFFINS
3. Manufacture of fatty acids, dicarboxylic acids and alcohols by the oxidation of paraffins, and utilization of the products
The possibility of obtaining fatty acids by oxidation of paraffins was already known at the beginning of the 20th century. Large-scale production by construction of commercial paraffin-oxidizing plants took place in the period between World Wars I and 11. Meanwhile the process was further developed into variants yielding alcohols or dicarboxylic acids as products. During the first half of this century the increasing amounts of vegetable and animal fats and oils being processed was in keen competition with the paraffin oxidation process. After World War 11, the rapidly developing petrochemical industry produced such a wide variety of products and processes that paraffin oxidation lost much of its importance. This is, however, valid for the Western world only. In the socialist countries, the situation is not quite the same. Here, and above all in the Soviet Union, large amounts of paraffin are still subjected to oxidation, and plants for the oxidation process are being built and enlarged even at the present time. The oxidation mechanism of paraffins was dealt with in Chapter I(B), so it will not be discussed here; only the technological processes will be explained. (a) The main variants of parafin oxidation
The final products to be obtained by paraffin oxidation are fatty acids, alcohols or dicarboxylic acids. For manufacturing fatty acids, the autoxidation of paraffins is carried out at 105-120 "C, in the presence of a catalyst, primarily'potassium permanganate, but manganese, cobalt or other salts of fatty acids are also used as catalysts. In this method, fatty acids and esters of fatty acids are found among the oxidation products. A range of fatty acids is obtained from the products of hydrolysis, thermal treatment and distillation. Splitting of the carbon chain always occurs in oxidation, so that the number of carbon atoms contained in the acids is less than those of the starting hydrocarbons. In another process, oxidation is carried out in the presence of boric acid or boric anhydride. The process yields secondary alcohols. After separation and purification, individual alcohols, or a mixture of alcohols within a narrow carbon atom range, are obtained. In contrast to the previous process, the number of carbon atoms in the product is identical with that of the starting hydrocarbon. In a further process, where oxidation is carried out at higher temperatures (160-170 "C) under pressure, the end products are C&, dicarboxylic acids.
(b) The manufacture of fatty acids by paraBn oxidation Starting materials. For the purpose of manufacturing C,&, fatty acids, a wide range of paraffins, usually in the molecular weight range of C18-C30, is suitable for use as starting material. Any member of the fatty acid series, from formic
(B) PARAFFIN WAXES AND LIQUID PARAFFINS AS STARTING MATERIALS
29 1
acid to that identical, with regard to carbon atom number, with the highest hydrocarbon present in the starting material, can be formed in the oxidation. Experience has shown that the fatty acids present in the largest amount in the reaction product are those, whose carbon atom number is approximately half of the average carbon atom number of the starting material. This is due to the oxidation rate being highest at the methylene group furthest from the methyl group. Emanuel, Denikov and Mayzus, amongst others, have studied the grade of products obtained by oxidation of paraffins having different compositions. The characteristics of the paraffins oxidized under identical conditions in their largescale laboratory experiments are listed in Table 111-49. In all cases the feed conTable 111-49. Characteristics of paraffin waxes suitable for the manufacture of fatty acids Paraffin wax
I
Melting point,
"C
Boiling range, ~
"C
1
Molecular weight
1
Average atom number
in molecule
Soft synthetic paraffin wax
34.0
280-390
275
19.4
Drogobych paraffin wax
52.8
340-470
396
28.1
Kuybishev paraffin wax C
54.2
370-430
432
30.7
High molecular weight synthetic paraffin wax
56.6
380-480
442
31.5
Kuybishev paraffin wax B
60.9
405495
450
32.0
sisted of 1/3 of fresh paraffin and 2/3 of recycled paraffin. Oxidation was carried out in the presence of 0.2 wt-% potassium permanganate. At the start, the temperature was 125 "C. After reaching an acid value of 6 to 7 mg KOH/g, the temperature was reduced to 107 "C at a cooling rate of 2 "C/h. Oxidation was terminated when an acid value of 70 mg KOH/g was reached. Air consumption was 100 l/kg h in all experiments. The results indicated that the acids had an average carbon atom number equivalent to 5240% of that in the original paraffins. Fractionation of the crude fatty acid mixture, with respect to carbon atom number, showed a distribution by mass depending on the average molecular weight of the starting material. Increases of the latter result in reduced yields of the C&, fraction, higher yields of the >C,, fraction, and highest values in the yields of the C,,-C,, fraction. The composition of the oxidation product is affected not only by the average molecular weight of the starting material, but also by its chemical composition. Table 111-50 presents the normal and branched hydrocarbon content of the paraffins characterized in Table 111-49, and the yield of branched acids obtained from them. Under the above oxidation conditions, the production of acids forming no complexes with urea increases parallel with the branched hydrocarbon content of the paraffins : it is 17.4 wt- % for the soft synthetic paraffin, and as high as 23.1 wt- % for Kuybishev paraffin C. These "iso-acids" are dark, foul-smelling
-
19'
292
111. APPLICATIONS OF PARAITIN WAXES AND LIQUID PARAFFINS
Table IZZ-50. Percentage of normal and branched hydrocarbons in the paraffin waxes listed in Table III-49, and share of branched fatty acids obtained from them [n-Hydrocarbon content
as determined with urea, branched hydrocarbon content as determined by nitric acid oxidation] ##-Hydro-
1
Yield of a c i d
Branched
wt- %
Paraffin waxes
I Soft synthetic paraffin wax High molecular weight synthetic paraffin wax Drogobych paraffin wax Kuybishev paraffi wax B Kuybishev paraffin wax C
I
in paraffin
____
I
total acid
yield
98.5
7.0
17.4
99.5 98.5 97.5 99.9
14.8 19.5 21.o 25.0
19.7 24.1 21.5 23.1
liquids. The study showed that branching close to the end of long carbon chains yield iso-acids. In such cases the oxidation does not start at the tertiary carbon atom, but further away from the branching, on some methylene group. From the viewpoint of producing straight-chain acids, therefore, short and chain-end branchings are drawbacks. Another important consequence follows from the data in Table 111-50. Knowledge of the normal hydrocarbon content as determined by the urea method is insufficient information to forecast the fatty acid composition to be expected. Paraffin oxidation experiments in an industrial-scale, bubble-type reactor were carried out at the Kuybishev Petrochemical Plant, with paraffins in the b.p. range of 262 to 360 "C and 356 to 450 "C, using manganese-sodium soap as catalyst. Catalyst concentration relative to manganese was 0.07 wt- %, air consumption 60 normal ms/t * h, reaction temperature 110 "C.The results confirmed, as shown in Table 111-51, that lower-boiling starting materials yield more C,-C,, acids and less >C1, acids than higher-boiling starting materials. Table ZZZ-51. Compositions of fatty acid mixtures from 356-450O C and 262-360 OC boiling-range paraffin waxes
Fatty acids
iI I
c 5 c I 3
c,-c9 C10-GI3
C,,-C20
c,,
Distillation residue and distillation loss
Composition of fatty acid mixture, wt-% from 356-450 ' C b.r. paraffin
'
from 262-360 "C b.r. paraffin
2.7 14.7
2.7 10.3 34.0 19.0 13.1
36.7 10.4 10.9
20.9
24.6
294
111. APPLICATIONS OF PARAFFIN WAXES AND LIQUID PARAFFINS
Catalysts. Salts of variable-valency metals are not only capable of accelerating or inhibiting the reaction, but also have an effect on its course. Iron, manganese and cobalt, for instance, promote ester formation. The acid value to saponification number ratio of the oxidized product is lower, when an iron catalyst is used, than with a manganese catalyst. To increase the selectivity of oxidation, mixed catalysts are frequently used by industry. They contain mainly manganese, potassium and sodium. Experiments with manganese catalysts demonstrated that potassium permanganate, which is relatively expensive, can successfully be replaced by waste containing manganese oxides. Such manganese containing wastes also occur in other branches of industry. To illustrate the catalyzing effect of such wastes, the peroxide value, acid value, ester value and carbonyl value for a 52.6 "C melting point paraffin wax starting material are plotted versus time of reaction in Fig. 111-6. The waste used as catalyst contained 3.5 wt- % MnO, 65.0 wt- % Mn,O, and MnO,, 7.0 wt- % KOH and 24.0 wt-% water. It was added to the reactants in the seventh hour of oxidation. In all runs the catalyst concentration was equivalent to 0.1 wt-% of metallic manganese. The figure clearly demonstrates the rapid decrease in the concentration of peroxide compounds, and the increase in the rate of acid formation, parallel to
.2 0 0 N
8 1.5
$16
-=
F12 a-
E aJ-
9
10
3 8
9
.-K 0.5
2 I?
2 4
'0
2
4 6 8 10 12 14 Time of reoction, h
16 Time of reaction, h
.
12
12
0
l
0
2 . 4 6 8 10 12 14 Time of reaction, h
/
!
l
16 Time of reaction, h
Fig. 111-6.Effect of manganese dioxide on the characteristics of the oxidized product
" 3
(B) PARAFFIN WAXES AND LIQUID PARAFFINS AS STARTING MATERIALS
293
Oxidation of microcrystalline paraffin waxes is also of interest. Such research works have been carried on at the Hungarian Oil and Gas Research Institute. The starting materials were a ceresin of foreign origin, and a ceresin prepared from Algy6 petrolatum by de-oiling at 0 and 20 "C. Their characteristics are presented in Table 111-52. The experiments were carried out in a 5 litre working volume tank Table ZII-52. Characteristics of microcrystalline paraffin wax feed for oxidation experiments - -
~~~
Ceresin from AlgyB petrdatum
I
Imported ceresin (A)
Characteristics
Density, dO : Drop melting point, OC Congealing point, OC Penetration at 25 'C, 0.1 mm* Oil content, wt- % Viscosity at 100 OC, mmys
I'
>iOiei
'
1-
+20"C(B)
,
0 ° C (C)
-
0.7671 75.0
-
78.0 75.0
76.0 70.0
9 0.2 4.64
13 3.1 9.86
21 5.0 11.18
With the needle used for testing bitumens
reactor equipped with a turbine agitator operating at 1720 rpm. The ratio of height to diameter of the liquid column in the reactor was 2.3 to 2.6. Experimental conditions were : 2.5 wt-% cobalt stearate catalyst, 120 "Coxidation temperature, 120 l/kg h air flow rate. The properties of the products obtained are listed in Table 111-53. By comparing the data referring to the two AlgyB starting materials it is clear that de-oiling at 20 "C resulted in a ceresin that is more readily oxidized than by de-oiling at 0 "C. It is remarkable how greatly the properties of the products obtained from these two starting materials differ although their acid value is identical. Table 111-53. Characteristics of the products obtained by oxidation of the microcrystalline paraffin waxes in Table 111-52 -
__
-
--
Characteristics ~
__
____~
Code-mark of product Oxidation time, h Acid value, mg KOH/g Saponification number, mg KOH/g Ester value, mg KOH/g Ester value/acid value Non-saponifiable part, wt- % Drop melting point, OC Penetration at 25 'C, 0.1 mm (ASTM needle) Viscosity at 100 OC, mm*/s
_
l--A
_
_
All 14 76 182 106 1.4 31.5 55
33 8.40
I
Obtained from feed
B
BII 17 75 161 87 1.7 41.2 68 42 20.88
1
_____
~~~
C
C/1 7 28 64 37 1.3 62.0 69
35 17.93
Cl2 17 58 141 83 1.4 48.2 65 74 34.80
c/3
22 12 170 98 1.4 42.8 63
95 49.09
(B) PARAFFIN WAXES AND LIQUID PARAFFINS AS STARTING MATERIALS
295
the decrease in the amount of carbonyl compounds that are being transformed into acids. Investigations showed that when potassium permanganate is used, the catalytic action is in fact effected by the manganese dioxide and manganese oxide, in a finely divided state, formed from potassium permanganate when the latter is added to the reactants, or at the start of oxidation. The manganese oxides initiate the chain reactions between molecular oxygen and paraffins, and accelerate the decomposition of peroxide compounds. The composition of the Mn,O,;MnO, mixtures formed from potassium permanganate depends on the conditions of mixing to the reactants. The oxide mixture always contains substantial amounts of potassium (about 40 wt- %) and water. The potassium content affects the rates of reaction and also the composition of the product. Potassium soaps, on the one hand, decelerate the reactions, and on the other hand increase the selectivity of the catalyst. Processes are also known in which manganese and sodium soaps of C,-C, fatty acids are used as catalysts. The advantage of using metal soaps that are soluble in the mixtures of paraffins and recycled non-saponified compounds, is that oxidation can be carried out at lower and constant temperatures. If sodium soaps are used, the non-saponifiable material must be freed from sodium, by washing, before it is recycled into the system to avoid undesirable sodium enrichment. Oxidation conditions for a 52 "C melting point paraffin, catalyzed by potassium permanganate, manganese dioxide and manganesesodium soaps, as well as the characteristics of the products obtained are summarized in Table 111-54. Table 111-54.Oxidation of 52 OC melting point paraffin wax in the presence of various catalysts
I 1
Catalyst
Temperature of o x i e p
Catalyst concentration, wt- %
Mn
I,
-~ Characteristics of product ~
K(Na)
I
Aqueous solution of KMnO,
105-120
0.1
Aqueous suspension of MnO, 105-1 20
0.1
Manganese and sodium soaps of C,-C, acids
0.07
110
0.071 0.0057-0.013
0.042
65
115
16
32
3.8
66
121
22.2
33.4
5.9
64
106
9.9
34
2.6
The feed consisted of 213 parts of non-saponifiable recycled material and 1/3 part of the paraffin starting material. As demonstrated by the data, manganesesodium soaps, as compared to potassium permanganate and manganese dioxide,
296
111. APPLICATIONS OF PARAFFIN WAXES AND LIQUID PARAFFINS
suppress, partly owing to the lower temperature of reaction, the formation of esters, carbonyl compounds and hydroxylic acids. Technology and equipment of parafin oxidation. The oxidation of paraffins can be carried out in both batchwise and continuous operation. The disadvantage of batchwise operation is the low level of air oxygen utilization, not exceeding 20 to 35 vol-%. Also, the yield of hydroxylic acids and water-soluble low fatty acids are relatively high, and finally, the distribution of the fatty acids obtained relative to carbon atom number is not uniform. For these reasons, much work has recently been done to develop continuous operation. Berdyansky operated a process on a pilot-plant scale. Four columns coupled in series are used. The inlet for the co-current paraffin and air is a t the bottom of the first column, the final product outlet at the top of the fourth column. The catalyst is mixed into the feed before introducing it into the column. The continuous process developed in the Grozny Institute for Petroleum Technology used three columns coupled in series. Before comniencing the continuous oxidation process, the starting material is oxidized in batchwise operation up to an acid value of 2 to 3 mg KOH/g. The catalyst is subsequently added and this material fed into the continuous equipment. The batchwise pre-oxidation requires about 30 minutes. The jacketed columns allow cooling and heating. Fresh air is blown in with the feed a t the bottom of each column and flows together with the liquid phase through all three columns, that is, no gas outflow takes place in the first and second columns. Table 111-55 summarizes the characteristics of the products leaving the successive columns, for a paraffin starting material boiling in the 350-470 "C range, having an average molecular weight of 375: It may be seen that oxidation is most intense in the first column: its product contains 18.5 wt-% acid non-soluble in water. In the fatty acid mixture finally obtained
Table 111-55. Main characteristics of the products from the continuous oxidation of a 350-470 OC boiling range, average molecular weight 375 paraffin wax Characteristics
Characteristics of the oxidation product acid value, mg KOH/g saponification number, mg KOH/g Composition of the oxidation product non-saponifiable part, wt- % water-soluble acids, wt- % hydroxylic acids, wt- % Characteristics of fatty acids acid value, mg KOH/g ester value, mg KOH/g
!-
No. of oxidation column __ 1
1
2
31 60
58 88
78.5 0.9 0.13
71.0
200 28
-
0.25 196 30
1
3
74 117
68.0 1.9 0.71 208 46
(B) PARAFFIN WAXES AND LIQUID PARAFFINS AS STARTING MATERIALS
297
from the third column, the C,,-C,, fraction represents 50 wt-%, the >Cz0 fraction 23 wt-%. In the chemical plant in Shebekino, not only fatty acids, but also fatty alcohols are manufactured by paraffin oxidation. The equipment consists of four columns coupled in series, with counter-current flow of the feed and the air. Air-lift pumps are used to transfer the liquid phase from column to column. The reaction mixture outlet is at the bottom of the columns, the inlet is at the top of the next column, above the level of the foaming liquid. Air outlet is at the top of each column. Air nozzles at the bottom of the columns blow air onto the bottom plates of the columns to prevent sedimentation of the catalyst in the form of mud. The catalyst is manganese dioxide or potassium permanganate, the latter in the form of a 10 wt-% aqueous solution, the former in the form of a suspension. The catalyst is added at 120 "C. The ratio of fresh starting material and recycled material in the feed is 1 : 2. The feed and the catalyst are mixed in two stirred tanks operated batchwise. In one of these is carried out the mixing, the other feeding the continuously operated columns. The temperatures in the columns are, in their order of operation, 116, 1 12, 110 and 104 "C,respectively. The acid value of the reaction products leaving the successive columns are 17 to 22, 30 to 35, 50 to 55 and 65 to 72 mg KOH/g, respectively. A continuous foam-phase paraffin oxidation process has been developed in a Kazan plant for synthetic lubricants. The type of air disperser that resulted in a foam height yielding high rates of acid formation, but requiring low air consumption, was determined experimentally. 2.0 mm hole diameter, 14.3% free crosssectional area grids, spaced at a distance of 5.7 mm were found to be the most efficient. The foam column in the pilot plant was 800 mm in diameter and 4960 mm in working height. The column was jacketed to allow cooling, and a coil tube for steam heating of the paraffin was installed in the reactor. The air disperser grids were fitted into the bottom of the column. The starting material was a 50 "C melting paraffin wax with an oil content of 4.4 to 4.7 wt-%. The feed had a ratio of fresh starting material and recycled material of 1 : 1. The catalyst used was 0.16 wt- % manganese oxide and 0.17 wt- % sodium carbonate. The characteristics Table 111-56. Characteristics of the oxidized product obtained in a foam column reactor at 13OoC (Starting material: paraffin wax, m.p. 50 "C, oil content 4.4-4.7 wt- %) Acid value, mg KOH/g Saponification number, mg KOH/g Carbonyl value, mg KOH/g Composition of product, wt-% fatty acids water-soluble acids hydroxylic acids non-saponifiable
39.7 84.7 12.9
25.7 3.3
0.9 70.3
298
111. APPLICATIONS OF PARAFFIN WAXES AND LIQUID PARAFFINS
of the product obtained at 130 "C are listed in Table 111-56. After hydrolysis, the product was subjected to heat treatment in an autoclave, first at 180 "C at a pressure of 12 MPa, and subsequentIy at 320 "C for 45 minutes. The characteristics of the fatty acid mixture obtained were as follows: acid value 216.11 mg KOH/g, saponification number 229.23 mg KOH/g, ester value 13.3 mg KOH/g, carbonyl value 21.9 mg KOH/g. Distillation of the mixture yielded 42.6 wt-% C,o-C,6 and 20.4 wt-% C17-C21fatty acids. The amount of water-soluble fatty acids in the fractions varied between 4 and 20 wt-%. These results allowed the conclusion that foam columns not only have a substantially larger output per volume as compared to bubble reactors, but also allow higher temperatures of oxidation, up to 140-160 "C, without impairing the grade of the product. A further advantage is that residence times are relatively short. (c) Manufacture of alcohols by parafin oxidation The processes in use are: (i) Manufacture of fatty acids by oxidation and subsequent hydrogenation of the fatty acids or their esters. The products are straight-chain primary alcohols. (ii) The Bashkirov synthesis : oxidation in the presence of boric acid, yielding fatty alcohol borates that are subsequently hydrolyzed to straight-chain secondary fatty alcohols. (iii) Starting from the "non-saponifiable" products of fatty acid manufacture a mixture of primary and secondary alcohols can be produced by extraction or through esters of boric acid. Alcohol manufacture by hydrogenation of esters of fatty acids. One of the recognized processes utilizes butyl esters of C,-C,, Clo-Cl, or C10-C20fatty acid fractions to manufacture primary fatty alcohols. 35 wt-% excess butanol is used in esterification. Maximum temperature is 250"C, the pressure does not exceed 1000 kPa, esterification time is 8 hours. Water formed in the esterification reaction is removed by distilling off the butanolwater azeotropic mixture. After condensation this mixture separates into two phases, and the upper phase containing about 20 wt- % of water is recycled into the esterification process. Esterification is terminated when the acid value of the reaction mixture decreases to 5 mg KOH/g. Excess butanol is removed by distillation. The crude esters are purified with sodium hydroxide solution at 90 "C, under pressure, by a continuous operation process. The soaps formed are separated from the esters by centrifuging. The latter are then washed with water, and dried at 90 "C under reduced pressure in packed columns. The purified esters, with an acid value below 0.5 mg KOH/g, are then hydrogenated at pressures of 20-25 MPa and temperatures of 230 to 270 "C, with basic zinc and copper carbonate as catalyst. The hydrogen content of the hydrogenating gas is 96 vol-%.
300
111. APPLICATIONS OF PARAFFIN WAXES AND LIQUID PARAFFINS
Table 111-57. Technological conditions of the Esso process -__
--
I
I
Conditions
Oxidation temperature, OC Paraffin conversion, % Rate of paraffin oxidation, %/h Oxygen concentration in inlet gas, vol- %
Batchwise operation
Continuous operation
166-171 10-30
145-177 5-17.5 10-30 7-21
10-1 6 7-21
Table 111-58. Composition of feed and products in the Esso process
I
I
Compounds
1
Feed, wt-%
Oxidized product, wt- %
~
I . _ _
I---.
Alcohols Ketones Acids Esters Lactones Bifunctional alcohols Ketoalcohols Paraffins
2.5 2.7 0.1 1.1 0.1 0.5 0.0 93.0
11.5 3.7 0.5 0.8 0.4 3.2 0.4 79.5
Percentage of compounds formed in the course of oxidation ~- .~
78 21 80 75 84 -
Table 111-59. Hydrogenation of distilled alcohols obtained in the Esso process Compounds
I
Composi’on Of crude alcohol before hydrogenation, wt- %
I Composition , Percentage of hydrogenat- of compounds ed product, wt- % removed
two-stage fractional distillation. The head product alcohols are refined by hydrogenation. The characteristics before and after hydrogenation are listed in Table 111-59. Alcohol recovery from the non-sapon8able part of the para@n oxidation product. In paraffin oxidation, in addition to fatty acids, neutral oxidation products including alcohols are also formed. These alcohols can be separated from the so-called non-saponifiable products in the course of processing the oxidation products. The average percentage of alcohols in the non-saponifiable product is 16 to 18 wt-%, primary alcohols yielding only 15 to 16 wt-% of total alcohol content.
(B) PARAFFIN WAXES AND LIQUID PARAFFINS AS STARTING MATERIALS
299
Manufacture of alcohols by the Bashkirov process. This process, used on an industrial scale, is based on paraffin oxidation at 165-170 "C in the presence of 5 wt- % boric acid, using a mixture of nitrogen and oxygen with an oxygen content of 3.5 to 4.2 vol-%. For a conversion of 15 %, the reaction time is about 4 hours. The major part of the converted paraffins yields alkyl borates. The unreacted part, separated by vacuum distillation and treated with alkali, is subsequently recycled to oxidation. Fatty alcohols are obtained from the alkyl borates by hydrolysis at 90-100 "C.Fatty acids contained in the alcohols are separated by saponification and subsequent distillation. The Esso process is largely similar to the Bashkirov process, with only the difference that two hydrogenation units are used. The alcohols contain only a few percentages of primary alcohols, their carbon atom number is identical with that of the starting paraffins. The grade, mainly the colour and odour of the crude alcohols is improved, after alkali treatment, by hydrogenation. Recycled paraffin is also subjected to hydrogenation, in order to convert the ketone content into alcohols. The flow scheme of the Esso process is presented in Fig. 111-7. Technological conditions are summarized in Table 111-57, and characteristics of the feed and the product of oxidation in Table 111-58. In the Esso process, too, the secondary alcohols are recovered from the borates by hydrolysis. Secondary alcohols are separated from bifunctional alcohols by Paraffin starting material
.--
Paraffin
-4
NaOHt H20
Pretreatment by hydrogenation
H,O+NaOH
H2
I
Waste gas
t
Fresh
Paraffin recycling Alcohols to distillation \
zi:n ,
I+
I
Air
I
Paraffin distillation
Boric acid recycling
1
1I
Hydrolysis and1 saponification
I
Fig. 111-7. Simplified flow diagram of the Esso process for the manufacture of alcohols by
p a r a h oxidation
(B) PARAFFIN WAXES AND LIQUID PARAFFINS AS STARTING MATERIALS
301
Table ZZZ-60. Yields of alcohols recovered from the second-grade non-saponifiable part
Second-grade non-saponifiable part Fraction 1 (up to 300 "C) Fraction 2 (300-350 "C) Fraction 3 (350-400 "C) Distillation residue
100 11.7 11.5 28.0 48.8
22.0 45.5 28.6 12.3 18.7
38.1 76.3 45.0 41.8 12.1
8.4 4.1 1.5 1.5 1.1
As mentioned earlier, the first stage in processing the crude product of oxidation in the manufacture of fatty acids is saponification. The separation of the soaps from the non-saponifiable product is carried out in three stages. In the first stage, carried out without using pressure, at 100 to110"C, about 30 wt-% of the non-saponifiable products are separated, and this is called the "zero-grade part". The residual part is transferred into a tubular furnace, where it is heated to 200 "C and pressure is increased to 2500 kPa. Separation takes place in an autoclave: the separated "first-grade part" is again about 30 wt-% of the total nonsaponifiable product. The "second-grade part" is recovered in the third stage, at 360 to 400 "C. In this stage, chemical reactions (e.g. decarboxylation) also take place. Primary alcohols are found in significant percentages in the second-grade part only. Table 111-60 presents the distribution, by boiling point, of the alcohol content in the second-grade non-saponifiable part recovered in the Shebekino synthetic fatty acid plant. When primary alcohols are recovered through their borates, hydrocarbons are separated by distillation, and alcohols are set free by hydrolysis. Primary alcohols, or fractions rich in primary alcohols, are prepared by vacuum distillation of the crude alcohols. According to the data in the literature the bottom product contains secondary alcohols only. In the enriched final product the percentage of primary alcohol may reach a value as high as 75 wt-%. In a Soviet process the non-saponifiable product is subjected to hydrogenation, in order to convert carbonyl groups into hydroxyl groups. Subsequently, alcohols are extracted using methanol. Batchwise hydrogenation is carried out at 160 to 190°C and 5 MPa pressure, in the presence of a copper-chromium catalyst. Hydrogenation time is 4 hours. In continuous hydrogenation, optimum conditions are: temperature 160 "C, pressure 30 MPa, space velocity 0.3 kg/h kg, nickel catalyst on chromium oxide support. The final alcohol product after hydrogenation, extraction with methanol and alkaline wash contains 20 to 22 wt-% C,-C12 and 24 to 26 wt- % C,,-Cl, alcohols. The C,,-C, alcohol percentage is around 50 wt- %.
-
302
111. APPLICATIONS OF PARAFFIN WAXES AND LIQUID PARAFFINS
(d) Utilization of paraffin oxidation products C,-C, fatty acid fraction : esterification and subsequent hydrogenation of the esters yields primary alcohols needed for the manufacture of plasticizers. C,,-C,, fatty acid fraction : esterification and subsequent hydrogenation yields fatty alcohols needed for detergents. C,,-C,, fatty acid fraction : additive in the polymerization of synthetic elastomers. C,,-C,, fatty acid fraction : utilized for manufacturing soaps. C,,-C,, fatty acid fraction: for soap manufacture and for fatty alcohols. C,,-C,, fatty acid fraction: for lubricants and for heavy metal soaps. The residues from fatty acid distillation are used in cable fillers, printing inks and in the manufacture of colorants. An interesting field of application for C,-C, fatty acids is conversion into ketones in the presence of iron catalyst. Symmetric ketones are formed at 300 "C,CO, and water being eliminated. These ketones can then be hydrogenated to secondary alcohols at 100 to 130°C and 10 MPa, in the presence of nickel catalysts. The secondary alcohols yield water-soluble ether alcohols with ethylene oxide, which are used directly, or after sulfonation, as surface-active agents in the textile industry. Higher fatty acids or their esters with mono- or multifunctional alcohols are used as lubricants for plastics in PVC processing.
Table ZZZ-61. Characteristics of products obtained by esterification of oxidation product A in Table 111-53 (acid value 76 mg KOH/g). Alcohol: ethylene glycol Products Characteristics
Initial saponification number of oxidized product, mg KOH/g
182
182
182
Initial ester value of oxidized product, rng KOH/g
106
106
106
Non-saponifiable part of oxidized product, wt- % Molar ratio of acid to alcohol Initial temperature of esterification, O
c
Final temperature of esterification, OC
31.5
31.5
31.5
1 : 0.5
1 :1
1 :2
106
106
107
114
112
112
Characteristics of esterified product Acid value, mg KOH/g
23.5
Congealing point,
55
55
55
40
50
40
O
c
Penetration at 25 OC, 0.1 mm (ASTM needle) Viscosity at 100 "C, mmE/s
9.9
9.21
5.5
8.68
303
(B) PARAFFIN WAXES AND LIQUID PARAFFINS AS STARTINGMATERIALS
Oxidation products of microcrystalline paraffin waxes are substitutes for natural waxes (carnauba wax, bees-wax, etc.). They are also used for manufacturing socalled emulsion waxes (esters of high fatty acids with multifunctional alcohols) and textile finishing agents. Some of the experimental results obtained in the Hungarian Oil and Gas Research Institute are summarized in Tables 111-61 and 111-62. Table 111-62. Characteristics 01 products obtained by esterification of oxidation product I3 in Table 111-53 (acid value 75 mg KOH/g). Alcohol: ethylene glycol Characteristics
I-
Initial saponification number of oxidized product, mg KOH/g Initial ester value of oxidized product, rng KOH/g Non-saponifiable part of oxidized product, wt- %
Molar ratio of acid to alcohol Initial temperature of esterification, "c Final temperature of esterification, "C
Products a
l
b
__ l
c
161 87
161 87
161 87
41.2 1 : 0.5 103 108
41.2 1 :1 99 I08
41.2 1 :2 106 110
16 67 41 -
15 67 48 -
Characteristics of esterifed product Acid value, mg KOH/g Congealing point, Oc Penetration at 25 OC, 0.1 mm (ASTM needle) Viscosity at 100 O c , mmys
32 66 40 37.66
In the U.S.A., oxidation of low oil-content ceresins is used to obtain highmelting products suitable for replacing bees-wax, carnauba wax and montan wax. The characteristics of such a product are listed in Table 111-63. Table 111-63. Characteristics of a product obtained by oxidation of ceresins, suitable for replacing natural waxes Melting point OC Acid value, mg KOH/g Saponification number, mg KOH/g Penetration at 25 OC, 0.1 mm
81 20 60 10
In Hungary too, the oxidation of ceresin in the presence of catalysts, from a starting material melting at 75 "C was carried out for some time, primarily to replace bees-wax. The colour, odour and the chief properties of the product listed in Table 111-64 were close to those of beeswax. Earlier Hungarian experiments demonstrated that 20 % of the wax comb foundation can be replaced by this product, and bees readily accept it in the period of acacia blossoming.
3 04
111. APPLICATIONS OF PARAFFIN WAXES AND LIQUID PARAFFINS
Table 111-64. Properties of oxidized ceresin suitable for replacing bees-wax ---________ Properties
Oxidized ceresin
Melting point, O C Acid value, mg KOH/g Saponification number, mg KOH/g
65-67 54-55 98-110
Bees-wax
63-66 19-24 90-110
Literature Anders, H., Feffe,Seifen, 54, No. 2, 77 (1952). Babaev-Rusinov: Khimiya Tekhnol. Topl. Masel, 8 , No. 1, 24 (1963). Babaev-Chelitseva: Neffepererab. Neftekhim., No. 12, 22 (1973). Badanov-Mutriskov: Khimiya Tekhnol. Topl. Masel, 21, No. 1, 38 (1976). Bashkirov-Kamzolin: Fifth World Petroleum Congress, Sec. IV, Paper 15, 175 (1959). Bawn, C. E., J. Oil Colour Chem. ASS., 36, 443 (1953). Broich, F., Chem. Zng. Tech., 34, 45 (1962). Brunshteyn-Klimenko: Khim. Prom., No. 9, 22 (1963). Coafing, 9 , No. 5 , 112 (1976). Dressler-Uhde: Fetfe, Seifen, Anstr-Mittel, 78, 235 (1976). Franke: Energie Tech., 25, 388 (1975). Gavrilov, V. G., Zh. Prikl. Khim, Leningr., 40, 1544 (1967). Geisbrecht-Daubert: Znd. Eng. Chem. Process Des. Deu., 15, 115 (1976). Gubanova-Stepanenko : Neftepererab. Neftekhim. Slantsepererab., N o 1, 39 (1 976). Gysovsky-Shcheglova: Zh. Priki. Khim,Leningr., 37, 1324 (1964). Igonin-Svitkin: Khimiya Tekhnol. Topl. Masel, 7,No. 2, 29 (1962). Igonin-Svitkin-Mitrofanov: Maslob. zhirov. Prom., 11, No. 11, 20 (1961). Ilina-Smagina: Khimiya Tekhnol. Topl. Masel, 20, No. 2, 5 (1975). Ilinova-Perchenko-Terechenko: Khimiya Tekhnol. Topl. Masel, 9, No. 7, 39 (1964). Ivanova-Rapoport-Sudarikova-Sheynina-Polina: Khimiya Tekhnol. Topl. Masel, 17, N o . 6, 24 (1972). Kirk-Othmer: Encyclopedia of Chemical Technology, 15, 102, J . Wiley Interscience Publ., New York (1968). Krylov-Vishinyakova: Neffepererab. Neftekhim., No. 2, 42 (1975). Leibnitz-Hager-Heinze-Herrmann-Kaiser-Mittelsteadt-Moll-Schlief: 1. prakt. Chem., 1, 337 (1955). Levina-Moskovich-Freydin-Gyskovisky : Khimiya Tekhnol. Topl. Masel, 10, No. 4,26 (1965). Madyakina, R. V., Khimiya Tekhnol. Topl. Masel, 8 , N o . 11, 15 (1963). Mushenko-Gyskovsky: Neftepererab. Neftekhim., No. 4, 35 (1968). Novak-Kashkirov: Neftekhimiya, 15, 863 (1975). Perchenko-Marchenko : Khimiya Tekhnol. Topl. Masel, 15, No. 4, 30 (1970). Perchenko-Kotelnikov-Marchenko : Khimiya Tekhnol. Topl. Masel, 9, No. 2, 22 (1964). Perchenko-Morgunov: Neftepererab. Neftekhim., No. 1, 41 (1978). Pereverzev-Roshchin : Neffepererab. Neftekhim., No. 6, 21 (1976). Rucker, G., Chem. Ind., 23,436 (1971). Sedachev-Nesmalov-Moyseeva: Khimiya Tekhnol. Topl. Masel, 8 , No. 5, 18 (1963). Strom, D. A., Khimiya Tekhnol. Topl. Masel, 7, No. 12, 26 (1962). Strom-Ekha-Novakov: Maslob. zhirou. Prom., 29, No. 3, 21 (1963). Sukhoterin, V. M., Neftepererab. Neftekhim., No. 2, 40 (1975). Toland, W. G., Ind. Engng. Chem., 52, No. 10. 873 (1960).
(B) PARAFFIN WAXES AND LIQUID PARAFFINS AS STARTING MATERIALS
305
Tyutyunikov: Pishch. Tekhnol., No. 5, 59 (1963). Tyutyunikov-Perchenko: Khimiya Tekhnol. Topl. Masel, 10, No. 5 , 27 (1965). Varalomov-Ilyina-Kudryashov-Udovenko: Maslob. zhiroo. Prom., 25, 39 (1959) Vorobeva-Sakharova: Neftepererab. Neftrskhim., No. 3 , 46 (1976).
4. Manufacture of olefins, liquid at ambient temperature, from paraiks, and utilization of the products A simple and relatively inexpensive process to obtain high molecular weight, mainly straight-chain olefins, with the double bond usually in the terminal position, is by the thermal cracking of paraffin waxes or petroleum fractions containing paraffin waxes at 500 to 600 "C. Another pathway is chlorination of paraffins and subsequent dehydrochlorination. This procedure has developed into a commercial-scale process parallel to the development of normal paraffin separation processes, and to the stricter specifications regarding the composition of synthetic detergents. Catalytic dehydrogenation of normal paraffins into straight-chain higher olefins is a recently developed process. Other potential methods for producing olefins, liquid at ambient temperature, will not be discussed in this book, which Will limit its scope to olefin manufacture from paraffin waxes and utilization of the products. (a) Manufacture of olefns from parafin waxes and para$% crudes Thermal cracking of alkanes and its mechanism. The simplest explanation of thermal cracking is direct splitting of the hydrocarbon molecules, that is, molecular decomposition, yielding lower alkane and olefin molecules. However, this interpretation does not explain the composition of the products of decomposition. A substantially more adequate explanation for the product distribution in thermal cracking is afforded by the free radical chain mechanism theory that has already briefly been discussed in Chapter I(B)3. Product distribution, calculated on the basis of this theory and experimentally determined distribution, are in good agreement in the case of thermal cracking of lower molecular weight paraffins. Substantial differences arise, however, in the case of higher molecular weight normal paraffins. Thermal cracking of these materials always yields relatively high percentages of ethylene, but never as much as should be expected by the Rice-Herzfeld mechanism. To explain this phenomenon, Rice and Kossiakoff introduced the concept of radical isomerization, assuming that this isomerization can take place Within the radical before decomposition in radicals higher than C,, so that in these cases higher olefins will be produced instead of ethylene. That radical isomerization takes place in the thermal cracking of higher paraffins was confirmed by the comparison of experimental and calculated values of the product distribution. 20
306
111. APPLICATIONS OF PARAFFIN WAXES AND LIQUID PARAFFINS
Forst and Dintsesh found, in 1933, that the initial stage of hydrocarbon decomposition is inhibited by the reaction products. Hinshelwood and co-workers, investigating the compounds inhibiting thermal cracking of hydrocarbons (N2, propylene, isobutylene, etc.), came to the conclusion that the decomposition of hydrocarbons includes two processes independent of one another. Free-radical chain reaction and molecular decomposition take place simultaneously. They confirmed their conclusion by the finding that an inhibited limit rate can always be assigned to given conditions. According to the mechanism of inhibition, inhibitor molecules react with the radicals formed in chain reactions, thereby reducing the activity of the radicals, and consequently the rate of reaction will decrease to a limit value depending on the amount of inhibitor. Those reactions that continue independently of the presence of the inhibitor are molecular decomposition reactions. However, a number of experimental findings are in contradiction to Hinshelwood's theory, namely the fact that the products of thermal decomposition of hydrocarbons are identical in fully inhibited and in non-inhibited reactions. It does not seem likely that decomposition taking place under different conditions and according to two different mechanisms, namely free-radical chain reaction and molecular decomposition, should yield similar distributions of products. Hence, the most widely accepted theory, at present, for interpreting the thermal decomposition of hydrocarbons, is free-radical chain mechanism. Panchenkov and co-workers investigated the mechanism of hydrocarbon decomposition initiated by irradiation and thermal energy. They found that initiation took place simultaneously under both effects. Recombination of the radicals formed is negligible, owing to the high reactivity of the radicals and to the presence of hydrocarbons. From the experimental data they determined the rate constants of free radical formation. Decompositions initiated in different ways took place in completely the same manner. Major conditions affecting thermal decomposition. In saturated hydrocarbons, the nearer the site of the break is to the middle of the molecule, the smaller is the energy required to break the bond. In high n-paraffins, however, the difference between bond energies at different sites of the carbon chain is so small that the slightest difference in changes of thermal decomposition conditions may cause a shift in the site of breaking. The nature and extent of thermal decomposition, as well as the composition of the products obtained are, hence, largely affected by the parameters of thermal decomposition, especially temperature, residence time, pressure and type of the starting material. (a) Effect of temperature. The rate of thermal decomposition depends most of all on temperature. Experience has shown that the rate of decomposition doubles with each 10 "C rise in temperature, until about 400 "C.At higher temperatures, in the range of 500 to 600 "C, however, a temperature rise of 15 to 20 "C is required to double the rate of reaction. This phenomenon is presumably due to secondary reactions of the products formed, isomerization, polymerization, condensation, etc.
(B) PARAFFIN WAXES AND LIQUID PARAFFINS AS STARTING MATERIALS
307
The situation is similar with increase of pressure. The higher the pressure in the system, the less the effect of temperature change on the rate of reaction, the temperature dependence of the rate of reaction being somewhat higher in this case. This may be interpreted partly by the lower activation energy of thermal decomposition under pressure, and partly by secondary reactions occurring to a greater extent. (b) Eflect of residence time.Because under conditions of equal temperature, pressure and feed the extent of thermal decomposition is controlled by residence time, the simplest method of eliminating secondary reactions of the decomposition products is by the appropriate choice of the residence time. Residence time and temperature rise affect the process in the same direction. For example, in the 450 to 600 "C temperature range a temperature rise of 10 to 20 "C is equivalent to doubling the residence time. The common effect of these two factors is expressed by the so-called severity number: M = Tro*06 where M is the severity number, T the temperature of reaction (K), and z the residence time (s). At temperatures exceeding 600 "Cthe effect of residence time is still more significant, owing to the exothermic secondary reactions of the primary decomposition products. The usual residence time in industrial equipment is 1 to 2 seconds at 500 to 600 "C. ( c ) Efect ofpressure. The rate of the decomposition reactions at low pressures is directly proportional to the pressure. Up to pressures of 6 to 7 MPa, the average increase in the rate of reaction is 20% for a pressure rise of 1 MPa. With greater increases of pressure, the change in the rate of reaction is less, and after attaining a maximum rate of reaction in the 10 to 30 MPa pressure range, the rate of reaction is decreasing. This reversal is interpreted as being due to the difference in the nature of the chain termination reactions becoming predominant in this pressure range. At low-pressure thermal decomposition, the chain reaction is terminated mainly by the interaction of smaller radicals, while the controlling factor a t higher pressures is the recombination of larger radicals. The ratio of the probabilities of chain termination, in the case of longer and shorter radicals, is quadratically proportional to the hydrocarbon concentration. The increase in the partial pressure of hydrocarbons results in a decrease of the primary thermal decomposition products, that is, in olefin content. The composition of the reaction product is shifted towards saturated hydrocarbons. Consequently, lower pressures yield more olefins, in addition to low alkanes (methane, ethane, etc.). Hence reduced partial pressure of hydrocarbons acts favourably from the viewpoint of olefin yield. For this reason, in industrial hydrocarbon cracking processes 5 to 50% steam are added to the feed, depending on cracking conditions. 20*
308
111. APPLICATIONS OF PARAFFIN WAXES AND LIQUID PARAFFINS
100
-' 80I
mi V
g
60-
40-
-L?+
0
0 g
-*."
20 -
0/-7
949 / I
I
I
I
I
(d) Effect of the chemical composition of the starting material. The chemical composition of raw materials used for thermal cracking varies greatly, and significantly affects the product distribution obtained. Valuable data are yielded by a comparison of results obtained with thermal decomposition of slack waxes, petrolatum and parafin distillates. In the Hungarian Oil and Gas Research Institute, the thermal decomposition of the materials listed in Table 111-65 was investigated. The percentage of liquid fraction up to the boiling limit of 320 "C versus conversion is plotted in Fig. 111-8. The maximum yield of this liquid fraction that could be obtained by one run was 30 to 35 wt-%. Up to conversions of 50 to 55 wt-%, the yields steadily increased and were independent of the chemical constitution of the feed. In the range of higher conversions, however, the chemical composition appeared to become significant: the paraffin distillate gave yields lower by 10 to 15 wt-% than those achieved with the feed containing more than 90 wt-% paraffin. One reason, of course, is the initially lower paraffin content. Another, however, is that at higher conversions, the extent of secondary reactions apparently increased. The yield of the liquid fraction could substantially be increased by repeatedly passing the material unchanged by the thermal cracking process through the equipment. For the slack wax and petrolatum feed the total yield obtained after repeated runs was about 50%. If, therefore, high-conversion thermal decomposition is aimed at, multistage decomposition will be favourable from the viewpoint of liquid products. In onestage thermal decomposition it is expedient to carry the process up to conversions of 50 to 55 wt-%, independently of the composition of the feed, this conversion resulting in the highest yield of liquid products. It should, however, be noted that industrial plants usually operate at lower conversions (25 to 45 wt- %), since at higher conversion the yield of gaseousproducts increases more rapidly than that of liquid products.
309
(B) PARAFFIN WAXES AND LIQUID PARAFFINS AS STARTING MATERIALS
Table 211-65. Characteristics of paraffin materials suitable for thermal cracking -
~
Paraffin oil
Slack wax Characteristics -
_____. .______
-
~-
Physical properties Density, d:' Melting point, "C Average molecular weight
0.8148 49 339
0.8178 47 317
0.8758 58 470
0.9012 25 321
Data of standard vacuum distillation Start of boiling, OC 10 vol- % 50 v01- % 90 vol-% Final boiling point, OC Characterization factor
323 370 397 440 45 1 13.1
322 360 390 436 448 12.9
355 414 468 516 519 12.4
337 368 401 438 446 11.8
Chemical properties Oil content, wt- % Sulfur content, wt- %
6.09 0.1
11.33 0.13
38.1 1.03
12.26* 2.06
Liquid chromatography analysis Saturated, wt- % (eluent: hexane) Aromatics, wt- % (eluent: benzene) Resin, wt- % (eluent: methanol chloroform)
99.10 0.47
95.70 3.44
84.00* 15.99
54.36 39.13
0.43
0.86
1.20
4.27
Bond analysis (IR) Paraffin C-content, wt- % Naphthenic C-content, wt- % Aromatic C-content, wt-%
95.00 5.00
91.50 8.50
67.30 16.70 16.0
64.10 17.40 18.50
3.2 0.1 0.4
19.0 9.5 8.4
17.6 14.0 1.3
+
+
Aromatics analysis ( U V ) Monocyclic, wt- % Bicyclic, wt- % Tricyclic, wt- %
non-detectable 2.7 0.7 0.4
* Paraffin content
The composition of the gaseous products obtained in the thermal decomposition, at 600 "C,of the starting materials listed in Table 111-65 is summarized in Table 111-66. With the decrease of the paraffin content of the feed, the olefin content of the gas decreased and that of saturated hydrocarbons increased. The decrease in ethylene content was particularly significant ; at the thermal decomposition of the paraffin distillate, the ratio of ethylene to propylene was almost 1 : 1. The olefin distribution of the liquid products obtained by the thermal cracking of the starting materials listed in Table 111-65 is summarized in Tables 111-67 and 111-68. The data were obtained by IR spectrometry. The total olefin content of the distillates from the thermal decomposition of slack wax was 95 to 98 wt-%, consisting mainly of vinyls (95 to 100 wt-% of total
310
IIJ. APPLICATIONS OF PARAFFIN WAXES AND LIQUID PARAFFINS
Table 111-66.Composition of gas produced in thermal cracking, at 600 "C, of the materials characterized in Table 111-65 ______ Slack wax Gas yield and composition
I
-~ _ _ _
H 2
CH4 C,H, C,H* C,H,o Total alkane hydrocarbons C2H4 C,H, C,H* Total olefin hydrocarbons C4H4
~
Petry;;turn
I
I
1
-__
Gas yield relative to feed, wt- % Gas composition, wt- %
-
1
1 f
[
-
~-
Paraffin oil distillate 1"
~-
-
36.0
32.4
34.5
51.9
0.3 9.8 9.5 1 .o 0.5
0.3 10.7 9.4 1.3 3.8
0.4 11.4 8.5 2.3 1.3
0.8 21.4 14.6 1.7 0.9
20.8
25.2
23.5
38.6
38.1 22.0 14.0
38.1 20.9 11.1
28.9 22.2 17.9
24.1 23.2 8.2
74.1
70.1
69.0
55.5
4.8
4.4
7.1
5.1
olefins). The olefin content of the liquid product from petrolatum was substantially less, and the non-terminal olefins represented a higher percentage. The olefin content of the liquid product from the paraffin distillate was also lower than in the case of the slack wax,
Non-vaporized product
Fresh paraffin Fig. ZZZ-9. Flow diagram of a thermal cracking plant for paraffin feed
(B) PARAFFIN WAXES AND LIQUID PARAFFINS AS STARTING MATERIALS
3 11
Table 111-67.Analysis of the olefin distribution of the liquid product obtained in thermal cracking, at 600 O C , of the materials characterized in Table 111-65 Materials
Total olefin content, voI- % From start of boiling to 90 OC 90-170 O C 170-270 OC 270-320 OC Average olefin content, vol- % Vinyls, vol- % relative to total olefin content: From start of boiling to 90 OC 90-170 OC 170-270 OC 270-320 O C Average olefin content, vol- % Vinylidenes, vol- % relative to total olefin content: From start of boiling to 90 OC 90-170 OC 170-270 OC 270-320 OC Average olefin content, vol- % Inter-chain trans-olefins, vol- % relative to total olefin content: From start of boiling to 90 'C 90-170 O C 170-270 O C 270-320 'C Average olefin content, vol- %
98.8 95.5 98.8 97.2 97.5
91.8 95.5 98.6 98.5 97.0
63.5 66.2 60.7 65.9 63.5
92.0 90.6 97.0 97.2 94.6
90.2 90.5 97.0 92.7 93.5
48.8 50.6 52.0 53.0 51.5
4.3 2.1
2.4
1.1
3.7 1.3
9.6 0.7 4.6 6.9 7.2
1.6 1.6 2.6 1.6 2.0
5.1 4.9 4.1 6.0 4.8
-
1.9 2.8 1.8
-
1.9
-
Industrial-scale thermal decomposition of parafins. The essential features of paraffin cracking plants are a tubular furnace, a predistiller and a fractional distillation column combined with the stabilizing operation. Figure 111-9 presents the flow diagram of a thermal cracking plant for paraffin feed. The starting material and the non-converted paraffins recovered from predistillation are mixed and, together with superheated steam, introduced into the tubular furnace 3, where the material will almost completely vaporize. The nonvaporized liquid residue is separated in the cyclone 2, the vapour-steam mixture passes into the cracker 4, where thermal decomposition takes place. The conditions here are set so as to achieve a conversion of 25 to 55 wt- % in one run. Cracking products are then quenched and pass into the distillation column 5, where non-converted paraffins are separated as residue and recycled into the tubular furnace. The head product of the column passes into a condenser, where the
3 12
Ternperature cracking,
111. APPLICATIONS OF PARAFFIN WAXES AND LIQUID PARAFFINS
1 Boiling range of fraction, "C
Alphaolefin vinyls,
Interchain Alpha-olefin vinylidenes, vol- %
"C
490
510
530
550
560
570
600
i
olefins, vol-%
Olefins total, vol- %
From start of boiling to 90 O C 90-170 170-270 270-320 Average olefin content
53 39 33 27 34.1
13 10 7 6 7.8
5 4 4 3 3.7
71 53 44 36 45.6
From start of boiling to 90 OC 90-1 70 170-270 270-320 Average olefin content
38 37 31 20 30.7
13 12 6 Non-detectable -
5 4 4 4 4.2
56 53 41 -
From start of boiling to 90 OC 90-170 170-270 270-320 Average olefin content
40 35 23 21 26.9
14 10 5 Non-detectable
6 4 3 3 3.5
60 49 31 -
From start of boiling to 90 OC 90-170 170-270 270-320
23 23 8
9 6 Non-detectable Non-detectable
4 2 3
36 31
From start of boiling to 90 O C 90-170 170-270 270-320
14 16 7
7 4 Non-detectable Non-detectable
3 1 4
24 21 -
From start of boiling to 90 O C 90-170 170-270 270-320
1s 13 8
8 4
3 2 4
26 19 14
-
-
-
-
Non-detectable Non-detectable
condensate is separated from the non-condensing gases. From the separator 6 the hydrocarbon phase passes into the stabilizer 7. Here gas and light hydrocarbons are obtained as head product. The bottom product, consisting of a mixture of cracked olefins, is further separated by rectification into the desired fractions.
(B) PARAFFIN WAXES AND LIQUID PARAFFINS AS STARTING MATERIALS
3 13
In other processes the mixture of paraffins and steam is heated in the tubular furnace, and the mixture, together with the liquid paraffin residue, is passed into the coil-tube cracker. Dehydrochlorination of chlorinated parafins. Another pathway to obtain high olefins from paraffins is catalytic dehydrochlorination of monochlorinated paraffins, as shown by the following equation:
R - CH, - CHCl- CH, - CH, - R‘ + NaOH --t + R-CH,-CH=CH-CH,-R’ + NaCl + H,O Dehydrochlorination based upon alkaline treatment does not, however, remove all chlorine. Figure 111-10 illustrates the catalytic activity of various metals. Aluminium chloride and activated aluminium also promote dehydrochlorination. In earlier times, chlorinated paraffins obtained from the mainly straight-chain hydrocarbons produced in the Fischer-Tropsch process were used. By molecular sieve and urea procedures, normal hydrocarbons with a purity of 95 to 97 wt-% can be obtained from hydrocarbon mixtures. These normal hydrocarbons are used, e.g. by Chemische Werke Huls AG, to manufacture, by dehydrochlorination, olefins for further processing to alkylbenzenes and to biologically degradable, so-called “soft” alkylbenzene sulfonates. The starting material of this plant is a C,,-C,, n-alkane mixture obtained by the Molex process. This is chlorinated at 120 “C with chlorine gas which is introduced into and distributed in a continuously operated vessel lined with lead and silver. Here 20 to 30 wt- % of the normal hydrocarbons are converted into monochlorinated paraffins. Dehydrochlorination is carried out by the Wulf-Schmidt process. Alkyl chlorides pass into a column packed with iron filings and heated to 250 “C, where catalytic dehydrochlorination takes place. The olefins formed vaporize at the 90 I
I
0 1 2 3 4 5 6 7 8 91011 12131415 Time, h Fig. III-10. Catalytic activity of various metals on dehydrochlorination of chlorinated paraffins. I Armco iron, 2 S, iron and copper, 3 S iron, 4 V2A steel, rough, 5 V2A steel, polished, 6 V4A steel, 7 Copper, 8 Copper(1) chloride, 9 Nickel, I 0 Calcium chloride
3 14
111. APPLICATIONS OF PARAFFIN WAXES AND LIQUID PARAFFINS
temperature of the reaction and leave the reactor, while unreacted alkyl chlorides and NaCl remain in the reaction zone. Alkyl dichlorides and paraffins chlorinated to a still higher extent will not be converted into hydrocarbons containing double bonds : intramolecular rearrangement of hydrogen will take place, and some molecules will be dehydrated down to coke, so that a few tenths of 1 % of this substance will convert into coke. Very pure hydrogen chloride is set free in the process, and this is used in the manufacture of vinyl chloride from acetylene. Tn the BASF process, a hydrocarbon mixture containing a low percentage of unsaturated compounds is chlorinated at low temperature and subsequently rapidly heated to 550 "C, resulting in thermal dehydrochlorination and olefin formation. Manufacture of olefins by dehydrogenation of normal parafins. Catalytic dehydrogenation, similarly to dehydrochlorination, yields a mixture of olefins equal to the starting material with regard to carbon atom number. Wide-spread industrial application of the process is retarded by the fact that cracking, aromatization and isomerization also take place to a large extect as well as dehydrogenation. For this reason, large-scale research is under way to find optimum conditions, that is, appropriate catalysts, temperature and residence time for suppressing side reactions. The researchers of Universal Oil Products Inc. (UOP) attempted to suppress the isomerization and cracking effect of the platinum catalyst, without affecting its dehydrogenating activity, by adding arsenic and lithium promoters. They
I]
c--.c-
Jr+1-
4I
--
5
-7
i
1
i
t
10
20
Fig. III-11. Flow diagram of a dehydrogenating plant manufacturing straight-chain olefins. I Tubular furnace, 2 Reactor, 3 Hydrogen exit gas, 4 Hydrogen separator, 5 Normal paraffins inlet 6 Separator for light products, 7 Light product vapours, 8 Condenser, 9 Transfer to adsorber, 10 Liquid light products, I 1 Adsorption tower, I 2 Distributor valve, 13 Desorbent, 14 Extract, 15 Raffinate, 16 Raffinate separator, 17 Desorbent collectors, I8 Desorbent heater, 19 Extract separator, 20 n-OIefin product
(B) PARAFFIN WAXES AND LIQUID PARAFFINS AS STARTING MATERIALS
3 15
succeeded in producing a 94 wt-% olefin-content product from normal paraffins with yields exceeding 90 wt- %. The by-product is 96 mol % pure hydrogen that can be used without further purification. The flow diagram of their first industrial-scale plant is presented in Fig. 111-11. A mixture of C,,-C,, n-alkanes, prepared by using molecular sieves, passes through the tubular furnace I into the reactor 2 packed with the catalyst. The reaction takes place in the presence of excess hydrogen, at low pressure, in the vapour phase. Its selectivity is 90 wt-% or higher. By-products are diolefins, aromatics, light cracked products and hydrogen. The product passes through the hydrogen separator 4, and through a fractionation column 6 to remove the cracked products, into the extraction tower 11. Separation is carried out on a solid adsorbent layer. The product to be separated and the desorbent are simultaneously and continuously introduced into the corresponding sectors of the tower through the distributor valve 12. The raffinate and the extract, respectively, are led for further separation into the separators 16 and 19, where the lower-boiling desorbent is removed. The unconverted n-alkanes recovered from the raffinate are recycled into the dehydrogenation reactor. Recent research work led to the development of catalysts more selective than those used earlier. U S . Patent No. 3 294 858 specifies crystalline aluminium silicate molecular sieves as catalysts. Dehydrogenation is carried out at 420 to 540 "C in the presence of H,, N,, CO, or some other inert gas.
(b) Applications of high molecular weight alpha-oieJns High molecular weight liquid alpha-olefins are important starting materials for the petrochemical industry. Owing to their double bond they are more reactive than alkanes. Valuable products can be obtained by their polymerization, alkylation, hydration, hydroformylation, etc. The many areas of application are summarized in Fig. 111-12. (a) The work of Sullivan and Koch regarding the applications of olefins demonstrated that high alpha-olefin content fractions, obtained by the thermal cracking of paraffin raw materials, are suitable for manufacturing synthetic lubricants, so that in earlier times this was an important field of application. (b) The polymerization of liquid alpha-olefins to produce plastics has also been studied thoroughly. High-melting polymers from alpha-olefins containing one or two methyl groups are of particular interest. For instance, 4-methylpentene-1 is polymerized by a Ziegler catalyst to a plastic melting at 240 "C. Its copolymerization with other olefins yielded heat-resistant fibres. Soviet researchers produced crystalline, tough polymers resistant to detergent media under prolonged tensile loads by copolymerization of liquid alpha-olefins and ethylene. (c) The application of liquid alpha-olefins for the alkylation of benzene and phenol is of growing importance. In the first step of alkylation, under the effect of a catalyst, a n-complex is formed between the aromatic nucleus and the alkylating agent. This is subsequently transformed, in the actual substitution step, into
316
111. APPLICATIONS OF PARAFFIN WAXES AND LIQUID PARAFFINS
sulfonates Sulfonation, Sulfation, neutralization Koch-synthesis
Po'Ymerlzation
Ethoxylation
Oxosynthesis
additives
I
I Primary alkyl sulfates
Sulfation, neirtralization
Ethoxylation
.-
Ethox ylated
~
Esterification
I Plasticizers
Fig.
iz-
2. Application areas for alpha-olefins
a a-complex, in which the alkylating agent is bound to the aromatic nucleus. From this complex, by elimination of one proton, a new n-complex, and through it the alkylated aromatic compound is formed. The effect of alkylating catalysts consists, on the one hand, in their interaction with the alkylating agent, increasing its electrophilic character, and on the other hand, they tend to coordinate with the proton split off from the a-complex, thereby promoting the termination of the reaction. For benzene alkylation, AICl,, H,SO, and H,F, are mainly used as industrial catalysts. For phenol alkylation, BF, and H,SO, are the most widely used catalysts. The most important factors in benzene alkylation that affect the yield and grade of the final product are: the nature of the alkylating agent, the molar ratio of benzene to olefin, the temperature of reaction and the reaction time. The importance of the nature of the alkylating agent, and of the molar ratio benzene to olefin are made clear by the data in Table 111-69. It may be observed that the extent of alkylation, under otherwise identical conditions, decreases
3 17
(B) PARAFFIN WAXES AND LIQUID PARAFFINS AS STARTING MATERIALS
Table 111-69. Effect of sulfuric acid/olefin molar ratio and carbon chain length on olefin conversion in benzene alkylation Reaction conditions:
Molar ratio of benzene to olefin 4 :1 Temperature of reaction: 5 "C Time of reaction: 60 min Alkylatinp agent* (alpha-olefin)
GI G 8
G
!
'
1:l
51.0 25.0
Molar ratio of H.SO, to o l d n ____
1
1:1.5
64.0 58.9 27.0
-
1
2:l
1
3:l
4:l
-
76.5 63.0 55.6
74.6 59.5 53.3
61.0 57.9
Composition, by carbon atom number, of alkylating agents: , Wt-% > Ci, Ca1: 19 wt-% Cio, 70.5 wt-% C ~ I 11.5 CIS: 2.5 wt- % Cis, 90.5 Wt- % Cis, 6.5 Wt- % > Cia Cia: 80 wt-% CIS, 14.0 wt-% C Clr 6.0 wt-% > C,,
with growing chain length. To ensure optimum yields when higher olefins are used, the amount of catalyst must be increased. In this case, however, more excess benzene must be used. In industrial plants, depending on the actual technological parameters, the benzene to olefin molar ratio is usually between 4 : 1 and 5 : 1. The temperature in benzene alkylation depends on the type of the catalyst. For instance, with H,SO, and H,F, the appropriate temperature is between - 1 and + 15 "C,with AlC1, between 30 and 50 "C. Some data of the effect of temperature on the yield of the final product and on its alkylbenzene content are listed in Table 111-70. Table Ill-70. Effect of temperature on the yield of the product and on its alkylbenzene content (catalyst: AICI,) Reaction condffions:
Molar ratio benzene to olefin 4 : 1 Time of reaction: 60 min Molar ratio AICI. to olefin: 0.06 .~
-
_ _
-
~
Temperature, "C Yield, wt-% 10
Product, wt- % relative to olefin Alkylbenzene content, wt- %
1
20
1
30
1
35
1
40
1
50
92.5
94.3
93.7
95.2
99.8
99.8
93.3
94.2
93.3
94.5
95.5
95.2
For a given equipment, other conditions being identical, residence time has no significant effect on product yield, but its grade deteriorates, owing to the greater extent of side reactions accompanying alkylation processes with longer residence times. In continuous operation the usual residence time is 40 to 60 minutes, in batchwise operation 2 to 3 hours.
318
111. APPLICATIONS OF PARAFFIN WAXES AND LIQUID PARAFFINS
Alkylbenzene sulfonates, the most widely used representatives of the group of anionic detergents, are manufactured by sulfonation of alkylbenzene and subsequent neutralization. Some trade names for C,,-C,, side chain alkylbenzene sulfonates are : F R G : “Marton” (Chemische Werke Hiils), “Korenyl” and “Lyneroe” (Reinprenssen AG), “Bosopal NA” and “Arylsulfonat” (BASF), “Phenylsulfonat HSR” (Hoechst); U.S.A.: “Alkylate Detergent 2” (Atlantic Refining), “Neolene” (Continental Oil Corp.), “Oronite” (Oronite Co.), etc. In phenol alkylation with olefins, the yield and grade of the products is also mainly controlied by the nature of the alkylating agent, the molar ratio of phenol to olefin, the temperature and residence time. The chain length and number of branching in the chain of the alkylating agent substantially affects the phenol to olefin molar ratio, the amount of catalyst required, temperature and time of reaction. These conditions are illustrated in Table 111-71.
Table 111-71. Changes in reaction conditions of phenol alkylation for different feeds (catalyst: BFJ _
_____ Feed and conditions
~
~~~~~~~
_ ____
Phenol BF,, wt- % relative to phenol Di-iso-butylene C,/C, olefin C,/C, olefin dimer Propylene tetramer Tri-iso-butylene 130-1 80 “C boiling-range olefin fraction Temperature of reaction, OC Time of reaction, hours Alkylphenol yield relative to theoretical yield, wt- %
I
Molecular weight
-
I
--
Amount of feed, mols ~
- ._ -
__
94 112 90 185 150 147
1 1.8 1 -
1 3.0 1 -
121
-
____
-
1 2.0 1 -
1 2.0 1 -
-
-
-
-
45 2
45 4
45 6
95
94
94
-
-
1 2.0
-
-
1 3.0
-
-
-
-
1
-
-
1
65 4
65 4
65 4
88
93
91
In contrast to benzene alkylation with molar ratios of 4 : 1 to 5 : 1, phenol alkylation is carried out with molar ratios of phenol to olefin equal to 1 : 1-2 : 1 . In industrial processes the temperature varies between 25 and 125 “ C , residence time between 30 minutes and 5 hours. Among the manifold applications of alkylphenols, the most important are in the manufacture of lubricant additives, surface-active agents, pesticides, formaldehyde resins, synthetic flavours, etc. ( d ) The manufacture of secondary alkyl sulfates used as detergents is a major field of application for liquid olefins. Such detergents are readily bio-degradable while their washing effect is similar to that of alkylaryl sulfonates and sulfates of primary alcohols.
(B) PARAFFIN WAXES AND LIQUID PARAFFINS AS STARTING MATERIALS
3 19
The structure of secondary alkyl sulfates is
where Me is a cation. Their surface-active properties are essentially defined by the nature of the carbon chain, namely its length and its straight or branched structure, by the position of the sulfate group and by the nature of the cation. The most widely used path to manufacture secondary alkyl sulfates is by treatment of olefins with sulfuric acid, and neutralizing the sulfoether obtained. Depending on reaction conditions used, and above all on the structure of the given olefins, detrimental side reactions can also take place with sulfuric acid treatment (polymerization, oxidation, formation of sulfonic acid and dialkyl sulfate, etc.). The starting materials for secondary alkyl sulfates are olefin mixtures from cracking and dehydrogenation of paraffin materials, olefins formed by oligomerization of lower olefins, and certain fractions of the Fischer-Tropsch synthesis products. From the viewpoint of surface-active properties, the most suitable materials are the C12-C,, fractions boiling in the 190 to 300 “C range, and consisting mainly of alkene-1 compounds. C8-Cl, olefins are also frequently used. Due to the lower boiling point range the viscosity of the sulfated compounds will be lower, and heat transfer conditions in the manufacturing process will become more favourable. The trade name of the most widely used alkyl sulfate detergents is “Teepol” (e.g. “Teepol 410”, is a 20-22 wt-% and “Teepol 710” a 40 wt-% aqueous solution). The products marketed in the Soviet Union under the trade name “Progress” are 20 to 50 wt- % solutions. Those for household purposes are 40-50 wt- %, for industrial cleaning 20 wt- % solutions, while the active agent concentration of various products for industry is 10 to 30 wt- %. ( e ) Oxosynthesis is also of growing interest in obtaining primary alcohols from C,-C, alpha-olefins and fatty alcohols from Cl,-C,, olefins, respectively, by their reaction with synthesis gas : R-CHzCH,
+ CO + H2f R - CH, -CH, - CHO% LR-CH- CH?RI
I
CHO
- CH, - CH, - CH, - OH
CH-CH, I
I
CH20H
The reaction takes place at 150 to 200°C and 20 to 30 MPa pressure in the presence of cobalt carbonyl hydride catalyst, and yields aldehydes containing one more carbon atom than the starting olefin. The aldehydes are usually hydrogenated in a second step to alcohols that are the starting materials in the manufacture of plasticizers for plastics and detergents.
320
111. APPLICATIONS OF PARAFFIN WAXES AND LIQUID PARAFFINS
Theoretically all olefins, and many other compounds containing double bonds, can be subjected to the basic reaction of oxosynthesis, i.e. hydroformylation. However, the rate of reaction varies greatly for different compounds. It is highest for straight-chain olefins with the double bond in the end position (alpha-olefins). The rate of reaction decreases with increasing molecular weight. As compared to oligomerized olefins, those obtained from hydrocarbon cracking are less branched and the majority of double bonds are in the end position, thus ensuring higher-grade alcohol products. A modified one-stage oxosynthesis technology has been developed for manufacturing octyl alcohol from cracked gasoline and put into practice on a pilot-plant scale by the Hungarian Oil and Gas Research Institute. The same procedure was also found to be successful for manufacturing higher fatty alcohols.
TubIe 111-72.Data of olefinic fractions utilizable for the manufacture of fatty alcohols
,
Material
i
I
I
I Obtained by
Olefin content, wt-%
Aver. mol. weight
1
1 i 1
Aver.
'-
cule
Boiling range,
"C
j
Dodecene-1
Dehydration of lauryl alcohol
95-97
108
12
195-205
Tetrapropylene
Tetramerization of propylene
98-100
168
12
180-200
Cracked gasoline distillate I
Distillation residue of gasoline obtained by selective cracking
30
133
9-10
140-170
Cracked gasoline distillate I1
High sulfur content gasoline from Szony crude obtained by selective cracking
21.2
140
9-11
150-180
Cracked gas oil I
Sample from cracking
9.5
168
12
200-220
Cracked gas oil I1
Sample from cracking
9.5
182
13
220-240
PAK 1
Cracking of paraffin blend in large-scale laboratory tubular furnace
97
146
11
180-210
PAK 2
Cracking of paraffin blend in large-scale laboratory tubular furnace
96
174
1
210-250
PEK 1
Cracking of petrolatum at 600 "C in large-scale laboratory tubular furnace
71.9
163 10-15
170-270
PEK 2
Cracking of petrolatum at 600 OC in large-scale laboratory tubular furnace
61.4
218 15-18
270-320
Thermal cracking of 280-450 OC boiling range paraffins obtained by the urea adduct method
78
230 15-18
260-310
Shell C1,-C,, olefin
alpha-
(B) PARAFFIN WAXES AND LIQUID PARAFFINS AS STARTINQ MATERIALS
32 1
Some examples of the olefinic fractions suitable for the process are listed in Table 111-72. The nature of impurities present in the starting material is of great importance in the synthesis. Saturated and aromatic hydrocarbons themselves do not interfere with the reaction, but reduce the concentration of olefin in the starting materia1 and hence high concentrations of the saturated and aromatic hydrocarbons are unfavourable. Diolefin impurities form peroxides with air and hence interfere. Acetylene and its derivatives, as well as organic sulfur compounds are also detrimental, since they react with the catalyst. (f)The importance of direct iso-carboxylic acid synthesis from olefins, discovered by Koch, is steadily increasing. Alpha-olefins, from the cracking of paraffins, are suitable starting materials for this process. Using isobutylene as an example, the (simplified) reaction is shown below:
HtC =C - CH, I CH3
CO(HSS0J
I * H3C-C-COOH
H2O
I
CH3
Manufacture is carried out in two separate stages. Due to this modification, reaction conditions are milder as compared to earlier processes. The temperature varies between -20 and + 100 "C, carbon monoxide pressure between 0.1 and 10 MPa. The products are very pure, their esters are thermally resistant and resistant to hydrolysis. They are used in synthetic lubricants, as drying components of paints, as additives for epoxy resins, as plasticizers and in pharmaceutical preparations. (g) More recently, hydrohalogenation, particularly hydrobromination of alphaolefins has begun to command attention. Alpha-brominated alkanes can successfully be converted into various primary-substituted alkyl derivatives, e.g. primary alcohols, amines, mercaptans.
Literature Asinger, F., Chemie u. Technologie der Paraffin-Kohlenwasserstofe.Akademie-Verlag, Berlin (1956). - : Chemie und Technologie der Monoolefine. Akademie-Verlag, Berlin (1957). - : Erdo'l, Kohle, 20,786 (1967). Avery-Lee: Erd61, Kohle, 15, No. 5 , 356 (1962). Baumann, P., Fourth Znternat. Congress on Surface-Active Substances. Brussels, 1964. Gordon and Breach Sci. Publ., London (1968). Belg. Pat., 632 808. Blackmore-Hinshelwood: Proc. SOC.,A 286,36 (1962). Block-Wickbold: Seven-Ole-Fette-Wachse, 89, 870 (1963). Brit. Pat. 559 179. 21
322
111. APPLICATIONS OF PARAFFIN WAXES AND LIQUID PARAFFINS
Brit. Pat. 584 763. Brit. Pat. 600 505. Brit. Pat. 746 407. Brit. Pat. 416 379. Brodsky-Lavrovt sky-Rumyant sev : Neftekhimiya, 6, 880 ( 1 964). Broughton-Berg: Chem. Eng., Albany 77, 86 (Jan. 26, 1970). Csikbs, R., Magy. Kkm. Lap., 25, 124 (1970). -: Proceedings of the 2nd Conference on Applied Physical Chemistry. Vol. 2. Akadbmiai Kiad6, Budapest (1971). Csik6s-SzCnyi: Magy. Kkm. Lap., 24, 239 (1969). Danby-Spall-Stubbs-Hinshelwood : Proc. R. SOC.,A 223,421 (1954). Dintses-Forst: Zh. obshch. Khim., 3, 747 (1933). Ellis-Roming: Hydrocarb. Process., 44, No. 6, 139 (1965). Erd61, Kohle, 12, No. 5, 406 (1959). Fabuss-Smith-Satterfield: Ady. Petrol. Chem. Refin., 9, 157 (1964). Ferguson, G. U., Chem. Ind., 17, 451 (1965). Fr. Pat. 766 903. Fr. Pat. 952 196 Fr. Pat. 1413 913. Freund-Mark6: MdFKI K6zZemtnyek (Comm. of the Hungarian Oil and Gas Research Institute), 10, 81 (1969). Genisse-Reuter : Ind. Engng. Chem., 22, 1274 (1930). Gonikberg-Voevodsky: Izv. Akad. Nauk, S S S R Otd. Khim. Nauk, No. 2, 370 (1954). Greensfelder-Voge-Good: Ind. Engng. Chem., 41, 2573 (1949). Hobbs-Hinshelwood: Proc. R. SOC.,A 167,447 (1938). Hoechst-Ruchrchemie: Produkteprospekt (Oxosynthese) (1969). Hoog, H., Chem. Process. Engng., 35, 124 (1954). Huibers-Waterman: Brennst.-Chem., 42, 50 (1961). Hydrocarb. Process., 49, 4 (1970). Ingold-Stubbs-Hinshelwood: Proc. R. SOC.,A 203,486 (1950). - : Proc. R. Soc., A 208,285 (1951). Jack-Hinshelwood: Proc. R. SOC.,A 231, 145 (1955). Jack-Stubbs-Hinshelwood: Proc. R. Soc., A 224, 283 (1954). Kheifets, V. A., Khimiya Tekhnol. Topl. Masel, 3, No. 9, 48 (1958). Kirk-Othmer: Encyclopedia of Chemical Technology, 14, 379, J. Wiley Interscience Publ. (1967). Koch-Hilberath: Brennst.-Chem., 23, 67 (1942). Koshchenko-Babilev: Neftepererab. Nefekhim., 7, 28 (1966). Kossiakoff-Rice: J. Am. Chem. SOC.,65, 590 (1943). Laky, J., MAFKZ jeZentks (Final Report of the Hungarian Oil and Gas Research Institute), NO. 5-53 (1968). Laky-Tr6csinyi: MAFKI jelentts (Final Report of the Hungarian Oil and Gas Research Institute), No. 5-139 (1969). Mark6-Szab6: Magy. Ktm. Lap., 18,461 (1963). Moller, K. E., Brennst.-Chem., 47, 10 (1966). Oleksin-Sereda: Neft. gaz. Prom., No. 2, 47 (1963). -: Neft’ i Gat, 18, No. 2, 52 (1964). Olson, A. C., Ind. Engng. Chem., 52, 833 (1960). Pauchenkov-Zhuravlev: Zh. jiz.Khim., 46, 1438 (1972). Pines-Wacker: J . Am. chem. Soc., 68, 595 (1946). Pisman-Ansheles-Dalin: Khim. Prom., No. 3,21 (1969). Pliev-Gordash: Khimiya Tekhnol. Topl. Masel, 14, NO. 9, 17 (1969). Repasi-Laky : MAFKI jelentb (Final Report o f the Hungarian Oil and Gas Research Institute), No. 5-50 (1967).
( C ) MANUFACTURE OF
PROTEINS AND ORGANIC ACIDS BY BIOSYNTHESIS
323
Roth, J. F., Znd. Eng. Chem. Process. Des. Dev., 7 , 254 (1968). Sachanen, A. N., Conversion of Petroleum. Reinhold Publ. Corp., New York (1948). Semenov, N. N., 0 nekotorye problemi khimicheskoy kinetiki i reaktsionnoy sposobnosti (On Some Problems of Chemical Kinetics and Reactivity). Acad. Nauk SSSR, Moscow (1958). Sharrah-Feigher: Znd. Engng. Chem., 46, 248 (1954). Smeykal, K., Chem. Tech., Berf., 13, No. 7, 431 (1961). Spoll-Stubbs-Hinshelwood: Proc. R. SOC.A 223, 429 (1954). Stubbs-Hinshelwood: Proc. R. SOC.,A 201, 18 (1950). Stubbs-Ingold-Spoll-Danby-Hinshelwood: Proc. R. SOC.,A 214, 20 (1952). Stupel, M., Fette, Seifen, Anstr-Mittel, 54, 458 (1952). Topchiev-Tumerman: Neft. gaz. Prom., 6 , 72 (1968). Trafford-Quartano : European Chemical News. Normal Paraffins Supplement (Dec. 2, 1966). Ullmanns Enzyklopadie der technischen Chemie. Vol. 13, 60, Munchen (1962). Ullmanns Enzyklopadie der technischen Chemie, Erganzungsband. Miinchen (1970). U.S.Pat. 2 065 323. U.S.Pat. 2 192 689. U.S. Pat. 2 220 090. U.S.Pat. 2 232 118. U.S.Pat. 2 256 610. US.Pat. 2 385 303. US.Pat. 2 413 161. U.S. Pat. 2 631 980. U.S. Pat. 2 732 408. U.S. Pat. 2 995 827. U.S. Pat. 3 248 451. U.S. Pat. 3 284 858. U.S. Pat. 6 517 032. U S .Pat. 6 605 910. van Dam-Waale: Chim. Znd., 90,511 (1963). Voevodsky: Trans. Faraday SOC.,55, 65 (1959). Voge-Good: J. Am. chem. Soc., 71, 593 (1949). Winnacker-Kiichler : Chemische Technologie, Vol. 111.3. ed., Hanser Verlag Miinchen (1971). Wulf-Bohm-Gossl-Rohrschneider : Fette, Seifen, Anstr.-Mittel, 69, No. 1, 32 (1967).
(C) The manufacture of proteins and organic acids from hydrocarbons by biosynthesis 1. Protein manufacture from hydrocarbons (a) Significance of the problem and present situation Even today, two thirds of the world population is inadequately nourished or undernourished. Inadequate nourishment consists mainly of protein deficiency, especially of deficiency of animal protein in nourishment. Another problem that has to be considered in this context is the exceedingly rapid growth of the world population. World consumption in animal proteins was estimated to be about 100 million tons in 1970. This figure, however, included the largely differing per capita consumption values in industrialized and developing countries. Assuming that a per capita consumption of animal protein of 80 glday is necessary and should be 21*
324
111. APPLICATIONS OF PARAFFIN WAXES AND LIQUID PARAFFINS
reached by the total population in the year 2000, the demand would amount to about 220 million tons, a figure that appears impossible to cover, even by increasing, however intensely, livestock breeding and fishing. Even if the much lower figures estimated by the U.N. Food and Agricultural Organization are valid, they cannot be satisfied by these means. Regarding vegetable proteins, the situation is better, but this does not solve the basic problem of inadequate nourishment. Among the numerous suggestions of how to remedy the lack in animal proteins, the most realistic process, and one well-suited for mass production, was the manufacture of protein containing nutriments and animal feed from petroleum products, especially from normal saturated hydrocarbons. As early as 1919, J. Tausz reported that certain bacterium cultures decompose paraffin hydrocarbons, leaving naphthenes unaffected. At that time, however, this finding was, at most, only of analytical importance. However, only 15 years ago A. Champagnat developed an industrial process for converting petroleum products into proteins. Yeasts with high protein and vitamin content can be obtained from straightchain hydrocarbons by means of appropriate cultures of microorganisms. The essential feature of the process is similar to the manufacture of conventional pressed yeast. Equipment used for both processes is the same, and the biosynthetic reactions, and even the compositions of pressed yeast and petroleum yeast are very similar. At the start, pilot plants and smaller industrial plants were built to process the n-hydrocarbon content of the gas oil fraction directly, without previousiseparation, and slack wax was also suggested as a starting material for protein production. However, these less expensive products were found to be unsuitable for obtaining a pure product meeting the requirements of specifications that prohibit the presence of compounds with possible carcinogenic effects. The use of methane as a starting material is also being examined, but explosion hazards occur in its technology. Methanol gives poor yields and is expensive. Ethanol would also be suitable, since it yields the purest protein, but it is even more expensive. Hence, there remained only normal paraffin as starting m a t e d for the largescale manufacture of proteins being developed. The amount of normal paraffin that could be produced, theoretically, on a world-wide scale by 1985 is said to be 154 million tons. The share for Western Europe included in this figure is 43 million tons. Since the yield of proteins, relative to normal paraffin, is l20%, and the petroleum yeast contains 60 to 62 % protein, the final protein yield is 75 %. Theoretically, by this route it would be possible to produce more than 100 million tons of protein on a world-wide scale, and more than 30 million tons of protein in Western Europe alone. In 1977, two plants, each having an output of 100,000 tons per year, were installed in Italy, but they are not working yet. Also, smaller plants were installed in other countries.
(c)
MANUFACTURE OF PROTEINS AND ORGANIC ACIDS BY BIOSYNTHESIS
325
(b) Manufacture of single cell protein (petroleum yeast) The starting material for the products has been mainly normal paraffin obtained by the urea or molecular sieve method, and subjected to special aftertreatment to remove aromatics having carcinogenic effects. The usual starting material consists of C,o-C,o n-alkanes. The specification for the grade of the starting material used in the pilot-plant of Liquichimica Biosintesi S.p.A. Company (Reggio Calabria, Italy) is presented in Table 111-73. Table 111-73.Specification for fermentation-gradenormal paraffins - ___..
Normal alkanes, wt-%, min. Total aromatics, ppm, max. Branched alkanes naphthenes,
+
Difference from 100
wt- %
Sulfur, ppm, max. Bromine index, max. Saybolt colour Carbon distribution, wt- % C14max.
G& Gq
cl 7
C1, over
99 50
G8max.
10 30 25
1 25-35 25-35 20-30 15-20 1
Much research work has been carried out on yeast cultures, especially in the Soviet Union. Cheppigo, Boiko and co-workers report the testing of more than 1500 yeast cultures in various research institutes, and the further breeding of lo00 strains from petroleum-drenched soils. As mentioned previously, the single cell protein (SCP) process is very similar to that of pressed yeast. The main difference between the two processes is that the carbohydrate starting material supplies the carbon and hydrogen, as well as the major part of the oxygen required for the build-up of the protein from an aqueous solution. On the other hand, the hydrocarbons are insoluble in water and have to be processed in the form of an emulsion. The total oxygen requirement must be provided by the air that is blown through the emulsion. It is very important that the liquid under fermentation contains no more than 1 to 2 wt-% hydrocarbons in the form of finely dispersed droplets to offer a large surface area for contact with the oxygen. To encourage yeast cell formation, nutritive salts containing K + , Mg2+,Fez+, Zn2+ cations and SO!-, PO:- anions must be added to the aqueous solution or emulsion. Microamounts of FeCl,, MnSO,, CuSO, and Na,MoO, salt are also required to enhance yeast cell accumulation and improve yields.
326
111. APPLICATIONS OF PARAFFIN WAXES AND LIQUID PARAFFINS
The further building block of the protein molecules, nitrogen, is introduced in the form of ammonia added to the air blown through. Ammonia also maintains the pH at the optimum value. Ammonia can also be added in the form of a 25 wt- % aqueous solution containing some (NH,),SO,. Finally, the presence of an antifoam agent is also necessary. Bennelt, Hondermarck and Todd made a comparison of microbial yeast synthesis from hydrocarbons and carbohydrates (e.g. molasses). Assuming that in both cases CO, and H,O will be evolved, and final products containing identical cell proteins, carbohydrates, lipids and ash will be formed, the respective overall reactions can be formulated as follows : For hydrocarbon starting material :
2 n CH, + 2 n 0, + 0.19 n NH: + mineral salts + + n (CHl,,00~5No~lg ash) + n CO, + 1.5 n H,O + n 8.4 - lo5 kJ For carbohydrate starting material:
+ 0.8 n 0, + 0.19 n NH: + mineral salts + n (CHl~,00,5No,lg ash) + 0.8 n CO, + 1.3 n H,O + n 3.3 lo5 kJ 1.8 n CH,O
+
It is important to stress that the oxygen demand is about 2.5 times as high for hydrocarbons as for carbohydrates, and correspondingly the heat evolved is also substantially more, namely, relative to the dry protein product, 32 000 kJ/kg as compared to 13000 kJ/kg. Since the optimum temperature of petroleum yeast breeding is around 30 "C,intense cooling of the reaction mixture in the fermentor must be provided for. Large-size fermentors, efficient cooling and control of optimum temperature are, therefore, required. Further, the fermentors must ensure intense agitation, proper oxygen transfer and efficient removal of carbon dioxide. Agitation is provided by the blown-through oxygen itself, which also enhances rapid circulation and atomization of the droplets. Cooling is controlled by means of bypassing through a heat exchanger. In the Liquichimica Biosintesi pilot-plant two fermentors will operate jointly for one week at a time. The SCP product accumulated in one fermentor is transferred into the second, where the process is completed. Subsequently, the aqueous phase containing the additives is separated in a centrifuge and recycled into the first fermentor. After one week, operation of the two-fermentor system will be stopped, and the accumulated impurities removed by washing. In this manner, previous sterilization of the feed, frequently used in other processes, becomes unnecessary. The pulp leaving the centrifuge is washed, concentrated in rotary vacuum filters to a dry matter content of 25 %, and subjected to the final drying operation which is carried out continuously in a two-stage fluid-bed dryer. In smaller pilot-plants processing gas oil the yield of petroleum yeast is only 10 to 20%, depending on the n-alkane content of the gas oil.
(c) MANUPACTURE OF PROTEINS AND ORGANIC ACIDS BY BIOSYNTHESIS
327
(c) Properties and use of single cell protein Petroleum yeast (single cell protein, SCP) is a dry, powder-like product, its protein content varying between 60 and 65%, according to data furnished by various pilot-plants. The composition of a typical petroleum yeast obtained in Japan is presented in Table 111-74. Table 111-74. Composition of SCP from normal paraffins, wt- %
I
General composition
Moisture Crude protein Crude lipid (ether extract) Crude fibre Ash Nitrogen-free extract
4-6 58-62 2-4 3-5 7-11 18-20
Composition of the protein
Aspartic acid Threonine Serine Glutamic acid Proline Glycine Alanine Cystine Valine
9.41 5.08 4.71 13.86 4.42 4.84 6.08 1.76 5.43
Methionine Isoleucine Leucine Tyrosine Phenylalanine Tryptophan Lysine Histidine Arginine
1.22 5.45 6.93 3.29 4.36 1.22 7.52 2.22 4.53
Total
92.33
These data reveal the presence of all amino acid constituents important from the viewpoint of nutritive value. The high lysine content should particularly be stressed. Some authors also identified vitamins as being present, e.g. vitamin B in percentages of 1 wt- %, ergosterol (provitamin D2) in amounts of 0.2 to 0.5 wt- %. Experiments based on nitrogen content showed the protein to be 80-90% digestible by animals. Petroleum yeast can be used solely for animal feed. Wide-spread experimental work has been carried out in this respect. Usually 20% of protein yeast could be mixed with the feed, in the case of fish feed even up to 75% was accepted. The SCP protein, in amounts exceeding 15%, was used to replace fish flour and soya bean flour in the feed mixture. Feeding tests were carried out for several generations with whole herds of cattle, pigs, sheep, goats, poultry, horses, monkeys, etc. Neither carcinogenic nor any other detrimental effects were observed. Cost of petroleum yeast is, of course, an important factor. The relative protein prices in various food are compared in Table 313-75, demonstrating that petroleum protein was in 1969 by far the least expensive. This price is, however, that of SCP manufactured from the cheapest starting material, namely gas oil. But, from the viewpoint of being a possible carcinogenic hazard, gas oil was not favoured as a starting material. Table 111-76 demonstrates the relationship between the price of the starting material and that of the petroleum protein. The data from 1974 show that if protein from gas oil is left out of consideration, protein obtained from normal paraffins was the least expensive of all the synthetic proteins available.
328
111. APPLICATIONS OF PARAFFIN WAXES AND LIQUID PARAFFINS
Table 111-75. Unit price of protein in various food (1969)
j
Foods
Eggs
Chicken meat Beef Dry beans Wheat flour Milk powder Fish flour Soya flour (defatted) Protein from gas oil (Institut Franqais du Wtrole process)
Prote$price,
4650 3640 3420 780 680 510 500 400 140-175
TubZe 111-76. Relationship between the prices
of the starting material and petroleum yeast Price of petroleum yeast containing -60 % protein
Price of starting material in S/t ( 1974)
Molasses, 50 % Normal paraffin Gas oil Methanol
20-40 60-80 20-30 40-60
90-175 84-116 53-81 91-145
Studies are being prepared on methods of using petroleum protein directly for human food. Such experiments are being made with meticulouslypurified petroleum yeast added to flour, sausages, etc. In this context, although the use of ethanol as starting material is expensive, the establishment of an industrial-scale experimental plant for the manufacture of single cell protein is being considered. 2. The manufacture of organic acids from paraffins
It is possible that the manufacture of L-lysine and L-aspartic acid will have a future under certain local conditions, for upgrading proteins if the production of synthetic proteins becomes wide-spread. The development of technologies for the microbiological syntheses of other amino acids have also been reported. Besides amino acids, the syntheses of a-ketoglutaric acid, fumaric acid, malic acid, certain dicarboxylic acids and fatty acids from normal paraffins have been carried out on a laboratory scale by means of different microorganisms. However, up to the present only the manufacture of citric acid and sodium citrate has attained commercial importance. The South-Italian plant of Liqui-
(c) MANUFACTURE
OF PROTEINS AND ORGANIC ACIDS BY BIOSYNTHESIS
329
chimica Biosintesi has supposedly a capacity of 50,000 tonslyear. In the U.S.S.R., a plant is operated in Riga, using the process developed by the Research Institute of the Latvian Academy of Sciences. The fermentation of n-paraffins is carried out in equipment and by processes similar to the manufacture of single cell protein, in the presence of mineral salts containing phosphorus and nitrogen, in aqueous media. Sodium hydroxide or ammonia are, however, used for the continuous neutralization of the citric acid formed. The most appropriate yeast culture for this purpose is Candida Lypolitica. In the process, the effluent from the fermentor is centrifuged to separate the cell mass formed, the aqueous solution is neutralized, concentrated, filtered through clarifying agents and sodium citrate obtained by crystallization. To obtain pure citric acid, the sodium citrate crystals are dissolved in water, and the sodium ions removed in an electrodialysis unit. Citric acid is obtained by crystallization. The advantage of the process is its high yield, attaining values as high as l50%, while the yield from carbohydrates (molasses from beet sugar and from cane sugar) does not exceed 80%. Also, a pure final product can obviously be obtained more readily from purely synthetic starting materials than from carbohydrate wastes that require many pretreatments. Citric acid is being used not only in the food industry, but also in other industries, e.g. in detergents.
Literature Bennett-Hondermarck-Fodd: Hydrocarb. Process., 48, 104 (1969). Champagnat-Vernet-Laine-Filosa: Proceedings of the 6th World Petroleum Congress. Vol. 8. 259, Frankfurt am Main (1963). Cheppigo-Boiko-Gololobov: Proceedings of the 7th World Petroleum Congress. Vol. 8 . 205, London (1967). Decerle-Franckowiak-Gatellier : Hydrocarb. Process., 48, 109 (1969). Laine, B., Hydrocarb. Process., 53, No. 41, 138 (1974). Laine-Vernet-Evans: Proceedings of the 7th World Petroleum Congress. Vol. 8 . 197, London (1967). Pass, F., Erdd Erdgas Z . Sonderausgabe 182 (1977). Takata, T., Hydrocarb. Process., 48,99 (1969).
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SUBJECT INDEX
Acid creams 265 Adduct formation with urea 175, 177, 185 Adhesion 133 - of macrocrystalline paraffin waxes 133 - of microcrystalline paraffin waxes 133 n-Alkanes 13, 24, 25, 27, 31, 91, 92, 95, 118, 179, 180 by means of molecular sieves 193, 195 - by means of urea 176 Alkyl- bromides 55 - chlorides 55, 280 - fluorides 55 - iodides 54 - sulfochlorides 58, 288 - sulfonic acids 59 Allotropic transition 75, 77, 119 - from a-phase into /%phase 75,77,96,119 - of macrocrystalline paraffins 85, 86, 96 Alpha-olefins 305, 315 - for alkylation 315 - for Koch synthesis 321 - for manufacture of alcohols 316, 320 - for manufacture of alkyl sulfates 318 - for manufacture of lubricants 315 - for manufacture of plastics 315 - for oxosynthesis 319 Asymmetry value 26 Automobile polishes 250, 256
-
Bashkirov process 299 Beauty masks 266 Blending 223 with ethylene-vinyl acetate copolymer 228, 230 with natural waxes 241 with microcrystalline paraffin waxes 224, 229, 243 with polyethylenes 225, 230, 233, 245 with polyisobutylenes 225, 229
-
with polymers 225, 241 with synthetic waxes 241 Blocking point 133, 244 - of macrocrystalline paraffin waxes 134 - of microcrystalline paraffin waxes 134 Boiling point of n-alkanes 91 Brittle microcrystalline paraffin waxes 18, 20
-
Candles 249, 260 Centrifugation 144 Ceramic-casting slurries containing paraffin waxes 273 Ceresins 18 n-Ceresins 189 Chain splitting of alkanes 65 Chillers 159 Chlorinated paraffins 280, 283 - as intermediates for synthetic lubricants 283 - as lubricant-additives 285 - as paint additives 285 - for improving flame resistance 284 - for olefin-manufacture 313 - in plastics processing 284 Chlorination 55, 276, 280 - batchwise 278 - catalytic 57, 276 - continuous 279 gas-phase 57 - liquid-phase 57 - photocatalytic 55, 277, 278 - thermal 57, 277 Church candles 261 Coating of food 270 Coating of paper 242 - by discharge devices 243 - by nozzles 243 - by rollers 243 - with macrocrystalline and rnicrocrystalline paraffins 243
-
332
SUBJECT INDEX
-
- of microcrystalline paraffin waxes 96 - of n-alkanes 95 Deodorant products 268 De-oiling 168 - by solvents 169 - by sweating 168 - of slack waxes 168 Dewaxing 142 - by Bari-Sol process 147, 164 - by cold sedimentation 142 - by cooling and filter pressing 142, 144 by Dilchill process 146, 165 - by Di-Me process 165 - by Edeleanu process 145 - by electrical precipitation 146 - by Exxon process 163 - by methyl ethyl ketone 159 - by propane 160 - by simple cooling 142 - by solvent process 143 - by Weir process 143 Dicarboxylic acids by paraffin oxidation 290 Dielectric strength 139 Dissolving component of dewaxing solvents 147 Double refraction 104 Dry creams 263
-
Elastic deformation 107 - of crystalline substances 107 Elastic microcrystalline paraffin waxes 18, 20 Elastic post-effect 108 Elastic recovery 110 - of macrocrystalline paraffi waxes 110 Electrical insulation using paraffin waxes 274 Electrical volume resistivity 138 Etessam-Sawyer relationship 26 Eyebrow pencils 268
Coating of paper (cont.) - with paraffin waxes modified by polymers 243 Coating of plants 271 Colour 106 - of paraffin waxes 106, 204 - stability 106, 204 Composite candles 260 Composition of parafins 29 - liquid 29 - macrocrystalline 31, 38, 39, 44 - microcrystalline 32, 38, 39 - petrolatum 36, 39 slack wax 52 Composition of petroleums 13, 14 Composition of petroleum fractions 15, 16 Compressive deformation I10 - of macrocrystalline paraffin waxes 110, 226 - of microcrystalline paraffin waxes 112 Compressive strength 113, 228 Compressive stress 110 Concretes treated with paraffin wax emulsions 275 Conditioning creams 264 Cooling curves 74 Cosmetic preparations 262 Crystal 70 - growth 72 - nucleation 72 Crystallinity index 99 Crystallization 71, 87 - ability 72 mechanism of paraffins 71 - rate 73 - starting from melt 71, 87, 88 - starting from solution 75, 88 Crystal structure 70 hexagonal 76, 80 - monoclinic 75, 80 - orthorhombic 75 - triclinic 75, 80 Cubical expansion 95, 96 - of liquid state 98 - of macrocrystalline paraffin waxes 96,98 - of microcrystaIline paraffin waxes 96, 98 - of solid state 98
-
Dehydrochlorination of chlorinated paraffins 313 Dehydrogenation of alkanes 65, 66, 305, 314 Density 91, 94 - of branched alkanes 95 - of macrocrystalline paraffin waxes 94
-
Fatigue limit 108 Fatty acid derivatives 302 - as additives for paints 302 - as detergents 302 as plasticizers 302 - as surface-active agents 302 - as synthetic waxes 302 - for lubricants 302 Fatty acids by paraffin oxidation 290, 297 Fatty alcohols by paraffin oxidation 297, 298 - and by hydrogenation of esters 298 - and by hydrolyzation of borate esters 298, 299 - and by recovery from neutral products 300
-
SUBJECT INDEX
Fatty creams 264 Filter aids 166 Filter pressing 144 Filtrability 147-149 Filtration rate 148, 151, 153, 165, 166 Flexibility of paraffin films 244 Floor polishes containing paraffin waxes 250, 252 Fraass breaking point 115 - of microcrystalline paraffin waxes 116 Fractional crystallization 168, 170 - of microcrystalline paraffin waxes 170 - of paraffin waxes 168 - of petrolatums 172 - of slack waxes 168 Furniture polishes containing paraffin waxes 250, 255 Gas chromatography methods 28 Habits of paraffin waxes 87, 143 Hair pomades 268 Hardness 108 Heat of evaporation 121 - of n-alkanes 122 Heat of formation for urea adducts 182 Heat of fusion 78, 120 - of allotropic transition 78, 120 - of macrocrystalline paraffin waxes 86, 120 - of microcrystalline paraffin waxes 121 Hot melts 243, 246 Impact-bending strength 113 - of macrocrystalline paraffin waxes 114, 227 - of microcrystalline paraffin waxes 114 Impregnations of matches 271 Impregnation of papers 241 by dipping 241 by spraying 241 with blends of paraffin waxes 242 with macrocrystalline and microcrystalline paraffins 242 with melts of paraffin waxes 242 with paraffin waxes modified by polymers 242 with solution of paraffin waxes 242 Intermediate fractions 17, 18 Intermediate paraffin waxes 19, 20, 101 iso-Alkanes 13, 24, 25, 27, 31, 38, 92,95 - by means of molecular sieves 193, 195 - by means of urea 176
333
iso-Ceresins 191 Isomerization of alkanes 65, 68 Lamination 247 - with hot melts 248 - with organic adhesives 248 - with unorganic adhesives 248 Lipsticks 266 Liquid paraffins 11, 13, 18, 19, 29, 30, 93 Macrocrystalline paraffin waxes 12, 18, 20, 29, 31, 39, 85, 86, 88, 93, 94, 96, 98, 99, 101, 103, 108, 110, 114, 117, 120, 123, 127, 131, 133, 134, 137, 143, 144, 204, 206, 219, 224-229, 231, 233, 234, 236, 238,242,262 Ma1 crystals 87 Manufacture of n-alkanes 176, 193, 195 - by BP process 200 - by Edeleanu process 192 - by Ensorb process 201 - by Gulf process 192 - by Hungarian Oil and Gas Research Institute process 186 - by Isosiv process 198 - by Molex process 197 - by Parex process 201 - by Texaco process 196 Melt viscosity 93 - of branched alkanes 93 - of liquid paraffins 93 - of n-alkanes 93 - of paraffin waxes 93, 229, 233, 238 Melting point 91 - of branched alkanes 92 - of n-alkanes 92 - of paraffin waxes 92, 226, 229, 238 Microcrystalline paraffin waxes 12, 18, 20, 29, 31, 39, 89, 93, 94, 96, 98, 99, 101, 103, 108, 112, 114, 116, 117, 121, 131, 133, 134, 137, 139, 143, 144, 170, 204, 206, 242, 250, 262 Miscibility 129 - of different melting point paraffin waxes 129 - of paraffin waxes with natural resins 130 - of paraffin waxes with natural waxes 129 - of paraffin waxes with synthetic resins 130 Molar refraction 103 Molecular sieves 194 Needle crystals 87, 143 Nitroalkanes 60
334
SUBJECT INDEX
Oil content 18, 20, 168 Oil uptake capacity 262 Olefins from chlorinated paraffin waxes 313 Olefins from paraffin waxes 305, 314 Organic acids from paraffins 328 Oxidation-mechanism of paraffins 62 Oxidation of n-alkanes 62, 291 Oxidation of branched alkanes 64, 291 Oxidation of paraffins 62 - in batchwise operation 292, 296 - in continuous operation 296 - with catalysts 65, 290, 294 - with modifiers 65, 290 Paper sizes containing paraffin waxes 248 Penetration 117 - of macrocrystalline paraffin waxes 117, 231, 234, 238 - of microcrystalline paraffin waxes 117 Petrolatums 17, 18, 39, 172 a-phase 75, 119 /%phase 75, 119 Phase-diagram 81 - of binary systems 81 Phase point 149 Picking of poultry 269 Pipeline waxes 17, 18, 144 Plastic deformation 107 - of crystalline substances 107 Plastic microcrystalline paraffin waxes 18, 20 Plate crystals 87, 143 Polishes containing paraffin waxes 249, 250 Precision casting using paraffin waxes 272 Protective creams 266 Pure paraffin wax candles 260 Purification of liquid paraffins 206, 21 8 Purification of paraffin waxes 204, 219 - by development chromatography 208 - by displacement chromatography 209 - by elution chromatography 208 - by frontal chromatography 208 - by hydrogenation 214 - by percolation 209 - with sulfuric acid 205 Rate of alkane-oxidation 64 Refined grade paraffins 18 Refining by hydrogenation 21 6 Refractive index 91, 102 - of hydrocarbons 104, 105 - of macrocrystalline paraffin waxes 103 - of microcrystalline paraffin waxes 103 Relative permittivity 139, 274 - of microcrystalline paraffin waxes 139
- of paraffin waxes 139 Ring analysis 28 Ring value 26 Rotary filters 155 Rubber goods containing paraffin waxes 272 Scale wax 17 Sealing strength 130, 246 - of macrocrystalline paraffin waxes 131 - of microcrystalline paraffin waxes 131 Selective component of dewaxing solvents 147, 148 Semi-fatty creams 264, 265 Semi-refined paraffins 18 Separation methods for paraffins 21 - adduct formation 22 - chromatography 22, 23, 25,40 - combined 24, 36 - fractional crystallization 22 - fractional distillation 21, 22 Shoe polishes containing paraffin waxes 250, 258 Single cell protein process 325 Slab paraffin wax 17 Slack waxes 17, 18, 39, 144 Slop waxes 17, 144 Solid brilliantines 268 Solid paraffin waxes 11, 13, 18, 19, 29, 31 Solid perfumes 263 Solubility 123, 127 - of macrocrystalline paraffin waxes 123, 127 - of paraffin waxes in petroleum distillates 126 Solvent absorption 250, 252, 262 Solvent dewaxing 145 - by chlorinated hydrocarbons 145 - by ketones 145, 146 - by propane 146 - by sulfur dioxide 145 Solvent retention capacity 250, 253 Specific heat 118 - of n-alkanes 118 Spectrometry methods 28 - infrared 29 - mass 28 Spread 147, 159, 162-166 Strength 108 Sulfochloride derivatives 288 Sulfochlorination 287 - batchwise 288 - continuous 288
SUBJECT INDEX
Surface gloss of solid parafin films 244 Sweating 144,168 Tank wax 17, 18 Technical grade paraffins 18 Tensile strength 108 of macrocrystalline paraffin waxes 108, 226, 236 of microcrystalline paraffin waxes 108 Thermal conductivity of para& waxes 123 Thermal decomposition (cracking) 65,66,305 - conditions 306 - mechanism 66, 305 - of alkanes 6 5 , 6 6 - of various starting materials 308 - products 309 - technology 31 1
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335
Unit cells 79 - in cycloalkanes 81 - in n-alkanes 79 - of hexagonal modification 80 - of monoclinic modification 80 - of triclinic modification 80 Vaselines 263 Washing of the filter cake 155 Water resistance 137 Water vapour permeability 136, 244 - of macrocrystalline para& waxes 137 - of microcrystalline paraffin waxes 137 Yeasts from n-paraflins 324, 326, 327 Yield point 107, 108
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