Extractive and Azeotropic Distillation (Advances in Chemistry Series 115)

Extractive and Azeotropic Distillation In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; ...

Author: Dimitrios P. Tassios (Editor)

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Extractive and Azeotropic Distillation

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

Extractive and Azeotropic Distillation

Based on papers presented at two symposia sponsored by the Division of Industrial and Engineering Chemistry of the American Chemical Society at the 160th Meeting, Chicago, Ill., Sept. 17, 1970, and the 163rd Meeting, Boston, Mass., April 14, 1972. Dimitrios P. Tassios Symposia

Chairman

115

ADVANCES IN CHEMISTRY SERIES

AMERICAN CHEMICAL SOCIETY WASHINGTON,

D.

C.

1972

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

ADCSAJ 115 1-176 (1972)

Copyright 1972 American Chemical Society All Rights Reserved

Library of Congress Catalog Card 72-92811 ISBN 8412-0157-9 PRINTED IN THE UNITED STATES OF AMERICA

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

Advances in Chemistry Series Robert F . G o u l d ,

Editor

Advisory Board Bernard D. Blaustein Paul N. Craig Gunther Eichhorn Ellis K . Fields Fred W. McLafferty Robert W. Parry Aaron A. Rosen Charles N. Satterfield Jack Weiner

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

FOREWORD

A D V A N C E S

I N

C H E M I S T R Y

SERIES

w a s f o u n d e d i n 1 9 4 9 b y the

A m e r i c a n C h e m i c a l S o c i e t y as a n outlet for s y m p o s i a a n d c o l lections of d a t a i n s p e c i a l areas o f t o p i c a l interest that c o u l d n o t b e a c c o m m o d a t e d i n the Society's journals. m e d i u m for symposia that w o u l d otherwise be

It provides a fragmented,

t h e i r p a p e r s d i s t r i b u t e d a m o n g s e v e r a l journals o r not p u b l i s h e d at a l l . P a p e r s are refereed c r i t i c a l l y a c c o r d i n g t o A C S e d i t o r i a l standards a n d r e c e i v e the c a r e f u l a t t e n t i o n a n d p r o c essing c h a r a c t e r i s t i c of A C S p u b l i c a t i o n s . in

A D V A N C E S

I N

C H E M I S T R Y

SERIES

Papers p u b l i s h e d

are o r i g i n a l c o n t r i b u t i o n s

not p u b l i s h e d elsewhere i n w h o l e o r major p a r t a n d i n c l u d e reports o f research as w e l l as r e v i e w s since s y m p o s i a m a y e m b r a c e b o t h types of presentation.

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

CONTENTS

PREFACE DIMITRIOS P. TASSIOS

ix-xi

1 Dehydration of Aqueous Ethanol Mixtures by Extractive Distillation C. BLACK and D. E. DITSLER

1-15

2 Process Design Considerations for Extractive Distillation: Separation of PropylenePropane ROMESH KUMAR, JOHN M. PRAUSNITZ, and C. JUDSON KING 16-34 3 Extractive Distillation by Salt Effect WILLIAM F. FURTER

35-45

4 Rapid Screening of Extractive Distillation Solvents: Predictive and Experimental Techniques DIMITRIOS P. TASSIOS 46-63 5 Azeotropic Distillation Results from Automatic Computer Calculations CLINE BLACK, R. A. GOLDING, and D. E. DITSLER

64-92

6 Prediction of Isobaric Vapor-Liquid Equilibrium Data for Mixtures of Water and Simple Alcohols A. ANDIAPPAN and A. Y. McLEAN 93-107 7 Demulsification of Crude Oils: Use of Azeotropic Distillation LESLIE L. BALASSA and DONALD F. OTHMER

108-121

8 Distillation Calculations with Nonideal Mixtures JOSEPH A. BRUNO, JOHN L. YANOSIK, and JOHN W. TIERNEY

122-135

9 Isobaric Vapor-Liquid Equilibrium in the Acetic Acid-Acetone System R. JOE BURKHEAD and J. THOMAS SCHRODT

136-147

10 Separation of Water, Methyl Ethyl Ketone, and Tetrahydrofuran Mixtures HUGH M. LYBARGER and HOWARD L. GREENE 148-158 11 Prediction of Vapor Composition in Isobaric Vapor-Liquid Systems Containing Salts at Saturation D. JAQUES and W. F. FURTER 159-168 INDEX

171-176

PREFACE z e o t r o p i c a n d extractive d i s t i l l a t i o n s h a v e b e e n u s e d t h r o u g h the years i n the c h e m i c a l i n d u s t r y to separate m i x t u r e s w h e r e the r e l a t i v e v o l a t i l i t y o f the k e y c o m p o n e n t s is v e r y close, o r e q u a l , to u n i t y .

Appli-

cations f r o m the c l a s s i c a l d e h y d r a t i o n o f a l c o h o l w i t h b e n z e n e

(J)

m o r e recent ones s u c h as the p r o p y l e n e - p r o p a n e s e p a r a t i o n

(2)

to and

aromatics recovery from hydrocarbon mixtures w i t h N-methylpyrrolidone ( 3 ) , i n d i c a t e a c o n t i n u o u s interest t h r o u g h the years i n this area. T h e s e s e p a r a t i o n m o d e s h a v e n o t b e e n u s e d as f r e q u e n t l y as t h e y s h o u l d i n i n d u s t r y , a n d the often u s e d reasons o f h i g h i n v e s t m e n t a n d h i g h o p e r a t i n g costs are often w e a k w h e n one does a n i n - d e p t h s t u d y . T h e r e a l reason lies w i t h t h e t i m e a n d m o n e y r e q u i r e d to o b t a i n a satisfactory d e s i g n (4).

B e c a u s e o f the h i g h n o n i d e a l i t y o f the systems

involved,

solvent selection, d e s c r i p t i o n o f the n o n i d e a l i t y o f the phases, a n d trayto-tray c a l c u l a t i o n s are rather difficult. R e c e n t d e v e l o p m e n t s i n this area, h o w e v e r , s h o u l d g r e a t l y f a c i l i t a t e this task, e s p e c i a l l y for e x t r a c t i v e d i s tillation.

S o l v e n t selection for a z e o t r o p i c d i s t i l l a t i o n is b a s e d o n r a t h e r

qualitative criteria discussed b y B e r g

( 5 ) , but

for e x t r a c t i v e

l a t i o n the q u a l i t a t i v e a p p r o a c h o f P r a u s n i t z a n d A n d e r s o n (6) e m p i r i c a l correlations o f P i e r o t t i et ah (7),

distil-

a n d the

W e i m e r and Prausnitz

(8),

H e l p i n s t i l l a n d V a n W i n k l e ( 9 ) , a l o n g w i t h the t e c h n i q u e u s i n g g a s l i q u i d c h r o m a t o g r a p h y b y Tassios (10, 11)

give reliable, r a p i d methods

for solvent selection. F o r e x a m p l e , f o u r to five solvents c a n b e screened i n one d a y b y u s i n g g a s - l i q u i d c h r o m a t o g r a p h y . e x t r a c t i v e agents (12)

A l s o use o f salts as

provides a n e w dimension i n extractive distillation

separations. T h e d e v e l o p m e n t o f e q u a t i o n s t h a t successfully p r e d i c t m u l t i c o m p o n e n t phase e q u i l i b r i u m d a t a f r o m b i n a r y d a t a w i t h r e m a r k a b l e a c c u r a c y for e n g i n e e r i n g purposes not o n l y i m p r o v e s the a c c u r a c y o f tray-tot r a y c a l c u l a t i o n s b u t also lessens the a m o u n t of e x p e r i m e n t a t i o n r e q u i r e d to e s t a b l i s h the p h a s e e q u i l i b r i u m d a t a . S u c h equations are: the W i l s o n e q u a t i o n ( 1 3 ) , the n o n - r a n d o m t w o - l i q u i d ( N R T L ) e q u a t i o n (14), the l o c a l effective m o l e fractions ( L E M F ) parameter

v e r s i o n o f the

L a r s o n a n d Tassios (17)

e q u a t i o n (15,

b a s i c a l l y three-parameter

16),

and

a two-

NRTL

equation.

s h o w e d that the W i l s o n a n d N R T L

equations

p r e d i c t a c c u r a t e l y t e r n a r y a c t i v i t y coefficients f r o m b i n a r y d a t a ; H a n k i n s o n et al (18)

d e m o n s t r a t e d t h a t the W i l s o n e q u a t i o n p r e d i c t s a c c u r a t e l y ix

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

m u l t i c o m p o n e n t v a p o r c o m p o s i t i o n s — u p to five c o m p o n e n t s — f r o m b i nary data.

T h e s a m e s t u d y i n d i c a t e s that w h e n l i m i t e d b i n a r y d a t a

a v a i l a b l e , t h e one p a r a m e t e r T a s s i o s - W i l s o n e q u a t i o n (19)

are

predicts m u l -

t i c o m p o n e n t — u p to five c o m p o n e n t s — d a t a w i t h g e n e r a l l y g o o d a c c u r a c y . T h e W i l s o n e q u a t i o n c a n also b e u s e d successfully to c o r r e l a t e p h a s e e q u i l i b r i u m d a t a i n the presence o f salts (20).

The N R T L and

LEMF

equations c a n also p r e d i c t successfully t e r n a r y l i q u i d - l i q u i d e q u i l i b r i u m d a t a f r o m the b i n a r y d a t a w i t h the latter p r o v i d i n g b e t t e r results

(21).

R e g a r d i n g v a p o r p h a s e n o n i d e a l i t i e s , the e m p i r i c a l c o r r e l a t i o n o f O ' C o n n e l l a n d P r a u s n i t z (22)

p r o v i d e f u g a c i t y coefficients o f sufficient a c c u r a c y

for e n g i n e e r i n g purposes.

D e s i g n considerations o f a z e o t r o p i c d i s t i l l a t i o n

schemes are d i s c u s s e d b y R o b i n s o n a n d G i l l i l a n d ( 2 3 ) , H o f f m a n a n d r e c e n t l y b y B l a c k et al.

(25),

w h o present a c o m p u t e r

(24),

oriented

approach. F o r e x t r a c t i v e d i s t i l l a t i o n t h e presence o f the s e c o n d feed

(solvent)

presents s o m e c o m p u t a t i o n a l c o m p l i c a t i o n s i n m a i n t a i n i n g s t a b l e c o n v e r g e n c e i n the s o l u t i o n b y c o m p u t e r s o f the a p p r o p r i a t e system o f e q u a tions—i.e., m a t e r i a l a n d e n t h a l p y balances a n d e q u i l i b r i u m r e l a t i o n s h i p . T h e a l g o r i t h m s t h a t c a n i n h e r e n t l y c o p e w i t h m u l t i p l e feeds are m a t r i x o r i e n t e d , a n d the N e w t o n - R a m p h s o n p r o c e d u r e o f s o l v i n g these e q u a tions shows the m a x i m u m d e g r e e o f s t a b i l i t y (4).

S e v e r a l p a p e r s discuss

computational approaches for extractive distillation calculations ( A m u d s o n a n d P o n t i n e n (26),

N a p h t h a l i (27),

R o c h e (4),

B r u n o et al.

(28),

Black and Ditsler ( 2 9 ) , a n d others). I n c o n c l u s i o n , r e c e n t d e v e l o p m e n t s i n solvent selection, p h a s e n o n i d e a l i t y d e s c r i p t i o n , a n d tray-to-tray c a l c u l a t i o n schemes

have

f a c i l i t a t e d the d e s i g n o f e x t r a c t i v e a n d a z e o t r o p i c d i s t i l l a t i o n

greatly schemes,

a n d use o f salts g i v e n e w m e t h o d s f o r extractive d i s t i l l a t i o n separations. F i n a l l y , the w o r k o f G e r s t e r ( 3 0 ) , B l a c k a n d D i t s l e r ( 2 9 ) , a n d B l a c k et al. (25)

c o m p a r e these t w o schemes. DIMITRIOS P. TASSIOS

Newark College of Engineering Newark, N . J. 07102 July, 1972

Literature Cited 1. Guinot, H., Clark, F. W., Trans. Inst. Chem. Engr. (London) (1938) 16, 187. 2. Hasflund, E. R., Chem. Eng. Progr. (1969) 65, 9. 3. Mueller, E., Hoehfeld, G., WorldPetrol.Congr., 8th, Moscow (June 1971). 4. Roche, Ed., 160th Natl. Meet. Amer. Chem. Soc., Chicago, 1970. 5. Berg, L., Chem. Eng. Progr. (1969) 65, 9, 52. x

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

6. Prausnitz, J. M., Anderson, R., A.I.Ch.E. J. (1961) 7, 96. 7. Pierotti, G. I., Deal, C. H., Derr, E. L., Ind. Eng. Chem. (1955) 51, 95. 8. Weimer, R. F., Prausnitz, J., Petrol. Refiner (1965) 44, 9, 237. 9. Helpinstill, J. G., Van Winkle, M., Ind. Eng. Chem. Process Des. Develop. (1968) 7, 213. 10. Tassios, D. P., Hydrocarbon Process. (1970) 49, 7, 144. 11. Tassios, D. P., Ind. Eng. Chem. Process Des. Develop. (1972) 11, 43. 12. Furter, W. F., Cook, R. Α., Int.J.Heat Mass Transfer (1967) 10, 23. 13. Wilson, G. M.,J.Amer. Chem. Soc. (1964) 86, 127. 14. Renon, H., Prausnitz, J. M., A.I.Ch.E.J.(1968) 14, 135. 15. Marina, J., Dissertation, Newark College of Engineering, Newark, 1972b. 16. Marina, J., Tassios, D. P., Ind. Eng. Chem. Process Des. Develop., in press. 17. Larson, C. D., Tassios, D. P., Ind. Eng. Chem. Process Des. Develop. (1972) 11, 35. 18. Hankinson, R. W., Langfitt, B. D., Tassios, D. P., Can. J. Chem. Eng., in press. 19. Tassios, D. P., A.I.Ch.E. J. (1971) 17, 1367. 20. Taques, D., Furter, W. F., Advan. Chem. Ser. (1972) 115, 159. 21. Marina, J., Tassios, D. P., Ind. Eng. Chem. Process Des. Develop., sub mitted for publication. 22. O'Connell, J., Prausnitz, T. M., Ind. Eng. Chem. Process Des. Develop. (1967) 6, 245. 23. Robinson, C. S., Gilliland, E. R., "Elements of Fractional Distillation," p. 312, McGraw-Hill, New York, 1950. 24. Hoffman, E. S., "Azeotropic and Extractive Distillation," Wiley, New York, 1964. 25. Black, C., Golding, R. Α., Ditsler, D. E., ADVAN. CHEM. SER. (1972) 115, 64. 26. Amudson, N. R., Pontinen, A. J., Ind. Eng. Chem. (1958) 50, 730. 27. Naphthali, L. M., 56th A.I.Ch.E. Meet., San Francisco (May 1965). 28. Bruno, J. Α., Yanosik, J. L., Tierney, J. W., ADVAN. CHEM. SER. (1972) 115, 122. 29. Black, C., Ditsler, D. E., ADVAN. CHEM. SER. (1972) 115, 1. 30. Gerster, J. Α., Chem. Eng. Progr. (1969) 65, 9, 43.

xi In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

1 Dehydration of Aqueous Ethanol Mixtures by Extractive Distillation C. BLACK and D. E. DITSLER Shell Development Co., Emeryville, Calif. 94608

Although nonidealities in vapor and liquid phases complicate the separation of components from mixtures, a knowledge of these nonidealities can be applied to design an extractive distillation step. Ethylene glycol is added to an aqueous ethanol mixture to produce the overhead separation of ethanol from water. Methods published earlier by one of the authors are applied to calculate phase equilibria in a computer calculation of the separation. The extractive distillation results are tabulated, represented graphically, and discussed to illustrate extractive distillation as a method for dehydrating aqueous ethanol mixtures. The results are compared with corresponding results obtained by azeotropic distillation with n-pentane as entrainer. They show extractive distillation with ethylene glycol is more expensive than azeotropic distillation with n-pentane.

C e p a r a t i n g c o m p o n e n t s f r o m m i x t u r e s is c o m p l i c a t e d b y n o n i d e a l i t i e s i n ^

the l i q u i d a n d v a p o r phases. N e v e r t h e l e s s , a k n o w l e d g e o f t h e factors

c o n t r i b u t i n g to the n o n i d e a l i t y of the m i x t u r e s h e l p s to p r o d u c e a j u d i c i o u s d e s i g n for the s e p a r a t i o n step. S o m e t i m e s c o m p o n e n t s are a d d e d t o the m i x t u r e to alter the n o n i d e a l i t y b y c h a n g i n g the m o l e c u l a r e n v i r o n m e n t . E x t r a c t i v e d i s t i l l a t i o n is u s e d because the c o m p o n e n t s are d i s t r i b u t e d differently b e t w e e n c o n t a c t i n g l i q u i d a n d v a p o r phases i n e q u i l i b r i u m w h e n a h i g h - b o i l i n g n o n i d e a l c o m p o n e n t is a d d e d to the m i x t u r e .

The

a d d e d c o m p o n e n t is i n t r o d u c e d i n the u p p e r p a r t of a d i s t i l l a t i o n c o l u m n a b o v e the f e e d a n d r e m a i n s i n a p p r e c i a b l e c o n c e n t r a t i o n i n the l i q u i d o n a l l of the l o w e r trays.

It is r e m o v e d f r o m the c o l u m n w i t h one of the

c o m p o n e n t s b e i n g separated as t h e bottoms p r o d u c t . A l t h o u g h a n o n i d e a l c o m p o n e n t is also i n t r o d u c e d for a z e o t r o p i c d i s t i l l a t i o n , t h e a d d e d c o m 1 In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

2

E X T R A C T I V E

Table I.

A N D

DISTILLATION

Constants for Calculating Imperfection-Pressure Coefficients E'

m

X

0.089 0.089 0.026

4.75 4.75 4.75

75.9 79.2 24.7

P ,Atm. c

Ethanol Ethylene glycol Water β

A Z E O T R O P I C

516.3 761.11 647.00

63.1 84.04 218.0

Α11 δα coefficients have been taken equal to zero.

p o n e n t is, i n that case, m o r e easily v o l a t i l i z e d f r o m t h e m i x t u r e t h a n one of the c o m p o n e n t s b e i n g separated. C o n s e q u e n t l y i t is r e m o v e d o v e r h e a d from the column. I n either case the r e l a t i v e d i s t r i b u t i o n s b e t w e e n t h e s e p a r a b l e l i q u i d a n d v a p o r phases are p r e d i c t e d f r o m t h e p u r e c o m p o n e n t v a p o r pressures Pi°,

l i q u i d p h a s e a c t i v i t y coefficients, γ/s, a n d i m p e r f e c t i o n - p r e s s u r e co

efficients 0/s.

U s i n g these three q u a n t i t i e s , the r e l a t i v e d i s t r i b u t i o n is

expressed as y*Pi°fl,°

m

E x t r a c t i v e d i s t i l l a t i o n has b e e n extensively u s e d for n e a r l y decades i n l a b o r a t o r y , p i l o t p l a n t , a n d c o m m e r c i a l p l a n t operations.

three Cal

c u l a t i o n or p r e d i c t i o n of p h a s e e q u i l i b r i a for s u c h separations has often b e e n d i s c u s s e d ( I , 2, 3 ) .

S o m e h a v e d i s c u s s e d t h e selection of solvents

f o r e x t r a c t i v e d i s t i l l a t i o n (4, 5 ) .

O t h e r s h a v e d i s c u s s e d its r e c e n t a p p l i

c a t i o n t o p a r t i c u l a r separations (6, 7, 8 ) .

A c o m p a r i s o n of

extractive

d i s t i l l a t i o n , as a s e p a r a t i o n m e t h o d , w i t h a z e o t r o p i c d i s t i l l a t i o n a n d w i t h l i q u i d - l i q u i d e x t r a c t i o n has r e c e n t l y b e e n d i s c u s s e d briefly b y G e r s t e r

(9).

T h e use of d i g i t a l c o m p u t e r s to c a r r y o u t c o m p l e t e c a l c u l a t i o n s i n the d e s i g n of s e p a r a t i o n processes has b e e n the g o a l of m a n y . T o d o this effectively, s u i t a b l e m e t h o d s for p h a s e e q u i l i b r i a a n d tray-to-tray d i s t i l l a t i o n c a l c u l a t i o n s are r e q u i r e d . R e s u l t s c a l c u l a t e d b y t h e a p p l i c a t i o n of s u c h m e t h o d s to d e h y d r a t e a q u e o u s e t h a n o l m i x t u r e s u s i n g e t h y l ene g l y c o l as the extractive d i s t i l l a t i o n solvent is d i s c u s s e d b e l o w .

A

b r i e f r e v i e w of t h e m e t h o d s u s e d for p h a s e e q u i l i b r i a a n d e n t h a l p i e s is f o l l o w e d b y a d i s c u s s i o n of t h e results f r o m d i s t i l l a t i o n c a l c u l a t i o n s . T h e s e are c o m p a r e d for extractive d i s t i l l a t i o n w i t h c o r r e s p o n d i n g results o b t a i n e d b y a z e o t r o p i c d i s t i l l a t i o n w i t h n-pentane. Phase

Equilibria

T h e i m p o r t a n t q u a n t i t i e s n e e d e d to represent the n o n i d e a l p h a s e e q u i l i b r i a for extractive d i s t i l l a t i o n are v a p o r pressures Ρ*°, l i q u i d - p h a s e a c t i v i t y coefficients

y% a n d i m p e r f e c t i o n - p r e s s u r e

coefficients

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

ft.

The

1.

B L A C K

A N D

Dehydration

DITSLER

Table II.

of Ethanol

Constants for Vapor Pressure Equations A

Ethanol Ethylene glycol Water a

5

3

Mixtures

B

8.16280 7.71147 20.844*

Antoine equations. Log Ρ = A - BIT -

0

C 1623.22 1816.34 2817.4*

228.98 178.603 4.04859*

C log Τ ; P, mm Hg, T , °K.

c r i t i c a l constants a n d other coefficients for c a l c u l a t i n g the i m p e r f e c t i o n pressure coefficients (1)

are g i v e n i n T a b l e I. E q u a t i o n s a n d coefficients

for c a l c u l a t i n g v a p o r pressures are g i v e n i n T a b l e II.

As binary vapor

i n t e r a c t i o n s h a v e b e e n neglected, the values for t h e δ*, coefficients

have

a l l b e e n t a k e n e q u a l to z e r o as s h o w n i n T a b l e I. T h e M o d i f i e d v a n L a a r equations ( I ) t h e l i q u i d phase a c t i v i t y coefficients. are g i v e n i n T a b l e III.

h a v e b e e n u s e d to c a l c u l a t e

Coefficients at three

temperatures

T h e s e are u s e d b y t h e c o m p u t e r to c a l c u l a t e ac

t i v i t y coefficients at a n y c o m p o s i t i o n a n d t e m p e r a t u r e i n the d i s t i l l a t i o n column. E n t h a l p i e s for s a t u r a t e d l i q u i d s a n d v a p o r s are g i v e n i n T a b l e for the p u r e c o m p o n e n t s r e f e r r e d to z e r o for t h e l i q u i d s at 32 ° F .

IV

Vapor

m i x t u r e s are c a l c u l a t e d a s s u m i n g z e r o heat of m i x i n g . L i q u i d e n t h a l p i e s for the m i x t u r e s are c a l c u l a t e d to i n c l u d e t h e i n t e g r a l heat of m i x i n g , g i v e n a c c o r d i n g to

(2)

H^^^iU), w h e r e t h e differential heat of m i x i n g (Li)

x

(L«). = Table III.

is g i v e n as

2.303#(Δ l o g γ < ) . / Δ ( 1 / Τ )

(3)

Modified van Laar Coefficients for the System Ethanol-Ethylene G l y c o l - W a t e r

Binary % Ethanol-ethylene glycol Ethanol-water Ethylene gly col-water Ethanol-ethylene glycol Ethanol-water E t h y l e n e glycol—water Ethanol-ethylene glycol Ethanol-water Ethylene glycol-water

Ai,

A»

c«

0.276000 0.728000 0.001680 0.251000 0.74600 0.00142 0.23000 0.76050 0.00130

0.259279 0.407000 0.001000 0.23579 0.40080 0.00081 0.21607 0.39250 0.000714

0.000000 0.000000 0.000000 0.000000 0.000000 0.000000 0.000000 0.000000 0.000000

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

t,°C 75.0 75.0 75.0 87.8 87.8 87.8 100.0 100.0 100.0

4

E X T R A C T I V E

Table IV.

Ethylene

glycol

Water

Distillation

A Z E O T R O P I C

DISTILLATION

Enthalpies for Liquid and Vapor h (liquid) Btu/lb. mole

t °F Ethanol

A N D

H ( vapor) Btu/lb. mole

32 100 200 300

0.00 2506.1 6034.9 10365.3

19800.0 20937.9 22573.3 23969.2

100 200 300 400

3637.0 7535.0 11600.0 15889.0

30724.0 32828.0 35193.0 37700.0

100 200 300

1225.0 3027.0 4820.0

19916.0 20649.0 21290.0

Calculations

C a l c u l a t i o n s for t h e extractive d i s t i l l a t i o n o f aqueous e t h a n o l m i x tures c o n t a i n i n g 8 5 . 6 4 % m e t h a n o l h a v e b e e n c a r r i e d o u t w i t h t h e a i d of a U N I V A C 1108 c o m p u t e r .

T h e c o m p u t e r p r o g r a m calculates a l l p h a s e

e q u i l i b r i a a n d tray-to-tray m a t e r i a l a n d heat balances for e a c h c o m p o n e n t

250

,71.43%

-

I Ο

ζ < χ ι— LU Ζ eg LU

200

S/F = 2.5 (MOLE)

150 y

75%

100 h•

^^77.78%

50 -

i

: .0 Figure I . 99%

1 1.8

— — — r

ι , 2.6 R/F (MOLE BASIS)

— 80% 1 3.4

Effects on product purity of changing solvent-feed feea ratios

and reflux-

recovery of ethanol in the extractive distilfotion with ethylene glycol at 14.7 psia

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

1.

B L A C K

A N D

2 Figure 2.

DITSLER

Dehydration

of Ethanol

5

Mixtures

3 4 ETHYLENE GLYCOL/ΕΤΗANOL (MOLE BASIS) Effect of solvent-feed ratio on product purity in the distillation of aqueous ethanol with ethylene glycol

5 extractive

i n the feed. F o r fixed e t h y l e n e - g l y c o l f e e d ratios c a l c u l a t i o n s w e r e m a d e for a n e t h a n o l r e c o v e r y of 9 9 % m i n the o v e r h e a d at f o u r different r e f l u x f e e d ratios i n the r a n g e 1-θ

+

m o l e basis. E a c h series o f c a l c u l a t i o n s w a s

m a d e at the constant s o l v e n t - f e e d

ratios o f 2.5, 3.0, 3.5, a n d 4.0 m o l e

basis. T h e pressure d r o p p e r tray w a s a s s u m e d t o b e 0.1 p s i w i t h the r e b o i l e r pressure set a t 14.7 p s i a .

A drop o f two psi from top tray t o

condenser w a s a s s u m e d for t h e c a l c u l a t i o n . T h e reflux t e m p e r a t u r e w a s set at 104.0°F. A t o t a l of 46 trays w i t h solvent a d d e d o n 43 a n d f e e d at t r a y 2 2 w a s u s e d for the c a l c u l a t i o n s . T h e f e e d a n d t h e solvent w e r e i n t r o d u c e d as l i q u i d at 110° a n d 173°F, respectively. T h e s e results h a v e b e e n u s e d to s h o w the effects o f c h a n g i n g r e f l u x f e e d r a t i o at fixed values of the s o l v e n t - f e e d ratio. I n F i g u r e 1 the w a t e r i n t h e e t h a n o l p r o d u c t is p l o t t e d vs. t h e r e f l u x - f e e d r a t i o , b o t h expressed o n a m o l e basis. F o u r curves are s h o w n , e a c h r e p r e s e n t i n g a different solvent-feed

ratio. E a c h c u r v e goes t h r o u g h a m i n i m u m as the r e f l u x -

f e e d r a t i o changes. pronounced.

A t low solvent-feed

A t high solvent-feed

ratios t h e m i n i m u m i s m o r e

ratios i t i s s h a l l o w , s h o w i n g

only

s m a l l changes as t h e r e f l u x - f e e d varies f r o m 1.4-1.8, m o l e basis. A t the r e f l u x - f e e d

r a t i o o f 1.5545 t h e w a t e r

content o f the

top

p r o d u c t , e t h a n o l , is near the m i n i m u m for e a c h s o l v e n t - f e e d r a t i o s h o w n . F o r this r e f l u x - f e e d r a t i o , t h e w a t e r content o f the t o p p r o d u c t has b e e n p l o t t e d vs. the ethylene g l y c o l - e t h a n o l ratios i n F i g u r e 2.

This curve

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

6

E X T R A C T I V E

A N D

A Z E O T R O P I C

DISTILLATION

24 REBOILER 20

16 CONDENSER 12 8

2

1

4 ETHYLENE GLYCOL/ETHANOL RATIO, MOLES 3

Reboiler and condenser heat loads vs. solvent-feed

Figure 3. 99%

ratio

recovery of ethanol, feed rate 242.02 moles ethanol/hour reflux/feed = 1.5545 mole basis

defines the w a t e r c o n t e n t o f the e t h a n o l p r o d u c t as a f u n c t i o n o f t h e solvent-ethanol ratio. If the f e e d rate is fixed at 242.02 moles o f e t h a n o l p e r h o u r a n d t h e heat loads for r e b o i l e r a n d condenser are c a l c u l a t e d , t h e effect o f c h a n g i n g s o l v e n t - e t h a n o l r a t i o c a n b e o b t a i n e d . T h e s e results are s h o w n i n F i g u r e 3.

Since ethanol is recovered

a t 9 9 % m o l e i n e a c h case a n d t h e

Table V . Extractive Distillation Column Ethanol-Ethylene G l y c o l - W a t e r at 14.7 Psia Material

Components

Feed/Moles

top

e

Balance

b

Solvent/Moles

Top Product Moles

Bottom Product Moles

Ethanol Ethylene glycol Water

0.8564 0.0000 0.1436

3.5000

0.856315 0.000001 0.000014

0.000085 3.499999 0.143586

Totals

1.000

3.5000

0.856330

3.643670

"Reboiler load 73,969 Btu/unit time, top load 46,433 Btu/unit time. * Liquid feed at 110°F on tray 22, liquid solvent at 173°F on tray 43.

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

1.

B L A C K

A N D

Dehydration

DITSLER

of Ethanol

7

Mixtures

Table VI. Extractive Distillation Column Ethanol-Ethylene G l y c o l - W a t e r Temperature,

Tray

No.

Condenser 46 44 43 42 40 38 36 34 32 30 28 26 24 22 20 18 16 14 12 10 8 6 4 2 1

Composition,

and Volatility

Profiles

t, °F

Ethanol in Vapor, Mole Fraction

Water in Liquid, Mole Fraction

Ρ psia

a W/E

104.0 156.9 158.7 195.3 195.8 196.6 197.5 198.4 199.2 200.0 200.9 201.7 202.7 203.7 194.8 195.5 196.3 197.0 197.7 198.5 199.5 202.0 218.5 246.2 297.9 362.1

0.999983 0.999984 0.999793 0.987189 0.987120 0.98696 0.98677 0.98648 0.98601 0.98517 0.98356 0.98037 0.97395 0.96087 0.93873 0.93854 0.93827 0.93772 0.93615 0.93079 0.91132 0.83701 0.53735 0.07283 0.00349 0.00054

0.000016 0.000015 0.000013 0.000011 0.000019 0.00005 0.00011 0.00024 0.00051 0.00107 0.00220 0.00454 0.00934 0.01926 0.04539 0.04546 0.04561 0.04600 0.04731 0.05201 0.06951 0.13805 0.35352 0.46407 0.19499 0.03941

8.20 10.20 10.4 10.5 10.6 10.8 11.0 11.2 11.4 11.6 11.8 12.0 12.2 12.4 12.6 12.8 13.0 13.2 13.4 13.6 13.8 14.0 14.2 14.4 14.6 14.6

— 1.11 1.09 0.485 0.486 0.488 0.489 0.490 0.492 0.493 0.493 0.492 0.489 0.482 0.532 0.533 0.534 0.535 0.535 0.532 0.516 0.452 0.274 0.208 0.311 0.428

p r o d u c t is a l w a y s h i g h p u r i t y e t h a n o l , the t o p l o a d for the

condenser

r e m a i n s n e a r l y constant. T h e r e b o i l e r l o a d , h o w e v e r , reflects the c h a n g e as t h e s o l v e n t - e t h a n o l r a t i o varies. C h a n g i n g the r e c o v e r y of e t h a n o l f r o m 9 9 - 9 9 . 9 9 % m p r o d u c e s o n l y m i n o r increases i n t h e heat loads.

A s u m m a r y of the c o l u m n m a t e r i a l

b a l a n c e for one m o l e of feed is s h o w n i n T a b l e V w h e n t h e r a t i o is 3.5 m o l e basis.

solvent-feed

T h i s c a l c u l a t i o n w a s m a d e for a r e c o v e r y

of

9 9 . 9 9 % m e t h a n o l u s i n g 46 e q u i l i b r i u m trays w i t h t h e solvent o n 43 a n d t h e f e e d o n 22. T h e r e f l u x - f e e d r a t i o w a s 1.5537 m o l e basis. T h e corre s p o n d i n g d a t a for t e m p e r a t u r e , c o m p o s i t i o n , a n d v o l a t i l i t y profiles summarized in Table VI.

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

are

8

E X T R A C T I V E

Figure 4. 99.99%

Temperature

A N D

A Z E O T R O P I C

DISTILLATION

profile in extractive distillation of aqueous

recovery of ethanol, ethylene glycol/ethanol feed 1.5537 moles

ratio =

ethanol

4.08688 moles, reflux-

NUMBER OF TRAYS (EQUIL.) Figure

5.

EG/Ε

Volatility =

profiles in the extractive distillation ethanol with ethylene glycol

4.08688, R/F

=

of

aqueous

1.5537 moles, 99.99% recovery, ethanol

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

1.

B L A C K

A N D

DITSLER

Dehydration

of Ethanol

9

Mixtures

T h e t e m p e r a t u r e profile for the extractive d i s t i l l a t i o n results of T a b l e V I has b e e n p l o t t e d i n F i g u r e 4.

T h e h i g h solvent i n p u t t e m p e r a t u r e

a n d the l o w f e e d i n p u t t e m p e r a t u r e cause s l i g h t l y h i g h e r

temperatures

i n m u c h m o r e of the r e c t i f y i n g section t h a n i n the u p p e r p a r t of

the

s t r i p p i n g section. T h e c o r r e s p o n d i n g v o l a t i l i t y profile for t h e c o l u m n is s h o w n i n F i g u r e 5. T h e i n d i v i d u a l Κ values are also s h o w n there. A s t h e t e m p e r a t u r e increases u p o n a p p r o a c h i n g t h e r e b o i l e r , the r e l a t i v e v o l a t i l i t y for w a t e r w i t h respect to e t h a n o l w o u l d decrease i f t h e

solvent

c o n c e n t r a t i o n r e m a i n e d fixed. H o w e v e r t h e ethylene g l y c o l c o n c e n t r a t i o n i n the l i q u i d increases, t e n d i n g t o m a k e t h e r e l a t i v e v o l a t i l i t y increase. These

two

opposing

influences m a k e the r e l a t i v e v o l a t i l i t y c u r v e

go

t h r o u g h a m i n i m u m n e a r t r a y n u m b e r four, as seen i n F i g u r e 5.

MOLE FRACTION Figure EG/Ε

6. =

Composition profiles in the extractive distillation aqueous ethanol with ethylene glycol 4.08688 moles, R/F

of

= 1.5537 moles, 99.99% recovery ethanol

C o m p o s i t i o n profiles for the same extractive d i s t i l l a t i o n c o l u m n are s h o w n i n F i g u r e 6. T h e w a t e r c o n c e n t r a t i o n i n the l i q u i d goes t h r o u g h a p r o n o u n c e d m a x i m u m at a b o u t t r a y n u m b e r f o u r (see

T a b l e V I ) , cor

r e s p o n d i n g to t h e m i n i m u m i n the relative v o l a t i l i t y of w a t e r w i t h respect to e t h a n o l . I n this r e g i o n the e t h a n o l c o n c e n t r a t i o n i n t h e v a p o r increases r a p i d l y , c h a n g i n g f r o m less t h a n 2 % at tray n u m b e r three to m o r e t h a n 50%

at t r a y n u m b e r six. T h i s r a p i d increase c o n t i n u e s to a b o u t t r a y

n u m b e r t e n w h e r e the c o n c e n t r a t i o n of e t h a n o l i n t h e v a p o r is a b o u t

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

10

E X T R A C T I V E

91 %m.

A N D

A Z E O T R O P I C

DISTILLATION

W a t e r d r o p s o u t of the v a p o r i n the r e c t i f y i n g section b e t w e e n

the f e e d t r a y a n d the solvent i n p u t t r a y w h i l e e t h a n o l c o n t i n u e s

to

concentrate. A b o v e the solvent i n l e t the ethylene g l y c o l d r o p s out r a p i d l y , so i n three e q u i l i b r i u m trays it is r e d u c e d f r o m a b o u t 1.3% m to less t h a n 2 p p m . T h e w a t e r content of the t o p p r o d u c t , e t h a n o l , is a b o u t 16 p p m o n a m o l e basis, as c a l c u l a t e d f r o m the results of T a b l e V . T h e b o t t o m p r o d u c t f r o m the extractive d i s t i l l a t i o n c o l u m n is aqueous ethylene g l y c o l w i t h 3 . 9 4 % m water.

T h i s is f e d to a solvent r e c o v e r y

c o l u m n w h e r e w a t e r is s t r i p p e d f r o m the e t h y l e n e g l y c o l w h i c h is t h e n r e c y c l e d as solvent to the extractive d i s t i l l a t i o n c o l u m n . C a l c u l a t e d results for the solvent r e c o v e r y c o l u m n w i t h n i n e t o t a l trays h a v i n g the f e e d i n l e t o n tray five are g i v e n i n T a b l e V I I .

T h e re

b o i l e r pressure has b e e n t a k e n as 14.7 p s i a . T h e pressure d r o p p e r tray has b e e n set at 0.09 p s i . A d r o p of 1.7 p s i f r o m t h e t o p tray to the c o n Table VII. Solvent Recovery Column Ethanol-Ethylene G l y c o l - W a t e r Temperature

Tray

No.

10 C o n d . 9 Top 8 7 6 5 Feed 4 3 2 1 Reboiler

t,

°F

and Composition

Water in Vapor, Mole Fraction

Ethylene Glycol in Liquid, Mole Fraction

Ρ psia

a EG/W

0.99936 0.99936 0.99830 0.93928 0.42680 0.15285 0.04343 0.01103 0.00265 0.00056

.00004 .00176 .06686 .64743 .95536 .98755 .99763 .99919 .99981 .99996

12.28 13.98 14.07 14.16 14.25 14.34 14.43 14.52 14.61 14.70

.0216 .0224 .0352 .0627 .0699 .0723 .0731 .0734 .0736

104.0 209.5 213.3 264.6 356.8 379.6 387.6 390.2 391.1 391.7

Material Components

Profiles

FeedMoles

a

Balance

Top Product

Moles

Bottom

Product

Ethanol Ethylene glycol Water

0.000085 3.499999 0.143586

.000085 .000006 .143442

.000000 3.499993 0.000144

Totals

3.643670

.143533

3.500137

R e b o i l e r l o a d 3,3015 B t u / U n i t Top load 2,8709 B t u / U n i t

—

Moles

Time Time

Based on one mole of feed to the extractive distillation column which precedes the solvent recovery column. a

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

1.

B L A C K

A N D

Figure

DITSLER

7.

Dehydration

Temperature

of Ethanol

11

Mixtures

profile for solvent recovery

column

Stripping water from aqueous ethylene glycol

denser has b e e n a s s u m e d . T h e reflux t e m p e r a t u r e w a s set at 104° F a n d t h e r e f l u x - f e e d r a t i o at 1.33491, m o l e basis. T h e f e e d t e m p e r a t u r e w a s 358 ° F , a f e w degrees less t h a n the b o t t o m t e m p e r a t u r e of the extractive d i s t i l l a t i o n c o l u m n . M a t e r i a l b a l a n c e a n d c o l u m n profiles are g i v e n i n T a b l e V I I for the r e c o v e r y c o l u m n . T h e t e m p e r a t u r e profile for this c o l u m n is s h o w n i n F i g u r e 7.

The

c o m p o s i t i o n profiles are p l o t t e d i n F i g u r e 8. T h e s e s h o w the e x p e c t e d trends, w a t e r i n the v a p o r i n c r e a s i n g a n d e t h y l e n e g l y c o l i n the l i q u i d d e c r e a s i n g as one proceeds f r o m the r e b o i l e r to t h e t o p of the c o l u m n . W i t h t h e n u m b e r of trays s h o w n a n d the r e f l u x - f e e d r a t i o g i v e n , e t h y l e n e g l y c o l i n the t o p p r o d u c t ( w a t e r ) is r e d u c e d to a b o u t 42 p p m , m o l e basis. E t h a n o l i n the w a t e r p r o d u c t is a b o u t 0 . 0 6 % m . R e d u c i n g e t h y l e n e g l y c o l i n the w a t e r p r o d u c t to a s i g n i f i c a n t l y l o w e r v a l u e r e q u i r e s o n l y the a d d i t i o n of one or m o r e r e c t i f y i n g trays i n t h e recovery

c o l u m n . A n increase i n the r e f l u x - f e e d

r a t i o w i l l d o as a n

alternate m e t h o d , b u t to c h a n g e t h e e t h a n o l i n the w a t e r p r o d u c t , the extractive d i s t i l l a t i o n c o l u m n w o u l d h a v e to b e o p e r a t e d for h i g h e r or l o w e r e t h a n o l r e c o v e r y t h a n the 9 9 . 9 9 % m v a l u e . T h i s c a n b e d o n e w i t h o u t difficulty. T h e b o t t o m p r o d u c t f r o m the solvent r e c o v e r y c o l u m n is e t h y l e n e g l y c o l w i t h a b o u t 41 p p m of w a t e r , m o l e basis. B y c h a n g i n g the n u m b e r of s t r i p p i n g trays i n the solvent r e c o v e r y c o l u m n , this w a t e r c o n t e n t c a n r e a d i l y be d e c r e a s e d or i n c r e a s e d .

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

12

E X T R A C T I V E

A N D

A Z E O T R O P I C

DISTILLATION

I f t h e t o p p r o d u c t ( w a t e r ) f r o m t h e solvent r e c o v e r y c o l u m n is to be discarded, the two distillation columns w o u l d be operated to reduce e t h a n o l a n d e t h y l e n e g l y c o l to l o w c o n c e n t r a t i o n s , as i l l u s t r a t e d i n the c a l c u l a t i o n s s h o w n here.

H o w e v e r , w h e r e the o v e r a l l p l a n t s c h e m e is

s u c h t h a t t h e w a t e r p r o d u c t m i g h t b e r e c y c l e d a n d used—e.g>, as solvent to a n a q u e o u s extractive d i s t i l l a t i o n , i t m i g h t u n d e r some c o n d i t i o n s b e m o r e e c o n o m i c a l to leave m o r e e t h a n o l i n the w a t e r p r o d u c t . T h e e t h a n o l w o u l d b e r e c o v e r e d i n the series of s e p a r a t i o n steps w h i c h f o l l o w i n the flow

scheme. W a t e r m i g h t b e rejected at a m o r e s u i t a b l e p o i n t i n the

flow s c h e m e t h a n f r o m the t o p of the solvent r e c o v e r y c o l u m n . T h e best o p e r a t i n g c o n d i t i o n s c a n b e d e t e r m i n e d o n l y w h e n the e n t i r e p l a n t

flow

scheme is k n o w n .

Comparison of Extractive

with Azeotropic

Distillation

A l t h o u g h e t h a n o l is o b t a i n e d as a t o p p r o d u c t f r o m a n extractive d i s t i l l a t i o n w i t h e t h y l e n e g l y c o l , it is o b t a i n e d as a b o t t o m p r o d u c t f r o m a n a z e o t r o p i c d i s t i l l a t i o n c o l u m n u s i n g a n entraîner s u c h as n-pentane. B a s e d o n a n e t h a n o l rate of 242.02 moles p e r h o u r , a r o u g h c o m p a r i s o n w i l l b e m a d e of the t w o s e p a r a t i o n m e t h o d s .

CONDENSER 10τ

1

MOLE FRACTION Figure

8.

Composition

profiles for solvent recovery

column

Stripping water from aqueous ethylene glycol

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

1.

B L A C K

A N D

DITSLER

Table VIII.

Dehydration

Distillation,

14.7

Ethanol psia

(85.64%m Azeotropic

13

Mixtures

Comparing Extractive and Azeotropic

Feed: Aqueous Extractive

of Ethanol

Distillation

Ethanol) Distillation,

50 psia

S o l v e n t = ethylene g l y c o l M o l e s s o l v e n t - e t h a n o l = 4.08688 R e f l u x - f e e d r a t i o = 1.55369 46 T r a y s t o t a l i n e x t r a c t i v e d i s t . c o l . S o l v e n t o n t r a y 43 F e e d on t r a y 22 R e b o i l e r l o a d = 20.9 m i l l i o n Btu/hour T o p l o a d = 13.12 m i l l i o n Btu/hour T o w e r d i a m e t e r = 5.3 feet Ethanol product: W a t e r 16 p p m (mole basis) S o l v e n t 1.2 p p m (mole basis) E t h a n o l recovery f r o m feed = 99.99%

Entraîner = n-pentane Moles n-pentane-ethanol =

S o l v e n t recovery c o l u m n 9 T r a y s , R / F = 1.33491 (mole) R e f l u x on t r a y 9 Feed on t r a y 5 R e b o i l e r l o a d = 9.33 m i l l i o n Btu/hour T o p l o a d = 8.11 m i l l i o n Btu/hour T o w e r d i a m e t e r = 4.1 feet

Stripping column

T o t a l heat to reboilers = 30.23 million Btu/hour T o t a l t o p loads = 21.23 m i l l i o n Btu/hour

T o t a l heat t o reboilers < 13 m i l l i o n Btu/hour T o t a l t o p loads < 14 m i l l i o n Btu/hour

e

e

3.214

18 T r a y s t o t a l i n azeotropic dist. c o l . Entraîner o n t r a y 18 F e e d o n t r a y 16 R e b o i l e r l o a d = 10.7 m i l l i o n Btu/hour C o n d e n s e r l o a d — 11.33 m i l l i o n Btu/hour T o w e r d i a m e t e r < 5 feet Ethanol product: W a t e r < 3 p p m ( m o l e basis) n - P e n t a n e < 1 p p m (mole basis) E t h a n o l r e c o v e r y f r o m feed >99.99% β

Reboiler load <2. million Btu/hour Top load <2. million Btu/hour α

T o w e r d i a m e t e r < 2 . feet

"Based on 242.02 moles/hour of ethanol in feed to plant.

F o r the extractive d i s t i l l a t i o n results of T a b l e s V a n d V I , the r e b o i l e r l o a d for the a b o v e e t h a n o l rate w o u l d b e a b o u t 20.9 m i l l i o n B t u p e r h o u r . T h e e t h a n o l p r o d u c t contains a b o u t 16 p p m of w a t e r a n d a b o u t 1.2 p p m of ethylene g l y c o l . F o r a n e t h a n o l r e c o v e r y of 9 9 . 9 9 % ra, 46 t o t a l e q u i l i b r i u m trays are r e q u i r e d w i t h a r e f l u x - f e e d r a t i o of 1.55 a n d a s o l v e n t +

e t h a n o l r a t i o of 4.09' m o l e basis. T h e condenser l o a d is a b o u t 13.1 m i l l i o n B t u / h o u r , a n d the t o w e r d i a m e t e r is a b o u t 5.3 feet, b a s e d o n a G l i t s c h sizing technique.

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

14

E X T R A C T I V E

A N D

A Z E O T R O P I C

DISTILLATION

I f n-pentane is selected as the entraîner for a n a z e o t r o p i c d i s t i l l a t i o n scheme, a n e t h a n o l p r o d u c t c o n t a i n i n g less w a t e r t h a n that o b t a i n e d i n the extractive d i s t i l l a t i o n m e t h o d is easily o b t a i n e d w i t h e n t r a i n e r - e t h a n o l ratios of 2.5-3.5, m o l e basis (10).

F o r a r a t i o of 3.214, t h e w a t e r

c o n t e n t of the e t h a n o l is less t h a n 3 p p m . O n l y 18 e q u i l i b r i u m trays are r e q u i r e d i n a c o l u m n of less t h a n 5 feet diameter.

T h e heat loads i n

m i l l i o n s B t u / h o u r are a b o u t 10.7 for the r e b o i l e r a n d 11.3 for t h e c o n denser.

A s t r i p p e r is u s e d to recover n-pentane a n d e t h a n o l f r o m the

a q u e o u s phase. T h e r e c o v e r e d n-pentane a n d e t h a n o l c a n b e r e c y c l e d either to the f e e d or to t h e reflux stream of the a z e o t r o p i c d i s t i l l a t i o n column. T h e s t r i p p e r r e q u i r e d to process the aqueous p h a s e for r e c o v e r i n g n-pentane a n d e t h a n o l r e q u i r e s a f e w m o r e trays, b u t i t has a c o l u m n d i a m e t e r less t h a n h a l f that of the solvent r e c o v e r y c o l u m n for the extract i v e d i s t i l l a t i o n scheme. T h e heat loads are also m u c h smaller. T h e t o p p r o d u c t , c o n s i s t i n g of n-pentane, e t h a n o l , a n d some w a t e r , is r e c y c l e d to t h e reflux stream of the extractive d i s t i l l a t i o n c o l u m n . T h e results of c a l c u l a t i o n s for the t w o s e p a r a t i o n m e t h o d s are s u m marized in Table VIII.

F e w e r trays are r e q u i r e d i n t h e a z e o t r o p i c dis-

t i l l a t i o n c o l u m n t h a n the extractive d i s t i l l a t i o n c o l u m n . T h e heat loads are also smaller. T h e q u a l i t y of the e t h a n o l p r o d u c t is also s l i g h t l y better for the a z e o t r o p i c d i s t i l l a t i o n m e t h o d . I n c l u d i n g t h e s t r i p p e r for processi n g the aqueous phase, the t o t a l heat l o a d for reboilers for the a z e o t r o p i c d i s t i l l a t i o n m e t h o d is less t h a n h a l f that for the extractive d i s t i l l a t i o n method.

T h e t o t a l c o n d e n s e r l o a d is r o u g h l y t w o - t h i r d s t h a t for

the

extractive d i s t i l l a t i o n m e t h o d . A l t h o u g h the a z e o t r o p i c d i s t i l l a t i o n scheme, u s i n g n-pentane, operates at a h i g h e r pressure, c o m p a r a t i v e c a l c u l a t i o n s i n d i c a t e this t o b e better t h a n the extractive d i s t i l l a t i o n scheme u s i n g d i e t h y l e n e g l y c o l to dehydrate aqueous ethanol. List of Symbols H

M

X

(Li)a-

the i n t e g r a l heat of m i x i n g for m i x t u r e of c o m p o s i t i o n χ the differential heat of m i x i n g f o r c o m p o n e n t i at c o m p o s i t i o n χ

Pi°

v a p o r pressure for c o m p o n e n t i

P,-°

v a p o r pressure for c o m p o n e n t /

αν

v o l a t i l i t y of c o m p o n e n t i r e l a t i v e to c o m p o n e n t /

γι

l i q u i d p h a s e a c t i v i t y coefficient for c o m p o n e n t i

jj

l i q u i d phase a c t i v i t y coefficient for c o m p o n e n t /

Οι

i m p e r f e c t i o n - p r e s s u r e coefficient for c o m p o n e n t i

6j

i m p e r f e c t i o n - p r e s s u r e coefficient for c o m p o n e n t /

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

1. BLACK AND DITSLER

Dehydration of Ethanol Mixtures

15

Literature Cited 1. Black, C., Derr, E. L., Papadopoulos, M. N., Ind. Eng. Chem. (1963) 55, No. 9, 38-47. 2. Garner, F. H., Ellis, S. R. M., Trans. Inst. Chem. Eng. (London) (1951) 29, 45. 3. Null, H. R., Palmer, D. Α., Chem. Eng. Progr. (1969) 65 (9), 47. 4. Berg, L., Chem. Eng. Progr. (1969) 65, (9), 53. 5. Tassios, Dimitrios, Chem. Eng. (Feb. 10, 1969) 76 (3), 118-22. 6. Bannister, R. R., Buck, E., Chem. Eng. Progr. (1969) 65 (9), 65. 7. Halflund, E. R., Chem. Eng. Progr. (1969) 65, 9. 8. Hoffman, E. S., "Azeotropic and Extractive Distillation," Wiley, New York, 1964. 9. Gerster, J. Α., Chem. Eng. Progr. (1969) 65 (9), 43. 10. Black, C., Golding, R. Α., Ditsler, D. E., Advan. Chem. Ser. (1972) 115, 64. RECEIVED November 24, 1970.

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

2 Process Design Considerations for Extractive Distillation: Separation of Propylene-Propane ROMESH KUMAR, JOHN M. PRAUSNITZ, and C. JUDSON KING Department of Chemical Engineering, University of California, Berkeley, Calif. 94720 Extractive distillation is evaluated as an alternative to ordinary distillation for the separation of propylene-propane mixtures. Varticular attention is given to the necessary compromises between different design factors: solvent concentration within the primary column, solvent selectivity, solvent loss, etc. A major expense is associated with the sensible heat requirements of the circulating solvent; process modifications so as to minimize this expense are discussed. The process analysis explores combinations of solvent selectivity and other solvent properties which might make extractive distillation attractive. It appears that in almost all cases extractive distillation offers no advantage compared with ordinary distillation. Only in special cases may circumstances warrant extractive distillation. External factors favoring the use of extractive distillation are identified.

' T p h i s w o r k explores the i m p o r t a n t v a r i a b l e s w h i c h m u s t be •*· to d e s i g n a n e x t r a c t i v e d i s t i l l a t i o n process. T h e the

e c o n o m i c effects o f these v a r i a b l e s a n d

S o m e of the

design variables may

s e p a r a t i o n cost w h i l e others m a y

considered

d i s c u s s i o n identifies

t h e i r p o s s i b l e interactions.

h a v e synergistic effects i n terms of not.

A s a result, the

optimum design

for a n e c o n o m i c extractive d i s t i l l a t i o n process m u s t be a c o m p r o m i s e set of values for the different process v a r i a b l e s . T h e s e c o m p r o m i s e s are

dis-

cussed and

pro-

are i l l u s t r a t e d for a p a r t i c u l a r case—i.e., separation of

p a n e - p r o p y l e n e mixtures.

For

this c o m m e r c i a l l y i m p o r t a n t s e p a r a t i o n

f r a c t i o n a l d i s t i l l a t i o n is m o s t often u s e d , regardless of the

low

relative

v o l a t i l i t y ( a b o u t 1.13-1.19 at 200 p s i a ) . E x t r a c t i v e d i s t i l l a t i o n is sometimes u s e d to

separate m i x t u r e s

w h i c h f r a c t i o n a l d i s t i l l a t i o n is difficult, s u c h as for

for

b i n a r y systems of

16

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

2.

K U M A R , PRAUSNITZ,

A N D

K I N G

Process Design

17

Considerations

c l o s e - b o i l i n g c o m p o n e n t s or for m u l t i c o m p o n e n t systems w h e r e t h e o r d e r of c o m p o n e n t v o l a t i l i t i e s does n o t c o r r e s p o n d to the d e s i r e d d i s t r i b u t i o n of c o m p o n e n t s b e t w e e n p r o d u c t s . I n extractive d i s t i l l a t i o n , a s e p a r a t i n g agent, often c a l l e d the solvent, is a d d e d to t h e m i x t u r e to b e separated. T h i s agent, or solvent, modifies the v o l a t i l i t y of e a c h c o m p o n e n t , one different f r o m the other, b y its effects o n l i q u i d - p h a s e p r o p e r t i e s .

Such

effects c a n i n c l u d e f o r m i n g a s s o c i a t i o n complexes, a l t e r i n g e x i s t i n g assoc i a t i o n structures, etc. A s a result, the c o m p o n e n t r e l a t i v e v o l a t i l i t i e s i n the presence of t h e solvent differ f r o m those i n t h e solvent-free m i x t u r e . T h e f u n d a m e n t a l flow d i a g r a m for a n extractive d i s t i l l a t i o n process is s h o w n i n F i g u r e 1. T h e f e e d enters the e x t r a c t i v e d i s t i l l a t i o n c o l u m n ( p r i m a r y c o l u m n ) i n w h i c h the solvent is a d d e d n e a r t h e t o p . T h e c o m p o n e n t ( o r c o m p o n e n t s ) w h o s e v o l a t i l i t y is the greatest i n t h e p r e s e n c e of the solvent is d r i v e n o v e r h e a d i n this c o l u m n . T h e b o t t o m s consist of the solvent a n d the o t h e r c o m p o n e n t

( o r c o m p o n e n t s ) ; these are f e d

to the solvent r e c o v e r y c o l u m n ( s e c o n d a r y c o l u m n ) .

The

regenerated

solvent is c o o l e d a n d f e d b a c k to t h e p r i m a r y c o l u m n . I n m o s t cases, t h e solvent is m u c h less v o l a t i l e t h a n the f e e d c o m p o n e n t s ; i t is therefore present m a i n l y i n the l i q u i d p h a s e i n t h e p r i m a r y column.

T h i s is d e s i r a b l e , as i t is the l i q u i d - p h a s e n o n i d e a l i t i e s w h i c h

g i v e r i s e to the greater s e p a r a t i o n factor b e t w e e n t h e f e e d c o m p o n e n t s . H o w e v e r , there is a r e l a t i v e l y s m a l l a m o u n t of solvent i n t h e v a p o r phase, a n d to a v o i d excessive loss of this solvent w i t h the t o p p r o d u c t i n t h e p r i m a r y c o l u m n , sufficient trays are p r o v i d e d a b o v e t h e solvent a d d i t i o n p l a t e to r e d u c e the solvent c o n c e n t r a t i o n i n the t o p p r o d u c t to a n acceptable level. General

Considerations

F o r the process s h o w n i n F i g u r e 1, t h e m a i n u n i t s are t h e

two

distillation columns ( w i t h their reboilers a n d overhead condensers) a n d the solvent cooler.

T h e major u t i l i t i e s are t h e heat r e q u i r e d i n t h e re-

boilers a n d the c o o l i n g duties of the condensers a n d t h e solvent cooler. T h e d e s i g n o f the p r i m a r y c o l u m n d e p e n d s p r i m a r i l y o n t h e r e l a t i v e v o l a t i l i t y of t h e k e y c o m p o n e n t s ; i t is therefore s t r o n g l y d e p e n d e n t u p o n the a c t i v i t y coefficients of these c o m p o n e n t s i n t h e solvent. T h e v o l a t i l i t i e s of t h e f e e d c o m p o n e n t s r e l a t i v e to the solvent are g e n e r a l l y h i g h ; therefore, the d e s i g n of the s e c o n d a r y c o l u m n is p r i m a r i l y a f u n c t i o n of the solvent c i r c u l a t i o n rate. T h e c o n d e n s e r d u t i e s d e p e n d o n the reflux ratios i n t h e t w o c o l u m n s w h i c h are thus affected b y the r e l a t i v e v o l a t i l i t i e s . T h e solvent cooler d u t y is a f u n c t i o n of t h e solvent c i r c u l a t i o n rate a n d t h e r e c o v e r y c o l u m n r e b o i l e r t e m p e r a t u r e w h i c h is d e t e r m i n e d b y the solvent v o l a t i l i t y . T h e s u m of t h e r e b o i l e r d u t i e s i n

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

18

E X T R A C T I V E

Solvent

£

A N D

A Z E O T R O P I C

DISTILLATION

• Propane Product

Extractive Distillation Column

Feed

Propylene Solvent Product Recovery Column Steam

Solvent Cooler Figure 1.

Extractive

distillation process flowsheet

t h e t w o c o l u m n s is a p p r o x i m a t e l y e q u a l to the s u m o f t h e heat r e m o v e d i n the condensers a n d i n t h e solvent cooler.

The thermodynamic prop-

erties o f the solvent a n d the solvent r e c i r c u l a t i o n rate are o f major i m p o r t a n c e i n the d e s i g n o f the extractive d i s t i l l a t i o n process. Solvent Selection

Criteria

I m p o r t a n t solvent characteristics are selectivity, m i s c i b i l i t y w i t h t h e feed, a n d v o l a t i l i t y . Selectivity. T h e selectivity, S , is d e f i n e d as the r a t i o o f t h e a c t i v i t y 00

coefficients o f the k e y c o m p o n e n t s w h e n e a c h a l o n e i s present i n t h e solvent at infinite d i l u t i o n . T h u s , for the p r o p a n e - p r o p y l e n e system S°° =

y-osHe/yoeHe

(D

T h e a c t i v i t y coefficients o f the c o m p o n e n t s at other t h a n t r a c e c o n centrations i n the solvent d e p e n d o n the m i x t u r e c o m p o s i t i o n a n d , f o r systems w i t h p o s i t i v e d e v i a t i o n f r o m R a o u l t ' s L a w , decrease t o w a r d u n i t y as the c o m p o n e n t m o l e f r a c t i o n tends t o w a r d one. I n a s i m p l e , s y m m e t r i c

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

2.

K U M A R ,

19

Process Design Considerations

PRAUSNITZ, A N D K I N G

b i n a r y system, t h e l o g a r i t h m of the a c t i v i t y coefficient of t h e h y d r o c a r b o n (A)

o r ( B ) is p r o p o r t i o n a l to t h e s q u a r e of the solvent m o l e f r a c t i o n ( I ) \ny

=

A

(lny«> )x A

l n y B = = (In

2

8

y°° )xs B

2

E q u a t i o n 2, a l t h o u g h not h i g h l y a c c u r a t e for m a n y p r a c t i c a l systems, was u s e d i n this w o r k as i t is c o n v e n i e n t to i m p l e m e n t a n d provides a good

first-order

generally

approximation.

N e g l e c t i n g vapor-phase corrections a n d t h e P o y n t i n g effect, t h e r e l a t i v e v o l a t i l i t y b e t w e e n the k e y c o m p o n e n t s i n the presence of t h e solvent is

"

A B

=

(ΎΑ)

(P°A)

(y )

(P%)

B

RT)

( 3 )

w h e r e P° is the p u r e - c o m p o n e n t s a t u r a t i o n ( v a p o r ) pressure. E q u a t i o n 3 m a y b e w r i t t e n as

<*AB

(4)

-(ft)

S = y A/y Β

where

=

S

œ

·

such t h a t and

î(x ) s

f (x ) f (x ) 8

8

-» 1 < 1

when x for x

8

8

1 < 1

A h i g h selectivity gives a h i g h relative v o l a t i l i t y , m a k i n g a n easier s e p a r a t i o n possible. S increases w i t h i n c r e a s i n g solvent c o n c e n t r a t i o n

(2),

b e c o m i n g a m a x i m u m at 1 0 0 % solvent, a n d u s u a l l y falls w i t h r i s i n g t e m p e r a t u r e . A n e x a m p l e is g i v e n i n F i g u r e 2, w h i c h shows the s e l e c t i v i t y of t h e solvents f u r f u r a l a n d a c e t o n i t r i l e for p r o p a n e - p r o p y l e n e , m a t e d b y the p r o c e d u r e s of W e i m e r a n d P r a u s n i t z ( 3 ) .

as esti-

S is largest at

h i g h solvent concentrations a n d at l o w t e m p e r a t u r e s ; therefore, the separ a t i o n w o u l d b e easiest u n d e r these c o n d i t i o n s . T h e search for a s u i t a b l e solvent for a p a r t i c u l a r s e p a r a t i o n w o u l d b e greatly a i d e d i f the f e e d c o m p o n e n t

a c t i v i t y coefficients

p r e d i c t e d f r o m t h e p u r e - c o m p o n e n t p r o p e r t i e s alone.

could

Tassios ( 2 )

be de-

scribes a five-step p r o c e d u r e for e v a l u a t i n g solvents for extractive d i s t i l l a t i o n of h y d r o c a r b o n s . T w o of t h e m o r e u s e f u l correlations for p r e d i c t i n g a c t i v i t y coefficients

are those p r o p o s e d b y W e i m e r

a n d b y P i e r o t t i , D e a l , a n d D e r r (4).

and Prausnitz

(3)

T h e f o r m e r is u s e f u l w h e r e t h e f e e d

c o m p o n e n t s are s a t u r a t e d h y d r o c a r b o n s , olefins, or aromatics. F o r o t h e r classes of h y d r o c a r b o n s , the latter is useful. F o r a paraffin-olefin system o f the same n u m b e r of c a r b o n atoms i n the absence of a solvent, the olefin is m o r e v o l a t i l e a n d is d r i v e n o v e r h e a d

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

20

E X T R A C T I V E

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DISTILLATION

Temperature, °C Figure 2. Effect of temperature on solvent selectivity and propane activity coefficient in furfural and in acetonitrile (calculated) i n o r d i n a r y d i s t i l l a t i o n ; for p r o p a n e - p r o p y l e n e , Ρ°ΟΛΉΛ/Ρ°€*ΉΒ is greater t h a n u n i t y . A p o l a r solvent is u s e d i n extractive d i s t i l l a t i o n o f p a r a f f i n olefin m i x t u r e s s i n c e the olefin, because o f t h e l a r g e p o l a r i z a b i l i t y o f the d o u b l e b o n d , forms a less n o n i d e a l system w i t h the solvent t h a n does t h e paraffin.

I n these systems t h e paraffin a c t i v i t y coefficient is greater t h a n

t h a t of the olefin, t h e r e b y t e n d i n g to reverse the n a t u r a l r e l a t i v e v o l a t i l i t y of t h e p a r a f f i n - o l e f i n s y s t e m ; f o r p r o p a n e - p r o p y l e n e , γο Ηβ/7ο Η8 is less 3

3

t h a n u n i t y . T o b e u s e f u l , a solvent m u s t reverse t h e r e l a t i v e v o l a t i l i t y to s u c h a n extent t h a t (a e) w i t h solvent > ( — — j w i t h o u t solvent. A

\<*AB

O n l y a few

)

e x p e r i m e n t a l investigations h a v e b e e n r e p o r t e d w h i c h

e v a l u a t e solvents for p a r a f f i n - o l e f i n separations.

Perhaps the most com-

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

2.

K U M A R ,

PRAUSNITZ,

A N D

Process Design

K I N G

21

Considerations

prehensive experimental data o n paraffin-olefin-solvent mixtures have been reported b y Gerster, Gorton, a n d E k l u n d (5).

T h e s e authors r e p o r t

a c t i v i t y coefficient d a t a for n-pentane a n d 1-pentene i n b i n a r y systems w i t h 33 different solvents at f o u r temperatures. T h e d a t a for n o n - h y d r o g e n b o n d i n g solvents w e r e c o r r e l a t e d i n a p l o t o f selectivity vs. In y°°c5Hi2> **s s h o w n i n F i g u r e 3. T h e c u r v e for h y d r o g e n b o n d i n g solvents falls l o w e r ; i.e., t h e same γ°°θ5Ηΐ2 corresponds to a l o w e r selectivity. F i g u r e 3 shows that f o r a p a i r o f h y d r o c a r b o n solutes c o n t a i n i n g t h e same n u m b e r o f c a r b o n atoms, the a c t i v i t y coefficient o f one h y d r o c a r b o n i n b i n a r y s o l u t i o n w i t h a p o l a r solvent is, t o a first a p p r o x i m a t i o n , a f u n c t i o n o f the a c t i v i t y coefficient o f t h e o t h e r i n that solvent. A c t i v i t y coefficients

for

p r o p a n e - p r o p y l e n e , as e s t i m a t e d b y t h e m e t h o d of W e i m e r a n d P r a u s n i t z ( 3 ) , e x h i b i t b e h a v i o r s i m i l a r to t h a t n o t e d for a c t i v i t y coefficients o f the n - p e n t a n e - l - p e n t e n e system w i t h i n the a c c u r a c y o f t h e e s t i m a t i o n p r o cedure. H o w e v e r , H a f s l u n d ( 6 ) has q u o t e d solvent selectivity d a t a for the propane-propylene

system w h i c h d e v i a t e

c o n s i d e r a b l y f r o m the p l o t

g i v e n i n F i g u r e 3. S o m e o f these d a t a are also s h o w n i n that figure. I t appears that a l t h o u g h most solvents m a y b e e x p e c t e d t o f a l l a l o n g the

2.2

X 2,2,3, Trichlorobutyronitrile y

2.0 χ Butyronitrilt Acrylonitrile y X y

1.8 -

y

y

y

y Gerster'· Plot •—Bostd on Dota for Ptfltant end Penttne

y

Acttone χ 1.6

1.4

y

^ χ '

_

^

y

S Acetonitrilt PrapiOMtril*

w « i U M H 111 IB

X Dota Quoted by HofthMd

X Furfural

κ y

1.2 0MF 1 1 1 1 11 1 1 3 4 5 6 7 8 9 β x

1.0

1

I 2

I l 15 20

I I I 30 40 50

Activity Coefficient of Propane, / ·

S 8 H

Figure 3.

Solvent selectivity as a function of activity coefficient of paraffin in the solvent

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

22

E X T R A C T I V E

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A Z E O T R O P I C

DISTILLATION

p l o t i n F i g u r e 3, there are s o m e solvents w h i c h s h o w s u b s t a n t i a l l y differ ent selectivity. I n this w o r k , t w o sets o f c a l c u l a t i o n s w e r e m a d e for the effect of s e l e c t i v i t y o n the process d e s i g n : ( 1 ) 7°°C3H v a r i e d w i t h S 8

00

a c c o r d i n g to t h e p l o t i n F i g u r e 3.

y°°c H8 w a s h e l d constant w i t h v a r y i n g values of S .

(2)

00

3

Miscibility with the Feed Components. I n a s o l u t e - s o l v e n t system e x h i b i t i n g s t r o n g p o s i t i v e d e v i a t i o n s f r o m R a o u l t ' s L a w , the solute has o n l y l i m i t e d s o l u b i l i t y i n the solvent. A b o v e a c e r t a i n solute c o n c e n t r a t i o n , t w o l i q u i d phases a r e f o r m e d .

T h e p r e s e n c e of t w o l i q u i d phases

o n t h e plates o f a d i s t i l l a t i o n c o l u m n leads to i n s t a b i l i t y a n d o p e r a t i o n a l p r o b l e m s . It is therefore necessary to ensure t h a t t h e solute c o n c e n t r a t i o n i n the l i q u i d phase never exceeds its s o l u b i l i t y l i m i t . T h i s s o l u b i l i t y l i m i t gives a m i n i m u m feasible solvent c o n c e n t r a t i o n i n t h e section b e l o w the solvent a d d i t i o n p l a t e of the p r i m a r y c o l u m n . A n a p p r o x i m a t i o n to the m i s c i b i l i t y l i m i t i n a b i n a r y system is o b t a i n e d b y a s s u m i n g t h a t the p o l a r solvent is essentially i n s o l u b l e i n the h y d r o c a r b o n . S i n c e the a c t i v i t y of the h y d r o c a r b o n i n t h e h y d r o c a r b o n p h a s e is near u n i t y , at e q u i l i b r i u m i t m u s t b e the same as t h a t i n the s o l v e n t - r i c h phase. yx A

Am

«

(5)

1

If w e f u r t h e r assume that E q u a t i o n 2 h o l d s for the b i n a r y system, w e h a v e

0=(1ηγ^)(1-ζ^) K n o w i n g In γ ^ , E q u a t i o n 6 y i e l d s x , 00

Am

2

+

1ηα^

(6)

t h e m o l e f r a c t i o n of A at the

l i m i t of its m i s c i b i l i t y i n t h e solvent. Volatility.

F o r a fixed t o w e r pressure, the v o l a t i l i t y of the solvent

determines the reboiler temperature.

It also influences t h e n u m b e r of

e q u i l i b r i u m stages r e q u i r e d i n t h e solvent-recovery c o l u m n , as w e l l as the n u m b e r of stages r e q u i r e d i n the solvent k n o c k - o u t section of t h e p r i m a r y c o l u m n . F o r process e c o n o m i c s , t h e m o r e i m p o r t a n t o f

these

factors is g e n e r a l l y the t e m p e r a t u r e of t h e b o t t o m s f r o m t h e solventrecovery

c o l u m n since this is the highest solvent t e m p e r a t u r e i n the

process. T h e lowest solvent t e m p e r a t u r e is w h e r e t h e solvent is f e d i n t o the p r i m a r y c o l u m n . T h e c h a n g e i n solvent t e m p e r a t u r e is p r o d u c e d b y the solvent cooler, a n d t h e greater t h e t e m p e r a t u r e s w i n g b e t w e e n the hottest a n d the coolest p o i n t s i n the solvent c i r c u i t , t h e h i g h e r is t h e heattransfer d u t y of the solvent cooler. T h e s u m of the heat d u t i e s i n t h e reboilers is a p p r o x i m a t e l y e q u a l to t h e s u m of the heat d u t i e s of the o v e r h e a d condensers a n d t h e solvent cooler.

S i n c e the solvent v o l a t i l i t y influences the t e m p e r a t u r e l e v e l i n

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

2.

K U M A R ,

PRAUSNITZ, A N D KING

Process Design

23

Considerations

the reboilers, i t affects the heat i n p u t to t h e reboilers as w e l l as the heat d u t y of the solvent cooler. A s e c o n d a r y effect of t h e solvent v o l a t i l i t y is o n the o p e r a t i n g t e m p e r a t u r e of the extractive d i s t i l l a t i o n c o l u m n . A m o r e v o l a t i l e solvent results i n a l o w e r average p l a t e t e m p e r a t u r e . A t the l o w e r t e m p e r a t u r e , the s e p a r a t i o n factor is g e n e r a l l y h i g h e r because of h i g h e r selectivity. Table I.

Design Basis

Rate = Composition = Condition =

415 l b m o l e s / h r 50 mole % C H , 50 mole % C H , s a t u r a t e d v a p o r a t the tower pressure"

Propylene

Purity = Recovery = Capacity =

99.0% 95.0% 75 m i l l i o n l b s / y r

Solvent

A m o u n t i n each h y d r o carbon product = N o r m a l boiling point = O t h e r p h y s i c a l properties = C o n c e n t r a t i o n at s o l v e n t feed p l a t e = S = y°°C3H8 =

Feed

œ

Coolant

Coolant = Inlet temperature = T e m p e r a t u r e rise i n condensers = M i n i m u m approach temperature =

Cooler/Process Heat Exchangers M i n i m u m approach temperature =

3

8

3

^ 0 . 0 1 mole % 140°F those of acetone 0.85 to 0.90 mole f r a c t i o n 1.7 to 3.1 6.0 to 16.0 water 70 ° F 20°F 10°F

20°F

" F o r binary distillation without solvent, the feed condition was taken as saturated liquid at the tower pressure.

Process Design Process c a l c u l a t i o n s w e r e m a d e for t h e s e p a r a t i o n of a p r o p a n e - p r o p y l e n e m i x t u r e w i t h the d e s i g n basis s h o w n i n T a b l e I. F o r t h e present c a l c u l a t i o n s , the solvent p h y s i c a l properties w e r e t a k e n as those of acetone. T h e solvent s e l e c t i v i t y a n d the h y d r o c a r b o n a c t i v i t y coefficients

were

v a r i e d over the ranges g i v e n i n T a b l e I. A stage-to-stage ( L e w i s - M a t h e s o n ) m e t h o d ( 7 ) w a s u s e d to c a l c u l a t e the n u m b e r of e q u i l i b r i u m stages r e q u i r e d i n the t w o towers, a l l o w i n g for v a r i a t i o n s i n

<X B A

a n d interstage

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

24

E X T R A C T I V E

A N D

A Z E O T R O P I C

DISTILLATION

m o l a r flows f r o m stage to stage. T h e stage-to-stage, m a t e r i a l - a n d ent h a l p y - b a l a n c e p r o c e d u r e w a s also u s e d f o r the f r a c t i o n a l d i s t i l l a t i o n altern a t i v e , u s i n g t h e v a p o r - l i q u i d e q u i l i b r i u m d a t a of R e a m e r a n d Sage

(8)

for t h e p r o p a n e - p r o p y l e n e b i n a r y system. T h e basis a n d v a r i o u s parameters f o r t h e e c o n o m i c analysis are g i v e n i n T a b l e II. T h e o v e r a l l c o l u m n efficiency u s e d w a s o b t a i n e d f r o m a p l o t of efficiency vs. the p r o d u c t of r e l a t i v e v o l a t i l i t y a n d l i q u i d v i s c o s i t y c o r r e c t e d to m a t c h p r e d i c t e d (10)

(9),

d a t a for the p r o p a n e - p r o p y l e n e sys-

t e m . T h e v a l u e f r o m the p l o t ( 9 ) w a s i n c r e a s e d b y a factor r e q u i r e d to m a k e the efficiency of t h e p r o p a n e - p r o p y l e n e b i n a r y d i s t i l l a t i o n e q u a l to 1 0 0 % . Costs were calculated b y the Venture Analysis method

(11),

because this m e t h o d y i e l d s t h e a p p r o p r i a t e w e i g h t i n g factors for t h e

fixed

a n d o p e r a t i n g costs i n o r d e r to c a l c u l a t e t h e t o t a l costs. R e s u l t s a r e exp r e s s e d as a n n u a l costs, b e f o r e taxes.

T h e i m p o r t a n t process v a r i a b l e s

are discussed below. Operating Temperature. T h e i m p o r t a n t temperatures for e c o n o m i c analysis are the o v e r h e a d c o n d e n s e r temperatures at w h i c h heat is rem o v e d f r o m the process a n d t h e r e b o i l e r temperatures at w h i c h h e a t is s u p p l i e d to t h e process. O f s i m i l a r i m p o r t a n c e is t h e t e m p e r a t u r e of t h e s o l v e n t - a d d i t i o n p l a t e of t h e p r i m a r y c o l u m n s i n c e this t e m p e r a t u r e , together w i t h t h a t of the r e c o v e r y c o l u m n , establishes t h e t e m p e r a t u r e s w i n g i n the solvent c i r c u i t . O n e m e t h o d for

fixing

t h e v a r i o u s temperatures is to specify

the

o v e r h e a d c o n d e n s e r temperatures i n the t w o c o l u m n s . I n these c a l c u lations, it w a s d e c i d e d to use c o o l i n g w a t e r i n the t w o condensers, t h e r e b y setting the reflux t e m p e r a t u r e at 100°F for b o t h c o l u m n s . T h e c o n d e n s e r t e m p e r a t u r e w o u l d n o r m a l l y b e set b y t h e a v a i l a b i l i t y of a n a d e q u a t e heat sink, i f o t h e r t h a n w a t e r . F o r b i n a r y d i s t i l l a t i o n , t h e reflux t e m p e r a t u r e was also set at 100 °F. T h e c o n d e n s e r t e m p e r a t u r e of 100° F c o r r e s p o n d s to a pressure o f 187 p s i a i n the p r i m a r y c o l u m n a n d 222 p s i a i n the s e c o n d a r y t o w e r .

The

r e c o v e r y c o l u m n r e b o i l e r t e m p e r a t u r e t h e n comes to 495°F, w h i l e the extractive d i s t i l l a t i o n c o l u m n r e b o i l e r t e m p e r a t u r e varies f r o m a b o u t 300° to 425°F.

T h e t e m p e r a t u r e of the s o l v e n t - a d d i t i o n p l a t e i n t h e m a i n

t o w e r v a r i e d f r o m 100° to 220°F. Solvent Loading.

T h e solvent c i r c u l a t i o n rate is a f u n c t i o n of the

reflux r a t i o i n t h e p r i m a r y t o w e r a n d the l i q u i d - p h a s e c o n c e n t r a t i o n of the solvent. F o r a g i v e n solvent selectivity, as the solvent c o n c e n t r a t i o n rises, the p r o p a n e - p r o p y l e n e relative v o l a t i l i t y increases a n d h e n c e the r e q u i r e d reflux rate falls. T h e i n c r e a s e d r e l a t i v e v o l a t i l i t y results i n a d e c r e a s e d n u m b e r of e q u i l i b r i u m stages r e q u i r e d f o r t h e d e s i r e d separat i o n . F i g u r e 4 shows t h e effect of solvent c o n c e n t r a t i o n o n the n u m b e r

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

2.

K U M A R ,

PRAUSNITZ,

A N D

Process Design

K I N G

Table II.

Considerations

25

Cost Calculation Basis

Materials =

a l l steel c o n s t r u c t i o n

T o w e r plates = costs =

sieve t r a y s Peters a n d T i m m e r h a u s {12),

H e a t exchangers = costs =

floating-head, % - i n c h tubes, 2 0 - f t - l o n g b u n d l e Peters a n d T i m m e r h a u s , F i g u r e 1 4 - 1 5 , p. 566

F i g u r e 1 5 - 2 6 , p. 659

Utilities H i g h pressure s t e a m (500 psig) =

$1.00/10

6

BTU

L o w pressure s t e a m

S0.40/10

6

BTU

(100 psig) =

Cooling water —

$0.02/1000 g a l

Solvent =

$5 to 15/lb mole

T o w e r a n d heat exchanger s i z i n g procedures = Venture Analysis (11):

where

Peters a n d T i m m e r h a u s

V =

Ρ — imlf -

Ρ =

R -

R =

S -

C

V =

S -

C

V Ρ i I i Iw R d t l S

v e n t u r e profit net profit rate of r e t u r n on h i g h r i s k i n v e s t m e n t , 2 0 % fixed c a p i t a l i n v e s t m e n t average rate of r e t u r n on i n v e s t m e n t , 1 2 % w o r k i n g c a p i t a l , 1 5 % of fixed c a p i t a l i n v e s t m e n t gross profit s t r a i g h t line d e p r e c i a t i o n factor, 0.1 corporate income t a x , 5 0 % s i n k i n g f u n d d e p r e c i a t i o n rate, 0.05 sales revenue

m f

d

= = = = = = = = = = =

C = maintenance =

V =

(R -

Hw dl,)t

- (S -

c •

m a n u f a c t u r i n g cost, u t i l i t i e s + 6%

maintenance

of fixed c a p i t a l i n v e s t m e n t

0.5 S -

0.5 C +

0.22 J

;

therefore adjusted v e n t u r e cost

where

C I I

u f

p

=

C +

= = =

cost of u t i l i t i e s 4.83 I (Peters a n d T i m m e r h a u s , T a b l e 17, p. 118) p u r c h a s e d e q u i p m e n t cost

0.44

— C

u

+

0.50 //

p

therefore the adjusted v e n t u r e cost, before taxes, is g i v e n b y

C

u

+

2.42

I

p

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

26

E X T R A C T I V E

0.84

0B6

0B8

A N D

A Z E O T R O P I C

DISTILLATION

0.90

Solvent Mole Fraction on Solvent Addition Plate, x

s

Figure 4. Effect of solvent concentration on the number of equilibrium stages and the solvent-to-feed ratio in primary column of stages r e q u i r e d a n d o n t h e s o l v e n t - t o - h y d r o c a r b o n feed r a t i o n e e d e d f o r a solvent s e l e c t i v i t y S

œ

= 1.7.

A rise i n solvent c o n c e n t r a t i o n decreases t h e reflux r a t i o i n t h e p r i m a r y c o l u m n , t h e r e b y l o w e r i n g the v a p o r flow rate i n t h e c o l u m n . C o n s e q u e n t l y , the t o w e r d i a m e t e r falls. A l s o , the i n c r e a s e d c o o l e r d u t y i s a c c o m p a n i e d b y e n h a n c e d r e b o i l e r duties, r e s u l t i n g i n l a r g e r u t i l i t y costs. W i t h rising solvent c o n c e n t r a t i o n , t h e m a i n t o w e r cost d e c l i n e s , b u t the s o l v e n t - c o o l e r cost a n d the u t i l i t y cost increase. T h e net r e s u l t i s s h o w n b y the s o l i d Unes i n F i g u r e 5 w h e r e the costs are r e p r e s e n t e d as fixed, o p e r a t i n g , a n d t o t a l costs. A c o m p r o m i s e m u s t b e m a d e b e t w e e n the t o w e r costs a n d the c o o l e r a n d u t i l i t y costs t o d e t e r m i n e the o p t i m u m solvent c o n c e n t r a t i o n .

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

2.

K U M A R , PRAUSNITZ,

A N D

Process Design

K I N G

Selectivity and A c t i v i t y Coefficients.

Considerations

27

T h e solvent s e l e c t i v i t y deter

m i n e s t h e r e l a t i v e v o l a t i l i t y o f t h e p r o p a n e - p r o p y l e n e system, w i t h a higher selectivity y i e l d i n g a higher relative volatility of propane to pro pylene.

A n i n c r e a s i n g s e l e c t i v i t y therefore

results i n a s m a l l e r reflux

r a t i o a n d f e w e r e q u i l i b r i u m stages r e q u i r e d for the s e p a r a t i o n . T h e l o w e r reflux rate 'corresponds t o a l o w e r v a p o r - f l o w rate i n t h e t o w e r a n d h e n c e to a t h i n n e r tower. T h e l o w e r reflux rate also results i n a s m a l l e r solventflow rate w i t h a c o n s e q u e n t decrease i n t h e s o l v e n t - c o o l e r size a n d d u t y a n d i n the r e b o i l e r duties. H o w e v e r , as s h o w n b y the p l o t i n F i g u r e 3 , t h e p r o p a n e a c t i v i t y coefficient increases w i t h r i s i n g selectivity. T h e p r o p a n e a c t i v i t y coeffi c i e n t p r i m a r i l y establishes the n u m b e r o f e q u i l i b r i u m stages i n the t o p m o s t section o f t h e m a i n tower.

T h e h i g h e r the a c t i v i t y coefficient, t h e

h i g h e r t h e v a p o r - p h a s e c o n c e n t r a t i o n o f t h e solvent a n d c o n s e q u e n t l y

2600 -

Totol

2400 2200 2000 ο ο

1800

•Sf ο ο

1600

I c «t

1400

1200 1000 800

tf-Total For Fractional Distillation

Fixed Without Heat Exchange System With Heat Exchange System

600 400

_L

-L

0.84

0B6

0B8

0.90

Solvent Concentration, x Figure 5.

Effect of solvent concentration

e

on annual costs

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

28

E X T R A C T I V E

A N D

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t h e greater the n u m b e r o f stages a b o v e the solvent a d d i t i o n plate.

For

instance, w h e n y°°c3H8 = 6-0, six stages are r e q u i r e d i n t h e t o p m o s t sec t i o n , whereas w h e n γ°°ο Η8 = 1 6 0 , 24 stages are n e e d e d . 3

M o r e o v e r , re

verse f r a c t i o n a t i o n occurs i n t h e t o p m o s t section o f t h e m a i n c o l u m n because, i n the absence o f the solvent, p r o p y l e n e is m o r e v o l a t i l e t h a n p r o p a n e a n d therefore

tends t o g o o v e r h e a d .

T h e greater the n u m b e r

of stages i n the t o p section, the greater i s the extent o f this

reverse

f r a c t i o n a t i o n ; the r e c t i f y i n g section m u s t fractionate to a h i g h e r p r o p a n e p u r i t y , a n d thus i t needs m o r e stages. A h i g h p r o p a n e a c t i v i t y coefficient tends to increase the e q u i l i b r i u m stage r e q u i r e m e n t s . C h a n g e s i n r e l a t i v e v o l a t i l i t y a n d a c t i v i t y coefficients w i t h c h a n g i n g selectivity act against e a c h other i n affecting the e q u i l i b r i u m - s t a g e re q u i r e m e n t s o f the m a i n c o l u m n . T h e net result i s s h o w n i n F i g u r e 6 w h e r e the t o t a l n u m b e r o f e q u i l i b r i u m stages i n the m a i n c o l u m n i s

Selectivity, χ

Λ

/

V e Figure 6.

Variation of the number of equilibrium stages and solvent/ feed ratio in the primary column with selectivity

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

2.

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Process Design

29

Considerations

Without Heat Exchange System

Selectivity, χω Figure 7.

/χ·

Effect of solvent selectivity on annual costs

p l o t t e d against solvent selectivity. T h e effect of s e l e c t i v i t y o n the solventt o - h y d r o c a r b o n r a t i o is also s h o w n i n F i g u r e 6. A h i g h e r s e l e c t i v i t y r e q u i r e s a t h i n n e r b u t t a l l e r tower.

I t also re

q u i r e s a s m a l l e r solvent cooler because o f t h e l o w e r solvent c i r c u l a t i o n rate a n d s m a l l e r cooler a n d r e b o i l e r heat duties. T h e net r e s u l t is s h o w n i n F i g u r e 7 w h e r e t h e s o l i d lines i n d i c a t e the a n n u a l costs as a f u n c t i o n of selectivity; t h e y s h o w a f a l l i n g a n n u a l cost w i t h i n c r e a s i n g selectivity. Process Modifications F i g u r e s 5 a n d 7 s h o w that the o p e r a t i n g costs c o n s t i t u t e a large f r a c t i o n o f the t o t a l a n n u a l cost o f the extractive d i s t i l l a t i o n process. I t is therefore d e s i r a b l e to m o d i f y the b a s i c process to r e d u c e these costs.

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

30

E X T R A C T I V E

Solvent

A N D

A Z E O T R O P I C

DISTILLATION

Propane Product Extractive Distillation Column

Feed Solvent Cooler

w

- 0

..Steam

-Main Column Reboiler

Bottoms Preheater Steam - « · - - - ( ρ

)

Extractive

Propylene Product Steam Recovery Column Reboiler

Waste Heàf Boiler Figure 8.

E3

Solvent Recovery Column

distillation with heat recovery

O n e process m o d i f i c a t i o n is s h o w n i n F i g u r e 8. I n t h i s m o d i f i c a t i o n , a h e a t r e c o v e r y system uses the heat o f t h e r e c o v e r y c o l u m n b o t t o m s i n t h e m a i n c o l u m n r e b o i l e r a n d i n a b o t t o m s preheater. I f a d d i t i o n a l heat is n e e d e d i n the m a i n c o l u m n r e b o i l e r , a u x i l i a r y h e a t i n g i s p r o v i d e d as s h o w n b y the ( d o t t e d ) steam c o i l i n F i g u r e 8. H o w e v e r , a waste heat b o i l e r is sometimes n e e d e d ( s h o w n d o t t e d ) to r e m o v e the excess heat i n t h e r e c o v e r y c o l u m n bottoms. C o s t c a l c u l a t i o n s w e r e m a d e for this m o d i f i e d e x t r a c t i v e d i s t i l l a t i o n process; t h e y are s h o w n b y the d a s h e d curves o n F i g u r e s 5 a n d 7. T h e p r o p o s e d h e a t exchange system p r o v i d e s c o n s i d e r a b l e r e d u c t i o n i n the a n n u a l costs of the extractive d i s t i l l a t i o n process. H o w e v e r , the extractive d i s t i l l a t i o n costs are s t i l l greater t h a n those for a b i n a r y p r o p a n e - p r o p y l e n e d i s t i l l a t i o n process as i n d i c a t e d o n F i g u r e s 5 a n d 7. T h e d e s i g n c a l c u l a t i o n s d e s c r i b e d i n the p r e c e d i n g p a r a g r a p h s h a v e b e e n m a d e u s i n g the f u n c t i o n a l r e l a t i o n b e t w e e n s e l e c t i v i t y a n d a c t i v i t y coefficient f o u n d b y G e r s t e r et al. ( 5 ) .

H o w e v e r , the d a t a f r o m H a f s l u n d

( 6 ) , s h o w n i n F i g u r e 3, i n d i c a t e that this r e l a t i o n m a y not necessarily

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

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Process Design

Considerations

31

h o l d f o r a l l solvents. T o i n v e s t i g a t e the effects o f i n c r e a s i n g s e l e c t i v i t y w i t h o u t a c o r r e s p o n d i n g increase i n the p r o p a n e a c t i v i t y coefficient, p r o c ess c a l c u l a t i o n s w e r e m a d e for v a r i o u s selectivities at a constant p r o p a n e a c t i v i t y coefficient.

C o s t s w e r e c a l c u l a t e d for the process i l l u s t r a t e d i n

F i g u r e 8; t h e y are s h o w n i n F i g u r e 9. T h e costs decrease w i t h i n c r e a s i n g selectivity, a n d the t o t a l extractive d i s t i l l a t i o n process cost i s a p p r o x i m a t e l y the same as that for b i n a r y d i s t i l l a t i o n for p r o p a n e - p r o p y l e n e at a selectivity of 2.6.

1100 r 1000

-

200 h 100-

I

0

I 2.0

I

I I I 2.4 2.8 Selectivity, ν · / 3 8 C

H

I γ C

ι 3.2

» 3.4

. 3 6 H

Figure 9. Effect of solvent selectivity on annual costs at con stant propane activity coefficient (process with heat exchange system) O t h e r process m o d i f i c a t i o n s m a y also b e i n v e s t i g a t e d . F o r e x a m p l e , F i g u r e 10 shows a n extractive d i s t i l l a t i o n process w i t h a n alternate m e t h o d for solvent recovery.

H e r e , the m a i n c o l u m n b o t t o m s are flashed t o a

pressure l o w e n o u g h for the solvent to c o o l to the solvent-feed t e m p e r a t u r e i n the m a i n c o l u m n . Besides d e c r e a s i n g the heat d u t y of the solvent

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

32

E X T R A C T I V E

η E3

Solvent

A N D

A Z E O T R O P I C

DISTILLATION

Propane Product

Extractive Distillation Column

Feed

Steam 1

r^C^^

» κ >i ^ fFlosh \ H^T^ D r u m

Solvent Recovery Column

Propylene Product

Steam

Solvent Cooler Figure 10.

Extractive

distilhtion

with alternate solvent recovery

cooler, this m o d i f i c a t i o n also l o w e r s the a m o u n t o f f e e d t o t h e r e c o v e r y c o l u m n a n d h e n c e leads t o a s m a l l e r s e c o n d a r y tower. H o w e v e r , s u c h a m o d i f i c a t i o n r e q u i r e s v a p o r c o m p r e s s i o n o r r e f r i g e r a t i o n to p r o v i d e reflux for t h e r e c o v e r y c o l u m n . Conclusions T h e costs o f s e p a r a t i n g p a r a f f i n - o l e f i n m i x t u r e s b y e x t r a c t i v e d i s t i l l a t i o n are g r e a t l y affected b y t h e solvent selectivity, the paraffin a c t i v i t y coefficient,

a n d t h e solvent v o l a t i l i t y ; t h e y d e p e n d

m o s t l y u p o n sol

v e n t characteristics. F o r a solvent t o b e effective t o separate k e y c o m ponents A a n d B , t h e solvent m u s t h a v e a h i g h v a l u e o f y™A/y™Β w h i l e i t m u s t also h a v e a l o w y°° A

F u r t h e r , t h e solvent v a p o r pressure s h o u l d b e

l o w e r , b u t n o t several orders o f m a g n i t u d e l o w e r , t h a n that o f the less volatile hydrocarbon. F o r the propane—propylene—solvent system, for the solvents e x h i b i t i n g the functional relationship between S

00

a n d y°°c3H s h o w n i n F i g u r e 3, 8

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

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33

Considerations

i t does n o t seem l i k e l y t h a t extractive d i s t i l l a t i o n costs c a n b e r e d u c e d b e l o w those of b i n a r y f r a c t i o n a l d i s t i l l a t i o n . F i g u r e 7 s h o w s d e c r e a s i n g costs w i t h i n c r e a s i n g s e l e c t i v i t y b u t the slope of the c u r v e of cost vs. S seems to be

flattening

out at S

0 0

0 0

of a b o u t 2, w h e r e e x t r a c t i v e d i s t i l l a t i o n

costs are s t i l l a b o u t 6 5 % greater t h a n t h e costs for b i n a r y d i s t i l l a t i o n . H o w e v e r , for solvents w h i c h g i v e a h i g h selectivity at r e l a t i v e l y l o w e r y°°C3H8> F i g u r e 9 shows a cost vs. S

œ

c u r v e w h i c h i n d i c a t e s a l o w e r cost

for t h e extractive d i s t i l l a t i o n process at a solvent s e l e c t i v i t y h i g h e r t h a n a b o u t 2.6. It is e v i d e n t therefore t h a t the t h e r m o d y n a m i c characteristics ( S , 00

γ°°θ3Η8> S, yc H > etc. ) of the p r o p a n e - p r o p y l e n e - s o l v e n t system a r e m o s t 3

8

i m p o r t a n t i n d e t e r m i n i n g the e c o n o m i c s of extractive d i s t i l l a t i o n for this separation. A c c u r a t e p r e d i c t i o n ( o r e x p e r i m e n t a l d e t e r m i n a t i o n ) of these factors is essential for e c o n o m i c analysis of a n extractive d i s t i l l a t i o n process. H a f s l u n d (6)

reports that extractive d i s t i l l a t i o n has b e e n u s e d c o m

m e r c i a l l y i n one p a r t i c u l a r case to separate p r o p a n e - p r o p y l e n e . T h e f e e d to the s e p a r a t i o n process w a s the off-gas f r o m a r e a c t o r i n a n e w process for m a k i n g a c r y l o n i t r i l e a n d c o n s i s t e d of 40 w t % inerts, 39 w t %

C H , 3

e

8 w t % C H , 7 w t % acrylonitrile, 5 w t % water, a n d 1 w t % by-product 3

8

i m p u r i t i e s . T h e p r o p y l e n e w a s to b e r e c o v e r e d for r e c y c l e to the reactor, a n d the p r o p a n e a n d inerts w e r e to b e p u r g e d f r o m t h e system. A c r y l o n i t r i l e w a s c h o s e n as the solvent for extractive d i s t i l l a t i o n . T h e t o p m o s t section of the p r i m a r y c o l u m n w a s r e p l a c e d b y a w a t e r s c r u b b e r to r e c o v e r t h e a c r y l o n i t r i l e i n the v e n t gas. T h e process r e p o r t e d b y H a f s l u n d ( 6 ) is therefore s o m e w h a t different f r o m the processes i l l u s t r a t e d i n F i g u r e s 1, 8, a n d 10. E x t r a c t i v e d i s t i l l a t i o n is c o m m e r c i a l l y u s e d for s e p a r a t i n g m i x t u r e s of butanes, butènes, b u t a d i e n e s , a n d v a r i o u s acetylenes w i t h f o u r c a r b o n atoms

(13).

S e p a r a t i n g these m u l t i c o m p o n e n t m i x t u r e s b y f r a c t i o n a l

d i s t i l l a t i o n is v e r y difficult b e c a u s e the n a t u r a l v o l a t i l i t i e s p f t h e v a r i o u s c o m p o n e n t s , paraffinic as w e l l as olefinic, o v e r l a p c o n s i d e r a b l y . F o r i n stance, η-butane is less v o l a t i l e t h a n 1-butene b u t m o r e v o l a t i l e t h a n cisa n d imrw-2-butenes. T h u s , s e p a r a t i o n of butanes f r o m butènes is m o r e difficult b y f r a c t i o n a l d i s t i l l a t i o n t h a n b y extractive d i s t i l l a t i o n w h e r e the solvent increases the v o l a t i l i t i e s of a l l the butanes to m a k e t h e m greater t h a n the b u t e n e volatilities. F o r 1,3-butadiene r e c o v e r y extractive dist i l l a t i o n is also m o r e attractive t h a n o r d i n a r y d i s t i l l a t i o n b e c a u s e the large p o l a r i z a b i l i t y of the c o n j u g a t e d d o u b l e b o n d s interacts s t r o n g l y w i t h t h e p o l a r solvent. A l s o , i n C

4

h y d r o c a r b o n separations the solvent often o n l y

enhances a n d does not reverse the n a t u r a l r e l a t i v e v o l a t i l i t y for m a n y of the c o m p o n e n t s ; h o w e v e r , e v e n for those c o m p o n e n t s for w h i c h the r e l a -

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

34

E X T R A C T I V E

A N D A Z E O T R O P I C

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t i v e v o l a t i l i t y is r e v e r s e d b y the solvent, the solvent-free r e l a t i v e v o l a t i l i t y is closer to u n i t y t h a n is that o f p r o p y l e n e to p r o p a n e i n the a b s e n c e of solvent.

A l l these factors c o m b i n e to e x p l a i n w h y extractive d i s t i l l a t i o n

is r e l a t i v e l y m o r e attractive for C

4

h y d r o c a r b o n m i x t u r e s t h a n for C

3

hydrocarbon mixtures. Acknowledgment F o r financial s u p p o r t the authors are grateful to the N a t i o n a l S c i e n c e F o u n d a t i o n . T h i s w o r k is b a s e d , i n part, o n a p r e v i o u s u n p u b l i s h e d s t u d y b y Ε . M . B a r r i s h ( U n i v e r s i t y of C a l i f o r n i a , B e r k e l e y , 1 9 6 4 ) .

Literature Cited 1. Prausnitz, J. M., "Molecular Thermodynamics of Fluid-Phase Equilibria," p. 193, Prentice-Hall, Englewood Cliffs, N. J., 1969. 2. Tassios, D., Chem. Eng. (1969) 76 (3), 118. 3. Weimer, R. F., Prausnitz, J. M., Hydrocarbon Process. Petrol. Refiner (1965) 44 (9), 237. 4. Pierotti, G. T., Deal, C. H., Derr, E. L., Ind. Eng. Chem. (1959) 51, 95. 5. Gerster, J. Α., Gorton, Τ. Α., Eklund, R-B., J. Chem. Eng. Data (1960) 5, 423. 6. Hafslund, E. R., Chem. Eng. Progr. (1969) 65 (9), 58. 7. King, C. J., "Separation Processes," Ch. 10, McGraw-Hill, New York, 1971. 8. Reamer, H. H., Sage, Β. H., Ind. Eng. Chem. (1951) 43, 1628. 9. Treybal, R. E., "Mass Transfer Operations," 2nd ed., p. 151, McGraw-Hill, New York, 1968. 10. American Institute of Chemical Engineers, "Bubble-Tray Design Manual," p. 63, New York, 1958. 11. Rudd, D. F., Watson, C. C., "Strategy of Process Engineering," p. 80, Wiley, New York, 1968. 12. Peters, M. S., Timmerhaus, K. D., "Plant Design and Economics for Chem ical Engineers," 2nd ed., McGraw-Hill, New York, 1968. 13. Happel, J., Cornell, P. W., Eastman, DuB., Fowle, M. J., Porter, C. Α., Schutte, A. H., Trans. Amer. Inst. Chem. Eng. (1946) 42, 189. RECEIVED November 24, 1970.

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

3 Extractive Distillation by Salt Effect WILLIAM F. FURTER Department of Chemical Engineering, Royal Military College of Canada, Kingston, Ontario A salt dissolved in a mixed solvent is capable, through such effects on the structure of the liquid phase as preferential association and others, of altering the composition of the equilibrium vapor. Hence salt effect on vapor-liquid equilibrium relationships provides a potential technique of extractive distillation. A review is presented of the use of dissolved salts, rather than liquid solvents, as separating agents for extractive distillation.

V l T T h e n a salt is d i s s o l v e d i n a b o i l i n g s o l u t i o n o f t w o l i q u i d c o m ponents, there are s e v e r a l salt effects that m a y o c c u r . T h e s e i n c l u d e a l t e r i n g o f the b o i l i n g p o i n t , the m u t u a l s o l u b i l i t i e s o f the t w o l i q u i d c o m p o n e n t s i n e a c h other, a n d the c o m p o s i t i o n of the e q u i l i b r i u m v a p o r phase.

T h i s p a p e r discusses the latter effect.

The

t e c h n i q u e o f u s i n g a salt rather t h a n a l i q u i d as a s e p a r a t i n g

agent for extractive d i s t i l l a t i o n is n o t n e w , b u t s u c h processes h a v e n o t been w i d e l y used.

T h e t e c h n o l o g y has t e n d e d to b e p r o p r i e t a r y , a n d

the c h e m i s t r y i n v o l v e d has n o t b e e n w e l l u n d e r s t o o d . A l s o the systems w h e r e a d i s s o l v e d s o l i d s e p a r a t i n g agent c a n b e a p p l i e d are l i m i t e d i n n u m b e r b y s o l u b i l i t y restrictions. L i t e r a t u r e r e l a t i n g to this t e c h n i q u e a n d its c h e m i s t r y has t e n d e d to b e f r a g m e n t a r y rather t h a n i n t e r r e l a t e d , a n d m u c h o f i t has n o t b e e n w i d e l y c i r c u l a t e d . T h e r e is n o w g o o d e v i d e n c e to s h o w that this t e c h n i q u e s h o u l d r e c e i v e m o r e attention. F o r s u c h a process the

flowsheet

is b a s i c a l l y the same as that for a

n o r m a l extractive d i s t i l l a t i o n . T h e o n l y r e a l difference is that the separ a t i n g agent is a salt i n s t e a d o f a l i q u i d .

S i n c e a d i s s o l v e d salt is n o n -

v o l a t i l e , a l l of i t is c o n t a i n e d i n the l i q u i d phase, a n d a l l o f i t w i l l

flow

d o w n w a r d i n the c o l u m n . H e n c e , for i t to o c c u r t h r o u g h o u t the c o l u m n , it must b e f e d at o r near the top. T h e n o r m a l p l a c e is i n the r e e n t e r i n g 35 In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

36

E X T R A C T I V E

EXTRACTIVE DISTILLATION COLUMN

REFLUX AND SALT

5

A N D

A Z E O T R O P I C

DISTILLATION

OVERHEAD PRODUCT DISSOLVER

SALT RECYCLE

FEED

BOTTOMS PRODUCT

Figure 1.

Flowsheet for extractive distillation as the separating agent

using a dissolved

salt

reflux stream, as s h o w n i n F i g u r e 1. T h e salt, w h i c h m u s t b e soluble t o some extent i n b o t h l i q u i d c o m p o n e n t s , is f e d b y d i s s o l v i n g i t at a steady rate i n t o the h o t reflux just before r e e n t e r i n g the c o l u m n .

It is then

r e m o v e d f r o m the bottoms p r o d u c t for reuse, as is a l i q u i d s e p a r a t i n g agent, b u t here i t is r e c o v e r e d b y e v a p o r a t i n g or d r y i n g i n s t e a d o f b y a subsequent rectification step. T h e i n t r o d u c t i o n , use, recovery, a n d r e c y c l e of the s e p a r a t i n g agent otherwise is the same for a d i s s o l v e d salt as i t is for a l i q u i d solvent. I n the simplest case the c h e m i c a l system i n v o l v e d w o u l d b e a f e e d s o l u t i o n c o n s i s t i n g o f t w o v o l a t i l e components

(the

key

components),

w h i c h are t o b e separated f r o m e a c h other, a n d a n a d d e d agent

(the

process.

third component),

separating

w h i c h circulates i n t e r n a l l y w i t h i n t h e

U s i n g the rectification o f e t h y l a l c o h o l - w a t e r

mixtures as a n

example, c u r r e n t i n d u s t r i a l processes use s e p a r a t i n g agents s u c h as b e n zene, toluene, o r 1-pentane i n a z e o t r o p i c d i s t i l l a t i o n or ethylene g l y c o l i n e x t r a c t i v e d i s t i l l a t i o n . I n the t e c h n i q u e d e s c r i b e d here, one o f several effective salts c a p a b l e o f e l i m i n a t i n g the e t h a n o l - w a t e r azeotrope, w o u l d b e u s e d as the s e p a r a t i n g agent i n a n extractive d i s t i l l a t i o n to concentrate e t h a n o l - w a t e r solutions to absolute a l c o h o l . A n e x a m p l e o f a p a r t i c u l a r l y

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

3.

F U R T E R

37

Salt Effect

effective salt w i t h this system is p o t a s s i u m acetate;

there are

several

others. Besides u s i n g a single d i s s o l v e d salt as the s e p a r a t i n g agent,

there

are other w a y s a n d c o m b i n a t i o n s i n w h i c h salt is u s e d . F o r e x a m p l e , the s e p a r a t i n g agent c o u l d consist of a m i x t u r e of t w o or m o r e salts, or one or m o r e salts a d d e d to a l i q u i d s e p a r a t i n g agent to m a k e i t m o r e effective a n d to r e d u c e the a m o u n t of the l i q u i d n e e d e d , o r one or m o r e salts d i s s o l v e d i n a n i n e r t l i q u i d solvent w h i c h acts o n l y as a c a r r i e r for the salt.

A l l possibilities h a v e

either b e e n u s e d or c o n s i d e r e d i n v a r i o u s

a p p l i c a t i o n s of this t e c h n i q u e .

H o w e v e r , o n l y the s i m p l e s t case, t h a t i n

w h i c h the s e p a r a t i n g agent consists o n l y of one c o m p o n e n t , a single salt, is d i s c u s s e d here. Advantages and

Disadvantages

W h y use a d i s s o l v e d salt i n s t e a d of a l i q u i d as a s e p a r a t i n g agent for extractive d i s t i l l a t i o n ? F i r s t w e w i l l c o n s i d e r the disadvantages.

A

l i q u i d is s u p e r i o r to a s o l i d w h e n c o n s i d e r i n g ease of t r a n s p o r t a b o u t the system, degree of s o l u b i l i t y i n the f e e d components, a n d rate of m i x i n g at its feedpoint.

L i q u i d s m i x q u i c k l y , b u t a salt has to dissolve first. T h e r e

are also m e c h a n i c a l p r o b l e m s to b e o v e r c o m e i n m e t e r i n g a

finely-divided

s o l i d at a constant rate to a b o i l i n g or n e a r b o i l i n g l i q u i d m i x t u r e , a n d i t m a y also b e difficult to a c h i e v e r a p i d d i s s o l v i n g of the salt after i t has b e e n fed. B e c a u s e of s o l u b i l i t y l i m i t a t i o n s r e s t r i c t i n g the c h o i c e of a salt, i t is also m o r e p r o b a b l e that a l i q u i d agent, r a t h e r t h a n a s o l i d , w h i c h is effective a n d s o l u b l e w i l l exist for a g i v e n system. H o w e v e r , i n the r e l a t i v e l y l i m i t e d n u m b e r of systems for w h i c h there is a salt w h i c h is s o l u b l e a n d effective, some major advantages o v e r a l i q u i d s e p a r a t i n g agent exist.

The

salt, b e i n g c o m p l e t e l y

nonvolatile,

exists o n l y i n t h e l i q u i d phase, a n d a l l of i t flows d o w n the c o l u m n a n d o u t i n the bottoms p r o d u c t . A p r i n c i p a l a d v a n t a g e is that the o v e r h e a d p r o d u c t , p r o v i d e d n o r m a l p r e c a u t i o n s are t a k e n against e n t r a i n m e n t , w i l l b e c o m p l e t e l y free of s e p a r a t i n g agent. H e n c e there is n o n e e d for a n o t h e r section of c o l u m n ( a solvent k n o c k b a c k section ) to b e l o c a t e d a b o v e the f e e d p o i n t of the s e p a r a t i n g agent to s t r i p s e p a r a t i n g agent f r o m o v e r h e a d p r o d u c t stream, as there is for a l i q u i d agent.

die

A l s o , less e n e r g y

is r e q u i r e d for the o p e r a t i o n since not e v e n p a r t of t h e s e p a r a t i n g agent is v a p o r i z e d a n d c o n d e n s e d i n its c y c l e t h r o u g h the extractive d i s t i l l a t i o n c o l u m n , as it w o u l d b e i f it w e r e a l i q u i d . A n o t h e r p r i n c i p a l a d v a n t a g e is that the effect c a n b e large, times m u c h larger t h a n is possible w i t h l i q u i d s e p a r a t i n g agents. is because m u c h stronger forces

of association w i t h f e e d

someThis

component

m o l e c u l e s c a n b e exerted b y salt ions t h a n b y molecules o f a l i q u i d agent.

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

38

E X T R A C T I V E

A N D

A Z E O T R O P I C

DISTILLATION

T h e r e s u l t is t h a t m u c h less s e p a r a t i n g agent w o u l d n o r m a l l y b e n e e d e d ; p e r h a p s o n l y a f e w p e r c e n t as c o m p a r e d w i t h the t y p i c a l 5 0 - 9 0 % o f the l i q u i d p h a s e w h i c h is c o m m o n f o r s e p a r a t i n g agent c o n c e n t r a t i o n i n extractive d i s t i l l a t i o n operations u s i n g l i q u i d t h i r d c o m p o n e n t s .

A re-

d u c e d r e q u i r e m e n t i n s e p a r a t i n g agent c o n c e n t r a t i o n a l l o w s savings t o be made i n reduced c o l u m n diameter, reduced recovery

and recycle

c a p a c i t y for the s e p a r a t i n g agent, a n d r e d u c e d e n e r g y r e q u i r e d f o r the r e c o v e r y a n d r e c y c l e step.

LIQUID COMPOSITION , MOLE % ETHANOL Figure 2. Vapor-liquid equilibrium data at atmospheric pressure for the boiling ethanol-water system containing potassium acetate at saturation and at various constant concentrations T o i l l u s t r a t e h o w large the effect of a d i s s o l v e d salt c a n be, F i g u r e 2, c a l c u l a t e d f r o m the d a t a o f M e r a n d a a n d F u r t e r ( J ) , i s i n c l u d e d t o d e m o n s t r a t e b y h o w m u c h p o t a s s i u m acetate alters t h e v a p o r - l i q u i d e q u i l i b r i u m r e l a t i o n s h i p o f the system, b o i l i n g e t h a n o l - w a t e r at a t m o s p h e r i c pressure. T h e d o t t e d c u r v e represents t h e e t h a n o l - w a t e r system alone, w h e r e the azeotrope o c c u r s a t a b o u t 87 m o l e % e t h a n o l .

The

other

c u r v e s are for v a r i o u s concentrations o f p o t a s s i u m acetate, a n d a l l are

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

3.

F U R T E R

39

Salt Effect

c a l c u l a t e d o n a salt-free basis to p r o v i d e a c o m m o n basis f o r c o m p a r i s o n . T h e upper curve, labelled # 5 i n the

figure,

acetate d i s s o l v e d i n the l i q u i d phase.

Its s a t u r a t i o n

its s o l u b i l i t y — r a n g e s

from

49 mole

is for s a t u r a t e d p o t a s s i u m concentration—i.e.,

% i n pure boiling water d o w n to

10 m o l e % i n p u r e b o i l i n g e t h a n o l , a n d i t increases r e l a t i v e

volatility

o v e r m u c h o f the r a n g e s h o w n b y a factor o f f o u r o r five times. T h e i n t e r m e d i a t e curves, l a b e l l e d # 2 ,

3, a n d 4, are for salt concentrations

h e l d constant at 5, 10, a n d 20 m o l e % respectively.

E v e n small concen-

trations o f this p a r t i c u l a r salt c o m p l e t e l y e l i m i n a t e t h e azeotrope. F i g u r e 3, t a k e n from t h e d a t a o f D o b r o s e r d o v

(2),

gives another

e x a m p l e of t h e s u b s t a n t i a l effect t h a t a salt, e v e n at r e a s o n a b l y c o n c e n t r a t i o n , c a n h a v e i n c e r t a i n systems.

The

moderate

key components

are

a g a i n e t h a n o l a n d water, b u t h e r e t h e salt is c a l c i u m c h l o r i d e , present at a constant c o n c e n t r a t i o n of 10 g r a m s / 1 0 0 m l of a l c o h o l - w a t e r s o l u t i o n . T h e azeotrope has b e e n c o m p l e t e l y

eliminated, a n d relative

volatility

increased substantially.

LIQUID COMPOSITION , MOLE % ETHANOL Figure 3. Vapor-liquid the boiling ethanol-water

equilibrium data at atmospheric pressure for system containing calcium chloride at constant concentration

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

40

E X T R A C T I V E

A N D

A Z E O T R O P I C

DISTILLATION

A l t h o u g h most p r e v i o u s investigators of salt effect i n v a p o r - l i q u i d e q u i l i b r i u m h a v e u s e d s a t u r a t e d r a t h e r t h a n constant salt concentrations to measure the largest salt effect possible at e a c h v a l u e of l i q u i d c o m p o s i t i o n for a g i v e n salt i n a g i v e n system, this c o n d i t i o n is not representat i v e o f salt c o n c e n t r a t i o n i n a n extractive d i s t i l l a t i o n c o l u m n u s i n g diss o l v e d salt as t h e s e p a r a t i n g agent.

M o l a l salt c o n c e n t r a t i o n i n the l i q u i d

p h a s e w o u l d r e m a i n essentially constant f r o m t r a y to t r a y w i t h i n e a c h of t h e r e c t i f y i n g a n d s t r i p p i n g sections just as constant as the a s s u m p t i o n of constant m o l a l o v e r f l o w is v a l i d . F r o m a k n o w l e d g e of salt effect at saturation, h o w e v e r , its effect at a constant c o n c e n t r a t i o n b e l o w s a t u r a t i o n is c a l c u l a t e d u s i n g the. salt effect e q u a t i o n

{3,4).

Chemistry of the Salt Effect I n extractive d i s t i l l a t i o n a n a d d e d s e p a r a t i n g agent c a n m o d i f y

the

v a p o r - l i q u i d e q u i l i b r i u m r e l a t i o n s h i p o f the c o m p o n e n t s to b e s e p a r a t e d i f it c a n a c h i e v e selective

m o l e c u l a r association w i t h one of t h e

key

c o m p o n e n t s o v e r t h e other i n the l i q u i d phase. T h e m o l e c u l e s o f a l i q u i d s e p a r a t i n g agent o r the ions of a salt t e n d to f o r m association c o m p l e x e s m o r e w i t h the m o l e c u l e s of one of the f e e d c o m p o n e n t s to b e separated t h a n w i t h t h e m o l e c u l e s of the other f e e d c o m p o n e n t .

It c a n alter the

v a l u e o f r e l a t i v e v o l a t i l i t y a n d the ease of s e p a r a t i o n of the system a n d shift o r e v e n e l i m i n a t e a n a z e o t r o p e i f p r o p e r l y chosen. S i n c e the a d d e d agent p r o b a b l y complexes to some extent w i t h b o t h k e y components, the v o l a t i l i t i e s of b o t h w i l l m o s t l i k e l y t e n d to b e l o w e r e d , b u t b y differing a m o u n t s d e p e n d i n g o n h o w selective the agent is i n its preference c o m p l e x i n g w i t h one k e y c o m p o n e n t o v e r t h e other.

for

Since a separating

a g e n t for extractive d i s t i l l a t i o n n o r m a l l y is chosen so t h a t it prefers t h e less v o l a t i l e of the f e e d c o m p o n e n t s , the v a l u e of r e l a t i v e v o l a t i l i t y is a c t u a l l y i n c r e a s e d b y the agent e v e n t h o u g h t h e i n d i v i d u a l v o l a t i l i t i e s of b o t h feed components may have been reduced i n value. T h e earliest references

to the p h e n o m e n o n of a salt i n t h e l i q u i d

i n f l u e n c i n g v a p o r c o m p o s i t i o n go b a c k to the 1 3 t h c e n t u r y A D chemists e x p e r i m e n t i n g w i t h the d i s t i l l a t i o n of a l c o h o l f r o m

when

fermented

m a s h r e c o r d e d t h a t t h e presence of p o t a s s i u m c a r b o n a t e i n the s t i l l p o t e n r i c h e d t h e a l c o h o l content of the v a p o r ( 5 ) .

M o s t of the w o r k d o n e i n

the field o f salt effect i n d i s t i l l a t i o n is g r o u p e d i n t o three g e n e r a l categories:

salt effect

o n v a p o r - l i q u i d e q u i l i b r i u m , extractive

distillation

u s i n g d i s s o l v e d salts as s e p a r a t i n g agents, a n d s o l u t i o n theory of electrolytes—e.g., d i s s o l v e d s a l t s — i n m i x e d solvents of t w o or m o r e components. T h e first t w o categories h a v e t e n d e d to interest c h e m i c a l engineers a n d chemists, w h i l e the t h i r d , g e n e r a l l y n e g l e c t i n g the effect o n v a p o r c o m -

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

3.

41

Salt Effect

F U R T E R

p o s i t i o n , has p r i m a r i l y interested p h y s i c a l chemists. A l l three categories, h o w e v e r , are i n t e r r e l a t e d . K a b l u k o v (6, 7, 8 )

i n 1891 a n d M i l l e r ( 9 )

i n 1897 o b s e r v e d

the

effects o f various salts, d i s s o l v e d i n t h e l i q u i d phase, o n the v a p o r - l i q u i d e q u i l i b r i u m r e l a t i o n s h i p of t h e s y s t e m e t h a n o l - w a t e r .

M o s t of the salts

t h e y i n v e s t i g a t e d w e r e m o r e s o l u b l e i n w a t e r t h a n i n e t h a n o l , a n d these w e r e o b s e r v e d t o e n r i c h the e q u i l i b r i u m v a p o r i n e t h a n o l . H o w e v e r ,

one

salt, m e r c u r i c c h l o r i d e , w h i c h is m o r e s o l u b l e i n e t h a n o l t h a n i n w a t e r , has the reverse effect.

B o t h investigators c o n c l u d e d t h a t a salt t e n d e d

to e n r i c h the v a p o r phase i n that c o m p o n e n t of the l i q u i d i n w h i c h i t w a s less s o l u b l e . T h e y also o b s e r v e d t h a t the m a g n i t u d e of t h e selective effect of a salt—i.e.,

the a m o u n t b y w h i c h i t alters v a p o r

r e l a t e d to the degree of difference

composition—is

i n its s o l u b i l i t i e s i n p u r e w a t e r a n d

p u r e a l c o h o l . M a g n i t u d e of salt effect is also a f u n c t i o n of t h e a m o u n t o f salt present a n d is l i m i t e d b y the d e g r e e of s o l u b i l i t y of the salt i n the l i q u i d phase. T h e s e b a s i c observations, m a d e o n this p a r t i c u l a r system, h a v e t e n d e d to b e c o n f i r m e d as g e n e r a l i n other systems b y m o r e recent investigators. T h e most p o p u l a r system i n w h i c h the effects of v a r i o u s salts h a v e b e e n i n v e s t i g a t e d o v e r the years has b e e n that of e t h a n o l - w a t e r .

Other

systems w h i c h h a v e b e e n s t u d i e d are e t h y l e n e g l y c o l - w a t e r , acetic a c i d water,

methanol-water,

acetone-methanol,

1-

and

2-propanol-water,

1-octane-propionic

nitric

acid, phenol-water,

acid-water, and

formic

a c i d - w a t e r . A q u e o u s systems h a v e b e e n choices for s u c h studies b e c a u s e of salt s o l u b i l i t y considerations. L i t e r a t u r e p e r t a i n i n g to salt effect i n v a p o r - l i q u i d e q u i l i b r i u m a n d to extractive d i s t i l l a t i o n u s i n g salt effect w a s r e c e n t l y r e v i e w e d b y F u r t e r a n d C o o k ( 1 0 ) , a n d the t h e o r y a n d t e c h n i c a l aspects w e r e r e v i e w e d F u r t e r (11).

by

V a p o r - l i q u i d e q u i l i b r i u m d a t a for 188 systems c o n t a i n i n g

salt w e r e p r e v i o u s l y c o m p i l e d b y C i p a r i s (12),

w h o has also p u b l i s h e d a

recent b o o k w i t h D o b r o s e r d o v a n d K o g a n o n t h e theory a n d p r a c t i c e of extractive d i s t i l l a t i o n b y salt effect

(13).

T h e c h e m i s t r y r e l a t i n g to the use of d i s s o l v e d salts as s e p a r a t i n g agents has not yet b e e n f u l l y u n d e r s t o o d . A p r i n c i p a l reason for this is the c o m p l e x i t y o f effects that the salt c a n h a v e , a n d h o w these c a n v a r y not o n l y f r o m system to system b u t , m o r e significantly, w i t h i n a g i v e n system as the concentrations of a n y or a l l of the system c o m p o n e n t s are varied.

F o r the a p p a r e n t l y s i m p l e system defined earlier, c o n s i s t i n g of

t w o v o l a t i l e c o m p o n e n t s p l u s a d i s s o l v e d salt, t h e salt c o u l d t h e o r e t i c a l l y range f r o m f u l l y d i s s o c i a t e d into t w o types of ions to t o t a l l y associated. If its d i s s o c i a t i o n is a n y w h e r e b e t w e e n these t w o extremes as i t p r o b a b l y is, it exists as three species: t w o types of ions, p l u s u n d i s s o c i a t e d salt molecules.

A l l three species c o n t r i b u t e t o the salt effect o n t h e ac-

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

42

E X T R A C T I V E

t i v i t y of

each volatile component,

A N D

A Z E O T R O P I C

DISTILLATION

a n d t h e i r parts are p r o b a b l y a l l

different b u t are i n t e r r e l a t e d . H e n c e , the effect of a salt e v e n i n a g i v e n s y s t e m is a f u n c t i o n o f its d e g r e e of d i s s o c i a t i o n , w h i c h i n t u r n is a f u n c t i o n o f l i q u i d p h a s e c o m p o s i t i o n , w h i c h varies f r o m p o i n t to p o i n t w i t h i n the r e c t i f i c a t i o n c o l u m n . T h e forces w h i c h cause association complexes w i t h i n the l i q u i d p h a s e to f o r m m a y also differ f r o m system to system a n d f r o m salt to salt, a n d c a n i n c l u d e , for e x a m p l e , forces s u c h as v a n d e r W a a l forces, electrostatic i n t e r a c t i o n s of a t t r a c t i o n a n d r e p u l s i o n , h y d r o g e n b o n d i n g , o r c o m b i n a tions of s u c h forces. T o c o m p l i c a t e matters m o r e , the association tendencies of salt ions i n f o r m i n g association complexes w i t h m o l e c u l e s o f the f e e d c o m p o n e n t s , besides a l t e r i n g t h e i r v o l a t i l i t i e s , t e n d to r e d u c e t h e s o l u b i l i t y of

one

v o l a t i l e c o m p o n e n t i n the other. U s i n g the o l d m a x i m of p h y s i c a l c h e m i s t r y t h a t " l i k e dissolves l i k e , " t h e selective c o m p l e x i n g of t h e salt w i t h t h e m o l e c u l e s of one v o l a t i l e c o m p o n e n t o v e r those of the other c a n

be

v i s u a l i z e d as m a k i n g the m o l e c u l e s of the t w o v o l a t i l e c o m p o n e n t s c h e m i c a l l y m o r e d i s s i m i l a r to e a c h other i n s o l u t i o n . T h e effect c a n b e so great i n extreme cases that t w o l i q u i d phases c a n b e m a d e to f o r m e v e n i n b o i l i n g solutions o f w h a t are n o r m a l l y h i g h l y m i s c i b l e l i q u i d s .

One

e x a m p l e o f a s y s t e m w h e r e this has b e e n o b s e r v e d is e t h a n o l - w a t e r c o n t a i n i n g a m m o n i u m sulfate d i s s o l v e d to s a t u r a t i o n . T h e r e are o t h e r c o m p l i c a t i o n s . T h e salt, besides f o r m i n g association complexes

w i t h s o l u t i o n m o l e c u l e s , p o s s i b l y c o u l d also alter or

even

destroy a l r e a d y - e x i s t i n g self-interactions of the m o l e c u l e s of a v o l a t i l e c o m p o n e n t e i t h e r w i t h themselves or w i t h those o f the other f e e d c o m ponent. A n e x a m p l e is the associated s t r u c t u r e i n w h i c h l i q u i d w a t e r a n d to a lesser extent s o m e alcohols exist. T h e effects of salt ions o n w a t e r w a t e r , w a t e r - a l c o h o l , a n d a l c o h o l - a l c o h o l c o m p l e x i n g , for e x a m p l e , m u s t b e p r o f o u n d at h i g h e r salt concentrations, a n d w i l l v a r y i n a g i v e n system w i t h salt c o n c e n t r a t i o n a n d w i t h a l c o h o l - w a t e r p r o p o r t i o n a l i t y i n t h e l i q u i d . A l s o , associations of several, r a t h e r t h a n just p a i r s , of l i q u i d - p h a s e species m a y f o r m .

T h e f u l l c o m p l e x i t y of w h a t i n i t i a l l y seems to b e a

r a t h e r s i m p l e s y s t e m finally becomes e v i d e n t w h e n i t is c o n s i d e r e d that t h e s u m of i n d i v i d u a l effects w h i c h m a k e u p the o v e r a l l effect of t h e salt o n t h e c o m p o s i t i o n o f the e q u i l i b r i u m v a p o r e v e n i n a g i v e n system are f u n c tions o f t h e r e l a t i v e p r o p o r t i o n s of a l l c o m p o n e n t s present a n d v a r y w i t h l i q u i d p h a s e c o m p o s i t i o n o v e r the entire r a n g e i n v o l v e d i n t h e s e p a r a t i o n . V a r i o u s theories h a v e b e e n p r o p o s e d a n d tested to e x p l a i n salt effect i n v a p o r - l i q u i d e q u i h b r i u m , i n c l u d i n g models based o n hydration, intern a l pressure, electrostatic i n t e r a c t i o n , a n d v a n d e r W a a l forces. A l t h o u g h the electrostatic t h e o r y o f D e b y e as m o d i f i e d for m i x e d solvents has h a d l i m i t e d success, n o s i n g l e t h e o r y has y e t b e e n a b l e to a c c o u n t for or to

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

3.

43

Salt Effect

F U R T E R

p r e d i c t salt effect o n v a p o r - l i q u i d e q u i l i b r i u m f r o m

pure-component

p r o p e r t i e s alone. P r e v i o u s investigators h a v e g e n e r a l l y a g r e e d that s u c h effects are c a u s e d b y a c o m p l e x i t y of forces a n d i n t e r a c t i o n s , n o o n e of w h i c h has b e e n f o u n d significant e n o u g h i n r e l a t i o n to a l l of the others to correlate w e l l other t h a n i n extremely l i m i t e d c i r c u m s t a n c e s . Nevertheless, this a b i l i t y of a salt, w h i c h is not present i n the v a p o r phase, to alter v a p o r

c o m p o s i t i o n , has n o t w h o l l y e s c a p e d

industrial

a t t e n t i o n a l t h o u g h its a p p l i c a t i o n s h a v e b e e n r e l a t i v e l y l i m i t e d .

Some Applications D o n a l d F . O t h m e r w h i l e at E a s t m a n K o d a k d u r i n g the 1920's e x p e r i m e n t e d u s i n g salts to concentrate a c e t i c a c i d ( 1 4 ) .

H e also d e v e l o p e d a n

i n d u s t r i a l process for d i s t i l l i n g acetone f r o m its a z e o t r o p e w i t h m e t h a n o l b y p a s s i n g a c o n c e n t r a t e d c a l c i u m c h l o r i d e b r i n e d o w n t h e rectification column (J5).

P u r e acetone w a s c o n d e n s e d o v e r h e a d , a n d acetone-free

m e t h a n o l was r e c o v e r e d i n a separate s t i l l f r o m the b r i n e w h i c h w a s t h e n recycled.

T h e i m p r o v e d O t h m e r r e c i r c u l a t i o n s t i l l (16)

has b e e n

the

a p p a r a t u s g e n e r a l l y f a v o r e d b y investigators w h o h a v e s t u d i e d the effects of salts o n v a p o r - l i q u i d e q u i l i b r i u m . C o o k a n d F u r t e r (17, 18)

r e p o r t e d the results of a s e m i w o r k s s t u d y

i n w h i c h aqueous e t h a n o l feedstocks w e r e f r a c t i o n a t e d i n a 12-tray b u b b l e c a p c o l u m n i n a n extractive d i s t i l l a t i o n u s i n g p o t a s s i u m acetate as t h e s e p a r a t i n g agent. A m e t h o d w a s d e v e l o p e d i n w h i c h the salt w a s f e d as a g r a n u l a r s o l i d b y p o s i t i v e - d i s p l a c e m e n t m e t e r i n g s c r e w to the h o t reflux, a l l o w i n g salt to b e f e d successfully at a steady rate w i t h o u t

backflow

o r loss of v a p o r a n d a v o i d i n g a n y c l o g g i n g o f salt b y c o n d e n s e d d u r i n g feeding.

R a p i d d i s s o l v i n g of the salt i n the reflux w a s

vapor

achieved

b y e s t a b l i s h i n g a fluidized b e d of d i s s o l v i n g salt at the salt feedpoint. e n t r a i n m e n t of salt i n t o t h e o v e r h e a d

product was encountered.

No The

a z e o t r o p e was e l i m i n a t e d c o m p l e t e l y b y as l i t t l e as 5 m o l e % salt present i n the l i q u i d phase, a l l o w i n g 9 9 . 9 % +

anhydrous alcohol,

completely

salt-free, to b e p r o d u c e d f r o m e v e n r e l a t i v e l y d i l u t e feedstocks

i n the

12-tray c o l u m n . T h e l o w salt c o n c e n t r a t i o n r e q u i r e d is i n s t r i k i n g c o n trast to the 1:1 to 4:1 r a n g e of t y p i c a l s o l v e n t - f e e d r a t i o r e q u i r e d for this system u s i n g l i q u i d s e p a r a t i n g agents e v e n w i t h h i g h l y

concentrated

e t h a n o l feedstocks. F o r m a n y years D E G U S S A i n G e r m a n y l i c e n s e d a t e c h n i q u e k n o w n as the H I A G process (19, 20)

for d i s t i l l i n g absolute e t h a n o l , u s i n g m i x e d

acetate salts as the s e p a r a t i n g agent, i n the days w h e n e t h a n o l w a s u s e d as a f u e l u p g r a d i n g a d d i t i v e i n a u t o m o t i v e gasolines p r o d u c e d i n c e r t a i n

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

44

E X T R A C T I V E

A N D

A Z E O T R O P I C

DISTILLATION

countries. O v e r 100 s u c h p l a n t s w e r e b u i l t b e t w e e n 1930 a n d 1950. U s e r s c l a i m e d l o w e r c a p i t a l costs a n d l o w e r e n e r g y r e q u i r e m e n t s i n c o m p a r i s o n w i t h c o n v e n t i o n a l processes w h i c h use b e n z e n e o r e t h y l e n e g l y c o l as the s e p a r a t i n g agent, a n d the 9 9 . 8 % e t h a n o l p r o d u c e d r e q u i r e d n o f u r t h e r p u r i f y i n g or solvent k n o c k b a c k to r i d i t of traces of s e p a r a t i n g agent. A n e x a m p l e of a c o m m e r c i a l extractive d i s t i l l a t i o n o p e r a t i o n i n c u r r e n t major use u s i n g a salt is t h e c o n c e n t r a t i o n of aqueous n i t r i c a c i d u s i n g m a g n e s i u m n i t r a t e as t h e s e p a r a t i n g agent i n s t e a d of t h e earlier process which

h a d used a l i q u i d separating

agent,

sulfuric acid.

developers of this process h a v e b e e n H e r c u l e s a n d Tennessee

Principal Eastman

i n the U n i t e d States a n d I m p e r i a l C h e m i c a l I n d u s t r i e s i n B r i t a i n .

Her-

cules, w h i c h i n s t a l l e d the process at P a r l i n , N . J . , 13 years ago, c l a i m s s e v e r a l s t r o n g advantages

for u s i n g m a g n e s i u m n i t r a t e , a salt, as the

s e p a r a t i n g agent i n s t e a d of s u l f u r i c a c i d (21).

T h e y report

operating

costs r e d u c e d b y h a l f l a r g e l y t h r o u g h savings i n r e d u c e d e n e r g y r e q u i r e ments, c a p i t a l costs r e d u c e d 3 0 to 4 0 % , a h i g h e r y i e l d of p r o d u c t at h i g h e r q u a l i t y , a n d less p o l l u t i o n of the atmosphere. O t h e r i n d u s t r i a l a p p l i c a t i o n s h a v e existed, a n d these are elsewhere

reviewed

(10).

Conclusions E x t r a c t i v e d i s t i l l a t i o n u s i n g a d i s s o l v e d salt i n p l a c e of a l i q u i d solvent as t h e s e p a r a t i n g agent is a n u n u s u a l u n i t o p e r a t i o n for a p p l i c a t i o n i n c e r t a i n specific systems w h e r e r e l a t i v e l y s m a l l concentrations of salt are c a p a b l e of a l t e r i n g c o n s i d e r a b l y t h e v a p o r - l i q u i d e q u i l i b r i u m r e l a t i o n s h i p . T h e systems to w h i c h the t e c h n i q u e is a p p l i c a b l e are r e l a t i v e l y l i m i t e d i n n u m b e r b y the a v a i l a b i l i t y of a n effective salt f o r a g i v e n system w h i c h is a d e q u a t e l y s o l u b l e i n t h e system o v e r the c o m p o s i t i o n r a n g e i n v o l v e d a n d is selective. W h e r e a p p l i c a b l e , h o w e v e r , the effect c a n sometimes b e v e r y large a n d as a result c a n g r e a t l y r e d u c e t h e a m o u n t of s e p a r a t i n g agent r e q u i r e d , a l o n g w i t h y i e l d i n g a n o v e r h e a d p r o d u c t c o m p l e t e l y free of s e p a r a t i n g agent d i r e c t l y f r o m the t o p of t h e c o l u m n without the requirement

for a k n o c k b a c k section.

T h i s t e c h n i q u e is

d e s e r v i n g of m o r e a t t e n t i o n t h a n the relative o b s c u r i t y to w h i c h i t has b e e n r e l e g a t e d to date. Acknowledgment T h e c o n t i n u e d r e s e a r c h p r o g r a m s o n extractive d i s t i l l a t i o n b y salt effect a n d o n salt effect i n v a p o r - l i q u i d e q u i h ' b r i u m at t h e R o y a l M i l i t a r y C o l l e g e of C a n a d a are s u p p o r t e d b y t h e D e f e n c e

R e s e a r c h B o a r d of

C a n a d a , G r a n t N o . 9530-40.

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

3.

FURTER

Salt Effect

45

Literature Cited 1. Meranda, D., Furter, W. F., Can.J.Chem. Eng. (1966) 44, 298. 2. Dobroserdov, L. L., Il'yina, V. P., Tr. Leningradskogo Tekhnol. Inst. Pish chevoi Prom. (1956) 13, 92. 3. Johnson, A. I., Furter, W. F., Can. J. Chem. Eng. (1960) 38, 78. 4. Meranda, D., Furter, W. F., A.I.Ch.E. J. (1971) 17, 38. 5. Lescoeur, H., Ann. Chim. Phys. (1896) 9 (7), 541. 6. Kablukov, I. Α., Zh. Russk. Fiz.-Khim. Obshch. (1891) 23, 388. 7. Kablukov, I. Α., ibid (1903) 35, 548. 8. Kablukov, I. Α., ibid (1904) 36, 573. 9. Miller, W. L., J. Phys. Chem. (1897) 1, 633. 10. Furter, W. F., Cook, R. Α., Intern. J. Heat Mass Transfer (1967) 10, 23. 11. Furter, W. F., Chem. Engr. (London) (1968) 219, CE 173. 12. Ciparis, J. N., "Data of Salt Effect in Vapour-Liquid Equilibrium," Lith uanian Agricultural Academy, Kaunas, Lithuania, USSR (1966). 13. Ciparis, J. N., Dobroserdov, L. L., Kogan, V. B., "Salt Rectification," Khimiya, Leningrad (1969). 14. Othmer, D. F., personal communication (April, 1969). 15. Othmer, D. F., personal communication to J. P. Hartnett (March 7, 1966). 16. Othmer, D. F., Anal. Chem. (1948) 20, 763. 17. Cook, R. Α., Furter, W. F., "Extractive Distillation Employing a Dissolved Salt as Separating Agent," A.I.Ch.E. 63rd National Meeting, St. Louis (Feb. 18-21, 1968). 18. Cook, R. Α., Furter, W. F., Can. J. Chem. Eng. (1968) 46, 119. 19. Intern. Sugar J. (1933) 35, 266. 20. "Herstellung von absolutem Alkohol nach dem HIAG-VERFAHREN DER DEGUSSA," Degussa, Deusche Gold-und-Silber-Scheideanstalt, Vormals Roessler, Frankfurt (Main), Germany. 21. Chem. Eng. News (June 9, 1958), 40. RECEIVED November 24, 1970.

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

4 Rapid Screening of Extractive Distillation Solvents Predictive and Experimental Techniques

DIMITRIOS P. TASSIOS Newark College of Engineering, Newark, N. J. 07102 Rapid predictive and experimental techniques for screening extractive distillation solvents are reviewed. In pre paring a list of potential solvents the method of Scheibel is recommended for non-hydrocarbon systems; for hydro carbon systems solvents of high polar cohesive density should be considered. For screening the potential sol vents the method of Pierotti, Deal, and Derr is recom mended. If it is not applicable, the method of Helpinstill and Van Winkle should be considered next. Finally, re liable screening is accomplished through a simple, rapid technique recently developed that uses gas-liquid chro matography.

" E x t r a c t i v e a n d a z e o t r o p i c d i s t i l l a t i o n i n different types o f c h e m i c a l i n d u s t r y has b e c o m e m o r e i m p o r t a n t as m o r e separations of c l o s e - b o i l i n g m i x t u r e s a n d a z e o t r o p i c ones are e n c o u n t e r e d . E x t r a c t i v e d i s t i l l a t i o n is u s e d m o r e because i t is g e n e r a l l y less expensive, s i m p l e r , a n d c a n use m o r e solvents t h a n a z e o t r o p i c d i s t i l l a t i o n . S o l v e n t s e l e c t i o n for a z e o t r o p i c d i s t i l l a t i o n has r e c e n t l y b e e n d i s c u s s e d b y B e r g ( I ) .

T h e r e f o r e , solvent

s c r e e n i n g for extractive d i s t i l l a t i o n is d i s c u s s e d here. T h e ease of s e p a r a t i o n o f a g i v e n m i x t u r e w i t h k e y c o m p o n e n t s i a n d / is g i v e n b y the r e l a t i v e v o l a t i l i t y :

w h e r e χ is the l i q u i d phase m o l e fraction, y is the v a p o r p h a s e m o l e f r a c t i o n , y is the a c t i v i t y coefficient, a n d P ° is the p u r e c o m p o n e n t v a p o r pressure. 46 In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

Library American Chemical Society 4.

Extractive

TASSIOS

Distilfotion

47

Solvents

T h e solvent is i n t r o d u c e d t o c h a n g e t h e r e l a t i v e v o l a t i l i t y ( α # ) as far a w a y f r o m one as possible. S i n c e the r a t i o

(P°i/P° )

is constant for s m a l l

;

t e m p e r a t u r e changes, t h e o n l y w a y t h a t t h e r e l a t i v e v o l a t i l i t y i s affected is b y i n t r o d u c i n g a solvent w h i c h changes the r a t i o

(yi/γ,).

This ratio, i n

the presence o f the solvent, is c a l l e d selectivity (S^) : Sii—

[yi/r;] solvent

(2)

I n some cases a significant c h a n g e i n o p e r a t i n g pressure, a n d h e n c e t e m p e r a t u r e , changes

e n o u g h t o e l i m i n a t e a n azeotrope ( 2 ) .

Besides a l t e r i n g t h e r e l a t i v e v o l a t i l i t y , t h e solvent s h o u l d also b e easily s e p a r a t e d

from

the distillation products.

Other

criteria—e.g.,

toxicity, cost, e t c . — d i s c u s s e d b y V a n W i n k l e ( 2 ) a n d others m u s t b e c o n s i d e r e d . R e l a t i v e v o l a t i l i t y e n h a n c e m e n t is d i s c u s s e d i n this p a p e r . S e l e c t i n g the p r o p e r solvent b y c o n s i d e r i n g this c r i t e r i o n is s t i l l b a s e d o n e m p i r i c a l a p p r o a c h e s because o f t h e large n o n i d e a l i t y o f the r e s u l t i n g mixtures.

However,

g e n e r a l selection patterns a n d r a p i d e x p e r i m e n t a l

techniques have been made presents a r e v i e w

a v a i l a b l e t h r o u g h t h e years.

o f some o f these m e t h o d s

This

paper

t o f a c i l i t a t e t h e solvent

selection process i n t h e c h e m i c a l i n d u s t r y . Q u a l i t a t i v e aspects a r e first considered, followed

b y e m p i r i c a l correlations a n d r a p i d e x p e r i m e n t a l

techniques. Qualitative

Considerations

Since the type

o f solutions e n c o u n t e r e d

i n extractive d i s t i l l a t i o n

i n v o l v e m i x t u r e s o f p o l a r c o m p o u n d s o r p o l a r w i t h n o n p o l a r ones, t h e solutions a r e u s u a l l y n o n i d e a l , a n d p r e d i c t i n g t h e phase e q u i l i b r i u m f r o m p u r e c o m p o n e n t d a t a o n l y is p r a c t i c a l l y i m p o s s i b l e . T h e o r e t i c a l a n d e x p e r i m e n t a l studies t h r o u g h the years, h o w e v e r , h a v e e s t a b l i s h e d c e r t a i n trends w h i c h are u s e d to s e a r c h f o r a n d screen p o t e n t i a l solvents. Non-Hydrocarbon Mixtures: The Scheibel Method. S c h e i b e l ( 3 ) has suggested that the p r o p e r solvent c a n b e f o u n d a m o n g t h e m e m b e r s o f the h o m o l o g o u s series o f either k e y c o m p o n e n t s , i o r /

close t o o n e ) .

A n e x a m p l e p r e s e n t e d b y S c h e i b e l . ( 3 ) best demonstrates this a p p r o a c h . C o n s i d e r i n g the separation o f the m e t h a n o l - a c e t o n e azeotrope, t h e p o t e n t i a l solvents a c c o r d i n g t o this m e t h o d a r e presented i n T a b l e I. A n y m e m b e r o f either h o m o l o g o u s series c a n b e u s e d . T h e reason b e h i n d this a p p r o a c h is that w h i l e the m e m b e r s o f a h o m o l o g o u s series f o r m essen t i a l l y i d e a l solutions, t h e y f o r m n o n i d e a l solutions w i t h t h e other c o m ponent. with

F o r e x a m p l e w h i l e m e t h a n o l forms essentially i d e a l solutions

ethanol,

1-propanol,

a n d 1-butanol,

n o n i d e a l solutions w i t h t h e m .

acetone

forms

increasingly

W h i l e t h e p a r t i a l pressure o f m e t h a n o l

decreases i n t h e presence o f a h i g h e r a l c o h o l , that o f acetone increases.

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

48

E X T R A C T I V E

Table I.

A N D

A Z E O T R O P I C

Potential Solvents for the Acetone "-Methanol

B.P.,

Solvent Methylethyl

ketone

102.0

M e t h y l i s o b u t y l ketone M e t h y l n - a m y l ketone,

etc.

6

Separation

B.P.,

Solvent

°C

79.6

M e t h y l η-propyl ketone

DISTILLATION

°C

Ethanol

78.4

Propanol

97.8

115.9

Water

100.0

150.6

Butanol A m y l alcohol

117.0

Ethylene

197.4

137.8

glycol

"Boiling point: 54.6°C. B o i l i n g point: 64.7°C. b

So that a n a z e o t r o p e w i t h acetone does not f o r m , the a l c o h o l u s e d m u s t h a v e a h i g h e n o u g h b o i l i n g point.

T h i s r e q u i r e m e n t is r e l i a b l y

l i s h e d o n l y i f v a p o r - l i q u i d e q u i l i b r i u m d a t a for at least two,

estab

preferably

three, of the m e m b e r s of the series w i t h acetone are k n o w n . T h e P i e r o t t i Deal-Derr

method

(4)

( d i s c u s s e d l a t e r ) o r the T a s s i o s - V a n

Winkle

m e t h o d ( 5 ) c a n b e u s e d i n this case. I n the latter m e t h o d a l o g - l o g p l o t of y°i vs. P°i s h o u l d y i e l d a straight line. F i g u r e 1 presents results for n-alcohols a n d b e n z e n e f r o m t h e i s o b a r i c ( 7 6 0 m m H g ) Coates (6).

d a t a of W e h e a n d

R e l i a b l e infinite d i l u t i o n a c t i v i t y coefficients are established

for the o t h e r η-alcohols f r o m d a t a for at least t w o , a n d p r e f e r a b l y three, of t h e m . T h e s e y° or W i l s o n (7)

values are u s e d w i t h equations l i k e those of V a n L a a r to generate a c t i v i t y coefficients

at i n t e r m e d i a t e

composi

tions a n d to c h e c k for a n e x i s t i n g a z e o t r o p e o r a difficult separation c u r v e close to t h e 45°

(x-t/

line).

F r o m the t w o series the one of t h e alcohols is p r e f e r r e d because here acetone is the o v e r h e a d p r o d u c t a n d u s i n g a ketone causes the v o l a t i l i t y to invert.

Scheibel (3)

recommends

relative

that the lowest b o i l i n g

h o m o l o g , w h i c h does not f o r m a n azeotrope, is chosen.

An

alternative

a p p r o a c h suggests the h o m o l o g w h i c h b a r e l y meets the m i s c i b i l i t y re q u i r e m e n t , for this results i n h i g h selectivity

(8).

T h e choice between

these c o n f l i c t i n g suggestions m u s t b e m a d e o n the basis of

economical

considerations. Hydrocarbon Mixtures. H e r e i t is u s u a l l y n o t the existence of a n azeotrope b u t r a t h e r the close v a p o r pressure of the k e y

components

that often necessitates u s i n g extractive d i s t i l l a t i o n . T h e q u a l i t a t i v e c r i t e r i a for solvent selection for h y d r o c a r b o n tures h a v e b e e n d i s c u s s e d b y P r a u s n i t z a n d A n d e r s o n ( 9 ) a n d P r a u s n i t z (10). (II),

and

mix

Weimer

S i n c e a r e v i e w was p r e s e n t e d r e c e n t l y b y Tassios

o n l y the c o n c l u s i o n s are discussed here.

T h e types of possible interactions b e t w e e n a m i x t u r e of h y d r o c a r b o n s a n d a p o l a r solvent are:

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

4.

Extractive

TASSIOS

Distillation

49

Solvents

1. p h y s i c a l ( d i s p e r s i o n a n d d i p o l e - i n d u c e d d i p o l e ) 2. c h e m i c a l ( r e s u l t i n g f r o m t h e f o r m a t i o n of l o o s e l y b o u n d aggre gates) U s i n g p h y s i c a l i n t e r a c t i o n alone, P r a u s n i t z a n d A n d e r s o n ( 9 ) a n d W e i m e r a n d P r a u s n i t z (10)

h a v e d e v e l o p e d this s i m p l i f i e d expression

for h y d r o c a r b o n selectivity, S° 3, at infinite d i l u t i o n i n a solvent: 2

lnS°2s

oc ( r x W e - V a )

(3)

w h e r e η is the p o l a r cohesive e n e r g y d e n s i t y of the solvent, w h i c h is rer e l a t e d to the p o l a r i t y a n d t h e m o l a r v o l u m e of t h e solvent. References 10 a n d 11 e x p l a i n h o w to c a l c u l a t e τ. T h e s e l e c t i v i t y is h i g h e r , t h e l a r g e r the difference i n m o l a r v o l u m e b e t w e e n the h y d r o c a r b o n s a n d the l a r g e r the p o l a r cohesive e n e r g y d e n s i t y ( τ ) of t h e solvent. P r a u s n i t z a n d c o w o r k e r s (9, 10),

Gerster a n d his coworkers (12), Pierroti, D e a l , a n d D e r r

a n d D e a l a n d D e r r (14) conclusions.

F o r e x a m p l e , the selectivities of the p a i r h e x a n e - b e n z e n e

at 2 5 ° C w i t h v a r i o u s solvents (14) for τ

χ

(13),

g i v e e x p e r i m e n t a l e v i d e n c e to s u p p o r t the a b o v e are p r e s e n t e d a l o n g w i t h the values

i n T a b l e I I a n d p l o t t e d against e a c h other i n F i g u r e 2.

Here

3.0L.

l.ol 5.0

I

I

I

I

I 6.0

ι

ι

I

I

I 7.0

I

I

L

lnP°

Figure 1. Prediction of infinite dilution activity coefficients for numbers of a homologous series m a common solvent: n-Alcohols in Benzene at 1 atm

A 7°B

vs. P°B

·

7°A vs. P°A

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

50

E X T R A C T I V E

A N D

A Z E O T R O P I C

DISTILLATION

( V 3 - V 2 ) is constant, a n d the s e l e c t i v i t y tends to increase w i t h τ ,

indi

2

χ

c a t e d b y E q u a t i o n 3. L o o s e l y b o u n d aggregates ( c h e m i c a l effects) are f o r m e d w i t h the h y d r o c a r b o n s a c t i n g as e l e c t r o n d o n o r s ( L e w i s b a s e ) a n d t h e acting

as

electron

acceptors

(Lewis

acid).

The

forms the m o s t stable c o m p l e x w i t h the solvent experiences a i n volatility.

E l e c t r o n donors

are r a t e d b y

solvents

hydrocarbon

that

decrease

ionization potential,

e l e c t r o n acceptors are r a t e d b y t h e i r e l e c t r o n affinities.

The

and

selectivity

w i l l b e h i g h e r , the l a r g e r the difference i n i o n i z a t i o n p o t e n t i a l b e t w e e n the h y d r o c a r b o n s a n d the l a r g e r the e l e c t r o n affinity of the solvent While

data

(15, 16),

on

ionization potentials

of

hydrocarbons

can be

(9). found

e l e c t r o n affinities d a t a are r a r e because of difficulties i n t h e i r

experimental

determination.

Prausnitz and Anderson

that the s i g m a scale, p r o p o s e d b y H a m m e t t (17),

(8)

b e u s e d to

recommend determine

a p p r o x i m a t e l y the s o l v e n t s r e l a t i v e a b i l i t y to f o r m complexes w i t h the two hydrocarbons.

A t t e m p t s b y this a u t h o r , h o w e v e r , to use this scale

w e r e n o t c o n c l u s i v e . P r a u s n i t z a n d A n d e r s o n (8)

s h o u l d b e c o n s u l t e d to

u n d e r s t a n d better the p h y s i c a l a n d c h e m i c a l effects. The Effect of Solvent and Solute Concentration. T h e effect of solvent c o n c e n t r a t i o n o n selectivity is q u a l i t a t i v e l y d e s c r i b e d b y three types

(2,

11 ) s h o w n i n F i g u r e 3. I n the first t y p e the s e l e c t i v i t y increases a l m o s t l i n e a r l y w i t h solvent c o n c e n t r a t i o n , a n d this seems to represent the p r e d o m i n a n t p a t t e r n 19).

(18,

I n the s e c o n d t y p e the s e l e c t i v i t y increases m o r e t h a n l i n e a r l y w i t h

solvent c o n c e n t r a t i o n , b u t it is h a l t e d b y i m m i s c i b i l i t y at h i g h solvent c o n c e n t r a t i o n s (20).

T h e t h i r d t y p e shows a m a x i m u m a n d is a n u n u s u a l

p a t t e r n . O n e s u c h case was o b s e r v e d b y H e s s et al. (21)

i n s t u d y i n g the

s e p a r a t i o n of 1-butane f r o m butenes-2 w i t h the f u r f u r a l solvent Table II.

(96.5%

Selectivities and Polar Cohesive Energy Densities for the Hexane ( l ) - B e n z e n e (2) System at 25°C (12) Solvent

M E K Acetone Pyridine Aniline Acetonitrile Propionitrile Nitromethane Nitrobenzene Phenol Furfural Dimethyl-sulfoxide D i m e t h y l formamide

S°2J 3.6 3.8 5.2 12.2 9.4 6.5 15.0 5.8 6.0 10.9 22.0 12.5

T (cal/cc)

m

t

5.33 6.14 3.71 6.37 8.98 7.17 9.44 4.89 9.84 7.62 9.47 8.07

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

4.

TASSIOS

Extractive

Distilfotion

51

Solvents

1.4

•

1.2

-

1/1

•

•

1.0

0.8

0.6

1

1

•

•

•

•

•

•

•

•

•

•

20

I

1

I

40

60

80

ι

1

I g.molel Figure

2.

Variation of selectivity with solvent's polar cohesive system: hexane (l)-benzene (2) at 25°C (12)

weight furfural and 3 . 5 % water). that

selectivity

H o w e v e r , G e r s t e r et al

i n c r e a s e d w i t h solvent

c o n c e n t r a t i o n for

density;

(22)

report

the

system

b u t a n e - b u t e n e - 1 w i t h p u r e f u r f u r a l as solvent. C o n s i d e r i n g the extensive e x p e r i m e n t a l w o r k of the s e c o n d s t u d y , the results s h o u l d b e c o n s i d e r e d m o r e r e l i a b l e . A n o t h e r case i n v o l v e s the s e p a r a t i o n of e t h y l b e n z e n e f r o m e t h y l c y c l o h e x a n e w i t h h e x y l e n e g l y c o l as solvent ( 2 3 ) .

The maximum

appears i n this case i f definite, a n d t h e d a t a are r e p r o d u c e d . T h i s decrease i n s e l e c t i v i t y at h i g h e r solvent c o n c e n t r a t i o n results f r o m the

higher

temperatures r e s u l t i n g f r o m l a r g e r solvent c o n c e n t r a t i o n , for as t e m p e r a t u r e increases, s e l e c t i v i t y decreases. S e l e c t i v i t y is also affected b y the r e l a t i v e concentrations of the k e y c o m p o n e n t s . If c o m p o n e n t ( 1 ) forms a m o r e n o n i d e a l s o l u t i o n w i t h t h e solvent t h a n c o m p o n e n t ( 2 ) , a decrease i n Xi w i l l affect y χ m u c h m o r e t h a n a decrease of x w i l l affect y . 2

2

more rapidly than w h e n x

2

H e n c e , as X i decreases, οi2 increases

decreases.

Experimental evidence

(19,

20)

c l e a r l y shows this. F o r e x a m p l e , c o n s i d e r h o w p r o p a n o l affects the r e l a tive v o l a t i l i t y of the n-hexane ( l ) - b e n z e n e ( 2 )

system. H e x a n e forms a

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

52

E X T R A C T I V E

0 0

0.2

04

0.0

02

0.4

Figure •

A N D

A Z E O T R O P I C

Solvent Mole Fraction 06 08

0.6 Solvent V o l u m ^

1 0

0 8 y d r e e

1.0 V

o

|

3. Variation of refotive volatility with solvent Hydrocarbon ratio is 1:1. P: Constant. ethylcyclohexane (l)-ethyl

DISTILLATION

amount.

benzene (2)/hexylene glycol (22)

A n-hexane (l)-~benzene (2)/l-propanol (18) φ 2-4 dimethylpentane (l)-benzene (2)/aniline (19)

m o r e n o n i d e a l system w i t h p r o p a n o l t h a n b e n z e n e (xi/xo)

(19).

A s the r a t i o

decreases, Si increases. T h i s w a s o b s e r v e d e x p e r i m e n t a l l y 2

(19)

(see F i g u r e 4 ) . Mixed Solvents Effect.

U s i n g m i x e d solvents c a n i m p r o v e selectivity.

F o r e x a m p l e , a d d i n g s m a l l a m o u n t s o f w a t e r has i m p r o v e d the selectivity of f u r f u r a l i n s e p a r a t i n g C (25)

4

h y d r o c a r b o n s (24). B a u m g a r t e n a n d G e r s t e r

h a v e s t u d i e d h o w v a r i o u s solvents affect the selectivity o f f u r f u r a l

for t h e p e n t a n e - p e n t e n e p a i r . T h e y c o n c l u d e d t h a t for o n l y a f e w solvents some i m p r o v e m e n t w a s o b s e r v e d .

T h e r e s u l t i n g s e l e c t i v i t y lies b e t w e e n

t h e s e l e c t i v i t y of the p u r e solvents ( see T a b l e III ). T o a v o i d i m m i s c i b i l i t y at h i g h solvent c o n c e n t r a t i o n s , a s e c o n d solvent is sometimes a d d e d

(25).

The Effect of Temperature. T h e t e m p e r a t u r e effect o n s e l e c t i v i t y is given by:

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

4.

Extractive

TASSIOS

Distilfotion

53

Solvents

d(logS° ) 12

_

tf(l/T)

~

L \ - L \ 2.303R

v

'

w h e r e L° is p a r t i a l m o l a r heat of s o l u t i o n , c o m p o n e n t k at infinite d i l u t i o n i n the solvent. k

F o r h y d r o c a r b o n pairs i n different solvents a n d over m o d e r a t e t e m p e r a t u r e ranges (to 1 0 0 ° C ) , a l i n e a r d e p e n d e n c y of l o g S ° i o n ( 1 / T ) c a n b e a s s u m e d (12, 14, 26). A n e x a m p l e is s h o w n i n F i g u r e 5, w h e r e l o g S° for t h e h e x a n e - b e n z e n e p a i r i n five different solvents is p l o t t e d against t h e r e c i p r o c a l absolute temperature. T h e r e l a t i o n s h i p c a n b e c o n s i d e r e d l i n e a r for e n g i n e e r i n g a p p l i c a t i o n s . S e l e c t i v i t y decreases w i t h i n c r e a s i n g temperature, a n d this explains t h e u n u s u a l m a x i m u m i n t h e v a r i a t i o n of selectivity w i t h solvent c o n c e n t r a t i o n s h o w n b y t h e system e t h y l b e n z e n e - e t h y l c y c l o h e x a n e w i t h h e x y l e n e g l y c o l as solvent ( F i g ure 3 ) . 2

30

i.ol

0.0

ι

I

02

I

I

04

ι

I

1

0.6

1 0 8

1—

1.0

M. Van Winkle, "Distillation," McGraw-Hill Figure 4. Variation of relative volatility with composition (2). Sys tem: hexane (l)-benzene (2)/l-propanol (3) at 760 mm (18). x,/x : · 2

1:3, A

1:1, •

3:1

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

54

E X T R A C T I V E

Table III.

Mixed

1-Pentene(2)

P r o p a n e (3) P r o p y l e n e (2) α

A Z E O T R O P I C

DISTILLATION

Selectivity of Pure and Mixed Solvents

Solute

n-Pentane(3)

A N D

Solvents

B;

Vol%

s

a

A

Β

M e t h y l Cellosolve M e t h y l Cellosolve M e t h y l Cellosolve

Nitromethane Nitromethane Nitromethane

0 5 100

1.69 1.70 2.49

Pyridine Pyridine Pyridine

-Butyrolactone -Butyrolactone -Butyrolactone

0 32.1 100

1.60 1.79 2.17

E t h y l m e t h y l ketone E t h y l m e t h y l ketone E t h y l m e t h y l ketone

-Butyrolactone -Butyrolactone -Butyrolactone

100 50 0

2.17 1.79 1.62

Acetonitrile Acetonitrile Acetonitrile

Water Water Water

0 50 100

1.64 1.34 .98

Acetonitrile-water data from Reference 41, all others from Reference

Quantitative

Methods

Infinite d i l u t i o n a c t i v i t y coefficients are p r e d i c t e d b y several methods (4,5,10,

27,28, 29, 30, 31).

method

(4),

method

(10),

T h e m o s t g e n e r a l are the P i e r o t t i - D e a l - D e r r

the p a r a c h o r m e t h o d modified

(27),

a n d the

Weimer-Prausnitz

by Hellpinstill and V a n Winkle

a c c u r a c y is l i m i t e d i n these m e t h o d s

Since

(28).

a n d noninfinite dilution

tions p r e v a i l i n a c t u a l operations, the infinite d i l u t i o n a c t i v i t y

condi

coefficients

o b t a i n e d s h o u l d o n l y be u s e d for s c r e e n i n g purposes. Pierotti-Deal-Derr Method (4). (γ°)

Infinite d i l u t i o n a c t i v i t y

coefficients

of s t r u c t u r a l l y r e l a t e d systems are c o r r e l a t e d i n this m e t h o d to the

n u m b e r of c a r b o n atoms of the solute a n d solvent (n

x

m e m b e r s of the h o m o l o g o u s series H ( C H 2 )

w l

a n d n^).

F o r the

X i ( s o l u t e ) i n the m e m b e r s

of the h o m o l o g o u s series H ( C H ) „ Y 2 : 2

log o y

x

_

A

+

l l

+

n

2

2

B

2

^ + ^ no

w h e r e the constants are functions of t e m p e r a t u r e , B of t h e solvent series, C

x

of b o t h , a n d D

Q

(5)

+ Dofa-n*)* U\ 2

and F

is a f u n c t i o n of the solute series, A

lt2

2

are f u n c t i o n s is a f u n c t i o n

is i n d e p e n d e n t of b o t h .

F o r z e r o m e m b e r s of a series—e.g., w a t e r for a l c o h o l s — n o infinite v a l u e for y°

is o b t a i n e d .

Instead, b y c o n v e n t i o n , a n y terms c o n t a i n i n g

a n η for the z e r o m e m b e r are i n c o r p o r a t e d i n the c o r r e s p o n d i n g cient. So for η-alcohols i n w a t e r :

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

coeffi

4.

TASSIOS

Extractive

Distilhtion

l o g y\ Notice

= Κ + B % + 2

that the t e r m D

(%-n )

0

constant because D

G

55

Solvents

2

x

was

2

(6)

CJn

i n c o r p o r a t e d i n t o the

Κ

is s m a l l e r t h a n the other coefficients b y a factor of

1 0 ; therefore, this t e r m is insignificant. I n E q u a t i o n 6 o n l y Κ is a f u n c 3

t i o n of the solute a n d solvent, as stated before.

B

2

is a l w a y s the same

w h e n w a t e r is the solvent a n d C i is the same for η-alcohol solutes.

This

is s h o w n better f r o m t h e f o l l o w i n g h o m o l o g o u s series i n w a t e r at 100°C: η-Alcohols:

l o g y\

=

-0.420 +

(0.517)% +

(0.230)/%

η-Aldehydes: l o g y ° = - 0 . 6 5 0 + ( 0 . 5 1 7 ) % + ( 0 . 3 2 ) / % 1

T h e coefficient Β is the same i n b o t h cases. E q u a t i o n 6 assumes a different f o r m for c y c l i c c o m p o u n d s i n a solvent.

F o r unalkylated cyclic (aromatic

and/or naphthenic)

fixed

hydro

c a r b o n s i n fixed solvents: log y\ where

B

a

and B

n

=

Κ + Bn

are

solvent

a

+ Bn

a

n

n

+ C [l/r -

dependent

r

1]

constants, C

(8) r

is

constant,

d e p e n d i n g o n the t y p e of ring ( d i p h e n y l l i k e or n a p h t h a l e n e l i k e ) , r is the n u m b e r of rings, a n d n

a

bers, respectively.

a n d η% are a r o m a t i c a n d n a p t h e n i c c a r b o n n u m

F o r e x a m p l e for d i p h e n y l l i k e h y d r o c a r b o n s i n p h e n o l

at 2 5 ° C : logy\ =

0.383 + 0.1421 n + 0 . 2 4 0 6 n a

n

+

1.845[l/r -

1]

30 I

(9)

~

1

1.0 I

I.JU

Figure 5. Dependence of selectivity on temperature. System: hexane (1}benzene (2). φ nitrobenzene, A acetonitrile, + furfural, ψ dimethyl sulfolane, Ο diethylene glycol

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

56

E X T R A C T I V E

A N D AZEOTROPIC

DISTILLATION

C o r r e l a t i o n s f o r various systems, d e v e l o p e d b y u s i n g e x p e r i m e n t a l d a t a o n 2 6 5 systems, are a v a i l a b l e ( I I , 2 6 ) . T h e r e l a t i o n s h i p s u s e d , the n u m e r i c a l values o f t h e constants, a n d t h e c a l c u l a t e d a n d e x p e r i m e n t a l values f o r y° are a v a i l a b l e ( 1 3 ) a n d s h o u l d b e u s e d t o s t u d y solvent selection. The Parachor Method ( 2 7 ) . Infinite d i l u t i o n a c t i v i t y coefficients are o b t a i n e d a c c o r d i n g to this m e t h o d f r o m the f o l l o w i n g r e l a t i o n s h i p ( 2 7 ) :

^-^άκτ^ - ^

10

1/2 €υ

2

(10)

w h e r e 17* is p o t e n t i a l e n e r g y o f c o m p o n e n t i c a l c u l a t e d f r o m : C7< · = ( A H a p ) i — R T , Δ Η ρ is e n t h a l p y o f v a p o r i z a t i o n , c a l / g r a m m o l e , C is a constant, a f u n c t i o n o f temperature, t h e p a r a c h o r r a t i o o f the t w o c o m ponents, a n d t h e n u m b e r o f c a r b o n atoms i n t h e solute a n d solvent m o l e c u l e s ; R is t h e gas constant. V

ν Λ

E q u a t i o n 10 generalizes t h e expression o f E r d o s ( 3 1 ) a p p l i c a b l e to c o m p o n e n t s i n v o l v i n g t h e same f u n c t i o n a l g r o u p . R e t u r n i n g to t h e c o n stant C i n E q u a t i o n 10, u s u a l l y t h e n u m b e r o f c a r b o n atoms does n o t d i r e c t l y affect t h e constant. A p p a r e n t l y this effect is c o r r e c t e d b y t h e p a r a c h o r w h i c h changes w i t h t h e n u m b e r of c a r b o n atoms. F o r example, for aromatics i n f u r f u r a l : C — (0.5632 + 0.03 X 10" *) (Pi/P ) 4

2

02222

(11)

a n d f o r naphthenes i n f u r f u r a l : l o g C = (0.2658 + 14.53 X 10" £) (log P i / P 4

2

- 0.5982) - 0.2679 (12)

w h e r e P i is p a r a c h o r o f c o m p o n e n t i a n d t is temperature, ° C . A b o u t t h e same v a r i e t y o f systems, c o v e r e d i n t h e P D D m e t h o d , is c o v e r e d i n this a p p r o a c h , a n d t h e expressions f o r C are g i v e n elsewhere ( 2 7 ) . A c o m p a r i s o n b e t w e e n t h e P D D a n d t h e p a r a c h o r m e t h o d seems to suggest t h a t t h e latter is n o w o r s e t h a n t h e former, a n d often better ( 2 7 ) . F o r t h e systems c o n s i d e r e d , t h e p a r a c h o r m e t h o d gives l o w e r m a x i m u m deviations i n 11 cases, t h e P D D i n 7. A l s o , t h e authors o f t h e p a r a c h o r m e t h o d c l a i m better a c c u r a c y w h e n e x t r a p o l a t i o n w i t h respect to tempera ture is r e q u i r e d . F o r example, t h e case o f n-heptane ( 1 ) i n 1-butanol ( 2 ) is c i t e d . V a l u e s f o r y° c a l c u l a t e d b y e x t r a p o l a t i n g t h e P D D constants to temperatures r a n g i n g f r o m 114.5°C-171.9°C y i e l d error r a n g i n g f r o m 1 0 0 - 2 0 0 % ; t h e errors f o r t h e p a r a c h o r m e t h o d range b e t w e e n 0 . 5 - 3 . 6 % . H o w e v e r , this is t h e o n l y c o m p a r i s o n a v a i l a b l e ( 2 7 ) a n d m a y n o t a l w a y s b e v a l i d . T h e p a r a c h o r values are estimated f o r different c o m p o u n d s b y a g r o u p c o n t r i b u t i o n m e t h o d (32, 33). The Weimer-Prausnitz (WP) Method (10). S t a r t i n g w i t h t h e H i l d e b r a n d - S c h a t c h a r d m o d e l f o r n o n p o l a r mixtures (34), W e i m e r a n d P r a u s -

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

4.

Extractive

TASSIOS

DistiUation

Solvents

57

n i t z d e v e l o p e d a n expression for e v a l u a t i n g values of h y d r o c a r b o n s i n p o l a r solvents: R T lny°

-

2

RT[

ν [(λχ -

λ )

2

2

In V / V i + 2

+

2

η

2

-

2ψ ]

+

12

V2/V1]

1 -

(13)

w h e r e V * is t h e m o l a r v o l u m e of p u r e i, c c / g r a m m o l e , λ* is t h e n o n p o l a r s o l u b i l i t y parameter, c o m p o n e n t i , a n d r is the p o l a r s o l u b i h t y p a r a m e t e r , {

c o m p o n e n t i . T h e s u b s c r i p t 1 represents the p o l a r solvent a n d s u b s c r i p t 2 is the h y d r o c a r b o n solute w i t h f

1 2

—fc'n

(14)

2

Later H e l p i n s t i l l and V a n W i n k l e (28)

suggested that E q u a t i o n 13

is i m p r o v e d b y c o n s i d e r i n g the s m a l l p o l a r s o l u b i l i t y p a r a m e t e r of

the

h y d r o c a r b o n (olefins a n d a r o m a t i c s ) : RTZny

o

2

-V [(Ai -λ ) 2

2

2

R T [ l n V2/V1 +

+

(η -

τ*) 2

2ψ ] 12

+

V2/V1]

1 -

(13a)

A l s o E q u a t i o n 14 b e c o m e s : ψ

12

=

1ϊ(τ

1

-

τ ) 2

(14a)

2

T h e v a l u e of k was o b t a i n e d b y c u r v e - f i t t i n g e x p e r i m e n t a l

infinite

d i l u t i o n a c t i v i t y coefficients of paraffins, olefins, a n d aromatics i n several p o l a r solvents. Table IV.

T h e v a l u e of k for e a c h h y d r o c a r b o n g r o u p is g i v e n i n

T h e values for λ are t a k e n f r o m plots ( 2 8 ) . {

c a l c u l a t i n g ^ is also a v a i l a b l e T h e term ψ

12

The method

for

(28).

corresponds to the i n d u c t i o n e n e r g y b e t w e e n the p o l a r

a n d n o n p o l a r , or s l i g h t l y p o l a r , species.

S i n c e n o c h e m i c a l effects

are

i n c l u d e d , the c o r r e l a t i o n s h o u l d not b e u s e d for solvents s h o w i n g s t r o n g hydrogen bonding. Rapid Experimental

Techniques

T h e safest m e t h o d u s e d to choose extractive d i s t i l l a t i o n solvents is to m e a s u r e d i r e c t l y m u l t i c o m p o n e n t v a p o r - l i q u i d e q u i l i b r i u m d a t a of the c o m p o n e n t s i n v o l v e d w i t h the solvents b e i n g c o n s i d e r e d . T h i s , h o w ever, is a tedious, t i m e c o n s u m i n g a p p r o a c h . T h e r e are r a p i d e x p e r i m e n t a l t e c h n i q u e s w h i c h c a n at least be u s e d i n the s c r e e n i n g stage of selecting t h e solvent.

T w o m e t h o d s are d i s c u s s e d h e r e ; b o t h use g a s - l i q u i d c h r o

m a t o g r a p h y , a n d t h e y are s i m p l e a n d r a p i d . T h e first ( 3 5 ) to screen; the s e c o n d (36), tive volatilities.

is o n l y u s e d

besides screening, gives infinite d i l u t i o n r e l a

B o t h methods

r e q u i r e a solvent w i t h a l o w e r

pressure t h a n the solutes as i n extractive d i s t i l l a t i o n .

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

vapor

58

E X T R A C T I V E

A N D A Z E O T R O P I C

Values for k in Equation

Table IV.

DISTILLATION

(14a)

System

k

% Average Absolute Error in γ°

Paraffins Olefins Aromatics

0.399 0.388 0.447

11.6 8.5 13.5

Screening Solvents through G L C . I n g a s - l i q u i d (GLC)

separating mixture components

l i q u i d b e i n g a b l e to i n t e r a c t w i t h different w i t h t h e v a p o r pressure differences.

chromatography

is b a s e d o n the p a r t i t i o n i n g strengths w i t h t h e m , a l o n g

T h e same is true for a n extractive

d i s t i l l a t i o n solvent. It seems l o g i c a l , therefore, that extractive d i s t i l l a t i o n solvents c o u l d b e r a t e d o n t h e i r p e r f o r m a n c e as p a r t i t i o n i n g l i q u i d s w i t h the m i x t u r e u n d e r c o n s i d e r a t i o n . W a r r e n et al. (37)

a n d Sheets a n d M a r c h e l l o (38)

have

suggested

u s i n g g a s - l i q u i d c h r o m a t o g r a p h y to s t u d y extractive d i s t i l l a t i o n solvents. I n t h e first s t u d y (37) a n i n d i v i d u a l c o l u m n w a s p r e p a r e d f o r e a c h solvent b y u s i n g this solvent as a p a r t i t i o n i n g l i q u i d .

It is a tedious,

time-

c o n s u m i n g m e t h o d a n d w a s r e s t r i c t e d to solvents o f h i g h b o i l i n g p o i n t . F i n a l l y t h e e x p e r i m e n t a l e v i d e n c e b a s e d o n l i m i t e d d a t a is n o t c o n c l u s i v e . Sheets a n d M a r c h e l l o (38)

significantly s i m p l i f i e d i t b y r e p l a c i n g t h e

p r e p a r i n g o f i n d i v i d u a l c o l u m n s f o r e a c h solvent w i t h d i r e c t l y i n j e c t i n g the solvent i n a c h r o m a t o g r a p h c o n t a i n i n g a g e n e r a l p u r p o s e c o l u m n . N o e x p e r i m e n t a l e v i d e n c e w a s g i v e n to s u p p o r t a p p l y i n g G L C t o rate extractive d i s t i l l a t i o n solvents.

R e c e n t l y Tassios

( 3 5 ) has p r o v e d

that

the m e t h o d is effective for screening. T h e t e c h n i q u e consists o f i n j e c t i n g a c e r t a i n a m o u n t (e.g., 3 c c ) of the solvent b e i n g c o n s i d e r e d i n t o the c h r o m a t o g r a p h c o n t a i n i n g a g e n e r a l p u r p o s e c o l u m n o r a c o l u m n c o n t a i n i n g a n inert s u p p o r t . N e x t , f o u r o r five 5 - m l samples o f a m i x t u r e of t h e k e y c o m p o n e n t s are injected, a n d t h e s e p a r a t i o n factor, F , 12

is m e a s u r e d f o r e a c h s a m p l e : F

12

(15)

= D /£>i 2

w h e r e D is distance b e t w e e n a i r p e a k a n d p e a k f o r c o m p o n e n t i as s h o w n {

i n F i g u r e 6. T h e o b t a i n e d values o f F

12

f o r these samples a r e p l o t t e d

against

t i m e f r o m solvent injection to establish t h e m a x i m u m v a l u e f o r t h e sepa r a t i o n factor, F12 ( m a x ) .

F u r t h e r details a b o u t t h e e x p e r i m e n t a l t e c h

n i q u e are i n t h e o r i g i n a l p a p e r ( 3 5 ) . T h e larger t h e v a l u e o f F

12

(max),

the better t h e solvent c a n separate t h e m i x t u r e , i n d i c a t i n g a better ex t r a c t i v e d i s t i l l a t i o n solvent.

T h i s w a s v e r i f i e d b y c o m p a r i n g values f o r

F12 ( m a x ) a n d infinite d i l u t i o n r e l a t i v e v o l a t i l i t i e s ( « ° i 2 ) for t h e system n-hexane—benzene

w i t h six different solvents.

T h e results p r e s e n t e d i n

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

4.

TASSIOS

Extractive

Distilhtion

59

Solvents

1 Figure 6.

Evaluation

of the separation

factor

Fjg

T a b l e V a n d p l o t t e d i n F i g u r e 7 suggest t h a t the l a r g e r the v a l u e of a°i2, the l a r g e r the v a l u e of F

(max).

12

T h e deviations observed w i t h

d i e t h y l e n e g l y c o l m u s t r e s u l t f r o m the l i m i t e d s o l u b i l i t y of n-hexane a n d benzene i n this solvent ( 3 5 ) .

C o m p a r i n g the solvents b a s e d o n the same

v o l u m e is r e c o m m e n d e d because i t is easier a n d seems m o r e c o n c l u s i v e . Infinite Dilution Relative Volatilities through G L C . If the solvent a m o u n t injected i n the c o l u m n is h i g h e n o u g h so t h a t i n f i n i t e d i l u t i o n c o n d i t i o n s for the i n j e c t e d solute p r e v a i l , it is r e a d i l y s h o w n ( 3 8 ) the s e p a r a t i o n factor

becomes

e q u a l to the infinite d i l u t i o n

that

relative

volatility: (16)

<x ij =

D o r i n g ( 3 9 ) has s h o w n t h a t infinite d i l u t i o n r e l a t i v e v o l a t i l i t i e s c a n b e e v a l u a t e d t h r o u g h G L C . H e p r e p a r e d a s p e c i a l c o l u m n for solvent u n d e r c o n s i d e r a t i o n , a tedious project. M a r c h e l l o (38)

each

A y e a r l a t e r Sheets a n d

s h o w e d t h a t s e p a r a t i o n factors increase w i t h i n c r e a s e d

a m o u n t s of injected solvent. L a t e r Tassios ( 3 5 )

f o u n d o u t the same to

Table V . Separation Factors and Infinite Dilution Relative Volatilities for the System w-Hexane ( l ) - B e n z e n e (2) at 67°C (35) Fj2° Solvent Pyridine Propionitrile Furfural Nitromethane N-methylpyrrolidone Diethyleneglycol a

ο « 12 3.70 4.80 6.55 7.00 8.20 9.10

0.03 gram

moles

5.85 6.10 6.40 6.95 8.40 4.70

Calculated for two solvent amounts.

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

Sec 5.40 6.40 7.50 7.95 8.40 4.50

60

E X T R A C T I V E

A N D

A Z E O T R O P I C

DISTILLATION

b e true b u t o b s e r v e d that at h i g h e r solvent amounts, 5 - 6 c c for the c o l u m n u s e d i n that s t u d y , the separation factor seems to l e v e l off a p p r o a c h i n g the infinite d i l u t i o n v a l u e w h i c h was f o u n d f r o m static measurements. I n a later s t u d y Tassios (36)

u s e d a 6 ft c o l u m n c o n t a i n i n g o n l y c h r o m o -

sorb G a n d a 10 ft c o l u m n c o n t a i n i n g glass beads a n d f o u n d t h a t constant values for the separation factor w e r e o b t a i n e d at solvent levels e q u a l or a b o v e 2.0 cc. F o r four solvents w i t h t w o h y d r o c a r b o n b i n a r y m i x t u r e s , the separation factor m e a s u r e d at 2 c c of solvent agree w e l l w i t h e x p e r i m e n t a l infinite d i l u t i o n relative volatilities. T h e m a x i m u m d e v i a t i o n was 2 3 . 8 % , the m i n i m u m 3 . 1 % .

T h i s a p p r o a c h of d i r e c t solvent

injection

eliminates the tedious c o l u m n p r e p a r a t i o n .

•

4

1

3

5

7

9

C*Ï2

^

Hydrocarbon Processing Figure 7. Relationship between maximum separation factors and infinite dilution rehtive volatilities for the system: n-hexane-benzene with various solvents at 67°C (35)

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

4.

TASSIOS

Figure

Extractive

8.

Distilfotion

Variation

61

Solvents

of selectivity with solvent's energy density

φ propane (l)-propene Δ pentane (l)-pentene J . butyronitrile 2. acetone 4. acetonitrile 5. furfural

polar

cohesive

(2) at 27°C (24) (2) at 25°C (10) 3. propionitrile 6. DMF

LHscussion T h e c r i t e r i o n of h i g h solvent p o l a r i t y s h o u l d b e c a u t i o u s l y a p p l i e d ( E q u a t i o n 3 ) i n p r e p a r i n g a list o f p r o s p e c t i v e

solvents.

There are

exceptions a m o n g solvents s h o w i n g h y d r o g e n b o n d i n g w h i c h p r o d u c e s h i g h e r values o f p o l a r cohesive energy d e n s i t y t h a n t h e p h y s i c a l i n t e r a c tions alone. T h i s explains, f o r example, t h e r e l a t i v e l y l o w selectivities o b s e r v e d w i t h t h e t w o ketones a n d p h e n o l ( T a b l e I I a n d F i g u r e 2 ) . H a n s o n a n d V a n W i n k l e (40)

m a d e a s i m i l a r o b s e r v a t i o n for 2 - b u t a n o l w i t h t h e

binary hexane-hexene-1.

A s a general

r u l e solvents

showing

strong

h y d r o g e n b o n d i n g affect l o w selectivities. A n o t h e r e x c e p t i o n to t h e a b o v e c r i t e r i o n is p r e s e n t e d i n F i g u r e 8 w h e r e In S ° f o r t h e p r o p y l e n e - p r o p a n e p a i r w i t h six different solvents at 2 7 ° C (41)

is p l o t t e d against τ . D e 2

c r e a s i n g selectivity tends to o c c u r w i t h i n c r e a s i n g solvent p o l a r cohesive energy density.

I n t h e same figure t h e d a t a o n p e n t a n e - p e n t e n e

(12)

w i t h t h e same solvents a r e also p l o t t e d . H e r e a c l e a r t r e n d of i n c r e a s i n g selectivity w i t h i n c r e a s i n g solvent p o l a r cohesive energy d e n s i t y is o b -

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

62

E X T R A C T I V E

served.

A N D A Z E O T R O P I C

DISTILLATION

Because of the similarity between t h e t w o hydrocarbon

pairs

a n d because the d a t a o n the C p a i r are s u p p o r t e d b y f u r t h e r e x p e r i m e n t a l 5

evidence ( 3 9 ) , the C data are of questionable accuracy. 3

T h e p r e d i c t i v e t e c h n i q u e s a r e r a t h e r accurate.

H o w e v e r , significant

errors h a v e b e e n o b s e r v e d i n f e w cases (4, 13, 27, 40).

N o direct com

p a r i s o n b e t w e e n t h e three p r e d i c t i v e m e t h o d s is a v a i l a b l e .

T h e authors

of the p a r a c h o r m e t h o d (27) c l a i m that t h e i r m e t h o d y i e l d s e q u a l o r better results t h a n t h e P D D m e t h o d f o r t h e cases c o n s i d e r e d i n t h e i r s t u d y ; i t is b e l i e v e d (42), mended.

h o w e v e r , that t h e latter is m o r e r e l i a b l e a n d i t is r e c o m

T h e Weimer-Prausnitz

m e t h o d p r o b a b l y gives less a c c u r a c y

t h a n t h e P D D m e t h o d , b u t i t is m o r e general.

F o r example, H a n s o n a n d

V a n W i n k l e (40) r e p o r t t h a t t h e i r d a t a o n t h e h e x a n e - h e x e n e p a i r w e r e not successfully c o r r e l a t e d

b y the W P method.

W i n k l e m o d i f i c a t i o n is r e c o m m e n d e d N u l l a n d P a l m e r (43)

The Helpinstill-Van

over t h e W P method.

Recently,

h a v e presented a m o d i f i c a t i o n o f t h e W P m e t h o d

w h i c h p r o v i d e s better a c c u r a c y b u t i t is less general.

The P D D

method

s h o u l d b e u s e d c a u t i o u s l y w h e n e x t r a p o l a t i o n w i t h respect t o t e m p e r a t u r e is u s e d (27). expected. mended

W h e n t h e G L C m e t h o d is u s e d , r e l i a b l e results are

E v a l u a t i o n of infinite d i l u t i o n relative v o l a t i l i t i e s is r e c o m (36).

Literature Cited 1. Berg, L., Chem. Eng. Progr. (1969) 65, 9, 52. 2. Van Winkle, M., "Distillation," p. 436, McGraw-Hill, New York, 1968. 3. Scheibel, E. G., Chem. Eng. Progr. (1948) 44, 927. 4. Pierotti, G. I., Deal, C. H., Derr, E. L., Ind. Eng. Chem. (1955) 51, 95. 5. Tassios, D. P., Van Winkle, M.,J.Chem. Eng. Data (1967) 12, 555. 6. Wehe, A. H., Coates, J., A.I.Ch.E. J. (1955) 2, 241. 7. Orye, R. V., Prausnitz, J., Ind. Eng. Chem. (1965) 57, 96. 8. Oliver, E. D., "Diffusional Separation Processes: Theory, Design and Evalu ation," p. 189, Wiley, New York, 1966. 9. Prausnitz, J. M., Anderson, R., A.I.Ch.E. J. (1961) 7, 96. 10. Weimer, R. F., Prausnitz, J., Petrol. Refiner (1965) 44, 9, 237. 11. Tassios, D. P., Chem. Eng. (1969) 76, 3, 118. 12. Gerster, J. Α., Gordon, J., Eklund, R. B.,J.Chem. Eng. Data (1960) 5, 423. 13. Pierotti, G. I., Deal, C. H., Derr, E. L., Document No. 5782, American Documentation Institute, Washington, D. C., 1958. 14. Deal, C. H., Derr, E. L., Ind. Eng. Chem. Process Design Develop. (1964) 3, 394. 15. Prausnitz, J. M., "Molecular Thermodynamics of Fluid-Phase Equilibria," p. 63, Prentice-Hall, Englewood Cliffs, 1969. 16. Watanabe, K.,J.Chem. Phys. (1954) 22, 1564. 17. Hammet, L. P., "Physical Organic Chemistry," McGraw-Hill, New York, 1940. 18. Murti, P. S., Van Winkle, M., A.I.Ch.E. J. (1957) 3, 517. 19. Prabhu, P. S., Van Winkle, M., J. Chem. Eng. Data (1963) 8, 14, 210. 20. Stephenson, R. W., Van Winkle, M.,J.Chem. Eng. Data (1962) 7, 510. 21. Hess, Η. V., et al., "Phase Equilibrium," Amer. Inst. Chem. Engrs. Symp. Ser. 2 (1962) 72-79.

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

4.

TASSIOS

Extractive Distillation Solvents

63

22. Gerster, J. Α., Mertes, T. S., Colburn, A. P., Ind. Eng. Chem. (1947) 39, 797. 23. Quozati, Α., Van Winkle, M., J. Chem. Eng. Data (1960) 5, 269. 24. Jordan, D., Gerster, J. Α., Colbum, A. P., Nohl, K., Chem. Eng. Progr. (1950) 46, 601. 25. Baumgarten, P. K., Gerster, J. Α., Ind. Eng. Chem. (1964) 46, 2396. 26. Mertes, T. S., Colburn, A. P., Ind. Eng. Chem. (1947) 39, 787. 27. Balakrishnan, S., Krishnan, V., International Symp. on Distillation (1969), p. 49, Inst. Chem. Eng., Brighton, England. 28. Helpinstill, J. G., Van Winkle, M., Ind. Eng. Chem. Process Design De velop. (1968) 7, 213. 29. Wilson, G. M., Deal, C. H., Ind. Eng. Chem. Fundamentals (1962) 1, 20. 30. Deal, C. H., Derr, E. L., Papadopoulos, M. N., Ind. Eng. Chem. Funda mentals (1962) 1, 17. 31. Erdos, E., Collection Czech. Chem. Commun. (1956) 21, 1521. 32. Quale, O. R., Chem. Rev. (1953) 53, 439. 33. Reid, R. C., Sherwood, T. K., "The Properties of Gases and Liquids," p. 373, McGraw-Hill, New York, 1966. 34. Hildebrand, T. H., "Solubility of Non-Electrolyles," p. 131, Dover, New York, 1964. 35. Tassios, D. P., Hydrocarbon Process. Petrol. Refiner (1970) 49, 7, 114. 36. Tassios, D. P., Ind. Eng. Chem. Process Design Develop. (1972) 11, 43. 37. Warren, G. W., Warren, R. R., Yarborough, V. Α., Ind. Eng. Chem. (1959) 51, 1475. 38. Sheets, M. R., Marchello, J. M., Petrol. Refiner (1963) 42, 99. 39. Doring, C., Z. Chem. (1961) 1, 347. 40. Hanson, D. O., Van Winkle, M.,J.Chem. Eng. Data (1967) 12, 319. 41. Hafslund, E. R., Chem. Eng. Progr. (1969) 65, 9. 42. Prausnitz, J. M., private communication, 1970. 43. Null, H. R., Palmer, D. Α., Chem. Eng. Progr. (1969) 65, 9, 47. RECEIVED November 24, 1970.

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

5 Azeotropic Distillation Results from Automatic Computer Calculations CLINE BLACK, R. A. GOLDING, and D. E. DITSLER Shell Development Co., Emeryville, Calif. 94608

In azeotropic distillation the added component, or entrainer, is taken overhead with one of two or more components being separated in a distillation column. If a second liquid phase forms upon condensing the overhead vapors, the entrainer-rich phase is refluxed or recycled back to the col umn. The other liquid phase is discarded, recycled to some suitable point in the plant, or processed further to recover dissolved components before being discarded. Methods pre sented earlier by one of the authors are applied to calculate two and three phase equilibria required in a computer pro gram for calculating azeotropic distillations. A brief descrip tion of the program is given; a sample output is listed and described. Calculated results for dehydrating aqueous etha nol mixtures are compared for the entrainers, n-pentane, benzene, and diethyl ether. Column flows, heat loads, and stage requirements are lowest for n-pentane. The entrain ers are rated in decreasing order of suitability: n-pentane, benzene, and diethyl ether.

T ^ V i s t r i b u t i o n of c o m p o n e n t s b e t w e e n separable phases is the basis for **** most c o m m o n l y u s e d separation methods. R e g a r d l e s s of the t y p e of s e p a r a t i o n step, its d e s i g n d e p e n d s o n accurate d i s t r i b u t i o n coefficients for the c o m p o n e n t s b e t w e e n the c o n t a c t i n g phases.

T h e s e are g i v e n i n

c o m p o s i t i o n s or m o r e f u n d a m e n t a l properties of the e q u i l i b r i u m phases. In

d i s t i l l a t i o n the c o m p o n e n t s are d i s t r i b u t e d b e t w e e n

v a p o r a n d l i q u i d phases.

separable

T h e d i s t r i b u t i o n coefficients or Κ values are

the ratios o f the v a p o r - l i q u i d c o m p o s i t i o n s i n the e q u i l i b r i u m

phases.

T h e y are expressed as the l i q u i d phase a c t i v i t y coefficients, γ / s , the v a p o r 64 In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

5.

BLACK,

GOLDiNG,

Computer

A N D DITSLER

65

Calcufotions

pressures of t h e p u r e c o m p o n e n t s Ρ*° s, t h e t o t a l pressure P, a n d t h e i m p e r f e c t i o n - p r e s s u r e coefficients 0/s, as

T h e r e l a t i v e d i s t r i b u t i o n of c o m p o n e n t s i a n d ; is an = KJKt

-

yiP ° β , / τ Λ * 4

(2)

0

A z e o t r o p i c d i s t i l l a t i o n is a c c o m p l i s h e d b y a d d i n g t o t h e l i q u i d p h a s e a v o l a t i l e t h i r d c o m p o n e n t w h i c h changes t h e v o l a t i l i t y o f o n e of t h e t w o c o m p o n e n t s m o r e t h a n t h e other, so t h e c o m p o n e n t s a r e s e p a r a t e d b y d i s t i l l a t i o n . T h e t w o c o m p o n e n t s to b e s e p a r a t e d often are close b o i l i n g c o m p o n e n t s w h i c h d o o r d o n o t azeotrope i n t h e b i n a r y m i x t u r e , b u t sometimes t h e y are c o m p o n e n t s w h i c h d o a z e o t r o p e a l t h o u g h t h e y a r e n o t close b o i l i n g c o m p o n e n t s . T h e a d d e d t h i r d c o m p o n e n t , sometimes c a l l e d the entraîner, m a y f o r m a t e r n a r y azeotrope w i t h the t w o c o m p o n e n t s b e i n g separated. H o w e v e r , i t m u s t b e sufficiently v o l a t i l e f r o m t h e s o l u t i o n so t h a t i t is t a k e n o v e r h e a d w i t h one of the t w o c o m p o n e n t s i n the d i s t i l l a t i o n .

If

the entraîner a n d the c o m p o n e n t t a k e n o v e r h e a d separate i n t o t w o l i q u i d phases w h e n the v a p o r o v e r h e a d is c o n d e n s e d , t h e entraîner p h a s e is refluxed b a c k to the c o l u m n . T h e other phase c a n b e f r a c t i o n a t e d t o r e m o v e the d i s s o l v e d entraîner a n d the r e s i d u a l a m o u n t of the o t h e r c o m p o n e n t before i t is d i s c a r d e d . A l t e r n a t i v e l y , this s e c o n d l i q u i d p h a s e is r e c y c l e d to some a p p r o p r i a t e p l a c e i n t h e m a i n process scheme. A z e o t r o p i c d i s t i l l a t i o n has often b e e n d i s c u s s e d i n recent l i t e r a t u r e ( J , 2, 3 ) .

M e t h o d s for p r o v i d i n g phase e q u i l i b r i a f o r a z e o t r o p i c a n d

extractive d i s t i l l a t i o n h a v e b e e n s t u d i e d extensively ( J , 4, 5, 6, 7,

8,9).

S o m e h a v e d i s c u s s e d the d e s i g n ( J O ) o r c a l c u l a t i o n of a z e o t r o p i c d i s t i l l a tions ( 2 , 3 ) ; others o n l y d i s c u s s e d c h o o s i n g t h e entraîner for a z e o t r o p i c d i s t i l l a t i o n processes

(11).

A n u n d e r s t a n d i n g of the phase e q u i l i b r i a i n v o l v e d is also v i t a l i n c h o o s i n g the entraîner.

T h i s not only depends on k n o w i n g the pure

c o m p o n e n t v a p o r pressures b u t also k n o w i n g n o n i d e a l i t i e s of the c o m ponents i n the l i q u i d a n d v a p o r phases. T h e m e t h o d s u s e d here to g i v e t h e phase e q u i l i b r i a are r e v i e w e d , a n d the A z e o t r o p i c D i s t i l l a t i o n P r o g r a m A D P / A D P L L E is d e s c r i b e d . A p p l i c a t i o n of the p r o g r a m to c a l c u l a t e a n a z e o t r o p i c d i s t i l l a t i o n p r o b l e m is s h o w n a n d d i s c u s s e d , a n d a s a m p l e c o m p u t e r o u t p u t is g i v e n a n d is briefly discussed. F i n a l l y , c a l c u l a t e d a z e o t r o p i c d i s t i l l a t i o n results are c o m p a r e d for d e h y d r a t i n g a q u e o u s e t h a n o l f o r t h e three entrainers, n pentane, benzene, a n d d i e t h y l ether.

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

66

E X T R A C T I V E

Phase

A N D

A Z E O T R O P I C

DISTILLATION

Equilibria

T o c a l c u l a t e p h a s e e q u i l i b r i a s u i t a b l e for m o s t a z e o t r o p i c d i s t i l l a t i o n p r o b l e m s , the m e t h o d s s h o u l d b e a p p l i c a b l e to three-phase e q u i l i b r i a . V a p o r - l i q u i d a n d l i q u i d - l i q u i d e q u i l i b r i a are u s u a l l y r e q u i r e d . A suit a b l e m e t h o d for this p u r p o s e has a l r e a d y b e e n d i s c u s s e d ( 5 ) .

It is a p p l i e d

here to c a l c u l a t e c o m p l e t e l y a l l p h a s e e q u i l i b r i a i n v o l v e d i n the u s u a l a z e o t r o p i c d i s t i l l a t i o n process. F r o m E q u a t i o n s 1 a n d 2, the phase e q u i l i b r i a d e p e n d u p o n k n o w i n g the p u r e c o m p o n e n t v a p o r pressures Pi°,

l i q u i d p h a s e a c t i v i t y coefficients

ji a n d i m p e r f e c t i o n - p r e s s u r e coefficients 0 . T h e c o m p u t e r p r o g r a m w h i c h 4

has b e e n d e v e l o p e d uses a n y of f o u r different v a p o r pressure e q u a t i o n s for p r o v i d i n g Ρ °. 4

It uses the m o d i f i e d v a n L a a r E q u a t i o n s ( 5 )

to g i v e

l i q u i d phase a c t i v i t y coefficients a n d a M o d i f i e d v a n d e r W a a l s E q u a t i o n of State (4, 6) to g i v e i m p e r f e c t i o n - p r e s s u r e coefficients 0<. T h e M o d i f i e d v a n L a a r E q u a t i o n s c a n represent v a p o r - l i q u i d a n d l i q u i d - l i q u i d e q u i l i b r i a . A c c o r d i n g l y , t h e y c a n b e u s e d to p r e d i c t threephase e q u i l i b r i a w h e n c o n d i t i o n s a l l o w t w o l i q u i d phases as w e l l as a v a p o r phase to exist. T h i s m i g h t o c c u r o n the trays i n t h e d i s t i l l a t i o n c o l u m n or at the condenser a n d a c c u m u l a t o r for the o v e r h e a d p r o d u c t f r o m the a z e o t r o p i c d i s t i l l a t i o n c o l u m n . F o r e q u i l i b r i u m b e t w e e n phases the fugacities for e a c h c o m p o n e n t m u s t b e e q u a l i n the s e v e r a l phases. I f the f u g a c i t y coefficient φι for a n y c o m p o n e n t i i n a m i x t u r e is d e f i n e d as the r a t i o of t h e fugacity fi o v e r the v a p o r c o m p o s i t i o n Y a n d the t o t a l pressure P, 4

then

*i-/iVyj?

(3)

If Vi is the l i q u i d m o l a r v o l u m e of p u r e c o m p o n e n t i a n d V} is the p a r t i a l 1

m o l a r v o l u m e of c o m p o n e n t i i n the l i q u i d m i x t u r e , e q u i l i b r i u m b e t w e e n the l i q u i d a n d v a p o r phases is g i v e n as

ytxPf/Bi-Y?

(4)

and

w h e r e P*

is the reference pressure.

F o r most a z e o t r o p i c d i s t i l l a t i o n p r o b l e m s , the reference pressure is t a k e n e q u a l to t h e s a t u r a t i o n pressure; a c c o r d i n g l y , the s e c o n d t e r m o n the r i g h t h a n d side of E q u a t i o n 5 d i s a p p e a r s , to s i m p l i f y the e q u a t i o n to

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

5.

B L A C K ,

GOLDiNG,

Computer

A N D DITSLER

T h e f u g a c i t y coefficients

67

Calculations

are calculated using a simplified equation

of state d e s c r i b e d earlier (4,6).

F o r this treatment t h e constantsfc*a n d

Oi are c a l c u l a t e d b y k n o w i n g t h e c r i t i c a l t e m p e r a t u r e a n d pressure. T h e a t t r a c t i o n coefficient &° is g i v e n b y g e n e r a l i z e d coefficients f o r n o n p o l a r substances a n d w i t h t w o other i n d i v i d u a l constants f o r p o l a r substances. If Yi refers t p t h e v a p o r c o m p o s i t i o n a n d δ# refers t o b i n a r y v a p o r inter actions, t h e e q u a t i o n b e c o m e s log i = ( P / 2 . 3 R T )

- o A V R T ] + (P/2.3R T ) 2

+ (P/2.3R T ) [2δ„7,(1 -

(XGvY,)*-]

2

2

2

[SGW

7,) - 0 . 5 3 * * 7 , 7 * ]

-

2

(

?

)

jk

W h e n t h e S's a r e zero, t h e f u g a c i t y coefficients i n t h e m i x t u r e s are c a l c u l a t e d u s i n g t h e s i m p l e c o m b i n a t i o n rules f o r c o m b i n i n g t h e coefficients (4,6).

B y u s i n g b i n a r y interactions, t h e equations a r e flexible e n o u g h t o

h a n d l e almost a n y case, e v e n i f s e m i - c h e m i c a l interactions o c c u r i n t h e v a p o r phase (4, 6). In azeotropic

d i s t i l l a t i o n , t h e entraîner a n d t h e t w o c o m p o n e n t s

b e i n g separated c a n p r o d u c e u n d e r some c o n d i t i o n s three-phase

equi-

l i b r i a . T w o l i q u i d phases m a y b e i n e q u i l i b r i u m w i t h a v a p o r phase. F o r the three-phase e q u i l i b r i a t h e s o l u b i l i t y o f t h e n o n p o l a r substance i n t h e p o l a r phase is d e n o t e d b y x, t h e s o l u b i l i t y o f t h e p o l a r substance i n t h e n o n p o l a r phase b y y, a n d t h e c o r r e s p o n d i n g a c t i v i t y coefficients b y y a n d Γ, respectively.

T h e relative v o l a t i l i t y f o r c o m p o n e n t s i a n d / is r e l a t e d

to the t o t a l c o m p o s i t i o n X a c c o r d i n g to f

"

_ li

(y^\

[(y -X )Tj+ i

(Xj-xjyn

i

\ W [to -

Xi)T< +

/P,°flA

( R

(Xi - xjyi]

. w

O v e r t h e t w o - l i q u i d phase r e g i o n E q u a t i o n 8 gives r e l a t i v e

volatilities

for three-phase e q u i l i b r i a ( 5 ) . I n t h e c o m p o s i t i o n r a n g e w h e r e o n l y a p o l a r l i q u i d phase a n d a v a p o r phase exists, E q u a t i o n 8 reduces t o —yA°0i/y/^°*«

(9)

a n d w h e r e o n l y a n o n p o l a r l i q u i d phase is i n e q u i l i b r i u m w i t h a v a p o r phase, E q u a t i o n 8 b e c o m e s

^-rww

(io)

T h e isothermal l i q u i d - l i q u i d equilibria are predicted from the M o d i fied v a n L a a r E q u a t i o n s b y finding t h e c o m p o s i t i o n s f o r w h i c h t h e a c t i v i ties a r e e q u a l i n t h e t w o phases f o r e a c h i n d i v i d u a l c o m p o n e n t .

T h i s is

accomplished w i t h a subprogram called S O L T E R . Either isothermal or isobaric v a p o r - l i q u i d equilibria or both are calculated w i t h a subprogram

called V L E .

M o d i f i e d v a n L a a r coefficients

f o r t w o o r three temperatures

ForSOLTER

d a t a b y w h i c h l i q u i d phase a c t i v i t y coefficients

and V L E , give the

are calculated for both

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

68

E X T R A C T I V E

programs.

A N D

A Z E O T R O P I C

DISTILLATION

F o r the v a p o r - l i q u i d e q u i l i b r i a , v a p o r pressures of the p u r e

c o m p o n e n t s are c a l c u l a t e d b y one of f o u r different v a p o r pressure e q u a tions. T h e imperfection-pressure

coefficients

θ are c a l c u l a t e d a c c o r d i n g

to E q u a t i o n s 6 a n d 7, a s s u m i n g 8s e q u a l to zero. A p p r o x i m a t e values for the p a r t i a l m o l a r v o l u m e s of the l i q u i d are o b t a i n e d f r o m E q u a t i o n 4 given i n Reference Azeotropic

(6).

Distillation

Program

ADP/ADPLLE

T h i s t e r n a r y a z e o t r o p i c d i s t i l l a t i o n p r o g r a m uses a s p e c i a l system of u t i l i t y subroutines w i t h p r o g r a m m e d i n i t i a l i z a t i o n . E i g h t m a i n controls, K N T R L , are u s e d w i t h v a r i o u s options o n each. F o u r p a r a m e t e r

options

are b u i l t i n t o the p r o g r a m , b u t the values are c h a n g e d b y t h e user b y u s i n g P R M T R cards. the pertinent

Twenty-one D A T A

conditions

cards a l l o w the user to g i v e

a n d specifications

for

the

separation

to

be

calculated. A p r e l i m i n a r y p r i n t o u t , w h i c h prefaces the c a l c u l a t i o n , defines

the

controls K N T R L , the parameters P R M T R w h i c h are a v a i l a b l e , a n d the DATA

w h i c h must be supplied.

T h i s is f o l l o w e d

by a maximum

of

t w e n t y - o n e V cards w h i c h d e s c r i b e quantities w h i c h are c a l c u l a t e d i m m e d i a t e l y f r o m the i n p u t d a t a . T h i s completes the p r o g r a m m e d i n i t i a l i z a t i o n w h i c h describes a n d defines the controls, the parameters, the d a t a , a n d certain directly calculatable quantities. A p r i n t o u t t h e n f o l l o w s , g i v i n g the controls a n d parameters

which

h a v e b e e n set a n d the d a t a w h i c h h a v e b e e n s u p p l i e d b y the user o n cards. A n o p t i o n p r o v i d e s for p r i n t i n g o u t the d a t a , for c a l c u l a t i n g phase e q u i l i b r i a a n d enthalpies, o r for s u p p r e s s i n g these.

S o m e c a l c u l a t e d re

sults as V quantities are p r i n t e d out next, a n d this is f o l l o w e d b y a stageby-stage p r i n t o u t of m a t e r i a l flows, heat flows, a n d d e t a i l e d phase e q u i l i b r i u m quantities, Pi /0», x 9

h

Y

h

α, γ, 0*. T h e last p r i n t o u t for t h e most

rigorous c a l c u l a t i o n s gives the c o m p o s i t i o n s

of the t w o l i q u i d

phases

f r o m the o v e r h e a d condenser a n d a c c u m u l a t o r a n d the f r a c t i o n of

the

c o n d e n s e d o v e r h e a d w h i c h separates as a n aqueous phase. T h e p r o g r a m is o p e r a t e d i n three general w a y s .

Simplified calcula

tions are m a d e w i t h the s u b p r o g r a m A D P , w h i c h calculates the a z e o t r o p i c d i s t i l l a t i o n c o l u m n b u t does not c a l c u l a t e the l i q u i d - l i q u i d e q u i l i b r i a i n the a c c u m u l a t o r w h e n the o v e r h e a d vapors are c o n d e n s e d . does t r y via

H o w e v e r , it

a d i a g n o s t i c message to w a r n the user w h e n t w o

phases are e x p e c t e d

o n the trays.

The

liquid

c a l c u l a t i o n s are rigorous

and

r e l i a b l e o n l y w h e n a single l i q u i d phase exists. H o w e v e r , the s u b p r o g r a m A D P does not m a k e r e l i a b l e c a l c u l a t i o n s w h e n a s e c o n d l i q u i d appears.

phase

T h i s p r o g r a m is u s e d for o r i e n t a t i o n i n e s t a b l i s h i n g o p e r a t i n g

c o n d i t i o n s for a design.

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

5.

GOLDiNG,

B L A C K ,

A N D

DITSLER

Computer

69

Calculations

T h e s e c o n d w a y i n w h i c h the p r o g r a m is o p e r a t e d is to c a l c u l a t e r i g o r o u s l y w i t h the s u b p r o g r a m A D P L L E .

T h e s e c a l c u l a t i o n s are re-

l i a b l e for either t w o - or three-phase e q u i l i b r i a . T h e a z e o t r o p i c d i s t i l l a t i o n c o l u m n s a n d the l i q u i d - l i q u i d e q u i l i b r i a for the c o n d e n s e d o v e r h e a d i n the a c c u m u l a t o r is c a l c u l a t e d w i t h this p r o g r a m . T h e t h i r d w a y that the c o m p u t e r p r o g r a m is o p e r a t e d is to use the a u t o m a t e d feature. ADPLLE.

T h i s involves c o m b i n i n g c a l c u l a t i o n s via A D P

and

S t a r t i n g f r o m a set of o p e r a t i n g c o n d i t i o n s , w h i c h m i g h t h a v e

b e e n f o u n d b y u s i n g A D P earlier, the p r o g r a m proceeds

automatically

to find a better set of c o n d i t i o n s . T h e p r o g r a m proceeds w i t h A D P , a n d after

the

conditions

are established, a

final

c a l c u l a t i o n is m a d e

via

ADPLLE. I n these c a l c u l a t i o n s the p r o g r a m tries to adjust c o n d i t i o n s so that o n l y a single l i q u i d phase exists o n a l l of the trays i n the c o l u m n .

The

p r o g r a m first finds the f e e d t r a y l o c a t i o n at a p o i n t w h e r e the r a t i o of c o m p o n e n t s 2 a n d 3 is the same as the f e e d w h e n c a l c u l a t e d w i t h the initial operating

conditions.

The

f e e d t r a y is a u t o m a t i c a l l y

displaced

u p w a r d . T h e n the p r o g r a m determines the l o w e s t w a t e r content o b t a i n a b l e i n the e t h a n o l p r o d u c t i f a l l other c o n d i t i o n s except this a n d the n u m b e r of s t r i p p i n g trays are h e l d constant. U s i n g c o n d i t i o n s a p p r o a c h ing

this l i m i t , a

final

c a l c u l a t i o n is m a d e

with

ADPLLE.

Usually

w h e n i t is c o m p l e t e d , the t o p tray is near s a t u r a t i o n , a n d o n l y a single l i q u i d phase exists o n the other trays. F i n a l c a l c u l a t i o n s are m a d e , v a r y i n g the specification for

component

2 i n the o v e r h e a d u n t i l the c o n d i t i o n is f o u n d w h e r e the w a t e r is satisfied w h e n the entire aqueous phase is r e m o v e d . proceeds

balance

A s the c a l c u l a t i o n

i n steps of one f u l l tray, often a f r a c t i o n a l t r a y is n e e d e d to

satisfy this exactly, b u t the nearest f u l l tray to satisfying t h e v a l u e is a n acceptable calculation. A u s e r s m a n u a l is not r e q u i r e d w i t h this p r o g r a m ; the p r o g r a m is s u b m i t t e d w i t h o u t a n y d a t a , a n d the user obtains as o u t p u t a d e s c r i p t i o n of the p r o g r a m s features.

T h i s prefaces the r e g u l a r o u t p u t . It i n c l u d e s

a title a n d i d e n t i f i c a t i o n , a d e s c r i p t i o n of c o n t r o l options K N T R L , i d e n t i fication

of

parameters

PRMTR,

identification

of

data

DATA,

and

a

d e s c r i p t i o n of d i r e c t l y c a l c u l a t a b l e results, V quantities. O n a first r u n a l l options m u s t b e set; these are c a r r i e d f o r w a r d as set or as reset b y the user. T h e r u n o u t p u t shows a c o n t r o l o p t i o n p a r a g r a p h o n l y w h e n options are reset a n d o n l y those that are reset. Parameters are b u i l t i n a n d r e m a i n fixed unless c h a n g e d b y p a r a m e ter cards. T h e p a r a m e t e r p a r a g r a p h appears o n l y o n r u n s w h e r e resetting occurs a n d o n l y o n those that are reset. D a t a values are l o a d e d for a l l d a t a o n a first r u n ; these are c a r r i e d f o r w a r d u n t i l t h e y are reset.

T h e d a t a p r a g r a p h appears o n a l l runs for

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

70

E X T R A C T I V E

A N D

A Z E O T R O P I C

DISTILLATION

w h i c h at least one v a l u e w a s reset a n d shows a l l values w h e t h e r reset or n o t . B a s i c d a t a decks for phase e q u i l i b r i a a n d enthalpies a r e i n c l u d e d i n the p r o g r a m itself for t w e n t y different ternaries as s h o w n i n K N T R L 2, options 1-20. F o r other systems the d a t a are l o a d e d as i n d i c a t e d , K N T R L 2, o p t i o n 2 1 . T h e L e w i s a n d M a t h e s o n t e c h n i q u e makes tray-to-tray c a l c u l a t i o n s s t a r t i n g at the b o t t o m a n d c a l c u l a t i n g u p t h e c o l u m n . M a t e r i a l a n d heat balances are m a d e o n e a c h tray, t h e n u m b e r of trays is d e t e r m i n e d i n t h e calculations. Application A s a m p l e c a l c u l a t i o n is g i v e n s h o w i n g the use of the p r o g r a m to calculate the azeotropic

d i s t i l l a t i o n of aqueous e t h a n o l mixtures u s i n g

the entraîner n-pentane ( K N T R L 2, O p t i o n 7 ) . T h e f e e d to the c o l u m n is 242.02 m o l e s / h r of aqueous e t h a n o l at a temperature of 110°F. T h e f e e d c o m p o s i t i o n is 85.64 m o l e % T h e d i s t i l l a t i o n is c a r r i e d o u t at 5 0 p s i a at the reboiler.

ethanol.

T h e pressure

d r o p is a s s u m e d to b e 0.14 p s i p e r tray. T h e v a p o r b o i l - u p at t h e r e b o i l e r is set at 800 m o l e s / h r . T h e reflux t e m p e r a t u r e is 154.45°F. T h e aqueous phase is s t r i p p e d to r e m o v e d i s s o l v e d entraîner a n d r e s i d u a l e t h a n o l . T h e c a l c u l a t i o n c o n t r o l is set to r e d u c e e t h a n o l i n t h e o v e r h e a d 13.85 m o l e

vapors

to

%.

Another

specification

w h i c h is set at t h e b e g i n n i n g is t h e

f r a c t i o n of entraîner w h i c h w i l l b e a l l o w e d e t h a n o l ; this has b e e n set at 0.62 Χ

i n the bottom

mole

product,

10" . A starting a n d m a x i m u m 6

a l l o w a b l e v a l u e for the f r a c t i o n o f w a t e r i n the final b o t t o m p r o d u c t is set at 2.556 Χ

1 0 " . I f the p r o g r a m fails o n the first A D P c y c l e i n t h e 4

a u t o m a t e d c a l c u l a t i o n , t h e v a p o r b o i l - u p is increased. If a s t r i p p e r is u s e d to r e m o v e entraîner a n d r e s i d u a l e t h a n o l f r o m the aqueous phase, the d a t a i n p u t o n D A T A cards 13, 14 a n d 15 m u s t b e a p p r o p r i a t e l y specified.

T h e s e d a t a c a r d s g i v e the m o l e fractions of

entraîner, e t h a n o l , a n d w a t e r , respectively, f e r r e d to as D I S T I L L A T E .

i n t h e s t r i p p e r bottoms re-

I f n o s t r i p p e r is i n c l u d e d , the d a t a o f c a r d s

13, 14 a n d 15 c o r r e s p o n d to t h e c o m p o s i t i o n o f the aqueous phase b e i n g removed.

H e r e the i n p u t is o n l y a first a p p r o x i m a t i o n , a n d t h e p r o g r a m

w i l l c a l c u l a t e a n e w v a l u e i n t h e s e c o n d c y c l e , t h e n u m b e r of w h i c h m u s t b e specified o r the tolerance g i v e n i f n o s t r i p p e r is i n c l u d e d . A l t h o u g h t h e rigorous s t r i p p e r c a l c u l a t i o n is m a d e separately, a f a i r l y r e a l i s t i c b o t t o m p r o d u c t is a s s u m e d w h e n the s t r i p p e r is i n c l u d e d . F o r this c a l c u l a t i o n a trace o f p e n t a n e 1 Χ 1 0 " a n d a s m a l l f r a c t i o n o f e t h a n o l 5

9 Χ 1 0 " h a v e b e e n a s s u m e d i n the s t r i p p e r bottoms. 5

T h e accumulator

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

5.

B L A C K ,

GOLDING,

A N D

DITSLER

Computer

71

Calculations

t e m p e r a t u r e is a s s u m e d the same as the reflux, 154.45°F. F o r this s a m p l e c a l c u l a t i o n n o values are specified o n D A T A cards 7 , 1 2 , 1 8 , 1 9 , 20, a n d 21 since the p r o g r a m does n o t use these for this c a l c u l a t i o n , b u t the

DATA

cards s h o u l d b e i n c l u d e d i n the i n p u t deck. T h e s a m p l e c a l c u l a t i o n is s h o w n as T a b l e I. describe the features of the p r o g r a m .

T h e first four pages

T h e first p a g e of the

computer

o u t p u t shows c o n t r o l options K N T R L 1-8; the three w a y s i n w h i c h the p r o g r a m is u s e d are defined as options 1, 2, a n d 3 for K N T R L 1.

Data

for t w e n t y different ternary systems i n v o l v i n g a n entraîner a n d t w o c o m ponents b e i n g separated are i n c l u d e d i n the p r o g r a m ; these

constitute

options 1-20 of K N T R O L 2. O p t i o n 21 is u s e d w h e n a l l d a t a for a n e w system are u s e d a n d are l o a d e d as i n p u t . T h e t w o options 1 a n d 2 of K N T R L 3 d e t e r m i n e w h e n the c a l c u l a t i o n s are c o m p l e t e d .

The

options

1 a n d 2 of K N T R L 4 determines the f e e d tray l o c a t i o n ; the K N T R L ' s 5 - 8 a l l o w t h e user to choose reasonable r u n c o n d i t i o n s a n d o u t p u t . T h e s e c o n d p a g e of c o m p u t e r o u t p u t shows the options for p a r a m e ters w h i c h are w r i t t e n i n t o the p r o g r a m b u t c a n b e c h a n g e d b y p a r a m e t e r cards P 1 - P 4 .

T h e t h i r d p a g e of c o m p u t e r o u t p u t shows the d a t a i n p u t

as D 1 - D 2 1 w h i c h the user s u p p l i e s i n m a k i n g a r u n . T h e f o u r t h p a g e of o u t p u t shows t h e t w e n t y - o n e V q u a n t i t i e s w h i c h are c a l c u l a t e d i n the p r o g r a m f r o m the i n p u t . T h e fifth p a g e s u m m a r i z e s the options

selected

a n d the data i n t r o d u c e d as i n p u t for the s a m p l e p r o b l e m .

thermo-

The

d y n a m i c d a t a are g i v e n o n c o m p u t e r o u t p u t p a g e 6; q u a n t i t i e s c a l c u l a t e d i n the p r o g r a m f r o m the i n p u t d a t a are s u m m a r i z e d as V quantities o n o u t p u t p a g e 7. S h o w n o n o u t p u t pages 8 a n d 9 is the final A D P r u n i n the a u t o m a t e d c a l c u l a t i o n ; these p r o v i d e i n p u t to the A D P L L E r u n . T h e V quantities are s u m m a r i z e d o n o u t p u t p a g e 10, a n d the final stage-tostage results a p p e a r o n o u t p u t pages 1 1 - 1 5 . T h e s e last five pages of

computer

output provide

a

tray-to-tray

s u m m a r y of heat a n d m a t e r i a l flows a n d d e t a i l e d q u a n t i t i e s for the phase e q u i l i b r i a , also a s u m m a r y of the three-phase condenser a n d a c c u m u l a t o r results a n d the w a t e r p r o d u c t out. T h e last o u t p u t p a g e s h o w s the fract i o n of the aqueous phase t h a t satisfies the w a t e r b a l a n c e .

Since o n l y

f u l l stages are c a l c u l a t e d , this f r a c t i o n n o r m a l l y is n o t exactly u n i t y , b u t it s h o u l d reprsent the nearest f u l l stage result to satisfy the w a t e r b a l a n c e . T h e entraîner m a k e u p a n d the w a t e r p r o d u c t out is s h o w n last i n the computer printout. F r o m the c o m p u t e r results c o l u m n profiles h a v e b e e n

summarized

a n d are g i v e n i n T a b l e II. T h e pressure profile is l i n e a r w i t h t r a y n u m b e r r e s u l t i n g f r o m the a s s u m e d i n p u t d a t a for pressure d r o p p e r tray. i n the table is the t e m p e r a t u r e ,

the f r a c t i o n of p e n t a n e i n t h e

Also liquid

phase, the f r a c t i o n of w a t e r i n the v a p o r phase o n a pentane-free basis, a n d the f r a c t i o n of e t h a n o l i n the l i q u i d p h a s e for e a c h t r a y i n the c o l u m n .

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

a 15 8 16 a 17 3 18 3 19 8 20 S 21

KNTRL KNTRL

KNTRL KNTRL KNTRL KN RL KNTRL KNTRL

1 2 3

1 2

1 2 3

5) 3 5) 3 !>> 3

6) e 6) s

7) 3

KNTRL < KNTRL (

KNTRL KNTRL <

KNTRL KNTRL < KNTRL

7> 3 7) 3

1 2

4) a 4) a

KNTRL KNTRL <

KNTRL (

1 2

3) 3 3) 3

< < <

KNTRL KNTRL

KNTRL

T

<

2) 2) 2) 2> 2) 2) 2)

2) S 13 2) S 14

KNTRL < K N T R L *< KNTRL < KNTRL

KNTRL <

«

2) s 1 2) ζ 2 3 2) s 4 2) s S 2) 8 2) g 6 7 2) 3 2) S 9 2) 8 2) 8 3,0 2) 8 11 2) 3 12

KNTRL KNTRL

1 2 3

PROGRAM

11 i2

SYSTEM

SYSTEM SYSTEM

PROGRAMS

Λ

FROM CA

CALCULATION ISOBARIC MOT C A L C U L A T E D

STRIPPER STRIPPER STRIPPER

(IF

(lp

(IF

KNTRL(D*2

KNTRL(5)»1

KNTRL(D»2

A

2)

3)

3)

OAT

INITIALIZATION AS FOLLOWS

NOT P R E S E N T ( M U S T SET D(2(») IF KNTRL(1)«2 3) NOT P R E S E N T < M U S T S E T 0(2l> IF K N T R L ( 1 > « 2 3) PRESENT f P R O G R A M C Y C L E S OMf.E IF K N T R L U > » 2 3)

PRESENT MOT PRESENT

CALCULATION

ACCUMULATOR

ISOTHERMAL

M

UTILITY

PROGRAMMED

C O M P ( 2 ) / C O P ( 3 > *AT10 A S FEEO CARD INPUT )

ACCUMULATOR ACCUMULATOR

MEATER/SUBCOOLER HEATER/SJBCOOLER

A

F!.)S f-TFR

IN T O P S VAPOR IN REFLUX

Λ

TRAY AT SAME T ^ A V 3Y D A T A

SOMTFNT ΞΟΜΤΕΝΤ

ρ Τ

PNTANj.>ETHMOL-VfATE«

Λί-L C O M P O N E N T C0MP<2> C«MP(3)

SET F E E D SET F E E O

SET SET

A

LO D

S Y S T E M 14 S Y S T E M i5 SYSTEM 1 6 S Y S T E M i7 SySyEM 1 8

13

9

SY5TEM SYSTEM SYSTEM

SYSTEM

4 5 6 7 β

SYSTEM SYSTEM

1 2 3

SYSTEM SYSTEM SYSTEM

ADPLLE PROGRAM C O M B I N A T I O N OF A D P / A O P L L E

ADP

AVAILABLE.

SYSTEM OF UTILITY SUBROUTINES! W J T H

(ADP/ADPLLE)

Ternary Azeotropic Distillation Program ( A D P / A D P L L E )

AZEOTROPIC DISTILLATION PROGRAM

CONTROL OPTIONS ARE

1) 3 1) a 1) 8

KNTRL KNTRL KNTRL KNTRL KNTRL

TERNARY

PROGRAM USES A SPECIAL

KNTRL KNTRL KNTRL

THESE

THIS

Table I.

Computer Output Page 1

to

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

THROUGH

QUANTITIES

A L L COMPONENT

BUILT

INTO

THE

PROGRAM

THE USE OF PPMTR-CAROS.

ARE

PRINT

DATA P

N

NJ

*,0

f,0

3.0 25.0

χ) » 2) -

Ρ(

8

S

B

R

C

C°MP(3)

D

C

FAHRENHEIT MOLE F R A T I 0 N MOLES/HR MOLE F R A CT TION MOLE F R A CΓ I ON

T

FRACT

F^RENHEH

MOLE

MOLFS/HR

T

A

FORM T

FORMAT FORMAT FORMAT FORMAT FORMAT FORMAT FORMAT < I F KNTRL<3)»2> FORMAT FORMAT

Y

MOLF

C

Γ I ON FRA T

FORMAT (IF KNTRL(4)«2> FORMAT FORMAT ION FORMAT I ON C0MPÎ2) FORMAT ION C0MP(3) FORMAT ION 0 M P ( R (D I F KNTRL(5)P2> FORMAT T (IF K N T R L ( 5 ) « 2 ) FORMAT DP (TOP PRESS-AC PRESS) P S H FORMAT HFATER/SUBCOOLER TEMP FAHRENHEIT FORMAT NUM E ° F C C L E S FOR A ° L L E (IF KNTRL(7)«2) FORMAT

8

REFLUX

C0MP(2) C0MPÎ2)

V<

V(

8)

5) 6)

3)

1) 2)

V( sε V( ε V( 4)εV( V( ε V( 7)ε ε V )s v( d o )9 ε

FEED FEED BOTTOMS BOTTOMS BOTTOMS BOTTOMS DISTILLATE DISTILLATE

FEED FEED

COMP(1) C 0MP(2)

(,OMP{ i )) C0MP(2 C0MP(3) TOTAL

COMP(l)

C0MP(2) C0MP(3) TOUL MOLES/HR MOLES/HR MOLES/HR MOLES/HR MOLES/HR MOLES/HR MOLES/HR MOLES/HR MOLES/HR

MOLES/HR

FORMAT FORMAT FORMAT

FORMAT FORMAT FORMAT FORMAT FORMAT FORMAT

FORMAT

DESCRIPTIVE IDENTIFICATIONS HAVE BEEN ESTABl 1SHED FOR THESE VARIABLES.

Q(20)

1 ) 2)

D( = FEED I ON FEED D< *« FEED TEMPERATURE (SUBCOOLEO Lieuip) D< 3) ε REBOILER PRESSEE D( 4)* PRESSURE DROP PSIA PER TRAY PSIA D( 5)« REFLUX TEMPERATURE D( 6) D< 7) D( ft)« REBOILER VAPOR D( 9)* BOTTOMS COMP(l) D<10> * PTTOMS MP(3) ( I F KNTRL(3)«1) D<1D s TOPS VAPOR 0cOMP(2) D(12) * FEED TRAY LOCATION 0(13) r DISTILLATE COMP(l) MOLE FRACT D(14) * DISTILLATE MOLE FRACT D(15) = DISTILLATE MOLE FRACT n<16) FEED MOLe FRArT C *> 0(17) ACCUMULA OR yEMPERATU f FAHRENHEIT D(lh) ( I F KNTRL(6)«1) D(19) ( I F KNTRL(7)»1) D(2D TOLERANCE OF C0MP<7> AND CftMPO)

MAY

£15,8 £15.8 £15.8 E15.8 E15.8 £15.8 E15.8 £15.8 £15.8 £15.8

E15.8 £15.8 E15.8 gl5.8 E15.8 £15.8 £15.8 £15.8 £15.8 £15.8 E15.8 £15.8 ii5.8 E15.8 E15.8 FlO.l E15.8

Eis.e

E15.8 E15.8

BUT THE VALUES

A T A

PC 3> • Pt 41 »

Pt

PARAMETERSi

o

THESE UUAf-iTlTlES ARE TO BE SUPPLIED BY THE USER BY MEANS OF DATACARDS.

AS

SUPPRLKS P R A T I N G OF A L L C ° M O E T

MAX CYCLESUF KNTRL(1>»2#3 AND KNTR^(7)sj.) MAX CYCLES(JF KNTRL(l)s2.3 AND KNTR.(7),2> FEED TRAY DISPLACEMENT(ONLY IF KNTRL(Î)=3) MAXIMUM AQP PASSES ALLOWED (IF KNTRL<1>«3>

TMESE

KNTRL ( f t ) * 1 KNTRL < C) s 2

BP

CHANGED BY

THE USER

2

Computer Output Page k

Computer Output Page 3

Computer Output Page

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

R

L

C

T

C

T

D(1C> WHEN KNTFL(1>«3

EC

L )

U

T

FORMAT

T

R

E

mP

T U

E

A

£15.8

MOLES/MR

T

FOR THIS

CALCULATION

0

(2l)

0(15) 0(16) D(17> 0(18) 0(19) 0(20)

8!»

0( 9 ) 0(1C) 0 ( H ) 0(12)

o( a)

0( 2 ) 0( 3 ) Oi 4 ) D( 5 ) 0( 6 ) 0< 7 )

0 ( 1>

.00000000

0

.24202000*03 .85640000*00 ,11000000*03 .50000000*02 .14000000*00 ,15445000*03 .34999999*01 .80000000*03 ,61999999-06 ,25560000*03 .13850000*00 .15000000*02 .99999999* 5 ,89999999*04 .99990000*00 .00000000 .15445000*03 ,00000000 .00000000 .0

SET FEED A * AT SAME C O M P ( 2 > / C O M P ( 3 > R A T I O S F E E O ACCUMULATOR CALCULATION ISOTHERMAL ( I F KNTRL<1>«2»3) HE ATFR/S.jBCOOL N N Ç T P R E S E N T S T R I P P E R P R E S E N T (PROGRAM C Y C L E S ONCE I F KNTRL*1>«2|3> P R I N T A L L COMPONENT DATA

A P EUSED

COMP(?)

DATA

S E T AS FOLLOWS

C O M B I N A T I O N O F ADP/ADPLLE PROGRAMS SYSTEM 7 3NTAN2-ETHNOL-WATER S £ T cChP(2) ; C M T £ K T I N T O P S VAPOR

BEEN

TEST OF AQP/ADPLLE OPTION KNTRL(1>«3

OPTIONS HAVE

1) 2) 3) 4> b) 6) 7) t)

FOLLOWING

( ( ( < < ( < (

E C

OF

W

w

TERNARY AlEOTROPIC DISTILLATION PROGRAM ( A D P / A D P L L O

VALUE

n FL

T

h OLE FRACT I ON COMP(2) FAHRENHEIT FEEO TEMPERATURE (SUBCOOLED L I Q U I D ) PS I A REB°ILEP PRESSURE PSIA P R E S S U R E DROP P E R TRAY FAHRENHEIT REFLUX TEMPERATURE MOLE F R A C I 3 N ( I F KNTRL(3>«2> REFLUX OMP<3> MOLES/HR R E B I L E P VAPOP MOLF. F R A C T I BOTTOMS COMP(i) MOLE F R A C T I BOTTOMS COMP(3) (IF KNTRL(3)«1) MOLE F R A C T I TOPS VAPOR C0MP(2) (IF KNTRL<4>»2> F E E D TRAY L O C A T I O N MOLE FRACTI ON DISTILLATE COMPtj) MOLE FRACTI DN DISTILLATE C0NP{2) MOLE FRACTI ON DISTILLATE tOMP<3) MOLE FRAçT1 FEED COMP(l) ON ACC M ,LA OR E M P E R A R E FAHRENHEIJ <'T F K N T R L ( 5 > « 2 > ( I F KNTRL(5»)i2> DP ( T O P P R E S S - A C P R E S S ) PSjA ( I F KMTRL(6)sl) HEATER/SURCOOLER TEMP FAHRENHEIT (IF KNTRL(7)«1) NUMftER OF C Y C L E S F O R A D P L L E (IF KNTRL(7)t2) T O L E A N E OF C ° < 2 > ANp f.0MP<3)

FE£0 FEE"

THE

KNT^L KNT^L KNTRL KNTRL KNTRL KNTRL KNTRL KNTRL

THE" CONTROL

NO 9 9

RUN

C

2

* DISTILLATE cOMP(3> MOLES/hR FORMAT £15.8 DISTILLATE TOTAL MOLES/K& FORMAT Ε15.8 * COMP(l) VAPOR-LIOUID FLOW STRIPPING SECTION MOLES/HR FORMAT £15.8 β COMP( ) VAPOR-LIOUID F L O STRIPPING SECTION MOLES/HR FORMAT E«5,8 « COMP<3) VAPOR-LIQUID FLOW STRIPPING SECTION MOLES/HR FORMAT E15.8 * H E A FLOW STRIPPING SECTION βΤυ/HR FORMAT £15.8 «0MP<1) VAP0R-LiQU, OW R I F Y I N G S T i O N MOLES/H* FORMAT 1 5 . 8 * COMPi?) VAPOR-LIQUID FLOW RECTIFYING SECTION MOLES/HR FORMAT £15.8 * COMPt 3 ) yAPOR-LIOUlO FLO RECTlFylNG SECTION MOLES/HR FORMAT Ei5.8 « HEAT FLOW RECTIFYING SECTION BTU/HR FORMAT £15,8

*

χ

ε

V(21>

ν

V<11> V<12) V(13) V(i4) V(15, V<16) V<17) V(18) ( 9) V(20,

Computer Output Page 5 ι

Η Ρ

Η

>

w

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

DISTI.LATION

PROGRAM

(APP'A3PLLE>

l 2

0

WATER WATER WATER

ETHNOL ETHNOL ETHNOL

T

PN AN2

PNTAN2

PNTAN2

A

PNT N2 ETHNOL WATER

F

100.000 200.000 300Ό00 100.000 200.000 300.000 100.000 200.000 300,000

TEMP

TC Κ .470300*03 .516300*03 .647000*03

B

0 C

.13747500-00 •22500000*00 .00000000

9

EPR

,000000 .890000-01 .260000-01

9

VAP BTU/MOL ,ΐ5ΐ5ΐ500+θ5 ,17748900*05 .'20346300*05 .20 37 00+05 ,22573300*05 .23969200*05 .19916000*05 .20649000*05 .21290001*05

C4I CC/GM ,141000*03 ,759000*02 ,247000*02

R?SSURE EQUATIONS ,273160*03 ,525l7o*01 ,228980+03 .000000 ,273160*03 ,404859*01

L I O BTU/^OL •39682500*04 ,82972500*04 .132756 *Q5 .25061000*04 ,60349000*04 .10365300*05 .12250000*04 .30270000*04 ,48200000*04

PC ATMS ,331000*02 ,631000*02 ,218000*03

7 CLASSES COEFFICIENTS FOR VAPOR .226933*02 ,208645*04 PNTAN2 .816290*01 .162322*04 ETHNOL .208440*02 ,28i740*04 WATER

3

AI J

•475000*01 .475000*01

•oooooo

AMPR

,οοοοοο •oooooo

.0000 .0000 .0000

I J PNTAN2-ETHN0L PNTANs-WATER ETHNOL-WATER

,159785*01

TEMP lOOtOOQ

AJI .82406500-00 •2Q3noooo*oi .39250000-00

.83367725-00 . 77 936* i ,76050000-00

AI J

ciJ

1J PNTAN2-ETHN0L PNTAN2-WATER ETHNOL-WATER

TEMP 87,800 87,800 87.800

CÏJ .15507600-00 .25800000-00 .00000000

.87359000-00 .22125185*01 .40080000-00

.88388000-00 .39480000*01 .74600000-00

AJI

PNTAN2-ETHN0L PNTÂN2-WATER EfHNOt««ATER

.93892120-00 .41365440+01 .72799999-00

AI J

TEMP 75.000 C 75.000 C 75i00Q C

RUN CVCLES - 1

TEMP « 154,430 F

CU .17486900-00 .29700000-00 .00000000

PRESENT

CALCULATION

PRESENT

A JI .92929000-00 .24165000*01 .40700000-00

STRIPPER

NOT

ACCUMULATOR

HEATER/SUBCOOLER

ISOTHERMAL

MODIFICATION OF PROGRAM TO CALCULATE PHASE EQUILIBRIA B* ?R2£f5^?^?βίϊϊ2 COEFFICIENTS USED IN iVLE» PROGRAM, USES MODIFIED VAN L*A* COEFFICIENTS AT 3 TEMPS. CALCULATES THETAS. GAMMAS AND COMPLETE PHASE EQUILIBRIA AT EACH STAGE.

AZEOTROPIC

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

E

C

0MP(2) C0MP(3) TOTAL VALUE

COMP(l)

C0MP<3) TfTAL

COMP(2)

2

C0MP< > C0MP(3) TOTAL C0MP<1>

COMP(l)

R

T

A

e

S

S )

MOLE

A

WA

2

2

2

2

2

2

0

PRESSURE^ 49.7 0 TE^P« 234.558 VAPOR M/HR LIO M/HR LIQ BTU/M .5139 ,5i41 9921,9861 797.7091 1039,7 54 7421.5674 .0024 .0030 3639.4535 798. ?54 2425 77 ι5 3·4

F R A C T Τ ON

FTMNOL WATER TOTAL

PMTAN2

COMP

KTRAYs 2

T

KTRAYs J PRESSURE* 49.860 TE»lPe 234.74P CONP VAPOR M/MR LlQ M / H R LIQ βΤΙΙ/Μ PN AN2 ,0558 .0559 9944.2387 FTHNOL 799,1022 1C41.U86 7440.7544 WATER .O0 3 .00 e 3647.64i7 TOTAL 799,1602 1041,1773 7747273,7 MOI Ε FRACTION V TER (ENTRAINER FREF BASIS)

w

V<

2 2

2

2

0

M» 2 Ν· 6 VAP BTU/M 18646.5080 2308?,776o 20880.9200 ΐ84 97 ·ο

2

B

M» N» 5 VAP TU/M j865î.454 23085,5050 088 .ι670 18448765,0 2

)

• •

•

•

-·-

0

2

•

KNTRUiOi» VP/THETA 97,9429 49,6905 23,0212

2

98.Î421 49,8567 3·ΐ0 0

*NTRL<10 )• VP/THETA

98,3158 49,9997 23,1712

,000003

,000003

Y ,000644 ,999353 ,000003

,000003 X < 3) .000494 .999503 .000003

,000003 ,000003

11,993293 1,000000 1.117Î74

.ALPHA

1.000000 1·1ΐ···ΐ .OOOOO3

11· 9 8 9 7 7 1 ,999927

ALPHA

1.116915

1.000000

..ALPHA 11,947562

•00007o

Y

,000003

,000003 X ( 2) •000054 ,999944

,000007 ,999990 ,000003

X <01> ,000006 ,999992 .000003

.28260159*03 .15005057*03 .24201635*03 .56181042*03 .24201705*03 .40584534-03 .36526080*02 .40580475*02 .40584534*02 .23213671*05

.00000000

VP/THETA

• 9) • mo> • VUl> • W12) • VUl> •

2

V< 1 ) V< V( 3 ) V( 4 ) V( 5 ) V( 6 ) V< 7)

VAP BTU/M 18655,6430 23087.8140 20883,2230 18470220,0

MOLES/H MOLEE/WR MOLES/HR OF D(10> ^ H E N KNTPL<1>«3

MOLES/HR MOLES/HP MOLES/HR KOLES/HR MOLES/HR MOLES/HR MOLES/HR MOLES/HR MOLES/HR

REBOILER PRESSURE* 50.00C TEMPt 234.910 C0*P VAPOR M/HR L.!0 M/WR LIS BTU/M PNTAN2 ,0059 ,0061 9961,3993 FTHNOL 799.992C 1042.0083 7455.5545 WATER .0021 .0026 3653.9526 TOTAL 800.0000 1042,0l70 7768820.1 MOLE FACTION A E * <ENTR tNER F ^ E 3 A 1

BOTTOMS BOTTOMS DISTILLATE DlSTiLLAT DISTILLATE DISTILLAIE

BOTTOMS BOTTOMS

FEED FEED FEED FEED

PROGRAM HAS CALCULATED THE FOLLOWING VARIABLES

(

ENTWALPr EQUATION COEFFICIENTS VAPOR «.·335498*02 324675-01 ,125541+05 25974 *02 ,372529-08 '.232640*02 .400800-01 .190630*05 ,199465*02 *.119750*01 .l8l55o*02 -.450000-03 .l909lO*Q5 ,«71000*01 ·.460000-02

PREl IMINAPY RESULTS FOLLOW

— LIQUIO PNTAN2 288600+03 ETHNOL -'.221100*03 WATER -.566000*03

1,000000 2.41Î380

GAMMA 6,004698

GAMMA 6,θ·θ7ΐ0 i,000000 2«4l0589

6,076075 1,000000 2,410122

GAMMA

. TMËTA 1,146209 ,999943 ,913646

Ï.146420 ,999994 •983646

THïTA

THETA 1,144542 ,999999 ,983621

Computer Output Page 8

Computer Output Page 7

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

A

5

A

7

T

E

R

<

FREE

BASIS)

A

PRESSURE*

NATËR

V POR M / H R 656.3955 294,4158 .0022 950'8i35

PRESSURE"

E

WAT R

E

FREE

B A

S

I

S

>

2

0

49,020

3ASIS)

TEMP* 169,194

1ΐ92·83Π5 (ENTRAÎNER F R E E

6^94.4591 4862.3906 2472.8385 7ΐ33842·3

BTU/M

LIQ

E

=}A lS>

T *p« 178,640

E

656,3956 536.4321 .0028

E

L I Q M/HR

49.160

E

( NTRAIN R FR E

5

49,300 T E M P « 211.961 LlQ M / H R LIQ BTU/M 268,0906 7318,0396 759,9^ 52i3.8 5 ,0026 2*42,8492 1028,0062 5923958.0

A

<ENTR IN R

M/HR

8

268,0904 5i7,8967 ,0020 785.9892

VAPOR

FRACTION

6

A

f

(ENTRAINER

C

E

E

E

KTRAY* s PRESSURE* 48.880 ΤΕ^Ρβ 167.474 LIQ M/HR L I Q BTU/M VAPOR M/HR CO 1Ρ 824,6642 6797,2936 824,6641 PNJTAN2 445.87S3 4782.Ï087 203.8620 ETHNOL .0137 2433,4969 .0131 WATER 1270.5562 7737756.5 1028,5392 TOTAL MOLE FRA TJ0N WAT R ( NTRAIN R F*E? BASIS)

E

E

LIQ M/HR LIQ BTU/M COMP VAPOR M/HR 6817,9567 792.9420 PNTAN2 792,9419 47$9|i707 463.4319 ETHNOL 221.4156 2441.8741 ,0056 WAT R ,0050 7630346.8 1256.3795 TOTAL 1014.3625 M0L FRACTION VATER (ENTRAINER FREE BASIS}

KTRAY*

MOLE

C

0MP PNT N2 FTWNOL WATER TOTAL

KTRAY*

MOLE

W

PRESSURE

N

FRACTION

ETHNOL

WATER TOTAL

T

E

BTU/M

9783.6962 7302.4418 3588.4516 7566325.Q

LIQ

: 234.102

PRESSURE* 49.440 TEMP* 231.260 LIQ M/HR LfQ BTU/M VAPOR M/MR 39 8n52 0858,5103 39,8050 961.58 >6 6510.6443 719,5733 .0024 ,0030 3241,9305 759.3808 1001.3978 6613192.3

FRAC IO

rOMP PNTAN2

KTRAY*

MOLE

KTRAY* 4 COMP PNTAN2 ETHNOL WATER TOTAL

E

UAT R

TEMP PRESSURE* 49.580 LIQ M/HR V POR M/HR 4.6854 4,6852 1029.8574 787,8411 .0031 .0025 1034.5459 792.5288

ETHNOL WAT R TOTAL MOLE FRACTION

PNTAM2

KTRAY* 3 COMP

A

Ν" 5 BTU'M

KNTRL'tîO»» VP/THETA 47 Î540 13,7553 5,8866 M«

2 Ν· 7 VAP BTU/M 16904,0770 22067,6550 20420,6820 18439207,0

KNTRL(ÏO>« 0

VP/THETA -48,2035 14,3011 6,1290

N» 3

54,1901 17,5479 7,5945

KNTRL'(ÏO)VP/ΤΗΕΤΑ

VAP BTU/M 16948,7490 22095,0280 20432.9990 l«33l659,0

M» 3

17194,0960 22244,0940 20500.1590 Ι7835ΐ85·0

V P

Μ» 3 Y

,801782 ,198205 ,000013 ,000064 ,000031

Y

,000023

.78Ï7Ï4 ,218201 ,000005

Y

,000007

,690351 ,309646 ,000002

X ( 9) ,649058 .350932 .000011

,000012

X ( 8) .631133 .360863 ,000004

,000005

X ( 7) .550284 .449714 .000002

,000004

E

.000003

0

,341087 ,6589|i ,0000

2

Χ ( 6)

VAP

,260787 .739211 ,000002

,000003

.000003

78,7405 33,6685 15.Ï609

,052418 Î947579 ,000003

Y

,000003

VP/TH TA

*NTRL'<Ï0î« 0

Y

,005912 ,994085 ,000003

,0397Îo ,960247 .000003

Χ (

,000003

X ( 4) ,004529 ,995468 .000003

BTU/M

Ν» 5

*NTRLU0)« VP/THETA 95,0046 47,0586 2Ϊ.7125

KNTRL(10)« VP/THETA 97,5110 49,3110 22,8338

18059.5690 2275 ,β7ι 20730,5130 16625276,4

Me 3

1856ο 8360 23035!3850 20859,2590 17314512,0

M« 3 Ν· VAP BTU/M

5

N» 6 BTU/M

18634,6550 23076,2360 20877,9290 l8267766i0

VAP

M« 2

ALPHA 2,364207 1.000000 5.320614

ALPHA 2.926727 1.000000 4,413907

6.319559 1.000000 2.225791

ALPHA

.ALPHA 12,505131

ALPHA 12,158900 1.000000 1,120858

.ALPHA 12.028157 1.000000 1.118356

CAMMA

A

1,010203 ,947050 ,959809

TMBTA

TwiTA 1,00*142 .97Î059 ,969674

1,137047 ,999859 ,981333

THETA

THBTA Î,145188 ,999483 ,913429

GAMMA 1,316007 Î,909471 23,775542

GAMMA 1,444620 l|663730 17,£43143

THETA ,998997 ,945259 ,960337

THETA Ï,QQ17_ Ï735 ,944806 ,939835

Computer Output Page 9

2.40Î460 1.173503 6,035234

GAHM

cAMMA 9,372543 i,004769 2,.751069

GAMMA 6,023060 1,000061 2,446777

6.0826O6 1,000001 2,415163

78

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Ο ·«•> v*»-C» ^uio OC»--

Ο ^ ^

Σ. —· CV CM

ΙΟ

χ: Ο 2 30 cr\ X

ΓΟΛΙΝ

x o

Ο ί-tttw4.4'(£«A ^ Ο^ ΙΛΟ î-»^ ο to «ΟβίνίΜΐη 4 · «ν « Ν ^,

Ό ΙΛΟ * Λ 3 « · Η Ο Λ « f D r t H M f t " »D«K> N O « o CMO »-eif\uî »fv JN _IM>«rMrv _J««-CM " ' m . Ul » U1W 111 U UIW uia. m a . t u a . u i a . U??^i°^î\î uiccrvoKieou. UJ oc o CM « M I . tu or CM v4ao ri II. UI or «o rv κι β u. uts oco ν u. uiacm >. n7r^ Λ (ν κ j ^ * e « κ locu ν * μim*ct k-xoov ^. CN O tt N G 0C ΙΟ Ct "V <\IC» ΙΠ «ΟΟΤ >. CV Λ

Λ

Γ0 0

.-^ Σ*»βο*ω x-xtCMCM^ui ε(Μΐνιη·»ιυ t n u ; χ CMO ο OC3CMO Ό —t O O M U ΙΟ— OOCMO Γν, — ΟΟ τ « ri ft— Ο Ο « « ΙΛ ΛΙ«orv»CMul Ul N (M« Λ ^ _ ΓΖ " ,». . .

E

Œ i.

0

. . ^ orx»eoo»»-

in

orxincMCMOi-

o r x c M o i f » » ^

orx *4iv » iot-

iîSt ίο ΛΙΝΌ Ή 3 toareveo r<3 coarviiv WDÎ r*c or H or cv rr ro or " C M _ I ΙΛ , U . HΙΟΟΙΟΟ C M _ l K»U . HCOCΟMlO_OI IOU. CH CM_I C U. l i i n e^t^Ort-l V i uiS tOOlOO 0 OolOO M 4 ^ui tu ζοκ î? ^ 7 J** a en< ι^ o ui z " uia.ee ^ JUKUJ o zu u>-O.-«ZUI-«*UJ iζaocan _i ο ζ u ui οi uζ » £ ^. >• a. ζ LU<» >-a. z*x -a.aeo Î O Z K O O— a > z h < o n— c ·> — Q >Z K < o o i o or ο ζ »-·«» σ ο Ï O (-•cam 3 t- χ t- o a LU 3 *-τ. ι - ϋ α u: j h Σ ι- o a u. 3 ι- Σ" ι-·ο a u - ^ »- χ 11

ω

5

(

2

o

a

J

or τ CMO «C trorx»K, » HO CMO CM _l Ui cβoπ r ω *α χ> «aο. «» ζ a^ >~ ' '

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

«ο ω Σ: CM "0— OC»-l o«-CV war o _icc 2 r>U l » »-· or» «^or MXO OUI Ul\«M » κ

çc χ CM

^ 3 <Λ ο: ^ f>» _ tO O CM c z uja.ee « ^ a >

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

c

PRESSURE*

E

47.480

t

2

S )

TEMP* 160,367

A S

COMP(i) C0MR(2)

C0MP(3) TOTAL

DISTILLATE DISTILLATE

C0MP(2) C0MP(3)

W

VARIABLES

S E C T ] t ON S E C T ] ION

STRIPPING SECTION

MOLES/HR

MOLES/HR MOLES/HR

MOLES/H" MOLES/HR

VAPOR-LIQUID FLOW STRIPPING V A P O R - L I Q U I O FLOW STRIPPING

C O M P ( i ) VAPOR-LIQIJIO F L 0

COMP(3) TOTAL

C0M»(2>

MOLES/HR MOLES/HR MOLES/HP MOLES/MR

MOLES/HR

TOTAL COMP(i)

MOLES/HR MOLES/HR

C0MP(3)

THE FOLLOWINS

COMP(l) COMP(2>

CALCULATED

FEED FEED

HAS

FEED FEED BOTTOMS BOTTOMS BOTTOMS BOTTOMS DISTILLATE DISTILLATE

PROGRAM

FINAL RESULTS FOLLOW

LIQ M/wR LIQ BTU/M VAPOR M/HR 6244,8645 777,9226 777,9222 432*.1252 130.7335 130.7 99 2207,3051 8,9337 49,5142 917,5858 5443553,7 95«,1704 MOLE FRACTION WATER (ENTRAINER FREE BASIS )

KTRAY»18 COMP PNTAN2 ETHNOL WATER TOTAL

A

f

1 BTU/M

N» 5

Vt I t V( 2) VI 3 ) V< 4) Vt 5) V( 6) VI 71 V( 8) V( 9 ) V(10> vttr> VU2) MOLES/HR v t t 3 T MOLES/HR VC14J MOLES/HR V<15l

0

16719.4820 21953.799 20369,4990 16885141,0

VAP

M»

16765 3520 21982,2030 20382,2610 17063895,0

)•

•

«ρ

•

a

•

4

•

•

Y

Y ,811883 ,ΐ3644ι ,031676 ,274701

.063966

,228631

.783370 ÎÏ67097 ,049333

Χ IÏ9) .847792 .142472 ,009736

,041106

x ue> ,818033 ,174487 ,007480

,1072*4

.049112

.00000000 ,24202000+03 .405813884-02 .28260159*03 .15005057.03 ,24201635*03 ,5ei81042-03 .24201705*03 .40584334-03 ,36526080*02 .40380475*02 .40384534*02 *.15005057.03 -,242W*35*03 ·.56181042.03

KNTRK10)» VP/THETA 42,8265 11,7269 4,9839

43 8322 12.2352 5,2050

KNTRL'( io VP/TMETA

Y ,797334 ,180731 .02Ï7Î3

.

«045485

,020595

r

.187079 ,008915

.342798 ,007208

X (Î7Î .643332 ,339151 ,017317

KNTRL<10)» 0

M» 3 N« 5 VAP BTU/M

0MP

8

KTRAY*17 PRESSURE» 47,620 TEMP. 162.i33 COMP VAPOR M/MR LIQ M/HR LIQ BTU/M PNTAN2 75?,29o5 750,2900 65o3 6753 ETHNOL 160.0411 160.0374 4540.*4524 WATER 47,4410 6,«606 2313,8971 TOT L 957,7726 9ι7,ϊβ„0 5622309,8 MOLE FRA TjON WAT R ( NTRAiNF.R F * E E B I

C

KTRAY=16 Vp/T&Et* 45,0731 trJW 5,4569

B

13,0792 3,5864

M« 3 Ν· 4 VAP TU/M 16819,1180 22015,40*0 20397,1830 18006621.0

τ υ / Μ

22031.7840 20404,5470 18229770.0

PRESSURE 47.760 TE^P" 164,203 VAPOR M/HR LIQ M/HR LIQ β PNTAN2 805,1856 «05,1857 6581,6141 ETHNOL 182,4605 424,4768 4604,3625 WATgR 21.9231 21.9236 2345.7019 TOTAL I00'i569i 1251.5862 7305293.0 MOLE FRACTION WATER (ENTRAINER FRE5 3ASIS)

NEXT TRAY IS FEED TRAY

0

FTHNOL 191.0646 433.1010 4579,5937 WATER 9,1057 9,ï 62 2382.9789 TOTAL 1021.4107 1263.4277 7528436.8 MOLE FRACTION WATER (ENTRAINER FREE BASIS)

ALPHA 1.269234 1.000000 Θ,934943

2,471473 1.OOOOOO 5.739363

ALPHA

2.327323 1,000000 5,714574

ALPHA

1.000000 5.695273

ί94$«9 ,93942*

TM1TA

THfT* ,994187 ,94ΐ370 .938201

TgfT* ,991*23 ,«44073 .939741

,943163 ,9*0408

Computer Output Page 1 1

GAMMA 1,100325 3,165983 «3,815821

£.322906 1,917384 23,876892

GAMMA

Ï.30Ô16* 1,968342 26,369356

GAMMA

1,989408 26,327143

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

Y

C

T

W

.0023

.0028

3*47,4417

FREE

BASIS)

PRESSURE" 49.580 TE^P» 234,%Q2 LlQ M/HR LÎQ BTU/M VAPOR M/HR 4.6852 4.6854 9783.6962 787,8411 1029,8574 7302,44Ï8 .0025 ,0031 3588,4516 792,5288 1034.5459 7566325.0

(ENTRAINER

R

T

COMP PNTAN2

KtRAY»

E

5

W

A

T

E

R

LÎQ BTU/M 73l8,o396

ΤΕ*1Ρ· 211.961

L I Q M/HR 268,0906

49,300

E

<ENT«AIN R F ^ E E ?ASJS)

VAPOR M/HR 268,0904

PRESSURE»

N

49,440 TEMP» 231,260 PRESSURE» VAPOR M/HR LIQ M/HR LIQ.BTU/M 39 8052 8858 3103 39 8050 961.5896 65lo!6443 719î5733 .0030 3241,9305 ,0024 759,3808 1001,3978,, 6613192.3

.. TOTAL MOL F * C i °

«AÎE»

KfRAY* 4 COMP PNTAN2 ETHNOL

MOLE FRACTION WATER (ENTRAINER FRE5 3ASIS)

E

KTRAY* 3 COMP PNTAN2 ETHNOL WAT R TOTAL

WATER

2

TE^Pf 234,558 PRESSURE" 49,720 LIQ M/HR LIQ BTU/M VAPOR M/HR 99 i,986i .5i39 1039,7254 7421,5674 797,7091 .0030 3639,4535 .0024 7721503,4 1040,2425 798.2254

MOLE FRACTION

TOTAL

WATER

ETHNOL

PNTAN2

COMP

KTRAY*

VAP BTU/M 18655,6430 23087,8140 2Q883.2230 18470220,0

,231020*02

VP/THETA ,98315**02 ,499997*02 .231712*02

2 BTU/M

N«

6

N»

8

Ρ VAP BTU/M 18059.58^0

Mi 3

7

N» 7

VAP BTU/M 18560 83*023035,3850 20859,2591) Ϊ7314512.0

M» 3

VAP BTU/M 18634,6530 23076,2360 20877,9290 18267766,0

Ml 2

l8646,5n8o 23082,7760 20680,9200 18422972,0

VAP

M»

20882,1670 18448765,0

VP/THETA ,787405*02

950046*02 .470586*02 .217125*02

.493110*02 .226336*02

HE

Vp/T TA

,496905*02 .230212*02"

VP/THETA .979429+Q2

Me 2 N» 5 PRESSURE* 49,860 ΤΕ*Φ* 234,748 VAPOR M/HR LIQ M/HR L I Q BTU/M VAP BTU/M VP/THETA 18651.4540 «98i42Î*Ô2 .0558 ,0559 9944,2387 .498567*02 799.1022 1041,H86 7440.7544 23085.5050

TOTAL 799,1602 1041,1773 7747273.7 MOLE FRACyI ON wAyER (ENJRAINER FREE 9ASI8)

WATER

KTRAY* 1 COMP PNTAN2 ETHNOL

REBOILER PRESSURE» 50.000 TEMP* 234,910 COMP VAPOR M/HR LIQ M/HR L I Q BTU/M PNTAN2 .0059 ,QQ61 9961,3993 ETHNOL 799.9920 1042.0083 7455.5545 WATER .0021 .0026 3653.9526 TOTAL 800,0000 1042,0170 7768820,1 MOLE FRACTION ATER (ENTRAINER FREE 9ASIS)

.10701400*08 .40584534*03 ,36526080*02 .40580475*02 ·1ΐ44ΐ642*θβ Computer Output Page 12

X .039750

,000003

Υ ,341087

.000003

Y 052418 ,947579 ,000003

,000003

,000003

,000003

Υ •000*44 ,999353 .000003

,000003

Υ .0059Ϊ2 .994085 .000003

.004529 ,995468 ,000003

ALPHA

ALPHA .119476*02 .100000*01 .111692*01

GAMMA

GAMMA .607608*01 .100000*01 .241012*01

THETA

THETA .114654*01 .999999-00 .983621-00

0

0

GAMMA .6 β47 *01 ,100000*01 .241138*01

ALPHA .425051*02

ALPHA 121590*02 !ίθΟΟΟΟ*01 ,112886*01

THETA 113705*01 .995459-00 .981333*00

Τ

THÇTA GAMMA .537254*01 .108614*01

GAMMA ,602307*01 .100006*01 .244678*01

Τ

4 6

THETA ·11 21*01 ,999943-00 .983646*00

GAMMA ΗΕ * ALPHA .1202*2*02 .6Q826I*01 ,1ΐ45ΐ9*οι .100000*01 .100000*01 .999483-00 ,111836*01 ,241516*01 ,983429*00

ALPHA .Ïl9933*02 ,100000*01 .111717*01

,000070 .419698*02 .6θβθ7ΐ*01 .114642*01 ,999927 ,100000*01 .100000*01 .999994*00 ,000003 ,111699*01 .241059*01 .983646·00

X •000*94 ,999503 .000003

,000003

.000003

:wm;ï

.000003

•000006 ,999992 •000003

Y

•000003

•000002 X

Y ,000007 ,999990 ,000003

•000001 ,999997 ,000002

X

L I Q U I D AND VAPOR COMPOSITIONS ARE FOR THE FLOWS FROM THE TRAY

MOLES/HR V U 9 > * BTU/HR v<20* "

MOLES/HR V(18) •

BTU/HR V U 6 > Ρ MOLES/HR v U 7 > *

VAPOR MOLES AND ENTHALPIES ARE FLOWS FROM THE TRAY LIQUID MOLES A N D ENTHALPIES APE FLOwS TO THE TRAY

w

w

HEAT FLOW STRIPPING Sç Tl| iN COMP(i) vAPOR-LIQijID FLO> REC-flFylNG S E C ON C0MP(2) VAPOR-LIQUID FLOW RECTIFYING SECT ON C0MP<3) VAPOR-LIQUID FLOW RECTIFYING SECT ON HEAT FLO RECTIF IN6 SECT ON

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

PRESSUSE* 49.160 TEMP- 178,640 VAPOR M/HR L I Q M/HR L Î Q BTU/M 656.3955 656,3956 6894,4,59i 294,4158 036,4321 4862,3906 .0022 .0028 2472,8385

T

p

3

WATER

PRESSURE»

46,980 TE^P» 167,474 LIT M/HR LIQ BTU/M «24,6642 6797,2936 445.9783 4782.Ï087 .0137 2433.4969 1270.5562 7737756,5 ( E N T R A I M R R F*E5 3A5IS)

E

A

KTRAYs i l PRESSURE* 48,460 TE^P* 16*.557 CONP V P0R M/HR LIO M/HR LIQ BTU/M PNTAN2 932.5859 «32.5860 6767.7421 ETHNOL 198,2818 440.2982 4757.7173 WAT R ,2240 .2246 2421.5060 τΟγΑΙ. 1031.09i7 1273.1Q97 7730Q85.3 MOLE FRACTION WATER (ENTRAINER FREE B A S I S )

8

TEMP* 166.766 KTRAYs 1 PRESSURE* 4 8 , 6 0 0 COMP VAPOR M/HR LIT M/HR LIQ BTU/M 832.4717 6777.2436 332.4716 ΡΝΤΔΜ2 440· 649 4765.5584 l9R,8485 ETHNOL 2425,3626 ,Οβ'Ο ,0877 WATER 7743044.8 1273.4248 103Î.4078 TOT ΑΙMOLE FRACTION WATER (ENTRAINER FREî IUSIS)

C

KTRAY=

9

FRACTION

?

PRESSURE VA 0R M/HR 924,6641 203.8620 .0131 102*».5392

2

48.740 TE^P« 167,009 0MP V A P O R M/HR LlQ M/HR L I Û BTU/M PNTAN2 631.2025 «31·2θ26 6786.5001 ETHNOL 199.9386 441.9550 4773.Ï986 WATER .0341 ,0347 2429.1187 TOTAL 1031,1753 1273,Î9?2 7750579.6 M O L E F R A C T I O N v'ATER ( E N T R A I N E R F R E ? 3ASIS )

MOLE

KTRAYs CûMP PNT AM2 ETWNOL WAT^R TOTAL

T

COMP PNTAN2 FTH-NOL W AT(:R 0 AL

49,020 TE'1P« 1 6 9 . 1 9 4 PRESSURE VA OR M/HH LIQ M/HR LIQ BTU/M 792.9419 6*17,9567 792.94?0 4799.1707 221,4156 463,4319 2441,8741 .0056 .0050 7430346.8 1256.37?5 1014.3625 MOLE FRACTION WATER (ENTRAINER F3E" 3ASIS)

KTRAYs

TOTAL 95Γ1.8135 1192,*3T5 7133842.3 MOLE FRACTION WATER (ENTRAINER F"*E5 3ASIS)

KtRAY» 6 COMP PNTAN2 ETHNOL WATER

A

ETHNOL 517,8967 759,9131 5213,8250 W TER .0020 ,0026 2642,8492 TOTAL 785,9892 1028,3062 5923958,0 MOLE FRAfeTÎON WATER (ENTRAINER F^ES SASIS)

7

BTU/M

N" 6

VP/THETA

r+656-13*ô2 .134698*02 ,576065*01

k BTU/M

A

N*

22053.0310 20414,1040 18431551,0

V P

2

! 5*78907*01

.467014*02

VP/THETA

.468633^02 •136104*02 * 3822*9*01

VP/THETA

VP/THETA ,*7I540*02 .137553*02 ,588661*01

I6880.257o

M*

20415,6010 18444509,0

22056.36oo

16885,6750

M* 2 N* 6 VAP BTU/M

l689i,99io 22060,2390 20417.3430 18452055,0

VAP

Mi 2

16904,077ο 22067,6550 20420.6820 1.8439207,0

M* 2 Ν· VAP B T U / M

M»

3 N" 3 VAP BTU/M VP/THETA 16948,7490 . 4 * 2 0 3 5 * 0 2 22095,0280 . 1 4 3 0 1 1 * 0 2 20432.999Q ι*429θθ*04 l833î659,o

17835185,0

VP/THETA

•5îl9nï*g2 ,175479*02 1759«T5ô*Ôi

BTU/M

VAP

N* "3

.536685*02 il*I6-U**02

i7i94.b**0 22244,0940 20500,1590

M« 3

22752i8710 20730,5130 Ï6625276.4

GAMMA

THETA

Computer Output Page 13

THETA

TH|TA

,0002p0

X .6537127 .346204 ,0000^9

.000078

lg

X .652849 .347 4 .000027

ALPHA

GAMMA

THETA

,00112e

Y «80748Q

,000441 GÀMMA

THETA

222373*01 .128557*01 .998403-00 .945640-00 ,960670-00

ALPHA

:Œi ·ΜΜΚ& 'Minm $w&

,807122 ,222596*01 .128637*01 .998423-00

Y

.000171

GAMMA

.000031

ALPHA

,8o6o73 .224776*01 .129Ï63*Q1 .998512-00 ,193894 ,100000*01 ,197856*01 ,945469-09 ,000033 .556344*01 .237304*02 .980537-00

X .64905* .350932 .oooojii

Y

,000064

CÂMMA

,000012

ALPHA

,801762 .236421*04 .131689*01 ,998997-00 .Î98205 ,100000*01 .l9o947*ôl ,945259*00 .000013 .532861*01 .237755*02 ,960357-00

Y

,000023

Y GAMMA THETA ALPHA .781714 ,292673*01 .144463*01 .100173*01 .218281 ,100000*01 ,166373*01 .944806-00 .000005 ,441599*01 ,171431*02 ,959835*00

,000007

ALPHA

63l956*01 .240146*01 .101820*01 100000*01 ,117350+01 ,947050-00 222579*01 ,603523*01 .959809-00

X .6311-33 .368863 .000004

,000009

X .55Q284 .449714 .000002

.000003

0

.69 35i ,309646 .000002

,000004

.000003

,26Q7^7 ,739211 ,000002

,658911 ,100000*01 .100477*01 .971859-00 ,000003 ,123329*01 ,275187*01 ,969674*00

,960247 ,000003

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

14

E

PRESSURE*

A

48.040

T

PRESSURE* V A P O R M/HR 821.2204 191,0846 9.1057 1021,4107

TEMP*

LlO M / H R «21.2205 433.1010 9.1062 1263.4277

47,900

B

A

S

I

S

>

LIQ BTU/M 6672.9946 4679.5937 2382.9789 7528436.8

165.227

M

MOLE

E

WAT R

0

75fi.29 5 160,0411 47,4410 957.7726

PRESSURE V A P O R M/HR

FRACTION

ETHNOL WATER TOT »

C

0MP PNTAN2

KTRfiY* 1 7

8

E

( N T R A I N R FREÎ

E

TE^P*

M/HR 75O.29Q0 Ϊ60.0374 6,8606 917.Î89Q

LiQ

47,620 B

T

U

/

M

3ASI8)

4540.4524 2313.8971 5622309.8

65o3,8753

LÎQ

162,133

KTRAY* 1 6 PRESSURE 47.760 TEMP* 1 6 4 . 2 0 3 COMP VAPOR M/HR L I Q M/HR L I Q BTU/M ΡΝΤΔΝ2 8 0 51856 8Q5 1857 6581,6141 ETHNOL 182'.4605 424,4768 4604.3625 WATER 21.9231 21.9?36 2345.7019 TOJAL 1009.5691 1251.5862 7305293.0 M O L E F R A C T I O N WATER ( E N T R A I N E R F R E 5 3 A S I S )

8

NEXT TRAY IS FEED TRAY

/

165.766

MOLE FRAC i0N wAyER (ENyRAINER FREE BASIS)

KTRAY* 1 5 COMP PNTAN2 ETHNOL WATER TOTAL

E

U

LIQ B 6742,1831 4736.6308 2411.1252 7685310.7

T

166,097

L T Q BTU/M 6718,2870 4716,9242 2401.4117 763435Q.7 BASIS)

TE^P*

V

L I Q M/HR V A P O R M/HR COMP 828,2290 92«.22B8 ΡΝΤΑΝ2 436,99&8 194,9825 THNOL 3.65*4 3.6558 WATER 1026.8671 1269.8842 TOTAL MOLE F R A C T I O N WATER ( E N T R A I N E R F R E E

KTRAY*

C

8

TE »P« 48 1 8 0 KTRAY* 1 3 PRESSURE 0MP V A P O R M/HR L I Q M/HR 3 L 1 0 0 6 PNT AN2 «31.100* 196,7734 ETHNOL 438,7897 1,4478 1.4493 WATER 1271,3308 1 0 29,3218 TOTAL M O L E F R A Q T I ON W A T R ( J T N T R A I N E R F & E E

E

48,320 TEMP* 1 6 6 , 3 4 3 PRESSURE* KTRAY* 1 2 V A P O R M/HR L I Q M/HR L I Q BTU/M COUP 332,2150 832.2152 PNTAM2 6756,8310 439.7081 197,6918 ETWNOL 4748,7144 .5708 .5703 WAT R 2417.0756 1272.4941 1030.4771 TOTAL 77i2565.2 MOLE F R A C T I O N ' M A T E R ( E N T R A I N E R F R E E B A S I S )

N» 6

3 BTU/M

N»

Ν* 4

3

,450731+02 ,127925+02 ,545688+01

VP/THETA

VP/THETA .457047*02 .130792+02 ,558635*01

M« 3

B

N* 5 VP/THFTA V A P TU/M 16765,3520 .438322+Q2 21982,2030 .122352+02 20382,2610 ,520498+01 17063895,0

ll8o

VAP BTU/M 1.6819 2 2 0 1 5 * . 40*0 20397,1830 18006621.0

Ma 3

16845.7060 22031.7840 20404.5470 18229770,0

VAP

M*

VP/THETA ,460426*02 .132332*02 .565557*01

7

V A P BTU/M

Ν»

VP/THETA

»462556*TJ2 ,133303*02 ,569»9û*0l

16859,718ο 22040,4060 20408.4250 1.8335807.0

Ms 2

V A P gTU/M 16868,30?0 22045,6850 20410,7990 18386810.0

Ma 2

VP/THETA

,464180*02 ,134043*02 ,573175*01

N« * BTU/M

VAP

16874,6930 22049,6130 20412.5660 l84i4Q4liO

Ma 2

GAMMA

THETA

THETA

THETA

THETA

GAMMA

^HPTA

,228651

ALPHA

,049112

0

,78337 .247i47*oi ,l3229l*oi .994il7*oo ,167097 ,100000+01 .191758*01 ,941578*00. ,049533 ,573936*01 .2387Q9*02 ,936204·00

X .«43332 ,339151 .017517

Y

,107264

GAMMA

,020593

ALPHA

797554 232732*01 ,130017+01 99*623*00 ,180731 ,100000*01 .196836+01 .944075*00 ,021715 .571457+01 .2*3*94+02 .959741*00

X .649994 ,342798 ,007208

Y

,045485

GAMMA

,008298

ALPHA

,804006 .226759+01 .129094+01 ,997709-00 ,187079 .100000+01 .198941+01 .945163*00 ,008915 ,569528+01 .265271+02 ,9*0408*00

X ,652722 .344396 .002882

Y

,018404

w

.003290

GAMMA

_ ,998133-00 ,806559 ,224263*01 ,128732+01 ,189881 ,100000*01 199722+01 ,945570·00 ,003360 .568041*01 ,2*5457+02 ,960652*00

ALPHA

Page l A

X .653721 .345140 ,001139 Y

Computer Output

,007304

ALPHA

.001296

0

,8 7425 .223160+01 .128596*01 .998324-00 .Ï9Ï168 ,100000*01 ,199956*01 ,945688*00 ,001407 ,566762*01 .265084*02 .960717*00

Y

,002876

Y ALPHA GAMMA THfTA «8076Q2 .222620*01 .126551*01 ,998385*00 ,191845 .100000*01 .199964*01 ,945688*00 ,000553 ,565548*01 ,264472*02 .960708*00

X «654003 ,345548 .000449

,000510

,653979 ,345845 ,000176

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

AND HEATER OR SU3C00LER

ι

Ν· 5 BTU/M

CALCULATIONS

16719,4820 21953.7990 20369,4990 I6883l4li0

VAP

Μ»

.041106

,818033 ,174487 ,007460

CYCLE NO 1

VP/THETA ,428265*02 .117269*62 ,498386*01 ,274701

CONDENSER

TOTAL HFAT HEAT LOAD

T

T

COMP PNTAN2 ETHNOL WATER 0 AL

PRODUCT OUT

PRODUCT M/HR .0004 .0037 40.5805 40.5845

ENTRAINER MAKE-UP · .40584534-03 M/UR

FRACTION OF AQUEOUS PHASE TO SATISFY WATER BALANCE » ,956^1*22-00

NO HEATER OR SUBCOOLER

FRACTION OF AQUEOUS PHASE · .059107 ,55574808*07 BTU/HR ,11327660+08 BTU/HR

VAPOR-LIQUID EQUILIBRIA FOR AQUEOUS PHASE PRESSURE" 44,814 TEMP" 154.450 COMP Χ Υ Κ ALPHA GAMMA THETA VP/THETA PNTAN2 ,001251 ,808692 .646451*03 ,148266*04 ,737158*03 ,98874-00 ,39300*02 ETHNOL .249871 .108946 .436007-00 .100000*01 , l 9 n 4 i * o i ,94295-00 .10222*02 WATER ,748878 ,082363 .109981*00 ,252247-00 ,114030*01 ,95940-00 ,43223*01

Computer Output Page 16

Computer Output Page 15

THETA GAMMA Y ALPHA ,811883 .126923+01 .1Ï0033+01 ,991243*00 ,136441 .100000*01 .3Ï6598+01 ,943219*00 ,051676 .883494+01 .658Ï58+02 ,959426*00

VAPOR-LIQUIO EQUILIBRIA FOR ORGANIC PHASE PRESSURE- 44,815 TEMP* 154,450 COMP Χ Υ Κ ALPHA GAMMA THETA VP/THETA PNTAN2 .876890 .«C8694 .922230-00 .975464*00 ,105166+01 ,98874-00 ,39300*02 ETHNOL .115232 .108944 .945427-00 .100000*01 .414479*01 ,94295-00 ,10222*02 WATER .007878 .082362 .104550-02 .110584*02 ,108402*03 ,95940-00 ,43223*01

ACCUMULATOR

ACCUMULATOR

,480 TEMP* 160.367 PRESSURE» L I Q M/HR L I Q BTU/M VAPOR M/HR 777,9222 6244.8645 777,9226 130.7299 4328,Ϊ252 130.7335 ETHNOL 8,9337 2207.3051 49,5142 WATER 9!7.5858 5443553.7 958.1704 TOTAL MOLE FRACTION WATER (ENTRAINER FREE BASIS)

Α

ΡΝΤ Ν2

KTRAYs ΐβ COMP

84

E X T R A C T I V E

Table II.

A N D

A Z E O T R O P I C

DISTILLATION

Column Profiles in Azeotropic Distillation Dehydration of Aqueous Ethanol Using n-Pentane as Entraîner

Tray No. (Equil.) 18 17 16" 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 Reboiler

t, °F 160.37 162.13 164.20 165.23 165.77 166.10 166.34 166.56 166.77 167.01 167.47 169.19 178.64 211.96 231.26 234.10 234.56 234.75 234.91

Pressure, psia

Fraction Pentane in Liquid

Fraction Water in Vapor (Pentane-Free)

Fraction Ethanol in Liquid

47.48 47.62 47.76 47.90 48.04 48.18 48.32 48.46 48.60 48.74 48.88 49.02 49.16 49.30 49.44 49.58 49.72 49.86 50.00

0.818 0.643 0.650 0.653 0.654 0.654 0.654 0.654 0.653 0.649 0.631 0.550 0.261 0.040 0.0045 0.00049 0.00005 0.000006 0.000001

0.275 0.229 0.107 0.045 0.018 0.0073 0.0029 0.0011 0.00044 0.00017 0.000064 0.000023 0.000007 0.000004 0.000003 0.000003 0.000003 0.000003 0.000003

0.175 0.339 0.343 0.344 0.345 0.346 0.346 0.346 0.347 0.351 0.369 0.450 0.739 0.960 0.996 0.9995 0.99994 0.999992 0.999997

B o t t o m Product, M o l e fraction ethanol — M o l e fraction water — M o l e f r a c t i o n pentane =

0.99999706 0.00000232 0.00000062

Stripped Water Product, M o l e fraction water = M o l e fraction ethanol = M o l e f r a c t i o n pentane =

0.99999 0.000009 0.000001

Feed, 8 5 . 6 4 % m ethanol, 14.36%m water a

Tray No. 16 is the feed tray.

T h e t e m p e r a t u r e profile is most c l e a r l y seen i n F i g u r e 1. T h e t e m p e r a t u r e changes s l i g h t l y f r o m the r e b o i l e r u p a f e w trays; t h e n i t drops r a p i d l y for a b o u t three trays.

A f t e r this it d r o p s o n l y five degrees i n

the next n i n e trays a n d s l o w l y drops another f o u r degrees f r o m the f e e d to the t o p tray. T h e b e h a v i o r of the t e m p e r a t u r e profile is e x p l a i n e d w h e n the c o m p o s i t i o n profiles of F i g u r e 2 are e x a m i n e d . I n the first f e w trays n e a r the r e b o i l e r , the c o n c e n t r a t i o n of e t h a n o l i n the l i q u i d is h i g h , a b o v e 99 m o l e % . F r o m tray 4 to tray 7 the e t h a n o l c o n c e n t r a t i o n d r o p s 99.6-45.0 m o l e

%.

In

this

same

region

the

pentane

from

concentration

increases f r o m a p p r o x i m a t e l y 0.5-55.0 m o l e % . T h e w a t e r c o n c e n t r a t i o n ,

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

GOLDiNG,

B L A C K ,

160 Figure 1.

Computer Calculations

A N D DITSLER

200 TEMPERATURE, °F

240

Temperature profile for 50 psia column dehydration of aqueous ethanol using n-pentane n-pentane-to-ethanol ratio 3.22 (mole basis)

20 TOP ENTRAINER "IN LIQUID

FEED 16

3

><

/WATER IN Γ VAPOR 12 (ENTRAIN ER FREE) 8

ETHANOL IN LIQUID

—

4 0 0 Figure

.

1

20

.

1

.

1

40 60 MOLE, %

1

1

80

2. Composition profiles in 50 psia column dration of aqueous ethanol using n-pentane

.

100 dehy

n-pentane-to-ethanol ratio 3.22 (mole basis)

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

86

E X T R A C T I V E

A N D

A Z E O T R O P I C

DISTILLATION

100

TRAYS Figure

3.

Relative

volatility profiles in 50 psia column aqueous ethanol using n-pentane n-pentane-to-ethanol ratio 3.22 (mole basis)

dehydration

of

w h i c h is l o w , begins to increase. F r o m t r a y 8 t o t r a y 17 w a t e r c o n t i n u e s to b u i l d u p i n the v a p o r o n a pentane-free basis. O v e r this r e g i o n the c o n c e n t r a t i o n o f p e n t a n e i n t h e l i q u i d is n e a r l y constant w h i l e the e t h a n o l c o n c e n t r a t i o n decreases s l o w l y .

O n the t o p t w o trays p e n t a n e increases

a n d e t h a n o l decreases i n the l i q u i d w h i l e w a t e r continues to b u i l d u p i n the v a p o r . F i g u r e 3 gives the r e l a t i v e v o l a t i l i t y profiles also for the s a m p l e c o l u m n c a l c u l a t i o n ; these c o r r e s p o n d to the t e m p e r a t u r e a n d c o m p o s i t i o n profiles of F i g u r e s 1 a n d 2.

Pentane is easily s e p a r a t e d f r o m

ethanol

w h i l e w a t e r is not as r e a d i l y separated i n the b o t t o m of the c o l u m n , r e b o i l e r to t r a y 5.

T h e p e n t a n e v o l a t i l i t y decreases a n d that of

water

increases r a p i d l y , r e l a t i v e to ethanol, o n p r o c e e d i n g f r o m tray 5 to 8. T h e y r e m a i n n e a r l y constant for the next n i n e trays w h e r e the s e p a r a t i o n of w a t e r r e l a t i v e to e t h a n o l is f a v o r a b l e ; t h e s e p a r a t i o n of p e n t a n e relative to e t h a n o l is s t i l l f a v o r a b l e i n this r e g i o n . O n the t o p t r a y c o n d i t i o n s are f a v o r a b l e for s e p a r a t i n g w a t e r , b u t for s e p a r a t i n g p e n t a n e t h e y are less favorable. It becomes difficult to r e m o v e e t h a n o l f r o m the t o p p r o d u c t .

For

t h e c o n d i t i o n s o f this s a m p l e c a l c u l a t i o n , t h e r e d u c t i o n of e t h a n o l i n the o v e r h e a d vapors b e l o w a b o u t 13.5 m o l e % is a c c o m p a n i e d b y a b u i l d i n g

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

5.

B L A C K ,

GOLDING,

A N D

DITSLER

Computer

87

Calcuhtions

u p of w a t e r i n t h e o v e r h e a d vapors a n d a t e n d e n c y to f o r m a s e c o n d l i q u i d phase i n the top of the c o l u m n . T h e effect o n tray r e q u i r e m e n t s of c h a n g i n g the n-pentane-to-ethanol r a t i o is s h o w n i n F i g u r e 4. T h e w a t e r content of the b o t t o m p r o d u c t , e t h a n o l , is s h o w n vs. this r a t i o i n F i g u r e 5. W i t h n-pentane as entraîner the w a t e r content of the e t h a n o l p r o d u c t is r e d u c e d b e l o w ten p p m , o n a m o l e basis. Comparison of Entrainers T h e c h o i c e of a n entraîner u s e d to m a k e a d e s i r e d separation i n a n a z e o t r o p i c d i s t i l l a t i o n d e p e n d s o n the b i n a r y m i x t u r e b e i n g separated a n d the n o n i d e a l i t i e s of these c o m p o n e n t s w i t h the a d d e d entraîner. several different final

While

entrainers m i g h t b e u s e d to p r o v i d e a separation, the

selection m a y d e p e n d o n the r e q u i r e d p u r i t y of the p r o d u c t .

several entrainers c a n p r o d u c e a p r o d u c t of d e s i r e d p u r i t y , the

If final

c h o i c e m a y d e p e n d o n a n e c o n o m i c e v a l u a t i o n of the several schemes. F o r the a z e o t r o p i c

d e h y d r a t i o n of aqueous e t h a n o l m i x t u r e s a p -

p r o a c h i n g the constant b o i l i n g m i x t u r e , a b r i e f c o m p a r i s o n is s h o w n for the entrainers, n-pentane, benzene, a n d d i e t h y l ether. S i n c e w a t e r is most n o n - i d e a l i n n-pentane, the driest e t h a n o l is e x p e c t e d to b e p r o d u c e d i f n-pentane is u s e d .

8

12

16

20

TRAYS

Figure

4.

Effect of changing the n-pentane-to-ethanol basis) on trays required

ratio (mole

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

E X T R A C T I V E

^1 0

A N D

A Z E O T R O P I C

DISTILLATION

I ι I ι I I 2 4 6 MOLE FRACTION WATER IN BOTTOM PRODUCT, χ 10 1

6

5. Fraction

Figure

water in bottom product ethanol vs. to-ethanol ratio (mole basis)

n-pentane-

DIETHYL ETHER 135 psia

Τ 1

\ BENZENE \

14.7 psia

" \ PENTANE 50 psia

0

ι

ι , I L 1 40 80 120 MOLE FRACTION WATER IN BOTTOM PRODUCT, χ 10 LZ

6

Figure

6. Comparing entrainers, n-pentane, benzene, ether, for water content of ethanol product

and diethyl

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

5.

B L A C K ,

GOLDiNG,

A N D

DITSLER

Computer

89

Calculations

C a l c u l a t i o n s h a v e b e e n m a d e u s i n g the a u t o m a t e d feature o f the A z e o t r o p i c D i s t i l l a t i o n P r o g r a m A D P / A D P L L E . T h e same m o l e fract i o n o f entraîner i n the e t h a n o l p r o d u c t , 0.62 Χ 1 0 c a l c u l a t i o n s i n v o l v i n g e a c h entraîner.

- 6

has b e e n u s e d i n

U s i n g n-pentane, the

azeotropic

d i s t i l l a t i o n w a s c a l c u l a t e d for a c o l u m n w i t h a r e b o i l e r at 50 p s i a .

The

c o r r e s p o n d i n g pressures w e r e 14.7 p s i a a n d 135 p s i a for cases i n v o l v i n g b e n z e n e a n d d i e t h y l ether, r e s p e c t i v e l y . C a l c u l a t i o n s w e r e m a d e also at h i g h e r pressures for cases u s i n g n-pentane a n d benzene.

A l t h o u g h the

a b o v e pressures are n o t necessarily the o p t i m u m for e a c h solvent, c o m parisons h a v e b e e n m a d e for the three cases as i n d i c a t e d .

MILLIONS BTU/UNIT TIME Figure

7. Comparing the entrainers, n-pentane, benzene, and diethyl ether, for reboiler and condenser loads in dehydrating aqueous ethanol Condenser loads, heat removed, btu/unit time Reboiler loads, heat added, btu/unit time

T h e c a l c u l a t e d results, c o m p a r i n g t h e w a t e r content o f the e t h a n o l p r o d u c t for the entrainers, n-pentane, b e n z e n e , a n d d i e t h y l ether, are s h o w n i n F i g u r e 6. T h e m o l e f r a c t i o n w a t e r i n the e t h a n o l p r o d u c t i s p l o t t e d vs. t h e e n t r a i n e r - t o - e t h a n o l r a t i o , o n a m o l e basis. n - P e n t a n e p r o duces e t h a n o l o f lowest w a t e r content; b e n z e n e comes next, a n d d i e t h y l ether comes last. E n t r a i n e r - t o - e t h a n o l ratios o f 2.5-3.5, m o l e basis, are a d e q u a t e w h e n n-pentane o r b e n z e n e is u s e d ; for d i e t h y l ether, the r a t i o m u s t b e a b o v e four. C o n d e n s e r a n d r e b o i l e r loads are c o m p a r e d for the same three e n trainers i n F i g u r e 7. F o r d i e t h y l ether-to-ethanol ratios o f a b o u t 4.2, the

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

90

E X T R A C T I V E

A N D

A Z E O T R O P I C

DISTILLATION

DEE 135 p s ^ a ^ ^ ^ ^

PENTANE / 50 psia /

-

/

BENZENE 14.7 psia

'

1 1 1 1 16 24 32 40 MAXIMUM FLOW IN COLUMN, IN MOLES, χ 10" 2

Figure 8. Comparison of maximum flows on any tray for entrainers, n-pentane, benzene, and diethyl ether, in dehydrating aqueous ethanol by azeotropic distillation

\

1

DLETHYL\

-

1

\

1 !^ 3

ETHER

^ 135 psia

—

BENZENE

\ 14.7 psia

—

\N-PENTANE

L _

\

50 psia

I

.

20

TRAYS,

I

\

.

40

1 60

EQUILIBRIUM

Figure 9. Comparing tray requirements for the entrainers, n-pen tane, benzene, and diethyl ether, in dehydrating aqueous ethanol by azeotropic distillation

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

5.

B L A C K ,

GOLDiNG,

A N D

DITSLER

Computer

91

Calculations

condenser a n d r e b o i l e r loads c o m p a r e f a v o r a b l y w i t h those for

benzene-

to-ethanol ratios of a b o u t 3, m o l e basis. A t the h i g h e r r a t i o , heat loads w i t h n-pentane are a b o u t 8 0 % of those for d i e t h y l ether. A t the l o w r a t i o of a b o u t 3, the heat loads w i t h n-pentane are o n l y 6 0 % of those

for

benzene. T h e m a x i m u m flow o n a n y t r a y i n the c o l u m n is c o m p a r e d for the three entrainers, n-pentane, benzene, a n d d i e t h y l ether, i n F i g u r e 8.

At

the h i g h entrainer-to-ethanol r a t i o of 4.2, the m a x i m u m flow w h e n n pentane is u s e d is a b o u t 7 0 % of that for the case u s i n g d i e t h y l ether. F o r the l o w ratio of a b o u t 3, the flows w i t h n-pentane are a b o u t 7 5 % of those u s i n g benzene.

A s m a l l e r d i a m e t e r c o l u m n is r e q u i r e d w i t h n -

p e n t a n e t h a n w i t h either of the other entrainers. T o t a l tray r e q u i r e m e n t s for the three entrainers are c o m p a r e d i n F i g u r e 9. T h e least n u m b e r of trays is r e q u i r e d w h e n n-pentane is u s e d ; the most are r e q u i r e d w h e n d i e t h y l ether is the entraîner. If b e n z e n e is u s e d as entraîner at h i g h e r pressure t h a n 14.7 p s i a , the c o r r e s p o n d i n g c u r v e i n F i g u r e 9 is shifted to the r i g h t , m o r e trays b e i n g r e q u i r e d . The

c o m p u t e r p r o g r a m for

azeotropic

distillation A D P / A D P L L E

makes possible not o n l y a c o m p a r i s o n of entrainers for a separation b u t also gives results of a q u a l i t y r e q u i r e d for a c t u a l d e s i g n c a l c u l a t i o n s . Acknowledgment S o m e of the u t i l i t y subroutines d e s c r i b e d here w e r e d e s i g n e d

after

a g e n e r a l system of u t i l i t y - s u b r o u t i n e p r o g r a m m i n g d e v e l o p e d b y H . W . B r o u g h of S h e l l C h e m i c a l C o m p a n y .

W e also w i s h to a c k n o w l e d g e

s u p p o r t of E . G . F o s t e r a n d L . J . T i c h a c e k i n f a c i l i t a t i n g this w o r k . List

of

Symbols

OLi

v a n der W a a l s a t t r a c t i o n constant for c o m p o n e n t i

bi

v a n der W a a l s c o v o l u m e for c o m p o n e n t i

fi

f u g a c i t y of c o m p o n e n t i i n vapor-phase m i x t u r e

v

0.5

P* Ρ Pi° w w

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

the

92

E X T R A C T I V E

A N D AZEOTROPIC

DISTILLATION

Xi

t o t a l l i q u i d c o m p o s i t i o n i n r e g i o n o f t w o l i q u i d phases

Xi

l i q u i d c o m p o s i t i o n , m o l e f r a c t i o n , p o l a r phase

tji

l i q u i d c o m p o s i t i o n , m o l e f r a c t i o n , n o n p o l a r phase

Yi

vapor composition, mole fraction component i

an

v o l a t i l i t y o f c o m p o n e n t i relative to c o m p o n e n t /

ji

l i q u i d - p h a s e a c t i v i t y coefficient, p o l a r p h a s e

Yi

l i q u i d - p h a s e a c t i v i t y coefficient, n o n p o l a r phase

&a

b i n a r y v a p o r i n t e r a c t i o n coefficient

6i

imperfection-pressure

£°

n o n p o l a r p a r t o f the m o l e c u l a r attractive coefficient at zero pressure

(° ί°

p o l a r p a r t o f the m o l e c u l a r a t t r a c t i o n coefficient at zero pressure $ έ° + é°> the l i m i t i n g v a l u e o f the m o l e c u l a r a t t r a c t i o n coefficient at zero pressure

i°

f u g a c i t y coefficient f o r c o m p o n e n t i at saturation pressure Pi°

φί

fugacity coefficient f o r c o m p o n e n t i i n a v a p o r pressure

coefficient

Literature Cited 1. Gerster, J. Α., Chem. Eng. Progr. (1969) 65 (9), 43. 2. Hoffman, E. S., "Azeotropic and Extractive Distillation," Wiley, New York, 1964. 3. Robinson, C. S., Gilliland, E. R., "Elements of Fractional Distillation," p. 312, McGraw-Hill, New York, 1950. 4. Black, C., Ind. Eng. Chem. (1958) 50, 391. 5. Black, C., Ind. Eng. Chem. (1958) 50, 403. 6. Black, C., A.I.Ch.E. J. (1959) 5 (2), 251. 7. Black, C., Ind. Eng. Chem. (1959) 51, 211. 8. Black, C., Derr, E. L., Papadopoulos, M. N., Ind. Eng. Chem. (1963) 55 (9), 38. 9. Null, H. R., Palmer, D. Α., Chem. Eng. Progr. (1969.) 65 (9), 47. 10. Yamada, I., S. Hidezumi, A. Kanji Kagaku Kogaku (1967) 31, 395-398. 11. Berg, L., Chem. Eng. Progr. (1969) 65, (9), 53. RECEIVED November 24, 1970.

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

6 Prediction of Isobaric Vapor-Liquid Equilibrium Data for Mixtures of Water and Simple Alcohols A. ANDIAPPAN and A. Y. McLEAN Annamalainagas University, Tamifnedu, India and Nova Scotia Technical College, Halifax, Nova Scotia

The Non-Random, Two Liquid Equation was used in an attempt to develop a method for predicting isobaric vapor– liquid equilibrium data for multicomponent systems of water and simple alcohols—i.e., ethanol, 1-propanol, 2-methyl-1propanol (2-butanol), and 3-methyl-1-butanol (isoamyl alcohol). Methods were developed to obtain binary equilibrium data indirectly from boiling point measurements. The binary data were used in the Non-Random, Two Liquid Equation to predict vapor-liquid equilibrium data for the ternary mixtures, water-ethanol-1-propanol, water—ethanol-2-methyl1-propanol, and water-ethanol-3-methyl-1-butanol. Equilibrium data for these systems are reported.

/

T p h e d e s i g n of a z e o t r o p i c o r extractive d i s t i l l a t i o n c o l u m n s , as w i t h c o n A

v e n t i o n a l c o l u m n s , d e m a n d s a k n o w l e d g e of the v a p o r - l i q u i d e q u i l i b -

r i u m p r o p e r t i e s o f the system to b e d i s t i l l e d . S u c h k n o w l e d g e is o b t a i n e d e x p e r i m e n t a l l y o r c a l c u l a t e d f r o m o t h e r properties of the c o m p o n e n t s o f the system.

S i n c e the systems i n a z e o t r o p i c o r e x t r a c t i v e d i s t i l l a t i o n

processes h a v e at least three c o m p o n e n t s , d i r e c t m e a s u r e m e n t

of t h e

e q u i l i b r i u m p r o p e r t i e s is l a b o r i o u s a n d , therefore, expensive, so m e t h o d s of c a l c u l a t i o n o f these d a t a are d e s i r a b l e . F o r a z e o t r o p i c d i s t i l l a t i o n e s p e c i a l l y the systems are n o n - i d e a l w h i c h makes c a l c u l a t i n g v a p o r - l i q u i d e q u i l i b r i u m p r o p e r t i e s m o r e difficult t h a n , for e x a m p l e , i n d i s t i l l a t i o n of m i x t u r e s of s i m p l e h y d r o c a r b o n s . W o r k p r e d i c t i n g the v a p o r - l i q u i d e q u i l i b r i u m properties of t e r n a r y m i x t u r e s o f 93 In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

94

E X T R A C T I V E

A N D

A Z E O T R O P I C

DISTILLATION

water, e t h a n o l , a n d o n e of the s i m p l e alcohols—i.e., 1-propanol, 2 - m e t h y l 1-propanol, 3 - m e t h y l - l - b u t a n o l , ( a l l f o r m b i n a r y azeotropes w i t h w a t e r ) — i s p r e s e n t e d here. A q u e o u s solutions of these alcohols o c c u r w h e n sugar solutions are fermented

a n d m a y b e separated b y d i s t i l l i n g t h e m i x t u r e s .

It is a

c o m m o n , e c o n o m i c a l l y v a l u a b l e process for m a n u f a c t u r i n g p o t a b l e l i q u o r s a n d for p r o d u c i n g i n d u s t r i a l a l c o h o l f r o m f e r m e n t e d molasses solutions o r p u l p m i l l wastes.

O n e of the authors ( A . Y . M . ) reports t h a t d e s i g n

a n d o p e r a t i o n of these c o l u m n s is h a m p e r e d b y l a c k of v a p o r - l i q u i d e q u i l i b r i u m d a t a , e s p e c i a l l y for m a k i n g p o t a b l e l i q u o r s , w h e r e

small

a m o u n t s of t h e alcohols other t h a n e t h a n o l greatly affect the flavor a n d , therefore, the p r o d u c t ' s m a r k e t a b i l i t y . Prediction of Vapor—Liquid Equilibrium

Data

A system c o n s i s t i n g of a l i q u i d m i x t u r e a n d v a p o r is i n e q u i l i b r i u m if, for a n y c o m p o n e n t i, the fugacities i n the v a p o r a n d l i q u i d phases, fi

Y

a n d /i

L

are e q u a l .

/i = /, V

(1)

L

A s the fugacities are not i n themselves q u a n t i t i e s w h i c h are easily estab l i s h e d e x p e r i m e n t a l l y , i t is necessary to relate t h e m to easily d e t e r m i n a b l e quantities—e.g., t e m p e r a t u r e , pressure, a n d c o m p o s i t i o n .

T h i s is d o n e

b y i n t r o d u c i n g the f u g a c i t y a n d a c t i v i t y coefficients Φ* a n d y ι w h i c h are defined as f o l l o w s ,

w h e r e y is t h e c o m p o s i t i o n o f c o m p o n e n t f i n t h e v a p o r phase, Ρ is the {

t o t a l pressure of t h e system, x is t h e c o m p o s i t i o n of c o m p o n e n t i i n the {

l i q u i d phase, a n d

fi

0L

is the f u g a c i t y of c o m p o n e n t i i n the l i q u i d at a

reference state. T h i s reference state is the f u g a c i t y of p u r e l i q u i d i at the t e m p e r a t u r e a n d pressure of t h e system. E q u a t i o n 1 t h e n becomes Φ-ϊ^Ρ

=

JiXiU

(3)

0lj

A t c o n d i t i o n s w h e n it is safe to assume t h a t t h e gas p h a s e w i l l b e h a v e i n a n ideal manner—i.e.,

at l o w

pressure w i t h a l l c o m p o n e n t s

con

densable—

«^land/^^P, Pi

s

8

is t h e v a p o r pressure of p u r e l i q u i d i at t h e t e m p e r a t u r e o f t h e system,

a n d e q u i l i b r i u m is d e s c r i b e d b y the e q u a t i o n , yP

— ytiPi*

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

(4)

6.

ANDiAPPAN

A N D M C L E A N

Isobaric Vapor-Liquid

Equilibrium

95

A t c o n d i t i o n s w h e r e i t is i n c o r r e c t t o assume i d e a l b e h a v i o r f o r t h e gas a n d /i

phase, et al.

are calculated b y procedures described b y Prausnitz

0L

(1).

T h e calculation of y

i9

t h e a c t i v i t y coefficient, establishes γ* as a f u n c

t i o n of c o m p o s i t i o n , as w e l l as t e m p e r a t u r e a n d pressure. T h i s is d o n e b y r e l a t i n g γ* t o t h e excess G i b b s energy G , — L e . , b y t h e e q u a t i o n E

a n d expressing G

E

o r g , t h e m o l a r excess G i b b s energy, i n terms of E

composition. T h e p r o b l e m o f expressing t h e excess G i b b s energy as a f u n c t i o n o f c o m p o s i t i o n has b e e n researched extensively, a n d m a n y m e t h o d s of v a r y i n g a c c u r a c y a n d usefulness h a v e b e e n p r o p o s e d . A n extensive d i s c u s s i o n of these m e t h o d s is g i v e n b y H a l a et al. (2), m o n expressions—e.g.,

w h o s h o w that m a n y c o m

those o f v a n L a a r a n d M a r g u l e s — a r e

f r o m t h e g e n e r a l expression of W o h l C u k o r a n d P r a u s n i t z (4),

deduced

(3).

h o w e v e r , p o i n t o u t that W o h l ' s

expression p r e c l u d e s other expressions f o r t h e c o m p o s i t i o n

general

dependence

of t h e excess free energy, i n c l u d i n g that o f W i l s o n ( 5 ) , w h i c h has b e e n u s e d b y several authors t o p r e d i c t a n d correlate v a p o r - l i q u i d e q u i l i b r i u m W i l s o n s equation and the modification proposed b y Renon and

(1,6,7).

P r a u s n i t z (8)

u s e t h e l o c a l m o l e f r a c t i o n concept, p r o d u c e d

because

molecules i n s o l u t i o n aggregate as a result o f t h e v a r i a t i o n i n i n t e r m o l e c u l a r forces.

T h e l o c a l m o l e f r a c t i o n c o n c e p t results i n a m o r e u s e f u l

d e s c r i p t i o n o f t h e b e h a v i o r of m o l e c u l e s i n a n o n - i d e a l m i x t u r e . The Wilson Equation and the Two-Liquid

(NRTL)

Non-Random

Equation

T h e W i l s o n e q u a t i o n , u s e d b y P r a u s n i t z et al. (1) (6,7),

a n d other w o r k e r s

equals or surpasses earlier t w o - p a r a m e t e r equations i n c o r r e l a t i n g

v a p o r - l i q u i d e q u i l i b r i u m d a t a f o r a large n u m b e r of n o n - i d e a l systems. T h e e q u a t i o n w h i c h is sufficiently d i s c u s s e d elsewhere

( J ) contains t w o

adjustable parameters p e r b i n a r y a n d p r e d i c t s m u l t i c o m p o n e n t e q u i l i b r i u m d a t a u s i n g t h e b i n a r y parameters only. N o m u l t i c o m p o n e n t e x p e r i m e n t a l d a t a are necessary as f o r t h e v a n L a a r t y p e e q u a t i o n s o f t h i r d o r d e r a n d above. O n e l i m i t a t i o n of t h e W i l s o n e q u a t i o n has b e e n that i t c a n n o t b e a p p l i e d t o systems w h e r e t h e n o n - i d e a l i t y is s u c h that t w o l i q u i d phases are

formed—e.g.,

water-2-methyl-l-propanol

and

water-3-methyl-l-

butanol.

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

96

E X T R A C T I V E

A N D A Z E O T R O P I C

DISTILLATION

R e n o n a n d P r a u s n i t z ( 8 ) p r o p o s e d a n o t h e r e q u a t i o n , b a s e d also o n the l o c a l m o l e f r a c t i o n c o n c e p t , w h i c h w o u l d a v o i d this l i m i t a t i o n a n d c o u l d b e a p p l i e d to partially miscible mixtures. T h e relationship between a c t i v i t y coefficient a n d l i q u i d p h a s e c o m p o s i t i o n is g i v e n b y t h e e q u a t i o n Ν

/

i n y ^ i f ^ 2

+ t ^ ^ K - i ^ M ^

Gx ki

'

k

k-\

where Ν =

(ëa

Ν

=

2 Gx

1

kj

k

k=l

I

2

\

k=l

1

)

)

(5

GjcjXk

number of components

~~ ëu) is t h e adjustable p a r a m e t e r ( t w o p e r b i n a r y ) s i m i l a r t o that

contained i n the W i l s o n equation.

is a n e m p i r i c a l non-randomness

parameter. R e n o n a n d P r a u s n i t z ( 8 ) r e c o m m e n d values o f

f o r v a r i o u s classes

of m i x t u r e s . I f these v a l u e s a r e v a l i d t h e n E q u a t i o n 5 has o n l y t w o a d justable p a r a m e t e r s p e r b i n a r y .

T h e N R T L e q u a t i o n w a s u s e d i n this

work. Experimental T o test t h e N R T L

equation for predicting V L E data for ternary

mixtures, experimental data for the ternary mixtures a n d for the binary c o m p o n e n t s o f t h e m i x t u r e s a r e necessary.

A literature survey

showed

t h a t d a t a w e r e n o t r e a d i l y a v a i l a b l e f o r a n y o f t h e ternaries o r f o r t h e two binaries ethanol-3-methyl-l-propanol a n d 3-methyl-l-butanol-water, a n d i t w a s therefore necessary to o b t a i n these d a t a e x p e r i m e n t a l l y . T h e direct measurement of v a p o r - l i q u i d e q u i l i b r i u m data for part i a l l y m i s c i b l e m i x t u r e s s u c h as 3 - m e t h y l - l - b u t a n o l - w a t e r is difficult, a n d a l t h o u g h stills h a v e b e e n d e s i g n e d f o r this p u r p o s e (9, 10), t h e d a t a w a s i n d i r e c t l y o b t a i n e d f r o m measurements

o f pressure, P , t e m p e r a t u r e , t,

a n d l i q u i d c o m p o s i t i o n , x. I t w a s also felt that a test o f t h e v a l i d i t y o f the N R T L

equation i n predicting the V L E data for the ternary mix-

tures w o u l d b e t h e successful p r e d i c t i o n o f t h e b o i l i n g p o i n t . T h i s e l i m inates

the complicated

analytical procedures

necessary

i n the direct

measurement of ternary V L E data. A modified version of the M-100 b o i l i n g point apparatus, made b y the James F . S c a n l o n C o . , W h i t t i e r , C a l i f , w a s u s e d ; t e m p e r a t u r e w a s measured b y a H e w l e t t - P a c k a r d m o d e l 2801A quartz thermometer. A l l measurements w e r e m a d e at a t m o s p h e r i c pressure w i t h t h e t e m p e r a t u r e c o r r e c t e d t h e n t o 760 m m H g .

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

6.

ANDiAPPAN

A N D

Isobaric Vapor-Liquid

M C L E A N

T a b l e I.

Equilibrium

97

F u g a c i t y Coefficients

Component

Temperature,

°C

Φ,

Water

80 90 130 100

0.9925 0.9960 1.0150 1.0000

Ethanol

80 90 100

1.0015 1.0119 1.0240

1-Propanol

80 90 100

0.9898 0.9954 1.0018

2-Methyl-l-propanol

80 90 100

0.9726 0.9809 0.9904

3-Methyl-l-butanol

80 90 100 130

0.9535 0.9608 0.9686 C.9991

T o extract y f r o m P, t, x, d a t a o b t a i n e d for the b i n a r y system, a c o m p u t e r p r o g r a m u s i n g the N R T L e q u a t i o n w a s p r e p a r e d . U p o n re c e i v i n g the i n p u t data—i.e., P, x 1 a n d a v a l u e of a, u s u a l l y a r o u n d 0.475 — v a l u e s of the adjustable parameters (gi2-g22) a n d ( g 2 i - g n ) w e r e as s u m e d . T h e a c t i v i t y coefficients w e r e c a l c u l a t e d u s i n g E q u a t i o n 5 a n d values of y w e r e c a l c u l a t e d u s i n g E q u a t i o n 4. T o justify u s i n g E q u a t i o n 4, values of the f u g a c i t y coefficients w e r e c a l c u l a t e d . T h e s e values ( T a b l e I ) are b e l i e v e d sufficiently near u n i t y to p e r m i t that the effects of gas p h a s e n o n i d e a l i t y c a n b e i g n o r e d . T h e s u m of t/i a n d y w a s c o m p a r e d w i t h u n i t y , a n d the p r o c e d u r e w a s r e p e a t e d u n t i l s u m y w a s w i t h i n a g r e e d l i m i t s of u n i t y . T h i s p r o g r a m also a l l o w e d the c a l c u l a t i n g of b i n a r y energy parameters u s e d i n p r e d i c t i n g properties of the t e r n a r y systems. 9

2

A n a d d i t i o n a l p r o g r a m took the energy parameters of the b i n a r y systems m a k i n g u p ternary m i x t u r e s a n d c a l c u l a t e d t h e b o i l i n g p o i n t of the t e r n a r y a n d the e q u i l i b r i u m c o m p o s i t i o n of the v a p o r phase. C o m p a r i s o n of the m e a s u r e d b o i l i n g p o i n t w i t h the p r e d i c t e d b o i l i n g p o i n t for the same c o m p o s i t i o n a n d pressure was u s e d as a c r i t e r i o n of successful p e r f o r m a n c e of the N R T L e q u a t i o n . T o illustrate the consistency b e t w e e n the t w o programs, d a t a for the e t h a n o l - w a t e r system r e p o r t e d b y R i e d e r a n d T h o m p s o n ( 11 ) w e r e u s e d . T h e first p r o g r a m estimated the values of the energy parameters a n d c a l c u l a t e d the vapor-phase c o m p o s i t i o n , y, w i t h a root m e a n square d e v i a t i o n ( R M S D ) of 0.00847. T h e m e a n a r i t h m e t i c d e v i a t i o n b e t w e e n the

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

98

E X T R A C T I V E

A N D

A Z E O T R O P I C

DISTILLATION

s u m y a n d u n i t y w a s 0.0064. T h e e s t i m a t e d parameters w e r e u s e d i n the s e c o n d p r o g r a m w h i c h p r e d i c t e d t h e same values of y a n d also p r e d i c t e d the t e m p e r a t u r e of the b o i l i n g m i x t u r e . T h e p r e d i c t e d a n d e x p e r i m e n t a l t e m p e r a t u r e a g r e e d w i t h a R M S D v a l u e of 0.22°C. T h e p r o c e d u r e e s t a b l i s h i n g the v a p o r - l i q u i d e q u i l i b r i u m d a t a for t h e b i n a r y system was tested u s i n g the homogeneous water, a n d the heterogeneous

system,

1-propanol-

system, 2 - m e t h y l - l - p r o p a n o l - w a t e r , u s i n g

the d a t a of M u r t i a n d V a n W i n k l e (12)

and Ellis and Garbett

(9).

T h e R M S D v a l u e b e t w e e n the e x p e r i m e n t a l a n d t h e c a l c u l a t e d values of y w e r e 0.011 a n d 0.0155, respectively, T h e c o m p a r i s o n b e t w e e n

ex

p e r i m e n t a l a n d c a l c u l a t e d V L E d a t a is s h o w n i n F i g u r e 1 a n d F i g -

Figure

1. Comparison of calculated librium data at 760 mm Hg.

•

Indirectly

Ο

Directly

measured, Gadwa

ψ

Directly

measured, Murti and Van

and experimental vapor-liquid 1-Propanol (1)-Water (2).

measured, present work (15) Winkle

(12)

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

equi

6.

ANDiAPPAN

Figure 2. librium

A N D

M C L E A N

Isobaric Vapor-Liquid

Equilibrium

99

Comparison of calculated and experimental vapor-liquid equi data at 760 mm Hg. 2-Methyl-l-Propanol (1)-Water (2).

ψ Indirectly measured, present work Ο Directly measured, Ellis and Garbett

(9)

u r e 2, a n d they agree w e l l e n o u g h to justify u s i n g t h e i n d i r e c t m e t h o d of e s t a b l i s h i n g t h e V L E d a t a o n t h e system, e t h a n o l - 2 - m e t h y l - l - p r o p a n o l and 3-methyl-l-butanol-water. D i r e c t m e a s u r e m e n t of t h e V L E d a t a for t h e e t h a n o l - 2 - m e t h y l - l p r o p a n o l system w e r e also m a d e , u s i n g a M E S 1 0 0 m o d e l e q u i l i b r i u m s u p p l i e d b y the James F . S c a n l o n C o . Results and Discussion Binary System.

T h e e t h a n o l - 2 - m e t h y l - p r o p a n o l system was

to b e h a v e i n a n e x p e c t e d i d e a l w a y .

T h e x-y

found

d a t a , that was d i r e c t l y

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

100

E X T R A C T I V E AND

Table II.

AZEOTROPIC DISTILLATION

Vapor—Liquid Equilibrium Data at 760 mm. H g Ethanol ( l ) - M e t h y l - l - P r o p a n o l (2) t°c 104.15 101.88 101.55 101.03 98.07 94.67 94.08 90.96 89.34 87.56 86.75 86.11 85.24 84.18 83.67 82.54 81.45 81.11 80.06

Table III.

0.050 0.080 0.085 0.090 0.155 0.220 0.243 0.330 0.382 0.465 0.490 0.510 0.560 0.610 0.635 0.705 0.770 0.800 0.870

0.126 0.200 0.215 0.235 0.332 0.460 0.479 0.595 0.658 0.712 0.742 0.770 0.790 0.817 0.845 0.875 0.915 0.920 0.950

Vapor—Liquid Equilibrium Data at 760 mm. H g 3-Methyl-1-Butanol ( l ) - W a t e r (2) t

°c

99.17 97.99 97.82

XJ

Yi

0.0009 0.0024

0.0386

0.0155

0.0031

0.0482

96.60

0.0051

96.27

0.0072

0.0725 0.0932

96.14

0.0073

0.0942

95.90

0.0205

95.26

0.0616

0.1603 0.1694

97.32

0.5766

0.1810

104.03

0.6536

0.2323

109.86

0.7698

0.3495

119.65

0.8873

125.76 126.96

0.9347 0.9427

0.5710 0.7158

128.54

0.9696

0.7449 0.8512

129.84

0.9884

0.9394

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

6.

ANDiAPPAN

A N D

M C L E A N

Isobaric Vapor-Liquid

0

Figure

Equilibrium

5

3.

Vapor-liquid

101

1

equilibrium data at 760 mm Hg. 2-Methyl-l-Propanol (2).

Ethanol

(1)-

Ο Directly measured y Indirectly measured — Ideal behavior m e a s u r e d , are p r e s e n t e d i n T a b l e II.

F i g u r e 3 shows t h e c o m p a r i s o n

w i t h the d i r e c t l y m e a s u r e d d a t a , the i n d i r e c t l y m e a s u r e d d a t a , a n d the data calculated from Raoult's L a w . T h e v a p o r - l i q u i d e q u i l i b r i u m d a t a for t h e 3 - m e t h y l - l - b u t a n o l - w a t e r system are s h o w n i n T a b l e I I I a n d F i g u r e 4. T h e b o i l i n g p o i n t measure ments a g r e e d w i t h those r e p o r t e d i n T i m m e r m a n s (13).

T h e v a l u e of

a =

alcohol-water

0.45 as suggested b y R e n o n a n d P r a u s n i t z ( 8 )

for

systems w a s not suitable. V a r i o u s other values of a w e r e t r i e d , a n d a v a l u e of

a

=

0.3 w a s f o u n d to agree best. T h i s fit c a n b e e s t a b l i s h e d b y u s i n g

the m e t h o d d e s c r i b e d to test t h e consistency of t h e equations—i.e.,

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

the

102

E X T R A C T I V E

0

Figure

A N D AZEOTROPIC

DISTILLATION

5

4.

Vapor-liquid

Table IV.

1

equilibrium data at 760 mm Hg. Butanol (1)-Water ( 2 ) .

3-Methyl-l-

N R T L Parameters for the Binary Systems Isobaric Systems at 1 A t m . Reference

E t h a n o l U ) - W a t e r (2) 1 - P r o p a n o l ( i ) - W a t e r (2) 2 - M e t h y l - l - P r o p a n o l (1)-Water (2) 3 - M e t h y l - l - B u t a n o l U ) - W a t e r (2) E t h a n o l (1 ) - l - P r o p a n o l (2) Ethanol (i)-3-Methyl-lB u t a n o l (2) Ethanol (J)-2-Methyl-lP r o p a n o l [2)

( gia-fW

a

cal./gram mole

(

gai-gu) cal./gram mole

16

0.475 0.500 0.475 0.300 0.500

121.0 438.4 611.5 -386.9 465.5

1161.5 1762.9 2475.7 3483.8 -324.5

16

0.475

20.8

7.4

11 15,12 9 —

—

—

0

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

0

6.

ANDiAPPAN

A N D

Table V . Xj

103

Equilibrium

Vapor—Liquid Equilibrium Data at 760 mm H g Water ( l ) - E t h a n o l (2)-l-Propanol (3)

, χ*

0.1763 0.3742 0.5397 0.7271 0.1642 0.3216 0.4759 0.6350 0.1293 0.2707 0.4214 0.5519 0.1201 0.2421 0 3764 0.4812 0.1246 0.2046 0.3030 0.4071 0.0962 0.1896 0.3096 0.0853 0.1911 0.1125 0.1524 0.0851

Isobaric Vapor-Liquid

M C L E A N

0.0905 0.0992 0.0944 0.0987 0.1920 0.1949 0.1966 0.1984 0.2698 0.2956 0.3123 0.3076 0.4024 0.3935 0.3777 0.3934 0.4861 0.4837 0.4944 0.4939 0.6059 0.6054 0.5907 0.7030 0.7026 0.7007 0.7319 0.8319

y/ 0.3133 0.4527 0.5143 0.5345 0.2720 0.3909 0.4526 0.4768 0.2152 0.3297 0.3932 0.4217 0.1793 0.2852 0.3566 0.3797 0.1702 0.2388 0.2936 0.3312 0.1248 0.2045 0.2731 0.1036 0.1889 0.1264 0.1579 0.0920

0.1353 0.1426 0.1503 0.2100 0.2730 0.2649 0.2828 0.3395 0.3752 0.3822 0.4123 0.4510 0.5203 0.4857 0.4750 0.5214 0.5966 0.5744 0.5797 0.5994 0.7064 0.6785 0.6652 0.7814 0.7518 0.7691 0.7792 0.8648

t°C

t

89.13 86.70 86.14 85.75 87.57 85.55 84.63 84.04 86.89 84.47 83.12 82.54 84.85 83.30 82.43 81.60 83.47 82.42 81.35 80.63 82.14 80.92 80.03 80.94 79.65 80.59 79.69 79.24

89.07 86.40 85.60 85.46 87.65 85.47 84.57 83.94 87.19 84.59 83.12 82.51 85.12 83.45 82.47 81.52 83.79 82.65 81.47 80.67 82.39 81.03 80.01 81.11 79.68 80.01 79.30 79.07

°C

"Predicted using N R T L equation. Measured. 5

c a l c u l a t i o n of the parameters w i t h the first p r o g r a m a n d the use of the p a r a m e t e r s to c a l c u l a t e t h e i n i t i a l t e m p e r a t u r e . Ternary System. T h e values of a l l b i n a r y parameters u s e d i n p r e d i c t i n g t h e t e r n a r y d a t a are s h o w n i n T a b l e I V . T h e p r e d i c t e d values of the v a p o r - l i q u i d e q u i l i b r i u m data—i.e., the b o i l i n g p o i n t , a n d t h e c o m p o s i t i o n of the v a p o r phase, y, f o r g i v e n values of t h e l i q u i d c o m p o s i t i o n , x, are p r e s e n t e d i n T a b l e s V , V I , a n d V I I .

A l s o s h o w n are t h e m e a s u r e d

b o i l i n g p o i n t s for the g i v e n values of the l i q u i d c o m p o s i t i o n . T h e R M S D v a l u e b e t w e e n t h e p r e d i c t e d a n d m e a s u r e d b o i l i n g p o i n t s for the sys tems w a t e r - e t h a n o l - l - p r o p a n o l , w a t e r - e t h a n o l - 2 - m e t h y l - l - p r o p a n o l , a n d w a t e r - e t h a n o l - 2 - m e t h y l - l - b u t a n o l are 0.23°C, 0.69°C, a n d 2.14°C.

It

seems therefore that since t h e N R T L e q u a t i o n successfully p r e d i c t s t e m p e r a t u r e , t h e p r e d i c t e d values of y c a n b e a c c e p t e d confidently.

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

104

E X T R A C T I V E

A N D

A Z E O T R O P I C

DISTILLATION

T o test the m e t h o d of p r e d i c t i n g some d i r e c t l y m e a s u r e d t e r n a r y d a t a , t h e p r e d i c t e d results for the system w a t e r - e t h a n o l - l - p r o p a n o l w e r e u s e d to c a l c u l a t e r e l a t i v e v o l a t i l i t i e s w h i c h w e r e c o m p a r e d w i t h t h e ex p e r i m e n t a l l y d e t e r m i n e d v a l u e s of C a r l s o n et al. (14).

This comparison

is s h o w n o n F i g u r e 5. T h e c o m p a r i s o n seems to i n d i c a t e that the m e t h o d of p r e d i c t i n g is satisfactory a n d gives less scatter t h a n t h e e x p e r i m e n t a l l y d e t e r m i n e d values of r e l a t i v e v o l a t i l i t y .

Table VI. Vapor—Liquid Equilibrium Data at 760 mm H g Water ( l ) - E t h a n o l (2)-2-Methyl-l-Propanol (3) x»

y."

t°C

t°C

0.1937

0.0999

0.4203

0.1632

93.28

93.0

0.3582

0.1062

0.5294

0.1574

90.13

89.25

0.5377

0.1003

0.5945

0.1548

88.78

87.67

0.7115

0.1014

0.6098

0.1912

88.09

86.93

0.1589

0.2002

0.3300

0.3163

91.78

0.3156

0.1996

0.4521

0.2854

88.68

91.46 87.72

0.5570

0.1820

0.5377

0.2813

86.88

85.92

0.6352

0.2066

0.5208

0.3492

85.71

84.87

0.1264

0.3072

0.2468

0.4635

90.05

89.89

0.3006

0.2943

0.3947

0.4012

86.86

86.09

0.4103

0.3056

0.4323

0.4161

85.33

84.59 85.1 87.76

0.5562

0.2981

0.4572

0.4474

84.09

0.1255

0.3990

0.2158

0.5602

0.2611

0.3974

0.3274

87.85 85.24

0.3722

0.3897

0.3791

0.5145 0.5041

0.4789

0.3993

0.3930

0.5414

82.53

82.23

0.0959

0.4984

0.1556

0.6666

86.29

86.38

0.1934

0.5010

0.2470

0.6228

84.18

83.96

0.3099

0.4949

0.3135

0.4991

0.3385

82.55 81.32

82.28

0.4006

0.6009 0.6149

0.0954

0.6042

0.7448

83.97

84.08

0.1347

83.95

85.09 83.46

81.10

0.2124

0.5908

0.2339

0.6877

82.05

81.93

0.4614

0.4118

0.3870

0.5465

80.23

0.1021

0.6959

0.1266

0.7982

82.46 81.94

0.1952

0.1955 0.0865

0.7680 0.8764

80.14

0.0757

0.7051 0.8162

80.15

80.11 80.25

0.1805

0.7530

0.1768

0.7997

79.49

79.49

0.0526

0.8987

0.0577

0.9264

79.09

79.19

Predicted using N R T L equation. * Measured.

β

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

81.99

6.

ANDiAPPAN

Isobaric Vapor-Liquid

A N D M C L E A N

105

Equilibrium

Table VII. V a p o r - L i q u i d Equilibrium Data at 760 mm H g Water ( l ) - E t h a n o l ( 2 ) - 3 - M e t h y l - l - B u t a n o l (3) Xi

XJ

y/

y/

t°C

t °C

0.7422

0.0101

0.8790

0.0198

95.08

94.37

0.4982

0.0127

0.8318

0.0266

97.93

94.67

0.3477

0.0120

0.7503

0.0311

103.20

99.58

0.8455

0.0589

94.46

93.57 100.44

0.7248

0.0303

0.6809 0.8464

0.0729

104.88

0.0565

93.78

0.8412

0.0277

94.56 95.22

0.0241

0.8492

0.0456

95.14

94.13

0.0384

0.7685

0.0826

98.26

95.68

0.6338

0.1773

0.6234

0.3225

89.45

89.41

0.5055

0.2112

05744

0.3604

89.97

89.71

96.20

92.15

0.2944

0.0263

0.7784 0.8878

0.0269 0.0094

0.0344 0.4465

95.40

0.2774

0.1984

0.4574

0.4082

0.2087

0.1867

0.3944

0.4306

99.46

93.92

0.3781

0.3232

0.4331

0.5084

88.31

88.31 86.25

0.6071

0.2999

0.4801

0.4971

84.75

0.1377

0.3002

0.2369

0.6182

96.57

91.73

0.1984

0.3953

0.2684

0.6495

90.32

88.62

0.2802

0.4149

0.3265

0.6180

87.35

87.39

0.4460

0.3727

0.4225

0.5431

85.22

86.62

0.1335

0.4835

0.1774

0.7491

89.05

87.69

0.1857

0.5114

0.2212

0.7262

86.56

86.65

0.3912

0.5172

0.3319

0.6538

81.75

84.07

0.1047

0.6257

0.1248

0.8307

85.20

85.37

0.1939

0.6103

0.2054

0.7648

83.33

84.63

0.2963

0.5946

0.2709

0.7134

81.50

83.62

0.1112

0.6845

0.1247

0.8441

83.31

84.20

0.1353

0.7158

0.1428

0.8359

81.85

83.40

0.2135

0.6820

0.2050

0.7806

83.94

82.97

0.0453

0.8104

0.0511

0.9280

81.67

82.76

0.1022

0.8118

0.1059

0.8824

80.21

82.00

0.1547

0.7925

0.1498

0.8434

79.49

81.51

0.9551

80.02

80.09

0.0312

0.8920

0.0499

0.8998

0.0532

0.9402

79.38

79.45

0.0680

0.8989

0.0706

0.9252

78.96

78.99

α 6

0.0343

Predicted using N R T L equation. Measured.

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

106

E X T R A C T I V E

A N D

A Z E O T R O P I C

DISTILLATION

Ο >

•

> < L—OOfCpCBDO

MOLE Figure

5.

FRACTION

OF WATER IN

LIQUID

Comparison of calculated and experimental volatilities panol relative to ethanol in presence of water

of 1-pro-

Ο Indirectly measured, present work ψ Directly measured, Carbon et al. (14) Conclusion T h e n o n - r a n d o m , t w o - l i q u i d (NRTL) a n d P r a u s n i t z (8)

equation proposed b y Renon

seems to p r e d i c t successfully m u l t i c o m p o n e n t ( t e r n a r y )

m i x t u r e s of a l c o h o l s a n d w a t e r .

T h e alcohols s t u d i e d i n t h i s w o r k etha

n o l , 1 - p r o p a n o l , 2 - m e t h y l - l - p r o p a n o l , a n d 3 - m e t h y l - l - b u t a n o l , w h i c h oc c u r f r o m the f e r m e n t a t i o n

of

sugar solutions, s h o w h i g h l y n o n - i d e a l

b e h a v i o r i n a q u e o u s solutions a n d present a severe test of t h e effectiveness of a n y p r e d i c t i o n m e t h o d . T h e success of the N R T L e q u a t i o n i n u n d e r g o i n g this test w o u l d suggest that i t w i l l b e a p o w e r f u l t o o l i n t h e d e s i g n of processes i n v o l v i n g a z e o t r o p i c or extractive d i s t i l l a t i o n . T h e effect of the a d d i t i o n of a t h i r d

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

6.

ANDiAPPAN

A N D

M C L E A N

Isobaric Vapor-Liquid

Equilibrium

107

c o m p o n e n t t o a difficult to separate b i n a r y m i x t u r e c a n b e p r e d i c t e d w i t h a d e g r e e of confidence, c e r t a i n l y f o r a l c o h o l - w a t e r mixtures. O n l y e q u i l i b r i u m d a t a f o r t h e b i n a r y c o m p o n e n t s of t h e system are necessary, a n d this w o r k shows that e v e n f o r systems of l i m i t e d l i q u i d - p h a s e m i s c i b i l i t y , t h e N R T L e q u a t i o n c a n b e u s e d to extract t h e necessary i n f o r m a t i o n

from

measurements of b o i l i n g p o i n t , l i q u i d c o m p o s i t i o n , a n d pressure alone.

Literature Cited 1. Prausnitz, J. M., Eckert, C. Α., Orye, R. V., O'Connell, J. P., "Computer Calculations for Multicomponent Vapor-Liquid Equilibria," p. 14, Prentice Hall, New Jersey, 1967. 2. Hala, E., Pick, J., Fried, V., Vilim, O., "Vapor-Liquid Equilibrium," p. 33, Pergamon, London, 1967. 3. Wohl, K., Trans. Amer. Inst. Chem. Eng. (1946) 42, 215. 4. Cukor, P. M., Prausnitz, J. M., Int. Symp. "Distillation," p. 73, Inst. Chem. Eng., London (Sept. 9, 1969). 5. Wilson, G. M.,J.Amer. Chem. Soc. (1964) 86, 127. 6. Garrett, G. R., VanWinkle, Matthew,J.Chem. Eng. Data (1969) 14, 302. 7. Gurukul, S. Μ. Κ. Α., Raju, Β. N.,J.Chem. Eng. Data (1966) 11, 501. 8. Renon, H., Prausnitz, J. M., A.I.Ch.E. J. (1968) 14, 135. 9. Ellis, S. R. M., Garbett, R. D., Ind. Eng. Chem. (1960) 52, 385. 10. Othmer, D. F., Gilmont, R., Conti, J. J., Ind. Eng. Chem. (1960) 52, 625. 11. Rieder, R. M., Thompson, A. R., Ind. Eng. Chem. (1949) 41, 2905. 12. Murti, P. S., VanWinkle, Matthew, Ind. Eng. Chem., J. Chem. Eng. Data (1958) 3, 72. 13. Timmermans, J., "The Physico Chemical Constants of Binary Systems," Vol. 4, p. 237, Interscience, New York (1960). 14. Carlson, C. S., Smith, P. V., Jr., Morrell, C. E., Ind. Eng. Chem. (1954) 46, 350. 15. Gadwa, T. W., Chemical Engineering Thesis, M.I.T., 1936. 16. Gay, L., Chim. et Ind. (1927) 18, 187.

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

7 Demulsification of Crude Oils Use of Azeotropic

Distillation

LESLIE L. BALASSA and DONALD F. OTHMER Slate Hill, Ν. Y. 10973 and Polytechnic Institute, Brooklyn, Ν. Y. 11201

Water and often fine sand and silt are held in various crude oils in permanent emulsions. Particularly crudes obtained by secondary methods and those from tar sands where water or steam are used contain water and mineral matter emulsified therein by the surface forces on small particles and drops. Azeotropic distillation removes the relatively small amount of water, using the solvent as an entrainer which dilutes the crude. This allows: the mineral matter to be separated easily without using centrifuges with their substantial cost and wear, free of organic material, so it may be discarded with out hazards of fire or odors; the bitumen to be recovered for such use or cracked to give volatile fractions and coked to an ash-free coke; the water to be obtained as distilled water for reuse.

" p e t r o l e u m crudes p r o d u c e d b y w a t e r

flooding,

hot water displacement,

pressure steam, or steam i n j e c t i o n u s u a l l y are e m u l s i o n s , either w a t e r i n - o i l o r o i l - i n - w a t e r , a n d are f r e q u e n t l y a c o m b i n a t i o n o f b o t h . E m u l s i o n s of these h i g h v i s c o s i t y oils often c a n n o t b e b r o k e n a n d d e h y d r a t e d b y conventional methods. A n e v e n m o r e difficult p r o c e s s i n g c o n d i t i o n arises w i t h h e a v y b i t u m i n o u s oils w h i c h a l w a y s c a r r y m u c h sand, c l a y , a n d silt of coarse a n d s m a l l p a r t i c l e sizes w h i c h s t a b i l i z e the oil—water e m u l s i o n s e v e n m o r e . T h e b i t u m i n o u s oils h a v e specific gravities of 0.9-1.4 a n d h a v e h i g h viscosi ties; thus t h e y c a n n o t b e separated f r o m the w a t e r or solids present b y s e t t l i n g or b y u s i n g the most efficient centrifuges. D i l u t i n g these e m u l s i o n s o f h e a v y oils w i t h l i g h t

solvents—e.g.,

kerosene, solvent n a p h t h a , b e n z e n e , etc.—reduces the specific g r a v i t y of the o i l phase of the e m u l s i o n s b e l o w t h a t of w a t e r a n d l o w e r s the v i s 108

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

7.

B A L A S S A

A N D

O T H M E R

Demulsification

of Crude

109

Oils

cosity so that some of the w a t e r a n d m i n e r a l matters u s u a l l y c a n b e r e m o v e d b y s e d i m e n t a t i o n , centrifuge, or h y d r o - c y c l o n e . A d d i t i o n of a l o w viscosity h y d r o c a r b o n solvent often extracts t h e o i l f r o m the w a t e r ; t h e extract l a y e r of solvent a n d solute separates f r o m the water. T h e large a m o u n t of solvent n e e d e d to separate e m u l s i o n s of w a t e r i n a viscous h e a v y o i l is u n e c o n o m i c because of t h e d i l u t e s o l u t i o n n e e d e d to o b t a i n a c o n t i n u o u s w a t e r phase. A d d i t i o n of solvent, p o s s i b l y u p to a n e q u a l a m o u n t , is reasonable a n d is d e s i r a b l e to r e d u c e t h e v i s c o s i t y suffic i e n t l y to p u m p a n d transport the h e a v y o i l . A c h e a p a l i p h a t i c s o l v e n t — e.g., k e r o s e n e — i s preferable, b u t b i t u m i n o u s o i l fractions are m u c h m o r e s o l u b l e i n a r o m a t i c solvents, p a r t i c u l a r l y at temperatures near t h e a m bient. H o w e v e r , the w a t e r a n d s o l i d particles are not at a c c e p t a b l e l i m i t s e v e n after m u c h d i l u t i o n , e s p e c i a l l y i n the presence of fine p a r t i c l e s as i n some crudes f r o m C a l i f o r n i a a n d V e n e z u e l a a n d p a r t i c u l a r l y f r o m t a r sands as those i n A t h a b a s c a ( A l b e r t a , C a n a d a ) . P r o c e s s i n g o i l emulsions f r o m t a r sands is difficult w i t h t h e o i l a n d the aqueous phase. T h e o i l phase carries m u c h c l a y a n d silt ( s a n d ) of s m a l l p a r t i c l e size w h i c h are s u s p e n d e d a n d d o not settle o u t e v e n o n p r o l o n g e d storage.

T h e surface or m o l e c u l a r forces b e t w e e n viscous oils a n d s u c h

fine p a r t i c l e s are m o r e i m p o r t a n t i n d e t e r m i n i n g t h e latter's m o t i o n s , or l a c k of m o t i o n , t h a n t h e m e c h a n i c a l forces r e s u l t i n g f r o m differences i n specific gravity. S o m e particles i n the a q u e o u s phase are w e t b y o i l i n s t e a d of

by

water, a n d these o i l - c o a t e d p a r t i c l e s g i v e a n u n u s u a l l y stable s u s p e n s i o n for a b o u t the same reason. T h i s o i l i n t h e oil-wet m i n e r a l matter, susp e n d e d i n t h e aqueous phase, makes it u n s u i t a b l e for r e c y c l i n g i n t h e p r o c e s s i n g o p e r a t i o n or d i s c h a r g i n g b a c k i n t o surface waters.

Also, the

m i n e r a l sludge w h i c h is separated f r o m w a t e r s t i l l contains a s u b s t a n t i a l percentage of o i l ; it c a n n o t b e d i s p o s e d of e v e n b y r e t u r n i n g i t t o t h e p l a c e w h e r e it w a s m i n e d or p r o d u c e d . F i r e s h a v e o c c u r r e d f r o m s p o n taneous c o m b u s t i o n r e s u l t i n g f r o m this s l u d g e of fine p a r t i c l e s a n d o i l . P r i o r processes p r o p o s e d to d e m u l s i f y it are unsatisfactory because so m u c h o i l is a l w a y s lost i n the aqueous p h a s e o r i n t h e d e w a t e r e d sludge. A l s o , the content of w a t e r a n d m i n e r a l s i n the o i l separated b y c o n v e n t i o n a l processes is u s u a l l y a b o v e a c c e p t a b l e l i m i t s for p i p e l i n e t r a n s p o r t a t i o n or for r e f i n i n g purposes. F i n a n c i a l losses are e x p e r i e n c e d i n o i l w a s t e d , i n e q u i p m e n t a n d c a p i t a l charges of w o r n e q u i p m e n t i n plants, a n d i n l a n d v a l u e of d i s p o s a l p o n d s . T r e m e n d o u s d i s p o s a l p o n d s of d i s c a r d e d emulsions i n V e n e z u e l a a n d elsewhere

take u p available land.

I n separating emulsions from

tar sands, the extremely abrasive silt has r u i n e d expensive

centrifuges

a n d makes u s i n g t h e m i m p r a c t i c a l .

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

110

E X T R A C T I V E

Azeotropic

A N D A Z E O T R O P I C

DISTILLATION

Distillation

T h e w a t e r content of a n e m u l s i o n is r e m o v e d b y d i s t i l l a t i o n , h o w e v e r , d i r e c t a n d s i m p l e d i s t i l l a t i o n presents several p r a c t i c a l p r o b l e m s .

I n the

presence of a s o l v e n t - d i l u e n t after p r e l i m i n a r y s e p a r a t i o n of m u c h of the water

as a c o n t i n u o u s phase, the b a l a n c e is r e m o v e d

by

azeotropic

distillation. F o r m a n y years w a t e r has b e e n separated f r o m m a n y l i q u i d s b y a z e o t r o p i c d i s t i l l a t i o n . W a t e r is s u b s t a n t i a l l y i n s o l u b l e n o t o n l y i n the oils b u t also i n the d i l u e n t s o r solvents. T h u s , the v a p o r pressures of t h e w a t e r a n d d i l u e n t are a d d i t i v e as i n t h e f a m i l i a r steam d i s t i l l a t i o n s . A heterogeneous

azeotrope is f o r m e d ; this a l w a y s b o i l s b e l o w t h e b o i l i n g

p o i n t of w a t e r because pressure m u s t b e r e d u c e d f o r w a t e r t o b o i l at t h e v a p o r pressure of t h e h y d r o c a r b o n . T h e p r i n c i p l e s of a z e o t r o p i c d i s t i l l a t i o n h a v e often b e e n (1,2,3,4,5,6,7),

described

a n d a p p l y i n g t h e m gives a s i m p l e m e t h o d of s e p a r a t i n g

w a t e r f r o m its o i l emulsions. T h e l o w - b o i l i n g constituents of a n o i l — o r the d i l u e n t u s e d — w o u l d b e t h e entraîner ( w i t h d r a w i n g a g e n t ) w h i c h forms t h e heterogeneous

azeotrope or steam d i s t i l l a t i o n w i t h t h e water.

B e c a u s e of n o n e q u i l i b r i u m b o i l i n g c o n d i t i o n s i n a s i m p l e d i s t i l l a t i o n , the vapors m a y n o t c o n t a i n t h e t r u e azeotrope, a n d t h e heat cost m a y b e too h i g h . T h e r e f o r e a c o l u m n is s t i l l u s e d to r e c t i f y the exact azeotrope at t h e h e a d of the c o l u m n ; h o w e v e r , o n l y a f e w trays are r e q u i r e d . T h e azeotrope contains t h e l o w e r h y d r o c a r b o n s of t h e d i l u e n t . I f a w i d e - c u t f r a c t i o n is u s e d , t h e m o r e v o l a t i l e ones c o m e to t h e t o p of t h e c o l u m n w i t h the water. A t a n y t e m p e r a t u r e t h e v a p o r pressure of w a t e r p l u s that o f t h e entraîner, o r t h e effective v a p o r pressure of the m i x t u r e of l i q u i d s o p e r a t i n g as t h e entraîner, gives t h e azeotrope's v a p o r pressure. T h e t e m p e r a t u r e w h e r e this s u m m a t i o n c u r v e crosses the a t m o s p h e r i c l i n e , o r other o p e r a t i n g pressure of t h e d i s t i l l a t i o n , is t h e a z e o t r o p i c point.

boiling

A close-cut f r a c t i o n o r a single m o r e or less p u r e c o m p o u n d as

a d i l u e n t a n d a z e o t r o p i c w i t h d r a w i n g agent is preferable, a l t h o u g h n o t necessary.

I f the m i x t u r e loses some o f its m o r e v o l a t i l e

components

at t h e h e a d of the c o l u m n o v e r a p e r i o d of t i m e , t h e a z e o t r o p i c b o i l i n g p o i n t w i l l g r a d u a l l y rise. T h e condensate has t w o l i q u i d phases. It r u n s f r o m t h e condenser to a separator o r decanter w h e r e the w a t e r layer is r e m o v e d f o r d i s c a r d a n d t h e solvent layer is r e t u r n e d , u s u a l l y as reflux to t h e c o l u m n . T h i s reflux of " a l l o r p a r t " ( t h e solvent l a y e r ) of the condensate after décantation, r a t h e r t h a n " p a r t of a l l , " w a s d e v e l o p e d i n 1927 (2)

f o r acetic a c i d d e h y -

d r a t i o n w i t h a n a d d e d solvent as entraîner a n d for b u t a n o l d e h y d r a t i o n u s i n g b u t a n o l itself as t h e entraîner.

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

7.

B A L A S S A

A N D

O T H M E R

Demulsification

of Crude

111

Oils

S e p a r a t i n g w a t e r f r o m a n o i l e m u l s i o n is best d o n e b y a n entraîner a d d e d as a d i l u e n t to the o i l . F o r example, the d i l u e n t a d d e d to t h e o i l e m u l s i o n is a n a p h t h a f r a c t i o n h a v i n g a n effective v a p o r pressure e q u a l to that of octane. T h i s n a p h t h a is a d d e d to the o i l , a n d as m u c h w a t e r as possible is separated; the o i l e m u l s i o n layer w h i c h is n o t b r o k e n contains the a d d e d n a p h t h a .

OIL, SILT β DILUENT OUT Figure 1. Flow sheet for removing emulsified water from crude oil and diluent using azeotropic distilfotion with fixed amount of entraîner

F i g u r e 1 i n d i c a t e s one o p e r a b l e

flow

sheet w h e n this o i l e m u l s i o n

c o n t a i n i n g the n a p h t h a w i l l h a v e a sufficiently l o w v i s c o s i t y to b e p u m p e d t h r o u g h a t u b u l a r condenser a n d t h e n t h r o u g h a t u b u l a r bottoms

cooler

for heat i n t e r c h a n g i n g a n d r e c o v e r y . It is t h e n p u m p e d to a n u p p e r p l a t e of a c o l u m n s t i l l . T h i s m i g h t h a v e 1 0 - 1 5 trays d e s i g n e d to a l l o w

ready

passage d o w n w a r d of a n y silt. T h e c o l u m n is thus self-cleaning as m u c h as possible, b u t p r o v i s i o n s are also m a d e for o p e n i n g to c l e a n m e c h a n i c a l l y , i f necessary. T a b l e I gives several azeotropes o f w a t e r w i t h h y d r o c a r b o n s

and

b u t a n o l , u s e d as entrainers. A s s u m i n g t h e entraîner—diluent has the p r o p -

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

112

e x t r a c t i v e

Table I.

a z e o t r o p i c

d i s t i l l a t i o n

Azeotropes of Water and Entrainers Composition by Weight

Temperature, °C (1 atm) Boiling Point Compound

a n d

Azeo. Temp.

Azeo. Vapors

%

Upper Layers

Lower Layers

Separated Layers

Volume,

%

Toluene Water

110.6 100

85

79.8 20.2

99.9 0.1

0.1 99.9

82 18

Up Low

m-Xylene Water

139.1 100

94.5

60 40

99.95 0.05

0.05 99.95

63.4 36.6

Up Low

n-Octane Water

125.7 100

89.6

74.5 25.5

99.98 0.02

0.02 99.98

80 20

Up Low

Butanol Water

117.7 100

93

55.5 45.5

77.5 22.5

8.0 92.0

71.5 28.5

Up Low

erties of o c t a n e , the c o l u m n has a t o p v a p o r t e m p e r a t u r e of 89.6 ° C . T h e s e v a p o r s are c o n d e n s e d i n p r e h e a t i n g the f e e d a n d i n another w a t e r c o o l e d condenser i f n e e d e d .

T h e condensate flows to a decanter w h i c h

c o n t i n u o u s l y separates 8 0 %

b y v o l u m e as the d i l u e n t - e n t r a i n e r l a y e r

a n d 2 0 % b y v o l u m e of a w a t e r layer. T h e a m o u n t of e a c h c o m p o n e n t d i s s o l v e d i n the other layer is so s m a l l that it is d i s r e g a r d e d ; t h u s the w a t e r l a y e r flows to waste. T h e entraîner l a y e r is r e t u r n e d to the t o p of t h e c o l u m n as reflux to w i t h d r a w m o r e w a t e r , a n d the d r y o i l w i t h sedim e n t passes o u t the b o t t o m a n d t h r o u g h a bottoms exchanger.

T h e silt

n o w settles a n d separates r e l a t i v e l y easily f r o m the o i l w h i c h is d e c a n t e d . T h e silt is w a s h e d w i t h t h e s o l v e n t - d i l u e n t w h i c h is t h e n r e u s e d w i t h a f o l l o w i n g o i l e m u l s i o n a n d t h e n s t e a m e d to recover the n a p h t h a . I n this flow sheet the solvent-diluent—entraîner passes t h r o u g h t h e system a n d o u t w i t h t h e o i l f o r t r a n s p o r t o r r e f i n i n g — a first step w h i c h m a y r e c o v e r n a p h t h a for reuse. H o w e v e r , i n the c y c l e at the h e a d of the a z e o t r o p i c c o l u m n w i t h t h e condenser a n d the decanter, f r a c t i o n a t i n g l i g h t - e n d s f r o m the n a p h t h a p a s s i n g t h r o u g h w i t h the o i l occurs to g i v e the a z e o t r o p e w i t h w a t e r w h i c h has a c o m p o s i t i o n d e p e n d i n g o n the effective v a p o r p r e s s u r e of the m i x t u r e of h y d r o c a r b o n s w h i c h stabilizes t h e r e as t i m e passes. T h i s m a y h a v e a c o n s i d e r a b l y l o w e r b o i l i n g p o i n t t h a n the n a p h t h a f r a c t i o n , a n d the light-ends congregate a n d b e c o m e the entraîner. S o m e of this m a y b e r e m o v e d f r o m the system b y w i t h d r a w i n g f r o m the reflux s t r e a m to the c o l u m n . If there are so m a n y l o w ends that the azeot r o p i c b o i l i n g p o i n t goes d o w n , a n a p h t h a f r a c t i o n of s o m e w h a t h i g h e r b o i l i n g r a n g e is u s e d as the d i l u e n t . A c t u a l l y this i n d i c a t e s a n o p e r a t i o n c o m p a r a b l e w i t h the d e h y d r a t i o n of m a n y other l i q u i d s w i t h a separate entraîner. T h u s , i f no d i l u e n t

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

7

ΒA L A S SA

A N D

O T H M E R

Demulsification

of Crude

113

Oils

is necessary to r e d u c e t h e v i s c o s i t y of t h e o i l so that i t m a y b e h a n d l e d a n d n o d i l u e n t is u s e d to g i v e a p r e v i o u s p a r t i a l d e m u l s i f i c a t i o n , e n o u g h entraîner c o u l d b e selected a n d s u p p l i e d to t h e a z e o t r o p i c system t o charge the u p p e r p a r t o f the c o l u m n , t h e condenser, decanter, a n d c o n nections. T h e a d d e d entraîner w o u l d t h e n w i t h d r a w w a t e r f r o m t h e o i l e m u l s i o n f e d i n t o a n d o u t of t h e c o l u m n , a n d t h e entraîner w o u l d t h e n act l i k e a m e c h a n i c a l p a r t of t h e system. T a b l e I shows that, as t h e b o i l i n g p o i n t of the h y d r o c a r b o n u s e d as t h e entraîner increases so does that of t h e azeotrope w i t h w a t e r a n d t h e p e r c e n t of w a t e r t h e r e i n . A h i g h percentage

of w a t e r i n t h e a z e o t r o p e

is d e s i r e d for the heat r e q u i r e d for t h e d i s t i l l a t i o n , w h i c h is m a i n l y t h a t of t h e latent heat of t h e w a t e r p l u s that of t h e entraîner. Sufficient e n t r a i n e r s h o u l d b e a v a i l a b l e i n the azeotrope f o r reflux to t h e c o l u m n a l t h o u g h this r e q u i r e m e n t is n o t large.

A l s o , the s o l u b i l i t y o r d i l u t i o n

effect is better w i t h l o w e r - b o i l i n g h y d r o c a r b o n s .

T h u s t h e r e a r e several

factors to be b a l a n c e d i n c h o o s i n g t h e azeotrope.

T h e effect of r e l a t i v e

b o i l i n g points, v a p o r pressures, a n d amounts of different

entrainers i n

t h e i r azeotropes w i t h w a t e r has b e e n d i s c u s s e d as affecting the c h o i c e o f entrainers for s e p a r a t i n g w a t e r f r o m acetic a c i d ( 5 ) .

However,

that

represents a m u c h m o r e difficult selection because there t h e q u a n t i t y of reflux is i m p o r t a n t a n d also the solvent characteristics of the entraîner for t h e acetic a c i d also c o n t r o l t h e choice. However,

t h e o p t i m u m a z e o t r o p i c entraîner for w a t e r f r o m a n o i l

e m u l s i o n is p a r t i a l l y selected a c c o r d i n g to those p r i n c i p l e s . T h e highest b o i l i n g l i q u i d s o b v i o u s l y c a r r y m o r e w a t e r for a g i v e n heat i n p u t .

A

selected a n d stable t e m p e r a t u r e at t h e t o p of t h e azeo c o l u m n is necessary f o r o p t i m u m o p e r a t i o n , a n d this m i g h t seem to b e s e c u r e d best b y a pure aromatic.

A l t e r n a t e l y , a p u r e a l i p h a t i c or a close-cut n a p h t h a

f r a c t i o n m i g h t b e o b t a i n e d a n d m a i n t a i n e d i n the a z e o t r o p i c

column.

T h e use of a p u r e c o m p o u n d is n o t advantageous i f a close-cut n a p h t h a f r a c t i o n is u s e d as a n entraîner i n this c o n t i n u o u s o p e r a t i o n because t h e losses a n d m a k e - u p of s u c h entraîner i n a c o l u m n are so s m a l l ; thus, the effective a z e o t r o p i c b o i l i n g p o i n t r e m a i n s constant. T h e entraîner s h o u l d b e a h y d r o c a r b o n w h i c h has a l o w e r b o i l i n g p o i n t t h a n t h e light-ends, w h a t e v e r the feedstock of o i l e m u l s i o n ; otherw i s e l i g h t ends c o n t i n u a l l y fractionate i n t o the azeotrope a n d h a v e to b e removed.

I n other systems i n v o l v i n g a z e o t r o p i c w i t h d r a w i n g agents w i t h

a m i x t u r e of v a r i o u s volatilities, a stable entraîner is d e v e l o p e d a n d m a i n t a i n e d at t h e d e s i r e d b o i l i n g p o i n t b y r e m o v i n g p e r i o d i c a l l y some o f t h e entraîner to k e e p its effective b o i l i n g p o i n t sufficiently h i g h .

Sometimes

s m a l l heads c o l u m n s h a v e b e e n i n c o r p o r a t e d to d o this c o n t i n u o u s l y .

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

114

EXTRACTIVE

Laboratory

AND

AZEOTROPIC

DISTILLATION

Testing

H a v i n g c o n s i d e r e d a b a s i c flow sheet a n d the e l e m e n t a r y p r i n c i p l e s of a z e o t r o p i c d i s t i l l a t i o n as t h e y m a y b e u s e d , w e c o n s i d e r e d t e s t i n g emulsions i n the l a b o r a t o r y p r i o r to process design. T h e first step i n t e s t i n g t h e m a t e r i a l f o r s u i t a b i l i t y o f t h e d e m u l s i f y i n g , d e h y d r a t i n g process is to d i l u t e t h e c r u d e o i l w i t h a solvent w h i c h is u s e d b y itself or m i x e d w i t h another i n a z e o t r o p i c d e h y d r a t i o n of the emulsion.

T h e m i n i m u m a m o u n t of solvent w h i c h is sufficient for the

first step is t h a t w h i c h cuts t h e viscosity of the c r u d e e n o u g h to a l l o w a z e o t r o p i c d i s t i l l a t i o n w i t h o u t excessive f o a m i n g . T h i s m a y r e q u i r e a b o u t 4 0 - 6 0 v o l u m e s solvent p e r 100 v o l u m e s of c r u d e , b u t this r a t i o of solvent, h o w e v e r , m a y not b e sufficient to r e d u c e the g r a v i t y of the c r u d e b e l o w that of w a t e r to a l l o w p r e l i m i n a r y décantation of some of the w a t e r . T o a c h i e v e this, a v o l u m e of solvent a b o u t e q u a l to t h a t of the c r u d e m a y h a v e to b e u s e d (sometimes a n e v e n h i g h e r r a t i o of s o l v e n t ) .

By

d i l u t i n g the c r u d e first w i t h t o l u e n e u p to a v o l u m e of 2 0 % of the c r u d e a n d c o n t i n u i n g the d i l u t i o n w i t h a l i g h t gasoline f r a c t i o n i n the r a n g e of hexane, octane, or h i g h e r , the g r a v i t y is l o w e r e d w i t h less t o t a l solvent. A l s o d i l u t i o n w i t h a n a p h t h a f r a c t i o n a l o n e m a y suffice at 80 ° C .

Each

c r u d e has to b e separately e v a l u a t e d b a s e d o n its properties a n d w a t e r content. If the w a t e r i n the p e r m a n e n t e m u l s i o n is l o w , it m a y not b e w o r t h w h i l e to a d d sufficient solvent to separate a w a t e r layer. T h e w a t e r i n the c r u d e w h i c h is not i n a p e r m a n e n t e m u l s i o n is d e t e r m i n e d b y d i l u t i n g the c r u d e w i t h a m i x t u r e of toluene a n d a n a p h t h a f r a c t i o n ; m u c h of the w a t e r together w i t h the water-set i n o r g a n i c m a t t e r t h e n settles out i n a separatory f u n n e l . If a centrifuge is u s e d , the h i g h g r a v i t y oil-wet i n o r g a n i c m a t t e r separates w i t h the w a t e r c a r r y i n g w i t h i t a s u b s t a n t i a l a m o u n t of o i l . T h u s , s i m p l e g r a v i t y s e p a r a t i o n is preferable. T h e o i l d i l u t e d w i t h the solvent only m a y b e d i s t i l l e d i n a glass flask, fitted

w i t h a r e l a t i v e l y s i m p l e l a b o r a t o r y c o l u m n . B o i l i n g i n the flask is

a c c o m p l i s h e d w i t h o u t b u m p i n g i f a n i n t e r n a l electric heater w h i c h a l l o w s l i t t l e superheat is u s e d . T h e a z e o t r o p i c d i s t i l l a t i o n b r i n g s o v e r v a p o r s w h i c h are c o n d e n s e d . C o n d e n s a t e is separated i n a c o n t i n u o u s glass dec a n t e r w h i c h returns the h y d r o c a r b o n l a y e r to the c o l u m n a n d discharges the w a t e r layer. W h e n the w a t e r content of the s o l u t i o n is r e d u c e d to b e l o w 0 . 1 - 0 . 2 % , no w a t e r is v i s i b l e i n the condensate; the t e m p e r a t u r e at the h e a d of the c o l u m n rises to the b o i l i n g p o i n t of the entraîner itself, a n d the d e h y d r a t i o n is c o m p l e t e . T h e t o t a l w a t e r separated is m e a s u r e d . T h i s v o l u m e w i t h the w a t e r w h i c h has b e e n separated b y décantation after d i l u t i o n a n d before d i s t i l l a t i o n represents the o r i g i n a l a m o u n t of w a t e r present.

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

7.

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A N D

O T H M E R

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of Crude

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115

B a t c h a z e o t r o p i c d i s t i l l a t i o n is also a c c o m p l i s h e d i n t h e l a b o r a t o r y w i t h a s i m p l e flask, condenser, a n d r e c e i v e r w i t h o u t a c o l u m n , c o n t i n u o u s decanter, a n d c o n t i n u o u s reflux, b u t i t takes m u c h l o n g e r a n d is n o t c o m p a r a b l e to a p l a n t o p e r a t i o n , w h i c h is d e v e l o p e d f r o m s u c h l a b o r a t o r y testing. T h e oil-wet s l u d g e is r e m o v e d f r o m t h e d e h y d r a t e d o i l s o l u t i o n i n the flask b y s e t t l i n g a n d d e c a n t i n g or c e n t r i f u g i n g . solvent to free i t of o i l , d r i e d , a n d w e i g h e d .

It is w a s h e d w i t h

T h e w a s h s o l u t i o n is c o m -

b i n e d w i t h the d e h y d r a t e d o i l s o l u t i o n w h i c h contains other solvent a n d the separate entraîner, i f o n e w a s u s e d . S o l v e n t is s t r i p p e d f r o m t h e s o l u t i o n b y d i s t i l l a t i o n to d e t e r m i n e t h e a v a i l a b l e o i l of the c r u d e w h i c h remains. A s m a l l a m o u n t of a d d i t i o n a l i n o r g a n i c m a t t e r m a y settle o u t of c r u d e after a f e w days storage. T h i s is a n extremely s m a l l p a r t i c l e size silt w h i c h is u s u a l l y less t h a n 0 . 0 5 % of t h e o i l . It m i g h t b e r e m o v e d b y a m o r e efficient, h i g h e r speed, centrifuge t h a n u s u a l l y a v a i l a b l e . H o w e v e r , s u c h h i g h s p e e d centrifuges m i g h t b e b a d l y a b r a d e d b y t h e fine silt a n d w o u l d b e too expensive to u s e i n a c t u a l p r a c t i c e . O n e o r t w o days s e t t l i n g at 120°C for example, is a better test m e t h o d a n d is a better p r a c t i c e i n p r o d u c t i o n i f the necessary storage facilities a r e a v a i l a b l e . A d d i t i v e s t o flocculate

the fine silt m i g h t also b e u s e d .

Modified Azeotropic

Distillation

C o n t i n u o u s d i s t i l l a t i o n a l w a y s gives a better, m o r e u n i f o r m p r o d u c t at a l o w e r heat cost a n d u s u a l l y a l o w e r p l a n t cost. A c o n t i n u o u s o p e r a t i o n is essential i n a z e o t r o p i c d i s t i l l a t i o n w h e n a n entraîner is a d d e d , o r it w o u l d necessarily h a v e to b e f r a c t i o n a t e d off to reuse i t after e a c h b a t c h . S e v e r a l v a r i a t i o n s of t h e flow sheet for a z e o t r o p i c d i s t i l l a t i o n are possible, e a c h h a v i n g a c o n t i n u o u s d e c a n t e r w h i c h discharges p u r e w a t e r (less t h a n 0 . 1 % d i s s o l v e d h y d r o c a r b o n o r a r o m a t i c s a n d less t h a n 0 . 0 1 % for a l i p h a t i c s ). F i g u r e 1 is the s i m p l e s t flow sheet. T h e entraîner selected is c h a r g e d to t h e a z e o t r o p i c c o l u m n a n d r e m a i n s s u b s t a n t i a l l y there, rem o v i n g w a t e r c o n t i n u o u s l y b u t b e i n g a l m o s t u n c h a n g e d i f i t has a l o w e r b o i l i n g p o i n t t h a n t h e l i g h t ends of t h e feedstock.

T h e reboiler m a y be

h e a t e d b y other w a y s t h a n b y t h e steam s h o w n i n F i g u r e 1. F i g u r e 2 shows a c o n t i n u o u s a z e o t r o p i c c o l u m n u s i n g a fixed a m o u n t of entraîner w h i c h r e m a i n s i n t h e u n i t . S i n c e reflux is l a r g e l y s u p p l i e d b y f e e d of the e m u l s i o n near the t o p of t h e c o l u m n , t h e entraîner f r o m the d e c a n t e r passes to a r e b o i l e r a n d is f e d b a c k to t h e t o w e r as vapors. T h i s gives a m o r e n e a r l y c o u n t e r - c u r r e n t a c t i o n of the a z e o t r o p i c d i s t i l l i n g o p e r a t i o n , a n d a lesser heat i n p u t r e q u i r e d i n t o t h e viscous o i l at the base of the c o l u m n , u s u a l l y w i t h m o r e or less silt i n suspension w h i l e

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

116

EXTRACTIVE

AND

AZEOTROPIC

DISTILLATION

CONDENSER >

Figure 2. Flow sheet for removing emulsified water by azeotropic distillation using a vapor feed of the reflux of a fixed amount of entraîner the b a l a n c e of the heat r e q u i r e m e n t s for the a z e o t r o p i c d i s t i l l a t i o n w o u l d b e s u p p l i e d to the t h i n , p u r e , entraîner i n a separate reboiler. F i g u r e 3 u t i l i z e s the d i l u t i n g of the o i l e m u l s i o n w i t h the entraîner c o m i n g f r o m the decanter.

T h i s occurs at or near t h e a z e o t r o p i c b o i l i n g

p o i n t . T h i s m i x e r dissolves t h e o i l i n the e m u l s i o n a n d p a r t i a l l y breaks i t w i t h some of the w a t e r a n d silt b e i n g d e c a n t e d off of the f e e d stream of p e r m a n e n t column.

e m u l s i o n a n d entrainer-solvent

g o i n g to the t o p of

the

M o r e entraîner m u s t b e u s e d i n this system to s u p p l y t h a t i n

the m i x e r a n d the decanter; h o w e v e r , it is m i x e d w i t h the o i l p a s s i n g through continuously. F i g u r e 4 is a m o d i f i c a t i o n o f F i g u r e 3 w h e r e the f u n c t i o n of the m i x e r i n d i s s o l v i n g the entraîner a n d the f e e d of o i l e m u l s i o n a n d t h e f u n c t i o n of t h e decanter i n s e p a r a t i n g t h e w a t e r layer f o r m e d is t a k e n o v e r b y a n extractor. I t is one o f the several m e c h a n i c a l l y a g i t a t e d types w h i c h washes o r extracts the o i l out of t h e e m u l s i o n a n d precipitates or discharges as a raffinate l a y e r the w a t e r a l o n g w i t h most of the silt. T h e r e m a i n i n g perm a n e n t e m u l s i o n o i l l a y e r c a r r i e d b y the d i s s o l v i n g entraîner solvent goes to t h e top of the c o l u m n .

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

7.

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A N D

O T H M E R

Demulsification

of Crude

Oils

117

T h e b o t t o m of F i g u r e 4 i n d i c a t e s one system for the h a n d l i n g of t h e c r u d e w i t h silt f r o m the b o t t o m of t h e c o l u m n before, after, or w i t h o u t a heat exchanger to r e c o v e r the sensible heat of the bottoms f r o m this still. A c o n t i n u o u s t h i c k e n e r , of t h e u s u a l r o t a t i n g t y p e w i t h hoes, t h i c k e n s the s u s p e n d e d silt i n t o a n o i l - m u d w h i c h is r e m o v e d , w a s h e d , a n d steamed b e f o r e d i s c a r d . T h e solvent r e c o v e r e d f r o m this w a s h i n g of m u d goes b a c k to t h e f e e d d i s s o l u t i o n . T h e c l e a r c r u d e kerosene s o l u t i o n , n o w free of w a t e r a n d silt, has kerosene r e m o v e d b y d i s t i l l a t i o n , o r i t is p u m p e d t o the refinery. O f t e n w h e r e the c r u d e does not c o n t a i n too m u c h w a t e r i n a p e r m a n e n t e m u l s i o n o r is not too difficult to p u m p , i t w o u l d n o t r e q u i r e the i n i t i a l d i l u t i o n . O t h e r v a r i a t i o n s of flows are p o s s i b l e ; i n e a c h case i f m o r e solvente n t r a i n e r is a d d e d to the e m u l s i o n i n a d v a n c e , it is r e c o v e r e d b y d r a w i n g off a c o r r e s p o n d i n g percentage

of the entraîner layer w h i c h discharges

f r o m the decanter a n d r e c y c l i n g i t b a c k to s o l u t i o n t a n k w h e r e i t is a d d e d to the o p t i m u m p r o p o r t i o n a l a m o u n t of f e e d e m u l s i o n . T h u s , i f kerosene a n d a n a r o m a t i c solvent—e.g., t o l u e n e or x y l e n e — a r e u s e d i n d i s s o l u t i o n of t h e e m u l s i o n , t h e a r o m a t i c c h o s e n as the entraîner is c o n t i n u o u s l y

Figure 3. Flow sheet using entraîner as diluent with premixer and predecanter for separating some of the silt and water

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

118

E X T R A C T I V E

A N D

A Z E O T R O P I C

DISTILLATION

Figure 4. Flow sheet using entraîner as diluent solvent in an extractor used to extract oil from an emulsion with water and to remove a raffinate layer of silt and water (with removal of final silt from the bottoms stream by a thickener, either before or after a heat exchanger) s e p a r a t e d i n the a m o u n t of its a r r i v a l i n the c o l u m n a n d r e c y c l e d b a c k for c o n t i n u o u s d i s s o l u t i o n i n t h e m i x e r . T h i s is c o n t r o l l e d b y o b s e r v i n g the temperatures at several m i d s e c t i o n plates, t h e same as t h e a m o u n t of b u t y l acetate i n the c o l u m n is c o n t r o l l e d i n acetic a c i d d e h y d r a t i o n

(5).

T h e h i g h e r b o i l i n g kerosene is d i s t i l l e d a w a y f r o m t h e c r u d e i n a separate c o l u m n , or it m a y r e m a i n to t h i n the c r u d e i n its t r a n s p o r t to the refinery. Comparison of Azeotropic

Demulsification

with GCOS Process

T o e x e m p l i f y the p r o b l e m s of d e m u l s i f i c a t i o n of o i l , some steps i n the r e c o v e r y of b i t u m i n o u s o i l f r o m t a r sands are c o n s i d e r e d . T h e G r e a t C a n a d i a n O i l Sands, L t d . ( G C O S ) Process has b e e n d e s c r i b e d i n v a r i o u s

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

7.

B A L A S S A

A N D

Demulsification

O T H M E R

p u b l i c a t i o n s (e.g., 8),

of Crude

119

Oils

a n d because of the major p r o b l e m s of s e p a r a t i n g

w a t e r a n d a b r a s i v e m i n e r a l s f r o m the c r u d e , o p e r a t i o n a l losses of m a n y m i l l i o n s of dollars h a v e r e s u l t e d . Mining—overburden,

r e m o v a l , a n d m i n i n g of tar sands

T r a n s p o r t — t a r sands c o n v e y e d , stored, a n d l o a d e d i n extractors Primary Extraction. T h i s is a c c o m p l i s h e d w i t h steam a n d hot w a t e r i n r o t a t i n g c o n d i t i o n i n g d r u m s at a b o u t 190 °F.

T h e t o t a l mass is p i p e d

i n t o a v e r t i c a l s e p a r a t i o n c e l l w h e r e — ( a ) t h e c r u d e b i t u m e n , as a f r o t h , rises to the surface a n d is r e m o v e d ; ( b )

a b o t t o m layer c o n t a i n i n g m a i n l y

sand, c l a y , a n d w a t e r w i t h n o t m o r e t h a n a b o u t 2 % b i t u m e n is p i p e d to the t a i l i n g p o n d ; ( c )

a " m i d d l i n g s " layer w i t h o u t s h a r p d i v i d i n g lines

b e t w e e n the f r o t h a b o v e or the s a n d a n d w a t e r b e l o w . T h i s is a tenacious e m u l s i o n of b i t u m e n i n w a t e r , s t a b i l i z e d b y a s u b s t a n t i a l a m o u n t of s a n d a n d c l a y — m o s t l y oil-wet.

M o s t of the b i t u m e n is r e m o v e d i n

cells b y a i r - f r o t h i n g . T h e s a n d , clay, a n d w a t e r a n d some b i t u m e n is p u m p e d to t h e t a i l i n g s p o n d .

scavenger

unrecoverable

B i t u m e n r e c o v e r y is n o t m o r e

t h a n 9 0 % , thus the tailings c a r r y off at least 1 0 % of that o r i g i n a l l y present. Final Extraction. T h e b i t u m e n f r o m the f r o t h , c o n t a i n i n g s u b s t a n t i a l q u a n t i t i e s of s a n d , clay, a n d w a t e r , is d i l u t e d w i t h n a p h t h a to r e d u c e its v i s c o s i t y so i t c a n b e p u m p e d r e a d i l y .

It is first p u m p e d to 14 s c r o l l -

t y p e centrifuges to r e m o v e l a r g e m i n e r a l particles a n d t h e n to 26 n o z z l e t y p e centrifuges A b r a s i o n i n the charge.

to r e m o v e m o s t of t h e r e m a i n i n g m i n e r a l s a n d expensive

centrifuges

has b e e n

a major

water.

operational

T h e d i l u t e d b i t u m e n s t i l l contains significant q u a n t i t i e s of w a t e r

a n d h y d r o p h i l i c s a n d a n d clay. Cracking and Coking.

T h e d i l u t e b i t u m e n is p u m p e d i n t o

d r u m s , w h e r e i t is c r a c k e d to y i e l d gas a n d c r u d e o i l o v e r h e a d , goes to the refinery.

coker which

R e s i d u a l c o k e contains a l l of the r e s i d u a l s a n d a n d

c l a y w h i c h c o u l d not b e r e m o v e d i n the final extraction, a n d therefore i t is u s e d o n l y as a f u e l for t h e boilers. I n the a z e o t r o p i c system ( J ) , the m i n i n g a n d transport steps are the same, also the c r a c k i n g a n d c o k i n g step, except t h a t i t gives a m u c h i m p r o v e d coke w h i c h is u s e d for m o r e v a l u a b l e p r o d u c t s t h a n as a h i g h ash f u e l . I n the p r i m a r y extraction, h o w e v e r , a h y d r o c a r b o n solvent is a d d e d . This allows a relatively sharp separation between the " m i d d l i n g s " a n d the aqueous b o t t o m layer.

A f r a c t i o n w i t h b o i l i n g r a n g e of octane

suitable, since i t t h e n becomes the a z e o t r o p i c

entraîner for the

A n a r o m a t i c solvent—e.g., t o l u e n e — m i g h t b e better, b u t i t m a y

is

water. require

another s e p a r a t i o n later. I n the final e x t r a c t i o n because of solvent a d d i t i o n i n t h e p r i m a r y extraction, the m i n e r a l matter r e a d i l y separates f r o m the b o t t o m

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

aqueous

120

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AND

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DISTILLATION

l a y e r i n s t e a d of r e q u i r i n g batteries of expensive centrifuges w i t h c o n s i d e r a b l e d a m a g e r e s u l t i n g f r o m a b r a s i o n of the fine s a n d . A

suitable

s e t t l i n g a i d assists this, a n d the w e t sediment, a l m o s t free of b i t u m e n , is u s e d as fill. T h e w a t e r contains o n l y a s m a l l a m o u n t of d i s s o l v e d solvent w h i c h is r e c o v e r e d b y s t r i p p i n g , o r w a s t e d , a n d the w a t e r itself is r e u s e d or d i s c a r d e d to surface waters as it is e n v i r o n m e n t a l l y

acceptable.

T h e t o p b i t u m e n l a y e r a n d t h e " m i d d l i n g s " l a y e r are c o m b i n e d a n d are p u m p e d to a n a z e o t r o p i c d i s t i l l a t i o n system, as d i a g r a m m e d i n F i g ures 1, 2, 3, a n d 4. T h e c h o i c e of

flow

sheet d e p e n d s o n the

relative

a m o u n t s of w a t e r r e m a i n i n g a n d the a m o u n t s a n d characteristics of the m i n e r a l matter. T h e systems of F i g u r e s 3 a n d 4 r e m o v e m o r e w a t e r a n d silt b e f o r e the a z e o t r o p i c d i s t i l l a t i o n , thus s a v i n g heat. U s i n g t h e system of F i g u r e 4 i n s t e a d of the t h i c k e n e r , a s i m p l e storage t a n k a l l o w i n g t w o days residence for settling o u t a l l silt, i n c l u d i n g c o l l o i d a l c l a y w h i c h passes t h r o u g h the c o l u m n , m a y b e u s e d after the heat exchanger. If a n a p h t h a f r a c t i o n has b e e n u s e d i n the d i l u t i o n a n d as the entrainer, it is left i n as a d i l u e n t for r e d u c i n g the v i s c o s i t y i n p u m p i n g the o i l to t h e refinery.

A l t e r n a t i v e l y , some o r a l l is r e m o v e d as a s l i p stream

f r o m t h e reflux g o i n g to the t o p of the a z e o t r o p i c c o l u m n . If toluene or other a r o m a t i c solvent is u s e d , i t w o u l d b e so r e m o v e d or r e m o v e d i n a separate d i s t i l l a t i o n for recycle. O i l - w e t materials, s a n d , a n d clay, s e p a r a t e d f r o m either o i l or w a t e r layers, are w a s h e d w i t h the solvent o r d i l u e n t u n t i l t h e y are free of b i t u m e n a n d the r e s i d u a l solvent is s t r i p p e d f r o m the m i n e r a l m a t t e r w i t h steam. T h e m i n e r a l m a t t e r is c l e a n a n d is sent to waste or u s e d as

fill

w i t h o u t d a n g e r of spontaneous c o m b u s t i o n , or i t is u s e d i n cement m a n u facture.

T h e aqueous phases c o n d e n s e d f r o m s u c h s t r i p p i n g a n d f r o m

the d e c a n t e r of the a z e o t r o p i c system has so l i t t l e solvent, i n h u n d r e d t h s of a percent, that i t is neglected.

It evaporates r e a d i l y i n o p e n storage.

T h i s d i s t i l l e d w a t e r is u s e d for a n y s u i t a b l e p u r p o s e . R e c o v e r y of the b i t u m e n b y this system has b e e n almost 9 8 % c o m p a r e d w i t h the losses i n the G C O S system, a n d the solvent losses are l o w . T h e major a d v a n t a g e of this system is e l i m i n a t i o n of the 14-scroll t y p e centrifuges a n d 26-nozzle t y p e m a c h i n e s u s e d i n the G C O S p l a n t w h i c h h a v e h a d excessive r e p l a c e m e n t , m a i n t e n a n c e , a n d r e p a i r costs because o f the a b r a s i v e a c t i o n of the fine solids o n these h i g h speed, p r e c i s i o n machines. T h e b i t u m e n o b t a i n e d is the u n m o d i f i e d n a t i v e b i t u m e n w i t h a s u b s t a n t i a l percentage of h i g h m e l t i n g , a l i p h a t i c s o l u b l e c o m p o n e n t s .

These

are separated f r o m t h e l o w m e l t i n g c o m p o n e n t s b y solvent e x t r a c t i o n or solvent p r e c i p i t a t i o n . T h e h i g h m e l t i n g c o m p o n e n t s are u t i l i z e d i n p r o tective coatings for metals o r i n heat resistant r o a d surface compositions. If coke is o b t a i n e d f r o m this process, it is free of m i n e r a l m a t t e r a n d

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

7.

BALASSA AND OTHMER

Demulsification of Crude Oils

121

is used for the same uses as other high grade petroleum cokes—e.g., in electrodes or activated carbon, as well as in metallurgical uses where the high ash content resulting from the residual minerals would prevent that from the GCOS system being used. Another advantage is that little water is required in the azeotropic process since most of the water is recycled and that which is not recycled is immediately passed to surface waters without environmental damage. Also, removing all organics from the mineral matters means that these can be used as fill or otherwise without fire hazard, odors, or other environmental problems caused by microbiological attacks on any residual bitumen left on the minerals as in the GCOS process. Literature Cited 1. Balassa, L. L., U.S. Patent 3,468,789 (Sept. 23, 1969). 2. Clarke, H. T., Othmer, D. F., U.S. Patent 1,804,745 (May 12, 1931). 3. Othmer, D. F., "Encyclopedia of Chemical Technology," 2nd ed., Vol. 2, p. 839, 1963. 4. Othmer, D. F., U.S. Patent 1,917,391 (July 11, 1933). 5. Othmer, D. F., Chem.&Met. Eng. (1941) 48, 91. 6. Othmer, D. F., Chem. Eng. Progr. (1963) 59, 6, 67. 7. Othmer, D. F., TenEyck, Ε. H., Ind. Eng. Chem. (1949) 41, 2897. 8. "Our Sun," Sun Oil Co., House Publication (Autumn, 1967). RECEIVED November 24, 1970.

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

8 Distillation Calculations with Nonideal Mixtures a

JOSEPH A. BRUNO, JOHN L . YANOSIK, and JOHN W. TIERNEY Chemical Engineering Department, University of Pittsburgh, Pittsburgh, Pa. 15213

A new iteration sequence is presented for solving distillation problems with composition dependent equilibrium and enthalpy relations. For a steady state, non-reacting system with m components and n stages, the procedure requires simultaneous iteration of n(m + 1) variables. These are the vapor flow rates, the stage temperatures, and all but one of the liquid compositions. The basic equations for an equilibrium stage system are presented using matrix notation. The calculation sequence is outlined, and a correction algorithm based on Newton's method is derived. This requires the calculation of the Jacobian matrix of partial derivatives, and an analytical method for obtaining these derivatives by vector differentiation of the system equations is presented. This method is much simpler than those used previously. Modification of the iteration process to hold selected vapor flows constant is described, and a method of obtaining starting values for the first iteration is presented. Results obtained from solution of a sample extractive distillation problem are presented. Quadratic convergence is obtained near the solution, indicating that the equations derived for the Jacobian matrix are correct.

^ p h e m a t h e m a t i c a l m o d e l for a steady state e q u i l i b r i u m stage s e p a r a t i o n process consists of a l a r g e set o f s i m u l t a n e o u s n o n l i n e a r e q u a t i o n s w h i c h m u s t b e s o l v e d to d e t e r m i n e the phase flow rates, the stage t e m peratures, a n d t h e phase c o m p o s i t i o n . A m a t r i x n o t a t i o n w a s p r e v i o u s l y p r e s e n t e d (1, 2) w h i c h p e r m i t s w r i t i n g t h e e q u a t i o n s i n a concise f o r m "Present address: A M O C O Production Co., Tulsa, Okla.

122

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

8.

BRUNO,

YANOsiK,

A N D

Nonideal

TiERNEY

a n d p r o v i d e s for a n y interstage

flow

123

Mixtures

pattern.

It w a s also s h o w n that

these equations c a n b e a n a l y t i c a l l y differentiated t o o b t a i n iterative algo r i t h m s w i t h q u a d r a t i c convergence rates near the s o l u t i o n . F o r t h e case w h e r e the e q u i l i b r i u m ratios are functions o n l y of stage

temperatures

a n d not of c o m p o s i t i o n s , it w a s s h o w n t h a t q u a d r a t i c convergence

can

be o b t a i n e d b y s i m u l t a n e o u s i t e r a t i o n of o n l y the stage temperatures a n d the v a p o r

flow

rates.

A l l other variables can be obtained b y

solving

n o t h i n g m o r e c o m p l i c a t e d t h a n sets of s i m u l t a n e o u s l i n e a r equations. O n c e a set of temperatures a n d v a p o r flows are a s s u m e d , t h e equations b e c o m e l i n e a r i n the r e m a i n i n g variables.

T h u s , for a system w i t h η

stages a n d m c o m p o n e n t s , i t is o n l y necessary to iterate o n 2 n v a r i a b l e s rather t h a n the c o m p l e t e set o f n ( 2 m + 3 ) u n k n o w n s . If the e q u i l i b r i u m ratios are functions of phase c o m p o s i t i o n s as occurs i n l i q u i d e x t r a c t i o n or extractive d i s t i l l a t i o n , it is necessary to i n c l u d e m o r e v a r i a b l e s i n the iterative process.

It w a s later s h o w n ( 3 )

t h a t for

l i q u i d e x t r a c t i o n p r o b l e m s w i t h k n o w n stage temperatures, t h e m i n i m u m n u m b e r of i t e r a t i o n variables for q u a d r a t i c convergence is ran, t h e η v a p o r flow rates, a n d n(m v a r i a b l e s is η(2m

— 1) of the phase compositions. T h e t o t a l n u m b e r of + 2 ) because t h e temperatures are k n o w n . T h e i t e r a

t i o n sequence is c o m p l e t e l y different for this case as c o m p a r e d w i t h the p r e v i o u s case w i t h c o m p o s i t i o n i n d e p e n d e n t e q u i l i b r i u m ratios. D e v e l o p e d here is a c o r r e c t i o n process w i t h q u a d r a t i c

convergence

near t h e s o l u t i o n for p r o b l e m s i n w h i c h the e q u i l i b r i u m ratios are c o m p o s i t i o n d e p e n d e n t a n d i n w h i c h the stage temperatures are n o t fixed b u t must be determined.

It is necessary to i n t r o d u c e t h e energy

equations to g i v e the a d d i t i o n a l equations n e e d e d .

balance

T h e derivation fol

l o w s t h e g e n e r a l lines o f that for the l i q u i d e x t r a c t i o n p r o b l e m , b u t t h e extension is not t r i v i a l . T h e m e t h o d r e q u i r e s the s i m u l t a n e o u s c o r r e c t i o n of n(m

-f- 1) variables. W e w i l l also present a s i m p l i f i e d m e t h o d of a n a

l y t i c a l l y differentiating the m a t r i x equations w h i c h g r e a t l y reduces

the

w o r k necessary to d e r i v e a c o r r e c t i o n a l g o r i t h m . I n related convergence

investigations

Roche

(4)

for c o m p o s i t i o n d e p e n d e n t

constant temperature.

has d e m o n s t r a t e d

quadratic

l i q u i d extraction problems

H e essentially iterates o n a l l η(2m

at

+ 2) variables.

N e l s o n ( 5 ) has u s e d the m a t r i x n o t a t i o n of References I a n d 2 t o i n v e s t i gate systems w h e r e c h e m i c a l r e a c t i o n occurs i n the stages. Equations for an Equilibrium The

Separation System

equations d e s c r i b i n g a steady-state

e q u i l i b r i u m stage system

w i t h o u t c h e m i c a l r e a c t i o n are s u m m a r i z e d here. has b e e n p r e v i o u s l y d i s c u s s e d (1,2,3),

T h e matrix notation

a n d a l l s y m b o l s are defined b e l o w .

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

124

E X T R A C T I V E AND

AZEOTROPIC DISTILLATION

T h e o v e r a l l m a t e r i a l b a l a n c e e q u a t i o n gives a n i m p o r t a n t r e l a t i o n b e t w e e n t h e l i q u i d a n d v a p o r flow rate vectors, V a n d L . BL

+ AV

+ Σ (F*) 3

= Ο

(1)

T h e m a t r i c e s A a n d Β a r e fixed b y t h e interstage flow p a t t e r n a n d together w i t h t h e f e e d m a t r i x F are a s s u m e d to b e g i v e n i n t h e p r o b l e m statement. T h e fact that t h e l i q u i d c o m p o s i t i o n s m u s t s u m to a constant (1.0 i f m o l e fractions are u s e d ) i n e a c h stage is g i v e n b y : Σ (ZO = U

(2)

A s i m i l a r e q u a t i o n c a n b e w r i t t e n f o r t h e v a p o r phase, b u t i t is n o t i n d e pendent a n d can be derived b y combining Equations ( 1 ) , ( 2 ) , a n d (3). A m a t e r i a l b a l a n c e c a n b e w r i t t e n f o r e a c h c o m p o n e n t i n e a c h stage, Β L X> + A V F> +

= 0; 1 < j < m

(3)

X a n d Y are vectors c o n t a i n i n g l i q u i d a n d v a p o r c o m p o s i t i o n s f o r c o m j

j

p o n e n t /'. T h e matrices L a n d V are d i a g o n a l a n d h a v e t h e same elements o n t h e d i a g o n a l as t h e vectors L a n d V. A n energy b a l a n c e a r o u n d e a c h stage gives BLH

+ AY

G +

Q +

Q

f

=

(4)

0

H a n d G are vectors c o n t a i n i n g t h e specific enthalpies of l i q u i d a n d v a p o r phases i n e a c h stage.

Q is t h e vector o f stage heat duties, a n d Q is t h e

f e e d e n t h a l p y vector.

Q a n d Q are a s s u m e d to b e g i v e n i n t h e p r o b l e m

f

f

statement. T h e e q u i l i b r i u m r e l a t i o n b e t w e e n l i q u i d a n d v a p o r c o m p o s i t i o n s is given by Λ> Υ

3

-

Γ ' K>" X> = Ο; 1 < j < m ?

(5)

Λ/ a n d Ρ a r e t h e a c t i v i t y coefficient m a t r i c e s for v a p o r a n d l i q u i d phases a n d are d i a g o n a l . F o r i d e a l solutions, t h e y b e c o m e t h e i d e n t i t y m a t r i x . K

;

is t h e f u g a c i t y ratio m a t r i x a n d is also d i a g o n a l . T h e enthalpies a n d e q u i l i b r i u m d a t a are p h y s i c a l properties o f t h e

m i x t u r e s b e i n g separated a n d are a s s u m e d to b e k n o w n e x p l i c i t f u n c t i o n s of c o m p o s i t i o n s a n d temperatures as f o l l o w s :

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

8.

B R U N O ,

YANOSIK,

A N D

Nonideal

T I E R N E Y

H{X\

G

G(Y ,

Y,

. . Y,

T)

(7)

Γ

Γ(Χ , X,

. . X,

T)

(8)

Λ

Λ ( F , 7», . . F » ,

T)

(9)

3

2

3

. . X",

T)

H

2

X\

125

Mixtures

m

m

2

(6)

K(T)

K

(10)

E a c h of the a b o v e functions is a s s u m e d to b e c o n t i n u o u s a n d to possess first derivatives w i t h respect to c o m p o s i t i o n a n d t e m p e r a t u r e .

Also, the

c o m p o s i t i o n of c o m p o n e n t 1 is n o t to b e c o n s i d e r e d as a n i n d e p e n d e n t v a r i a b l e i n the d e v e l o p m e n t omitting X The

1

and Y

Calculation

1

w h i c h f o l l o w s , a n d this is e m p h a s i z e d

by

as arguments i n E q u a t i o n s 6 - 9 .

Sequence

E q u a t i o n s 1-10 constitute a set of ( 5 m + 5 ) m a t r i x equations w h i c h are to b e s o l v e d s i m u l t a n e o u s l y to d e t e r m i n e 2 m c o m p o s i t i o n

vectors,

t w o flow vectors, a t e m p e r a t u r e vector, t w o e n t h a l p y vectors, 2 m a c t i v i t y coefficient vectors, a n d m f u g a c i t y r a t i o vectors.

T h e solution must be

iterative because the equations are n o n l i n e a r . H o w e v e r , there are v a r i o u s m e t h o d s of o r g a n i z i n g the c a l c u l a t i o n s , a n d one of o u r p r i m a r y objects here is to d e v e l o p a n efficient c a l c u l a t i o n order. A t one extreme i t w o u l d b e possible to c o n s i d e r a l l 5 m +

5 vectors as i t e r a t i o n v a r i a b l e s a n d thus

to h a v e a process w i t h ( 5 m + 5 ) η v a r i a b l e s of i t e r a t i o n . It seems o b v i o u s that a m o r e efficient m e t h o d is to r e d u c e the size of t h e iterative process b y e l i m i n a t i n g as m a n y of t h e v a r i a b l e s as possible.

I n p r a c t i c e , it is

u n d e s i r a b l e a c t u a l l y to e l i m i n a t e t h e v a r i a b l e s ; i n s t e a d the v a r i a b l e s w i l l b e d i v i d e d i n t o t w o groups.

T h e first g r o u p is the v a r i a b l e s w h i c h w i l l

b e i t e r a t e d a n d w i l l b e c a l l e d t h e i t e r a t e d or i n d e p e n d e n t v a r i a b l e s ; t h e second group w i l l be called dependent

variables.

One equation must

b e u s e d t o define e a c h d e p e n d e n t v a r i a b l e , a n d these equations w i l l b e c a l l e d the d e f i n i n g equations. T h e r e m a i n i n g equations, e q u a l i n n u m b e r to t h e i n d e p e n d e n t variables, w i l l b e c a l l e d the error equations.

The

i t e r a t i o n sequence w i l l t h e n b e to assume first a set of values for the i n d e p e n d e n t variables a n d t h e n to solve t h e d e f i n i n g equations for the de p e n d e n t variables.

T h e error equations are t h e n u s e d to correct

the

i n d e p e n d e n t v a r i a b l e s , a n d the process is repeated. T h e n u m b e r of i n d e p e n d e n t variables s h o u l d g e n e r a l l y b e as s m a l l as possible. A l s o , the d e f i n i n g equations s h o u l d p e r m i t s i m p l e c a l c u l a t i o n of the d e p e n d e n t variables, a n d t h e c o r r e c t i o n process itself s h o u l d b e s i m p l e a n d efficient.

H e r e the set of i n d e p e n d e n t v a r i a b l e s has b e e n

c h o s e n to b e as s m a l l as possible subject t o t h e l i m i t a t i o n t h a t the d e f i n i n g equations

r e m a i n l i n e a r i n the

dependent

variables.

The

correction

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

126

EXTRACTIVE

AND AZEOTROPIC

DISTILLATION

a l g o r i t h m is also l i n e a r a n d is t h e m u l t i v a r i a b l e f o r m o f t h e N e w t o n Raphson method. T h e set o f i n d e p e n d e n t v a r i a b l e s w h i c h satisfies these r e q u i r e m e n t s is the v a p o r flow v e c t o r V , the l i q u i d p h a s e c o m p o s i t i o n s , X t o X , a n d 2

m

the t e m p e r a t u r e v e c t o r T . T h e c a l c u l a t i o n sequence is, a. V a l u e s are a s s u m e d f o r ( V , X , X , . . X , T ) . 2

3

W

b. T h e l i q u i d flow vector L is c a l c u l a t e d u s i n g E q u a t i o n 1. c. E q u a t i o n 2 is u s e d to c a l c u l a t e X . 1

d . E q u a t i o n 3 is u s e d m times t o c a l c u l a t e Y ^ ,.. Y . e. E q u a t i o n s 6 - 1 0 a r e u s e d t o c a l c u l a t e t h e d e p e n d e n t v a r i a b l e s H, G, Λ, Γ, a n d K . A l l v a r i a b l e s h a v e n o w b e e n e v a l u a t e d f o r the c u r r e n t set o f i n d e p e n d e n t v a r i a b l e s . f. C u r r e n t values f o r a l l v a r i a b l e s are s u b s t i t u t e d i n t o the error e q u a tions, w h i c h a r e E q u a t i o n s 4 a n d 5. I f t h e equations a r e satisfied, t h e i t e r a t i v e process is t e r m i n a t e d . O t h e r w i s e , t h e i n d e p e n d e n t v a r i a b l e s m u s t b e c o r r e c t e d , a n d the c a l c u l a t i o n r e p e a t e d f r o m Step b . 1

The Jacobian

Correction

2

m

Matrix

T h e o n l y u n d e f i n e d step i n t h e c a l c u l a t i o n sequence p r o p o s e d a b o v e is t h e c o r r e c t i o n o f the i n d e p e n d e n t v a r i a b l e s i n step f. A l i n e a r correc t i o n process is g i v e n b y ( J ) v { ( C )

v

+

1

-

(C)v}

=

-

(11)

(D)v

w h e r e C is t h e d i r e c t s u m o f t h e i n d e p e n d e n t v a r i a b l e s i n t h e o r d e r ( V , X , X , . . X , T ) , a n d D is the d i r e c t s u m o f the error vectors, defined as 2

3

m

E

k

= AY k

k

-

Γ*Κ*Χ*; 1 < k < m

= BL H + AVG T h e most r a p i d convergence

+ Q+ Q

f

(12) (13)

o f E q u a t i o n 11 t o t h e s o l u t i o n is o b

t a i n e d w h e n J is t h e J a c o b i a n m a t r i x , defined as t h e m a t r i x i n w h i c h e a c h element is t h e p a r t i a l d e r i v a t i v e o f o n e of t h e errors w i t h respect to o n e o f t h e i t e r a t i o n v a r i a b l e s w i t h a l l other i t e r a t i o n v a r i a b l e s h e l d constant. T h u s , a n estimate o f the effect o f e a c h c h a n g e i n a n i t e r a t i o n v a r i a b l e o n e a c h o f t h e errors i s i n c l u d e d i n t h e c o r r e c t i o n . T h e d i s a d v a n t a g e i n u s i n g t h e J a c o b i a n m a t r i x is t h e large n u m b e r o f d e r i v a t i v e s n e e d e d , (mn + n ) , a n d a s i m p l e means o f o b t a i n i n g these d e r i v a t i v e s is 2

needed.

W e h a v e f o u n d that v e c t o r differentiation o f t h e m a t r i x e q u a

tions g i v e n a b o v e does g r e a t l y s i m p l i f y t h e d e r i v a t i o n of t h e e q u a t i o n s for c a l c u l a t i o n o f t h e J a c o b i a n . B y vector differentiation w e m e a n t h e o p e r a t i o n o f differentiating one v e c t o r w i t h respect to a s e c o n d vector.

T h e result is a m a t r i x i n

w h i c h e a c h c o l u m n is t h e d e r i v a t i v e o f t h e first v e c t o r w i t h respect t o

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

8.

B R U N O ,

YANOSiK,

Nonideal

A N D T B E R N E Y

127

Mixtures

one o f t h e elements o f t h e s e c o n d vector. F o r e x a m p l e ( dL/dV ) is a n η b y η m a t r i x i n w h i c h t h e j t h c o l u m n is (dL/dVj),

a n d t h e ij element is

(dk/dv,). J c a n n o w b e defined b y v e c t o r derivatives. p a r t i t i o n e d into (m + l )

2

F i r s t , h o w e v e r , i t is

s u b m a t r i c e s , e a c h o f size η b y n . S u b s c r i p t s

are u s e d t o designate t h e submatrices.

Thus, from the definition of the

Jacobian matrix, w e obtain

w ' ' * J* =

{ ~ ; 2

f^;k

1

(

4

)

(15)

< k <m

=

1

(16)

m+l

B e f o r e p r o c e e d i n g w i t h t h e e v a l u a t i o n o f E q u a t i o n s 1 4 - 1 6 , some use f u l relations a m o n g t h e v a r i a b l e s w i l l b e d e r i v e d b y differentiating t h e d e f i n i n g equations ( E q u a t i o n s 1-3 a n d 6 - 1 0 ) w i t h respect t o t h e i t e r a t i o n variables.

T h e s e results w i l l b e u s e d w h e n

t h e error equations a r e

differentiated i m p l i c i t l y . F r o m t h e o v e r a l l m a t e r i a l b a l a n c e , E q u a t i o n 1,

% Because X . . X

m

2

= -

B

_ 1

A = -

R

(17)

are iteration variables, I l ; 2 < j, k < m

(18)

jk

where 8

jk

=

0 if /^

t h e fact that X

1

k a n d equals 1.0 i f / — k. F r o m E q u a t i o n 2 a n d

is n o t a n i t e r a t i o n v a r i a b l e , g -

=

-

î; 2 < j < m

D i f f e r e n t i a t i n g E q u a t i o n 3 w i t h respect to i n d e p e n d e n t

(19) liquid

compo-

sitions. AY*

y^u= ~ Y-'S

-1

2

£ L = v-iR-i L; 2 < k < m

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

(20) (21)

128

EXTRACTIVE

AND

AZEOTROPIC

DISTILLATION

F o r Y , a different result is o b t a i n e d because of E q u a t i o n 19. 1

T o d e r i v e E q u a t i o n s 20 a n d 2 1 , i t m u s t b e r e m e m b e r e d differentiation is w i t h respect to X ,

that the

h o l d i n g V , T , a n d a l l other i n d e

k

p e n d e n t l i q u i d c o m p o s i t i o n s constant. W i t h V constant, L m u s t also b e constant because of E q u a t i o n 17. E q u a t i o n 3 w i l l n o w b e differentiated w i t h respect to V, h o l d i n g Τ and X . . X 2

constant. I n this case L is not constant, a n d differentiation

m

of the first t e r m B L X ' causes difficulty because L is a d i a g o n a l m a t r i x a n d not a vector.

T h i s c a n b e r e s o l v e d b y r e w r i t i n g B L X ' as BXJL,

n o w L is a vector.

and

T h i s s p e c i a l t y p e of c o m m u t a t i v i t y for t h e p r o d u c t

of a d i a g o n a l m a t r i x a n d a vector is u s e d a g a i n i n the p r o d u c t A V Y ' a n d frequently i n the derivations w h i c h follow. by V

T h e d e r i v a t i v e of E q u a t i o n 3

gives,

=Y

dV

P a r t i a l derivatives

-1

{R

- 1

S Ε - Y} ; ι 7

?

< j <

of the p h y s i c a l properties

(22)

™

given by

Equations

6 - 1 0 w i l l also b e n e e d e d i n the d e r i v a t i o n s of t h e J a c o b i a n submatrices. H o w e v e r , the exact f o r m of E q u a t i o n s 6 - 1 0 is not k n o w n a n d w i l l v a r y f r o m p r o b l e m to p r o b l e m .

T h e c o n v e n t i o n w i l l b e a d o p t e d that a n y

p a r t i a l d e r i v a t i v e i n v o l v i n g a p h y s i c a l p r o p e r t y is to b e i n t e r p r e t e d u s i n g the v a r i a b l e s

given

as arguments

i n Equations 6-10.

For

( d G / d Y ) means the p a r t i a l d e r i v a t i v e of G w i t h respect to Y 2

Y ... Y 3

and Τ

m

constant. A l l vector

derivatives

example, 2

holding

of p h y s i c a l p r o p e r t y

vectors w i l l b e d i a g o n a l matrices. T h i s is necessary because t h e p h y s i c a l properties i n a n y one stage are f u n c t i o n s o n l y of t h e c o m p o s i t i o n s a n d t e m p e r a t u r e i n that stage.

The Jacobian

Submatrices

S e v e n different e q u a t i o n s are n e e d e d to c a l c u l a t e the v a r i o u s s u b matrices of J : 1. T h e first g r o u p of s u b m a t r i c e s is o b t a i n e d b y differentiating t h e error vector w i t h respect to i n d e p e n d e n t c o m p o s i t i o n s . T h e g e n e r a l e q u a t i o n is

dX

k

" ~

dX

k

+

Y

1

(23)

K'X' - -

dX"

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

8.

YANOsiK,

B R U N O ,

Nonideal

A N D TiERNEY

129

Mixtures

F o r 2 ^ j,k ^ m, E q u a t i o n s 18 a n d 2 0 are u s e d t o o b t a i n

-

2. F o r / =

2<j,k<m

1 i n E q u a t i o n 23, E q u a t i o n s 19 a n d 21 are u s e d

Ju = A ^ R - i L

-

Y

Y^R-'L

1

+ P K

-

1

(24) K

1

^

^ ) ;

1

2 < k < m

3. T h e derivatives of t h e m a t e r i a l b a l a n c e errors w i t h respect t o v a p o r flows are e v a l u a t e d :

dE' dV a n d t h e n u s i n g E q u a t i o n 22

Jyi = à Y~ (Β^Χ'R ~ YO + Υ'Ύ 1

Σ (|γ^)

-1

l

( R X S - Y Ρ)

(y" ) 1

_ 1

p

(26)

1 < j < m

4. T h e energy b a l a n c e errors are next differentiated w i t h respect to v a p o r flows.

dE« dV

•

B

i

^

i

f

i

+

i

ï|,(|)(f)

<w

U s i n g E q u a t i o n s 17 a n d 22

lm i,i +

= - B H R + A G + A

v

f

(J^j Y"

1

(E X E -1

p

- Y ) (28) p

5. T h e derivatives of t h e energy balances w i t h respect to c o m p o sitions are,

dE ~dX

m+1

r

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

130

EXTRACTIVE

A N DAZEOTROPIC

DISTILLATION

T h e n , u s i n g E q u a t i o n 20, a n d after some rearrangement.

W

= B L

(J^ - A (Jf^j R - L 2

(30)

< k< m

6. T h e derivatives o f the m a t e r i a l b a l a n c e errors w i t h respect t o Τ are next c a l c u l a t e d .

%

-fa—I'(^)-M'(^)-S*(S.> 1<j < m

(31)

7. F i n a l l y , the d e r i v a t i v e o f the energy b a l a n c e w i t h respect t o Τ gives,

^ ' - W , Change

of Iteration

=

BL(g) Av(g)

(32)

+

Variable

T h e J a c o b i a n m a t r i x d e v e l o p e d a b o v e is b a s e d u p o n a specific m o d e l of a staged system i n w h i c h t h e flow rates, the temperatures, a n d the phase c o m p o s i t i o n s are a l l u n k n o w n a n d m u s t b e d e t e r m i n e d . A v a r i a t i o n o f this m o d e l w h i c h often occurs i n p r a c t i c e r e q u i r e s that a s o l u t i o n b e f o u n d i n w h i c h one or m o r e o f the flows has a fixed v a l u e . I t is r e l a t i v e l y s i m p l e t o m o d i f y t h e i t e r a t i o n p r o c e d u r e a n d the J a c o b i a n m a t r i x for the case o f fixed v a p o r flows b y s u b s t i t u t i n g one o f the elements o f Q, the heat e x c h a n g e vector, for e a c h o f the v a p o r flows w h i c h is to b e T o i n t e r c h a n g e t h e v a r i a b l e s Vi a n d q

jy

fixed.

the f o l l o w i n g p r o c e d u r e c a n

b e u s e d . T h e J a c o b i a n m a t r i x is first m o d i f i e d b y setting t o z e r o the i t h •column o f e a c h o f the s u b m a t r i c e s J * * for k =

1 t o m. T h e i t h c o l u m n

contains the effect o f c h a n g i n g of Vi o n e a c h element o f E; because q, does n o t enter i n t o a n y o f t h e m a t e r i a l b a l a n c e e q u a t i o n s , this c o l u m n b e comes zero. T h e i t h c o l u m n o f Jm+ι,ι is set e q u a l to the ; t h c o l u m n o f a n η b y η i d e n t i t y m a t r i x because q$ enters o n l y the o n e energy b a l a n c e e q u a t i o n . U p o n s o l v i n g for the c o r r e c t i o n vector [ ( C ) v + i — ( C ) v ] t h e i t h element is n o w the c o r r e c t i o n for q$. T h e c o r r e c t i o n to υ is zero. τ

T h i s p r o c e d u r e c a n o n l y b e u s e d for fixed v a p o r flows. I f l i q u i d

flows

are t o b e fixed, a m o r e c o m p l i c a t e d p r o c e d u r e is n e e d e d a n d w i l l n o t b e d e v e l o p e d here. F o r s i m p l e c o u n t e r c u r r e n t systems i t is u s u a l l y pos sible to fix p r o d u c t l i q u i d flows b y fixing c e r t a i n v a p o r flows. A n o b v i o u s m o d i f i c a t i o n o f the a b o v e p r o c e d u r e c a n b e u s e d t o fix temperatures i f desired.

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

8.

B R U N O ,

YANOsiK,

A N D

TiERNEY

Initial Values for Iteration

Nonideal

131

Mixtures

Variables

A n i m p o r t a n t p a r t of the i t e r a t i o n p r o c e d u r e is to select i n i t i a l values for t h e i t e r a t i o n v a r i a b l e s

( V,X

2

... X , T ) .

The

m

correction

sequence

g i v e n b y E q u a t i o n 11 w i l l c o n v e r g e for s t a r t i n g values sufficiently close to t h e s o l u t i o n . T h e r e is no s i m p l e w a y of k n o w i n g w h e t h e r a g i v e n set of i n i t i a l values is w i t h i n this convergence

range or not.

Every

effort

s h o u l d b e m a d e to m a k e t h e i n i t i a l values as g o o d as possible.

The

m e t h o d w e h a v e u s e d is d e s c r i b e d here. T h e temperatures of the r e b o i l e r a n d the condenser are first e s t i m a t e d u s i n g w h a t e v e r i n f o r m a t i o n is a v a i l a b l e . T h e temperatures of the i n t e r m e d i a t e stages are t h e n o b t a i n e d b y l i n e a r i n t e r p o l a t i o n b e t w e e n

con-

denser t e m p e r a t u r e a n d r e b o i l e r t e m p e r a t u r e . T h e i n i t i a l v a p o r flows are t h e n c a l c u l a t e d b y e s t i m a t i n g the l i q u i d a n d v a p o r enthalpies a n d s o l v i n g s i m u l t a n e o u s l y E q u a t i o n 1, t h e o v e r a l l m a t e r i a l b a l a n c e , a n d E q u a t i o n 4, t h e e n e r g y b a l a n c e . T h e c o m p o s i t i o n s are u n k n o w n for the e n t h a l p y c a l c u l a t i o n . T h e p r o c e d u r e w e h a v e u s e d is to set a l l c o m p o s i t i o n s i n a l l stages e q u a l to 1/m; this is a r o u g h approximation. A f t e r o b t a i n i n g V a n d L , the a c t i v i t y coefficients a n d f u g a c i t y ratios are c a l c u l a t e d u s i n g 1/m as t h e average c o m p o s i t i o n i n a l l stages.

Then

E q u a t i o n s 3 a n d 5 are s i m u l t a n e o u s l y s o l v e d to g i v e the l i q u i d phase c o m p o s i t i o n s . T h e s e c o m p o s i t i o n s for e a c h stage are t h e n s u m m e d a n d n o r m a l i z e d to one. T h e s e serve as t h e first estimates for X , . . X . 2

Modification The

of Correction

requirement

m

Algorithm

that a l l of the v a r i a b l e s l i e w i t h i n

reasonable

p h y s i c a l b o u n d s c a n b e i n c o r p o r a t e d i n t o the c o r r e c t i o n a l g o r i t h m . h a v e d o n e this b y s p e c i f y i n g t h a t at a l l times the v a p o r a n d l i q u i d m u s t b e p o s i t i v e or zero; t h e phase c o m p o s i t i o n s m u s t n o t b e

We flows

negative

or greater t h a n one; a n d the temperatures m u s t l i e w i t h i n p r e d e t e r m i n e d l i m i t s . I f at a n y t i m e d u r i n g t h e c o r r e c t i o n process these l i m i t s are exc e e d e d , the c u r r e n t i t e r a t i o n is t e r m i n a t e d . I f it is the first i t e r a t i o n , t h e n a n e w set of i n i t i a l values w i l l b e n e e d e d .

If i t is the s e c o n d or a later

i t e r a t i o n , t h e n i t is a s s u m e d t h a t the corrections m a d e i n t h e p r e v i o u s i t e r a t i o n w e r e too large, a n d the c u r r e n t i t e r a t i o n is r e p e a t e d u s i n g oneh a l f the corrections p r e d i c t e d i n t h e p r e v i o u s step. It m a y b e necessary to repeat this process several t i m e s b e f o r e a l l v a r i a b l e s satisfy t h e g i v e n b o u n d s . If d u r i n g a n y i t e r a t i o n , m o r e t h a n 10 h a l v i n g s of the c o r r e c t i o n are n e e d e d , w e h a v e t e r m i n a t e d c a l c u l a t i o n s a n d a s s u m e d t h e process was

diverging.

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

132

EXTRACTIVE

Application

AND

AZEOTROPIC

DISTILLATION

to a Sample Problem

T h e results o b t a i n e d i n the s o l u t i o n of a sample p r o b l e m are s u m m a r i z e d here to i l l u s t r a t e the a p p l i c a t i o n of the m e t h o d . distillation problem from Oliver

(6)

An

extractive

was used i n w h i c h methylcyclo-

hexane is separated f r o m toluene b y a d d i n g p h e n o l . T h e c o l u m n contains 11 stages ( i n c l u d i n g the r e b o i l e r a n d c o n d e n s e r ) a n d has a f e e d of 0.4 m o l e s / u n i t t i m e of m e t h y l c y c l o h e x a n e a n d 0.6 m o l e s / u n i t t i m e of toluene to the f o u r t h stage f r o m the r e b o i l e r a n d 4.848 m o l e s / u n i t t i m e of p h e n o l to t h e f o u r t h stage f r o m the condenser. W e u s e d t h e same p h y s i c a l p r o p e r t y correlations as O l i v e r . T h e a c t i v i t y coefficients w e r e o b t a i n e d f r o m a m u l t i c o m p o n e n t f o r m of the V a n L a a r E q u a t i o n Table I.

(7).

Norms for Successive Iterations of Sample Problem

Iteration

ρ

Composition,

1 2 3 4 5 6 7 8 9

Energy Balance,

2.9 1.6 1.5 1.4 1.2 5.8E-1 7.8E-2 1.7E-3 5.0E-6

σ

2.8E4 1.6E4 7.2E4 3.2E4 9.8E3 7.5E3 1.5E3 8.1 2.0E-1

Results for successive iterations of a t y p i c a l r u n are s h o w n i n T a b l e I. T h e c o m p o s i t i o n n o r m is defined as t h e E u c l i d e a n n o r m of the c o m p o s i t i o n errors

/ n

9 =

m

(Σ Σ V = i y=i

2\

(e ) i3

y

2

(33)

) /

a n d t h e energy b a l a n c e n o r m as

Σ

(<Wi)

)

(34)

V a l u e s for these n o r m s are g i v e n i n T a b l e I at e a c h i t e r a t i o n . A t i t e r a t i o n 9 the m a x i m u m error i n a n y e q u i l i b r i u m e q u a t i o n is 2 χ

10" , a n d the 6

m a x i m u m energy b a l a n c e error is 0.09 B t u / u n i t t i m e . T h e t o t a l t i m e r e q u i r e d for the n i n e iterations i n T a b l e I w a s a b o u t 4 m i n o n a n I B M 360/50 of w h i c h 1.5 m i n w a s e x e c u t i o n time.

The

J a c o b i a n w a s c a l c u l a t e d for e a c h iteration. T h e results f r o m some other runs are s u m m a r i z e d i n T a b l e II. e a c h r u n the values of v

±

and u

n

For

w e r e h e l d constant b y m a k i n g qx a n d

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

8.

B R U N O ,

YANOSiK,

A N D

<7u i t e r a t i o n variables.

Nonideal

TiERNEY

133

Mixtures

A U other heat duties,

w e r e set to zero.

F o r e a c h r u n i t is necessary to estimate the r e b o i l e r a n d condenser t e m peratures to i n i t i a t e c a l c u l a t i o n s . T h e s t a r t i n g v a l u e m e t h o d

described

p r e v i o u s l y w a s u s e d to c a l c u l a t e a l l other s t a r t i n g values for the i t e r a t i o n variables. V a l u e s of u n a r o u n d 0.4 m o l e s / u n i t t i m e are i n t e r e s t i n g because u n is the v a p o r p r o d u c t a n d s h o u l d b e m o s t l y m e t h y l c y c l o h e x a n e . Discussion T h e last t w o iterations i n T a b l e I c l e a r l y i n d i c a t e q u a d r a t i c c o n v e r g e n c e rates. T h i s is e s p e c i a l l y e v i d e n t i n the c o m p o s i t i o n n o r m w h e r e the error is r o u g h l y s q u a r i n g i n e a c h i t e r a t i o n . . T h e e n e r g y b a l a n c e n o r m for the last i t e r a t i o n does n o t decrease as m u c h as i t s h o u l d , b u t this u n d o u b t e d l y results f r o m round-off errors i n t h e c o m p u t e r w h e n u s i n g single

precision arithmetic.

The

m a x i m u m energy

balance

error

in

i t e r a t i o n 9 is 0.09 B t u / u n i t t i m e , a n d the enthalpies w h i c h are b e i n g s u m m e d i n the energy b a l a n c e e q u a t i o n are of the o r d e r of 50,000 B t u / unit time.

T h e fact that q u a d r a t i c convergence

is o b t a i n e d is s t r o n g

e v i d e n c e that the J a c o b i a n m a t r i x has b e e n c o r r e c t l y c a l c u l a t e d a n d t h a t the d e r i v e d equations are correct.

It is u n l i k e l y that the n o r m s c o u l d

decrease as t h e y d o i n the last t w o iterations i f the J a c o b i a n w e r e incorrect. T h e first seven iterations i n T a b l e I s h o w s l o w l i n e a r

convergence.

T h e c o r r e c t i o n - h a l v i n g p r o c e d u r e o u t l i n e d p r e v i o u s l y w a s u s e d at least once i n iterations 2 - 6 . T h e other r u n s i n T a b l e II b e h a v e d s i m i l a r l y . A l l took m o r e t h a n n i n e iterations, a n d for e a c h case the n o r m s w o u l d decrease s l o w l y ( e v e n o c c a s i o n a l l y r i s i n g for one i t e r a t i o n )

u n t i l the last

t w o or three iterations w h e n t h e y w o u l d d r a m a t i c a l l y decrease. the r u n s d i d not

Two

T h e results i n T a b l e I I i n d i c a t e that for a r e a s o n a b l y w i d e of v a p o r flows a n d starting c o n d i t i o n s the c o r r e c t i o n m e t h o d Table II.

range

proposed

Results for Different Vapor Flows and Starting Conditions for Sample Problems

Condenser

Reboiler Vapor

hi

Vu

h

Vl

Number of Iterations to Converge

210 270 210 210 220 210

.5 .8 .8 .1 .4 .4

270 330 275 275 300 275

1.5 1.5 1.0 1.5 1.0 1.0

10 17 Diverge 10 Diverge

Temp

0

of

converge.

Vapor

Flow

Temp.

Flow

9

a

This is run reported in Table I.

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

134

EXTRACTIVE

AND

AZEOTROPIC

DISTILLATION

h e r e w i l l g i v e a g o o d s o l u t i o n for this p r o b l e m . T h e system s t u d i e d s h o u l d b e a g o o d test because i t is h i g h l y n o n i d e a l . A n i n d i c a t i o n of this is t h a t t e m p e r a t u r e a n d c o m p o s i t i o n m a x i m a a n d m i n i m a w e r e f o u n d for most p r o b l e m s w h e n these v a r i a b l e s w e r e p l o t t e d against stage n u m b e r . M a n y v a r i a t i o n s of the c o r r e c t i o n m e t h o d w e h a v e p r o p o s e d c a n be u s e d . A m o n g these are the use of the same J a c o b i a n for several iterations a n d t h e use of m o d i f i e d N e w t o n m e t h o d s s u c h as M a r q u a r d t ' s (S).

We

h a v e t r i e d M a r q u a r d t ' s m e t h o d o n some of these

method problems

w i t h o u t o b s e r v i n g a n y significant i m p r o v e m e n t , b u t this is o n l y a tentative evaluation.

I m p r o v e d m e t h o d s for g e n e r a t i n g s t a r t i n g c o n d i t i o n s w o u l d

be helpful. A c o m p a r i s o n of the m e t h o d p r o p o s e d i n this p a p e r w i t h other m e t h ods is difficult because there are f e w distillation problems.

p u b l i s h e d solutions for

nonideal

W e w e r e u n a b l e to find a c o m p l e t e l y s o l v e d p r o b

l e m w i t h a l l m a t e r i a l a n d energy balances satisfied.

We

have

demon

strated that the J a c o b i a n m a t r i x gives r a p i d c o n v e r g e n c e i n the v i c i n i t y of t h e s o l u t i o n , a n d this m e t h o d m i g h t serve as a basis to e v a l u a t e other methods. Acknowledgment T h e authors w i s h to a c k n o w l e d g e

the assistance of the

Computer

C e n t e r at the U n i v e r s i t y of P i t t s b u r g h . List of

Symbols

G e n e r a l : A l o w e r case s y m b o l is a scalar. A n u p p e r case s y m b o l is a c o l u m n vector. A n u p p e r case s y m b o l w i t h a s u p e r s c r i p t is a c o l u m n v e c t o r f o r m e d b y r e m o v i n g the c o l u m n i n d i c a t e d b y t h e s u p e r s c r i p t f r o m t h e m a t r i x w i t h the same name. U n d e r l i n e d u p p e r case s y m b o l s are matrices. I f a s y m b o l is defined as a v e c t o r t h e n w h e n u n d e r l i n e d , i t represents a d i a g o n a l m a t r i x w i t h the same elements as the vector. A m a t r i x w i t h a s u p e r s c r i p t is a l w a y s a d i a g o n a l m a t r i x . A Β C D Ε F G H

V a p o r d i s t r i b u t i o n m a t r i x : au = — 1, α^ = f r a c t i o n of t o t a l v a p o r l e a v i n g stage / w h i c h goes to stage i L i q u i d d i s t r i b u t i o n m a t r i x : b = — 1, by = f r a c t i o n of t o t a l l i q u i d l e a v i n g stage / w h i c h goes to stage i T h e d i r e c t s u m of the i n d e p e n d e n t v a r i a b l e s , ( V,X ,... X ,T) T h e d i r e c t s u m of t h e error vectors, ( E , . . E ) E r r o r m a t r i x , the c o l u m n s are defined b y E q u a t i o n s 12 a n d 13 F e e d m a t r i x : fa is t o t a l f e e d of c o m p o n e n t / to stage i , mass p e r unit time V a p o r e n t h a l p y vector; gi is specific e n t h a l p y of v a p o r i n stage i, energy p e r u n i t mass L i q u i d e n t h a l p y vector; hi is specific e n t h a l p y of l i q u i d i n stage i, e n e r g y p e r u n i t mass u

2

1

m+1

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

m

8.

B R U N O ,

I J

YANOSIK,

A N D

T I E R N E Y

Nonideal

135

Mixtures

T h e identity matrix T h e J a c o b i a n m a t r i x ; i t is p a r t i t i o n e d i n t o ( r a + l ) s u b m a t r i c e s , e a c h of size η b y n. ] is t h e s u b m a t r i x i n r o w k a n d c o l u m n ; o f the p a r t i t i o n e d m a t r i x . L i q u i d flow rate vector; l is t o t a l l i q u i d l e a v i n g stage i, mass p e r unit time N u m b e r of components N u m b e r of e q u i l i b r i u m stages H e a t exchange vector; q is rate at w h i c h e n e r g y is a d d e d to stage i b y heat exchange, energy p e r u n i t t i m e F e e d e n t h a l p y vector; q is e n t h a l p y of f e e d e n t e r i n g stage i, e n e r g y per unit time D e f i n e d as B A ; R — A B T e m p e r a t u r e vector; t is t e m p e r a t u r e i n stage i A vector e a c h element of w h i c h is 1.0 V a p o r flow rate vector; t>< is t h e t o t a l v a p o r l e a v i n g stage i, mass per unit time L i q u i d c o m p o s i t i o n m a t r i x ; xy is c o m p o s i t i o n of c o m p o n e n t / i n l i q u i d i n stage i V a p o r composition matrix; is c o m p o s i t i o n of c o m p o n e n t / i n v a p o r i n stage i A c t i v i t y coefficient m a t r i x f o r t h e l i q u i d p h a s e ; t h e ij element is t h e a c t i v i t y coefficient f o r c o m p o n e n t / i n stage i E q u a l t o z e r o w h e n k ^ /; e q u a l to 1.0 w h e n k — / A c t i v i t y coefficient m a t r i x f o r v a p o r p h a s e ; t h e ij element is a c t i v i t y coefficient f o r c o m p o n e n t ; i n stage i S u b s c r i p t u s e d to i n d i c a t e i t e r a t i o n n u m b e r E u c l i d e a n n o r m of c o m p o s i t i o n errors, E q u a t i o n 3 3 E u c l i d e a n n o r m o f energy b a l a n c e errors, E q u a t i o n 34 2

kj

L

{

m η Q Q

f

R Τ U V X Y Γ Sjcj

Λ ν Ρ σ

{

t i

_ 1

1

_ 1

t

Literature Cited 1. Tierney, J. W., Bruno, J. Α., "Equilibrium Stage Calculations," AIChE J. (1967) 13, 556. 2. Tierney, J. W., Yanosik, J. L., "Simultaneous Flow and Temperature Correc tions in the Equilibrium Stage Problem," AIChE J. (1969) 15, 897. 3. Tierney, J. W., Yanosik, J. L., Bruno, J. Α., "Solution of Equilibrium Stage Models for Solvent Extraction Processes," Proceedings International Sol vent Extraction Conference 1971, pp. 1051-1061, Society of Chemical Industry, London, 1971. 4. Roche, E. C., "Rigorous Solution of Multicomponent, Multistage LiquidLiquid Extraction Problems," Brit. Chem. Eng. (1969) 14, 1393. 5. Nelson, P. Α., "Countercurrent Equilibrium Stage Separation with Reaction," AIChE J. (1971) 17, 1043. 6. Oliver, E. D., "Diffusional Separation Processes," pp. 189-197, Wiley, New York, 1966. 7. Drickamer, H. G., Brown, G. G., White, R. R., Trans. AIChE J. (1945) 41, 555. 8. Marquardt, D. W., "An Algorithm for Least-Squares Estimation of Non linear Parameters,"J.Soc. Ind. Appl. Math. (June 1963) 2, 431. RECEIVED December 10, 1971. In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

9 Isobaric Vapor-Liquid Equilibrium in the Acetic Acid-Acetone System R. JOE BURKHEAD and J. THOMAS SCHRODT University of Kentucky, Lexington, Ky. 40506

Isobaric vapor-liquid equilibrium data for the system acetic acid-acetone have been obtained at 760 and 500 mm Hg, using an Altsheler still Acetic acid associates in the liquid and vapor phases, and this is accounted for in evaluating modified activity coefficients for the components. This system primarily shows small negative deviations of the coefficients with a maximum and a minimum appearing at high acetone mole fractions for both pressures. In evaluating the thermodynamic consistency of the data, the Herington test for isobaric data gave values of D — J of 5.4 and 7.6 at 760 and 500 mm Hg, respectively. The Redlich-Kister integral area method with an estimate of the heat of mixing term gave areas of 0.023 and 0.025 at 760 and 500 mm Hg, respectively.

/ C o n s i s t e n t v a p o r - l i q u i d e q u i l i b r i u m d a t a are necessary to d e s i g n a l l ^

types o f r e c t i f i c a t i o n devices. H o w e v e r , m a n y i n d u s t r i a l l y i m p o r t a n t

m i x t u r e s are n o n i d e a l , p a r t i c u l a r l y i n the l i q u i d phase, a n d p r e d i c t i n g t h e i r e q u i l i b r i u m p r o p e r t i e s f r o m f u n d a m e n t a l t h e r m o d y n a m i c s is not possible. T h u s , the c o r r e l a t i n g o f e x p e r i m e n t a l x-y-t

a n d x-y-P

d a t a has d e v e l o p e d

as a n i m p o r t a n t b r a n c h of a p p l i e d t h e r m o d y n a m i c s . T h e n o n i d e a l i t i e s o f e q u i l i b r i u m m i x t u r e s result f r o m v a r i o u s c o m b i n a t i o n s of m o l e c u l a r interactions; o n e s u c h i n t e r a c t i o n that has

been

r e c e n t l y s t u d i e d is m o l e c u l a r association. M o l e c u l e s of fatty acids s u c h as acetic a c i d t y p i c a l l y f o r m d i m e r s a n d , to a lesser extent, t r i m e r s b y h y d r o g e n b o n d i n g i n the v a p o r a n d l i q u i d states. F a i l u r e of the e q u i l i b r i u m d a t a o f b i n a r y systems c o n t a i n i n g a c e t i c a c i d to m e e t e s t a b l i s h e d c r i t e r i a o f consistency b a s e d u p o n the G i b b s - D u h e m r e l a t i o n has o b s e r v e d b y R i u s et al. (1),

C a m p b e l l et al. (2),

been

Herington (3), and

136

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

9.

BURKHEAD

M a r e k (4).

AND

Acetic

SCHRODT

Acid-Acetone

H e r e w e t r y to o b t a i n x-y-t

System

137

d a t a for t h e acetic a c i d - a c e t o n e

system at 760 a n d 500 m m H g a n d to s h o w h o w c o n s i d e r i n g a c i d d i m e r i z a t i o n i m p r o v e s the results for t h e r m o d y n a m i c consistency tests. Equilibrium

Theory

T h e l i q u i d phase a c t i v i t y coefficient of a c o m p o n e n t i n a L — V m i x t u r e is u s u a l l y g i v e n b y

T,

L

=

Pf

θ,

(D

w h e r e 0* is the i m p e r f e c t i o n pressure c o r r e c t i o n f a c t o r a n d the absent v a p o r p h a s e a c t i v i t y coefficient is t a k e n as u n i t y . I n systems c o n t a i n i n g a dimerizing component

E q u a t i o n 1 w i l l not g i v e t h e r m o d y n a m i c a l l y

consistent y/s. C o n s i d e r for s u c h a c o m p o n e n t i n a b i n a r y m i x t u r e , t h e respective m o d i f i e d v a p o r a n d l i q u i d e q u i l i b r i u m expressions,

=

(2)

k =

(3)

Κ and

w h e r e η a n d c represent true m o l e fractions a n d t h e s u b s c r i p t s m2 a n d
K

»

=

π » T)

W

m±

o2

A s i n a n y t w o phase b i n a r y system, c o n s i d e r i n g the m o n o m e r a n d d i m e r as t h e t w o c o m p o n e n t s , η„ + η = ι

α

1 and e

m

+

1, w i l l a l l o w E q u a t i o n

e = d

4 a n d the p u r e c o m p o n e n t f o r m of E q u a t i o n 3 to b e r e d u c e d to

_ V

1 + 42f P Q

o2

-

1

, .

and

V

1 +4/c - 1 0

2k ο

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

(6)

138

E X T R A C T I V E AND

T h e a c t i v i t y coefficient

for t h e m o n o m e r

AZEOTROPIC DISTILLATION

of the p u r e a s s o c i a t i n g c o m

p o n e n t is g i v e n b y Po2

Y-

=

TQ τη θ m

p

(n\

—

e

(7)

a n d i n t h e presence of a n o n a s s o c i a t i n g c o m p o n e n t b y (8)

Θ,η2 = Pï)m2 Ρ m32

Tm2

m

C o m b i n i n g E q u a t i o n s 4, 5, 6, a n d 7 a n expression for t h e h y p o t h e t i c a l s a t u r a t i o n v a p o r pressure of the p u r e m o n o m e r is o b t a i n e d :

jy i

m =

Omko ΤΓ

·

V

1 + 4Ko?o2 ~

V

1 +

— 7 = = =

YmAo

4k

*

0

-

/ x

1

0

T h e s t o i c h i o m e t r i c m o l e fractions of t h e associating c o m p o n e n t given

W

1 are

by

yt

= 7

^2

=

η

+

2

(10)

2 η < ; 2

and £m2 + —j—r 1 +

2e

/-,-,χ u t ;

d 2

ε<*2

T h e s e g i v e w i t h E q u a t i o n s 2 a n d 3, r e s p e c t i v e l y ,

„ η

"

2

=

2/2

-

2

=

*

V

1 +

Ρ

4UL

2jfp

y

(2-2/ ) 2

2

~

1

(2-y0

y i

/iox ( 1 2 )

and V ε

2

1 + 4k x ( 2 - x ) 2k x, ( 2 - x ) 2

2

1

2

,

1 Q

N

( 1 3 )

I f E q u a t i o n s 9, 12, a n d 13 are s u b s t i t u t e d i n t o E q u a t i o n 8, a m o d i f i e d e q u i l i b r i u m r e l a t i o n c o n t a i n i n g v a p o r a n d l i q u i d associations factors and Γ

2

Z

2

results:

Ζ Θ 2/ Ρ = Γ γ ζ Ρ 2

2

2

2

2

2

ο 2

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

(14)

9.

B U R K H E A D

Acetic Acid-Acetone

A N D SCHRODT

System

139

where

z

1 +

=

V

1 +

4K

1 +

V

P„

0

1 +

2

4 t f Ρ 2/ (2-2/ ) 2

2

and i +

=

1 +

V

V

T

1 +

+ ¥ 4ifc z

.

=

(

1

6

)

(2-z )

2

2

F o r a nonassociating component, B , i n the mixture, the true m o l e fractions a r e r e l a t e d t o t h e s t o i c h i o m e t r i c m o l e fractions b y

*

=

r

r

xi

=

T-r

V

(

1

7

)

and

(18)

T h e s e a r e c o m b i n e d w i t h E q u a t i o n s 2, 3, 10, a n d 11 to o b t a i n e q u a t i o n s for t h e t r u e m o l e fractions o f 1 i n t h e v a p o r a n d l i q u i d phases, respec tively: „ ηι

=

yi

ε ι

=

1 +

*K

- V 1 + AK Ρ y (2-y ) 2K P(2-y y

P(2-2/ )

2

2

2

2

(19)

and 1 +

4fc(2-s ) 2

V

1 +

4fc s

2

(2-χ )

.

2

X i

(

2

0

. )

A m o d i f i e d e q u i l i b r i u m r e l a t i o n f o r c o m p o n e n t 1 is w r i t t e n i n terms o f Ζχ a n d Γ

χ

c o r r e c t i o n factors f o r t h e a s s o c i a t i o n o f A i n t h e v a p o r a n d

l i q u i d phases, b y c o m b i n i n g E q u a t i o n s 8 ( w r i t t e n f o r c o m p o n e n t

1),

19, a n d 2 0 : Ζ!θι»ιΡ = r

L T L

X!Poi

(21)

where z

=

2 y + V 1 + 4K Ρ y {2-y )) (2-y ) (1 + V 1 + 4K Ρ y , ( 2 - y , ) ) 2

2

2

2

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

140

EXTRACTIVE

AND

AZEOTROPIC

DISTILLATION

and 2 (l-x

+

2

(2-x ) 2

V

(1 +

V

1 +

4fc

1 +

4fc ζ ( 2 - ζ ) )

x {2-x )) 2

2

2

(23)

2

T h e p r e c e d i n g d e r i v a t i o n s are g i v e n i n m o r e d e t a i l b y M a r e k a n d S t a n d a r t ( 5 ) a n d are a p p l i e d b y M a r e k (4)

to several b i n a r y systems.

T h e terms θχ a n d 0 a r e e v a l u a t e d f r o m p a r t i a l m o l a l v o l u m e d a t a o r 2

a p p r o x i m a t e d f r o m g e n e r a l i z e d correlations.

A c c o r d i n g to M a r e k a n d

Standart, t h e p r o d u c t s ΓΊγι a n d Τ γ m u s t satisfy a l l c r i t e r i a o f t h e r m o 2

2

d y n a m i c consistency, as s h o u l d γ ι a n d y f o r nonassociating systems. 2

T o evaluate t h e a c t i v i t y coefficients, IYy*, o f a L - V system c o n t a i n i n g a n associating c o m p o n e n t , t h e o n l y other d a t a n e e d e d a r e t h e m o d i f i e d v a p o r phase association constants, K a n d K. T h e s e are a f u n c t i o n of t e m 0

p e r a t u r e a n d pressure, a n d f o r Κ t h e y a r e also a f u n c t i o n o f t h e n o n associating c o m p o n e n t .

V a l u e s of Κ a r e scarce; h o w e v e r , t h e y m a y b e

a p p r o x i m a t e d b y e x t r a p o l a t i n g K d a t a t o temperatures b e l o w t h e n o r m a l 0

b o i l i n g p o i n t of t h e associating c o m p o n e n t .

Modified Redlich-Kister

Test

O n e m e t h o d o f e v a l u a t i n g t h e o v e r a l l t h e r m o d y n a m i c consistency of b i n a r y , i s o b a r i c L - V e q u i l i b r i u m d a t a is b a s e d o n t h e e q u a t i o n

(24)

T h e greater t h e heats o f m i x i n g a n d differences of b o i l i n g points o f the c o m p o n e n t s , t h e greater t h e v a l u e o f t h e r h s i n t e g r a l .

I n systems

w h e r e this is true, this q u a n t i t y is e v a l u a t e d to test o v e r a l l consistency. If x-y-t

d a t a a r e a v a i l a b l e at m o r e t h a n o n e pressure a n d i f t h e

assumption

(25)

is v a l i d , t h e n Ah /R M

is d e t e r m i n e d as a f u n c t i o n of Χχ a n d of Τ b y o b

t a i n i n g values o f Xid In y / d ( l / T ) over a range o f Ρ ( 6 ) . T h e s e 4

values a n d E q u a t i o n 24 w i l l test f o r consistency.

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

Ah /R M

9.

BURKHEAD

AND

SCHRODT

Acetic

Acid-Acetone

141

System

Experimental A n A l t s h e l e r s t i l l w a s u s e d t o o b t a i n t h e x-y-t d a t a a t 760 a n d 500 m m H g (see R e f e r e n c e 7 f o r a d e s c r i p t i o n o f this s t i l l ) . A s c h e m a t i c d i a g r a m o f o u r a p p a r a t u s is g i v e n i n F i g u r e 1. T h e pressure o f t h e system w a s c o n t r o l l e d t o w i t h i n ± 0 . 5 m m H g for e a c h series b y a C a r t e s i a n d i v e r manostat c o n n e c t e d t o a p o s i t i v e a i r leak, a v a c u u m p u m p , a n d a surge v o l u m e o f 12 liters. A n a b s o l u t e mercury-in-glass m a n o m e t e r w i t h a 0.1 m m s l i d i n g v e r n i e r w a s u s e d t o measure t h e pressure. T e m p e r a t u r e s w e r e m o n i t o r e d via t w o c o p p e r c o n s t a n t a n t h e r m o c o u p l e s ; o n e w a s l o c a t e d just a b o v e t h e l i q u i d surface a n d the other just b e l o w it. M a x i m u m différences o f 0.4°C w e r e detected, b u t a n average o f t h e t w o r e a d i n g s w a s r e p o r t e d t o 0.2°C. G l a c i a l acetic a c i d a n d acetone, b o t h m e e t i n g A C S specifications, w e r e u s e d . T o b e g i n a r u n , t h e s t i l l w a s c h a r g e d w i t h 500 m l o f s o l u t i o n a n d a l l o w e d to b o i l for 3 - 4 h o u r s ; e q u i l i b r i u m w a s assured b y a constant b o i l i n g t e m p e r a t u r e f o r a t least one h o u r . F o r the series a t 500 m m H g , i c e w a t e r w a s c i r c u l a t e d t h r o u g h t h e condenser to m i n i m i z e v a p o r losses. S a m p l e s w e r e w i t h d r a w n a t t h e system o p e r a t i n g pressure, a n d t h e i r densities d e t e r m i n e d a t 2 5 ± 0.1°C. T h e c o m p o s i t i o n w a s a n a l y z e d b y this m e t h o d because o f the l a r g e difference i n densities o f t h e t w o c o m ponents; measurements accurate t o ± 0 . 2 m o l e % w e r e r e c o r d e d .

Condenser

_Air Leak

Drying Tube

Ice-Water Bath Surge Bottles

rtr

1

Manostat

Variac Transformer Liquid Phase Sampling Flasks

Vacuum Water Pump Manometer

Absolute Mercury Manometer

-Vapor Phase Sampling Flask Figure 1. Results

and

Schematic diagram of experimental

apparatus

Discussion

T h e x-y-t d a t a f o r the acetic a c i d - a c e t o n e system at 760 a n d 500 m m H g are presented i n F i g u r e 2 a l o n g w i t h the d a t a of Y o r k a n d H o l m e s ( 8 ) at 760 m m H g . V a l u e s o f the s t a n d a r d a c t i v i t y coefficients, y χ f o r acetone

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

142

E X T R A C T I V E

120 r—ι

1

1

1

1

1

1

1

1

1

1

A N DA Z E O T R O P I C

1

1

1

1

1

1

DISTILLATION

1 Γ

Mole Fraction Acetone Figure 2.

Isobaric equilibrium

data of acetic

acid-acetone

a n d γ f o r a c e t i c a c i d , w e r e c a l c u l a t e d u s i n g : E q u a t i o n 1, s m o o t h e d d a t a 2

f r o m F i g u r e 2, t h e A n t o i n e v a p o r pressure e q u a t i o n f o r acetone ( 9 ) , e x p e r i m e n t a l v a p o r pressure d a t a f o r a c e t i c a c i d (10, 11, 12), a n d a t a b l e of i m p e r f e c t i o n pressure c o r r e c t i o n factors (13).

0 Figure 3.

0.1 Activity

T h e s e y's are p r e s e n t e d

0.2 0.3 0.4 0.5 0.6 0.7 0.8 Mole Fraction Acetone in Liquid phase coefficients

of acetic acid-acetone

0.9

at 760 mm Hg

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

1.0

9.

BURKHEAD

AND

Acetic Acid-Acetone System

SCHRODT

143

as a f u n c t i o n o f Χχ i n F i g u r e s 3 a n d 4. B o t h sets o f curves s h o w p o s i t i v e a n d n e g a t i v e d e v i a t i o n s f r o m i d e a l i t y a n d a m a x i m u m a t Χχ = 0.24. Iso b a r i c e q u i l i b r i u m studies b y R i u s et al. (1) o f acetic a c i d a n d l o w m o l e c u l a r w e i g h t a l c o h o l b i n a r y solutions r e s u l t e d i n s i m i l a r l y s h a p e d curves. F i r s t , t h e d a t a seem t o b e inconsistent since the m a x i m a at x = 0.24 a r e x

not b a l a n c e d b y m i n i m a a t t h e same c o m p o s i t i o n .

I n c l u d i n g t h e heat o f

m i x i n g t e r m t h a t is necessary f o r i s o b a r i c d a t a d i d not c o n f i r m consistency. T o i n c l u d e t h e effect o f t h e association o f t h e a c i d , t h e m o d i f i e d a c t i v i t y coefficients, ΓΊγχ a n d Τ γ , w e r e e v a l u a t e d . 2

0.25 j

1

0

1

0.1

Figure 4.

1 1

2

1 1

1

1

1 1

1

1

1

1—ι 1 1 1 1 1

0.2 0.3 0.4 0.5 0.6 0.7 0.8 Mole Fraction Acetone in Liquid Phase

0.9 1.0

Activity coefficients of acetic acid-acetone at 500 mm Hg

T o c a l c u l a t e Z a n d Ζχ a p p e a r i n g i n E q u a t i o n s 14 a n d 2 1 , f r o m E q u a 2

tions 15 a n d 22, M a r e k ' s e q u a t i o n f o r K (4) 0

-log

K >^ 0{1

a n d e x p e r i m e n t a l values o f K

0

temperature

Ko(p^o) a n d

a n d pressure.

= 10.4205 -

0)

(26)

(14, 15) w e r e p l o t t e d as a f u n c t i o n o f

Differences

b e t w e e n t h e values

of —log

t h e e x p e r i m e n t a l values o f — l o g K at t h e same t e m p e r a t u r e 0

w e r e t h e n p l o t t e d as a f u n c t i o n o f t e m p e r a t u r e a n d pressure, a n d isobars through the points were extrapolated

to the e q u i l i b r i u m

temperatures.

A d d i t i o n o f c o r r e s p o n d i n g Δ l o g K a n d l o g K0(P-*0) f r o m E q u a t i o n 2 6 0

gave - l o g i f ο = 1.4040 l o g Ρ o2 -

1.8821

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

(27)

144

EXTRACTIVE

AND AZEOTROPIC

DISTILLATION

T o d e t e r m i n e K, the association constant o f acetic a c i d i n t h e m i x t u r e , t h e a p p r o p r i a t e isobars, 760 a n d 500 m m H g , w e r e e x t r a p o l a t e d t o t e m peratures b e l o w t h e b o i l i n g p o i n t . T h e equations o b t a i n e d for Κ w e r e

-log

#

(

= 9.9905 + 0.00224* -

7 6 0 )

%

( > 28

2

and - l o g # 5oo) = 10.0505 + 0.00209* (

%

(29)

g

T h e e x p e r i m e n t a l d a t a u s e d t o d e t e r m i n e these constants w e r e scant, a n d t h e i r q u a l i t y is d e b a t e d r e g a r d i n g t h e i r u s e f o r these d e t e r m i n a t i o n s . F o r m u l a t i o n o f Δ l o g K vs. Τ a t constant pressure as a l i n e a r f u n c t i o n is 0

n o t necessarily c o r r e c t a n d w a s d o n e for l a c k o f another m e t h o d . V a l u e s o f Z

2

a n d Ζχ, c a l c u l a t e d u s i n g E q u a t i o n s 15 a n d 23, w e r e u s e d i n E q u a t i o n s

14 a n d 21 to e v a l u a t e Γ γ a n d ΓΊγι. 2

2

F i g u r e s 3 a n d 4 also s h o w the curves o f In ΓΊγι a n d In Γ γ vs. x 2

2

i9

and

t h e a p p e a r a n c e o f these curves i m p r o v e i m m e d i a t e l y b y c o n s i d e r i n g t h e association i n c a l c u l a t i n g these m o d i f i e d a c t i v i t y coefficients.

T h e s e plots

s h o w t w o u n u s u a l f e a t u r e s — n e g a t i v e deviations i n t h e a c t i v i t y coefficients a n d a m a x i m u m - m i n i m u m set a t h i g h m o l e f r a c t i o n acetone. N e g a t i v e deviations s h o w e d b y b o t h sets o f data—i.e., values o f Γ γ less t h a n o n e — a r e c h a r a c t e r i s t i c o f electrolytes o r o f m i x t u r e s i n w h i c h association o r c o m p o u n d f o r m a t i o n b e t w e e n the t w o c o m p o n e n t s reduces 0.20 r — ι — \

1 — 1 — ι 1 — 1 1—1 1—1 1 — ι — ι

1—ι—ι—1—r

Mole Fraction Acetone in Liquid Phase Figure 5.

Thermodynamic consistency plot for acetic acid-acetone system at 760 mm Hg

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

9.

B U R K H E A D

Acetic Acid-Acetone

A N D SCHRODT

145

System

0.20 r — ι — ι — ι — ι — ι — ι — ι — ι — ι — ι — ι — ι — ι — ι — ι — ι — ι — ι — ι — 1

_0 inL 0 Figure 6.

1

1

0.1

1

— — — — — — — — — — — — 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 Mole Fraction Acetone in Liquid Phase

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

L

1

1.0

Thermodynamic consistency plot for acetic acid-acetone system at 500 mm H g

t h e i r v o l a t i l i t y . T h u s , i t seems that there is a s s o c i a t i o n o r a t t r a c t i o n b e t w e e n t h e a c e t i c a c i d a n d acetone m o l e c u l e s i n t h e l i q u i d , besides t h e acetic a c i d d i m e r i z a t i o n . A m a x i m u m a n d m i n i m u m a r e o b s e r v e d i n t h e curves o f In Τχγ a n d χ

In T j2 f o r b o t h sets o f d a t a . I n b o t h d a t a sets these o c c u r at x 2

x

about

e q u a l t o 0.65. T h e values o f Γ γ a r e s l i g h t l y greater a t 760 m m H g t h a n at 500 m m H g t h r o u g h o u t t h e range o f c o m p o s i t i o n s . N o other significant differences a r e n o t e d b e t w e e n t h e t w o sets o f curves. F r o m t h e plots o f In ( Γ 2 γ / Γ ι γ ι ) vs. Χχ, s h o w n i n F i g u r e s 5 a n d 6 2

for t h e t w o sets o f d a t a , values f o r t h e H e r i n g t o n test c a l c u l a t i o n s w e r e determined.

A c c o r d i n g t o H e r i n g t o n ( 3 ) , D — J m u s t b e less t h a n 10

i f t h e d a t a a r e consistent. A t 760 m m H g pressure, D is 33.6, a n d / is 28.2, giving D -

J = 5.4. A t 5 0 0 m m H g pressure, D =

36.4 a n d / = 28.8,

g i v i n g D — J= 7.6. T h u s b o t h sets o f d a t a seem t o b e t h e r m o d y n a m i c a l l y consistent b a s e d o n this test. F r o m F i g u r e s 5 a n d 6, t h e R e d l i c h - K i s t e r test a p p a r e n t l y w i l l n o t suffice f o r this system since t h e i n t e g r a t e d areas o f t h e curves a r e n o t zero.

R e t a i n i n g E q u a t i o n 24, v a l u e s o f A r V V R T

2

were calculated using

the p r o c e d u r e o u t l i n e d a b o v e . T h e results a r e p r e s e n t e d i n T a b l e I, a l o n g w i t h values o f 1 j

In ( Γ , tt/Tx γ ι ) dx

h

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

146

E X T R A C T I V E AND

Table I.

DISTILLATION

Modified Redlich-Kister Consistency Test Results

1 P ,mmHg

Γ@χι = 0 In ^

I

T

J O

760 500

AZEOTROPIC

l

dxi

m

-0.0234 - 0.0244

/ J T @ X

l ^ d T 1

=

1

H

Δ

Area

1

-0.0465 - 0.0492

0.0231 0.0248

as d e t e r m i n e d f r o m F i g u r e s 5 a n d 6. A l t h o u g h t h e differences

between

these values seem r a t h e r large, s t u d y i n g t h e p r o c e d u r e s u s e d i n e v a l u a t i n g In ( Γ γ / Γ ι γ ι ) a n d Ah /R 2

M

2

i n d i c a t e s t h a t t h e difference

b e t w e e n these

values is w e l l w i t h i n t h e l i m i t s o f t h e e x p e r i m e n t a l a n d p r o c e d u r a l errors. O n e difficulty i n e v a l u a t i n g these q u a n t i t i e s is t h e relative smallness of t h e d e v i a t i o n s f o r this system as c o m p a r e d w i t h m a n y other systems. V a l u e s of In Γ Ί γ ι close to z e r o t h r o u g h o u t t h e c o m p o s i t i o n r a n g e cause s l i g h t errors i n t h e system parameters t o b e significant i n t h e a r e a deter m i n a t i o n s . P r i m a r i l y i m p o r t a n t for i s o b a r i c systems is t h e fact t h a t t h e heat o f m i x i n g t e r m i n t h e equations d e r i v e d f r o m t h e b a s i c G i b b s - D u h e m relationship cannot be ignored a n d must b e calculated to indicate the d a t a consistency. W i t h i n t h e l i m i t s of e x p e r i m e n t a l error, t h e m o d i f i e d R e d l i c h - K i s t e r test i n d i c a t e s m a r g i n a l consistency of o u r d a t a . Acknowledgment G r a t e f u l a c k n o w l e d g m e n t is m a d e to t h e A s h l a n d O i l a n d R e f i n i n g C o . for s u p p o r t i n g this w o r k w i t h a f e l l o w s h i p . List

of

D Ak J Κ k Ρ R Τ t χ y Ζ Γ γ c η θ

H e r i n g t o n test p a r a m e t e r heat o f m i x i n g H e r i n g t o n test p a r a m e t e r v a p o r p h a s e association e q u i l i b r i u m constant l i q u i d p h a s e association e q u i l i b r i u m constant t o t a l pressure gas constant absolute t e m p e r a t u r e temperature s t o i c h i o m e t r i c l i q u i d m o l e fractions s t o i c h i o m e t r i c v a p o r m o l e fractions v a p o r phase association constant l i q u i d p h a s e association constant a c t i v i t y coefficient true mole fraction i n l i q u i d true mole fraction i n vapor i m p e r f e c t i o n pressure c o r r e c t i o n factor

31

Symbols

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

9.

B U R K H E A D A N D SCHRODT

Acetic

Acid-Acetone

System

147

Superscripts L V

l i q u i d phase vapor phase

Subscripts d dimer m monomer ο pure component 1 nonassociating component 2 associating c o m p o n e n t

Literature Cited 1. Rius, Α., Otero, J. L., Macorron, Α., Chem. Eng. Sci. (1959) 10, 105. 2. Campbell, A. N., Kartzmark, E. M., Gieskes, T. M. T. M., Can. J. Chem. (1963) 41,407. 3. Herington, E. F. G.,J.Inst. Petrol. (1951) 37, 457. 4. Marek, J., Collection Czech. Chem. Commun. (1955) 20, 1490. 5. Marek, J., Standart, G., ibid. (1954) 19, 1074. 6. Null, H. R., "Phase Equilibrium in Process Design," McGraw-Hill, New York, 1970. 7. Altsheler, W. B., Ind. Eng. Chem. (1951) 43, 2559. 8. York, R., Holmes, R., Ind. Eng. Chem. (1942) 34, 345. 9. Lange, Ν. Α., Ed., "Handbook of Chemistry," Rev. 10th ed., McGraw-Hill, New York, 1967. 10. MacDougall, J., Smith, H.,J.Amer. Chem. Soc. (1936) 58, 2585. 11. Ramsay, G., Young, R.,J.Chem. Soc. (1886) 49, 790. 12. Weast, R. C., Ed., "Handbook of Chemistry and Physics," 50th ed., The Chemical Rubber Company, Cleveland, 1970. 13. Burkhead, R. J., M.S. Thesis, University of Kentucky, Lexington, 1971. 14. Johnson, E. W., Nash, C. K.,J.Amer. Chem. Soc. (1936) 58, 2585. 15. Ritter, H. L., Simons, J. H.,J.Amer. Chem. Soc. (1945) 67, 757. RECEIVED February 10, 1972.

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

10 Separation of Water, Methyl Ethyl Ketone, and Tetrahydrofuran Mixtures HUGH M. LYBARGER and HOWARD L. GREENE Department of Chemical Engineering, The University of Akron, Akron, Ohio 44304

Ternary vapor-liquid equilibrium data for the system water-methyl ethyl ketone-tetrahydrofuran were determined with a vapor recirculating equilibrium still of the type used by Hipkin and Myers. All experimental points were checked for thermodynamic consistency using the test proposed by McDermott and Ellis. Calculated liquid phase activity coefficients were correlated over the range of solvent concentrations using regression analysis. These results indicate a low boiling valley between the binary azeotropes of water-tetrahydrofuran and water-methyl ethyl ketone, but no ternary azeotrope was found. A solvent purification scheme, aided by development of a modified Thiele-Geddes computer program, was designed to separate the ternary mixture into pure components. The resulting system requires use of three ordinary distillation columns and extractive distillation, using dimethylformamide as the solvent.

'^efrahydrofuran

( T H F ) a n d m e t h y l e t h y l k e t o n e ( M E K ) are c o m -

m o n l y u s e d as solvents for h i g h m o l e c u l a r w e i g h t p o l y v i n y l c h l o r i d e resins i n t o p c o a t i n g a n d a d h e s i v e a p p l i c a t i o n s . B l e n d s are u s e d to c o m b i n e the l o w cost o f m e t h y l e t h y l ketone w i t h the h i g h e r s o l v e n c y a n d greater v o l a t i l i t y of t e t r a h y d r o f u r a n .

B e c a u s e of the large a m o u n t of

T H F u s e d , its r e l a t i v e l y h i g h cost, a n d a i r p o l l u t i o n considerations, rec o v e r y is n o r m a l l y necessary. T h e solvent v a p o r m a y b e r e c o v e r e d i n c o m m e r c i a l l y a v a i l a b l e activ a t e d c a r b o n a d s o r p t i o n units.

W h e n the v a p o r - a i r m i x t u r e is passed

t h r o u g h a b e d of a c t i v a t e d c a r b o n , solvent vapors are a d s o r b e d w h i l e the s t r i p p e d a i r passes t h r o u g h . P e r i o d i c regeneration o f the a c t i v a t e d 148

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

10.

LYBARGER

AND

GREENE

Separation

of

149

Mixtures

c a r b o n w i t h l o w pressure steam, h o w e v e r , g e n e r a l l y contaminates t h e solvents w i t h a large a m o u n t o f w a t e r , i n c r e a s i n g greatly t h e difficulty of s u b s e q u e n t separations. T h i s s t u d y w a s u n d e r t a k e n to o b t a i n t h e necessary v a p o r - l i q u i d equilibrium

d a t a a n d to d e t e r m i n e

the distillation requirements

r e c o v e r i n g solvent f o r reuse f r o m t h e s o l v e n t - w a t e r f r o m a d s o r b e r regeneration. d a t a (2, 3)

for

mixture obtained

Previous binary v a p o r - l i q u i d e q u i l i b r i u m

i n d i c a t e d t w o b i n a r y azeotropes

M E K ) a n d a t w o phase region ( w a t e r - M E K ) .

(water-THF

and water-

T h e t e r n a r y system w a s

thus e x p e c t e d t o b e h i g h l y n o n i d e a l . Results of this s t u d y h a v e b e e n u s e d to d e s i g n a solvent

recovery

system c a p a b l e of s e p a r a t i n g e a c h solvent i n t o its o r i g i n a l p u r e state. I f s e p a r a t i o n o f t h e T H F - M E K m i x t u r e is unnecessary o r i f p u r i t y r e q u i r e ments are less d e m a n d i n g , t h e p r o p o s e d system c o u l d b e a p p r o p r i a t e l y simplified. Experimental A v a p o r - r e c i r c u l a t i n g e q u i l i b r i u m s t i l l s i m i l a r to t h a t d e s c r i b e d b y H i p k i n a n d M y e r s ( 1 ) w a s u s e d to d e t e r m i n e v a p o r - l i q u i d e q u i l i b r i u m d a t a f o r t h e system, w a t e r - M E K - T H F . I n this s t i l l s h o w n s c h e m a t i c a l l y i n F i g u r e 1, a r e c i r c u l a t i n g v a p o r is c o n t i n u o u s l y c o n t a c t e d w i t h a static l i q u i d sample. T h e v a p o r - l i q u i d system is e n c l o s e d b y a jacket w h e r e

KEY 1 2 3 4 5 β 7 8 9 IΟ II 12 13 14 15 16

Figure 1.

Schematic diagram of the equilibrium

Vacuum Pump Manometer Mtrcury Traps Jacket Condenser Sample Condenser Thermocouples Thermistors Jacket Heater Reboiler Jacket Contactor Body Contactor Throat Contactor Sample Valve Vapor Sample Volve Needle Valves Nitrogen Tank

still

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

150

EXTRACTIVE AND AZEOTROPIC

T a b l e I. Run No.

a

ywater.

ΎΜΕΚ,

DISTILLATION

Liquid

YTHF.

Phase

XMEK,

mole fr.

mole fr.

mole fr.

mole fr.

mole fr.

1 3 4 5 6 7 8 910 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29"

.288 .217 .256 .257 .275 .236 .199 .226 .297 .244 .226 .234 .267 .314 .250 .247 .121 .103 .230 .163 .248 .311 .269 .244 .215 .181 .206 .262

.181 .289 .177 .209 .388 .223 .102 .178 .478 .216 .058 .162 .327 .299 .182 .174 .039 .278 .619 .123 .477 .599 .291 .304 .040 .350 .284 .284

.532 .494 .566 .534 .337 .541 .699 .596 .225 .540 .717 .604 .407 .387 .568 .580 .841 .619 .152 .714 .275 .090 .440 .452 .746 .474 .510 .453

30 31 32 33 34 35 36 37 38 39 40 41*

.165 .201 .095 .219 .134 .153 .221 .211 .160 .141 .144 .293

.436 .149 .523 .006 .000 .000 .000 .000 .018 .031 .059 .366

.399 .650 .383 .775 .866 .847 .779 .790 .822 .828 .796 .342

42°

.353

.370

.277

43 44"

.197 .318

.071 .447

.732 .235

.561 .486 .866 .506 .377 .460 .322 .697 .375 .508 .585 .869 .379 .507 .507 .438 .071 .043 .110 .118 .184 .281 .438 .289 .296 .501 .169 .594 .862 .093 .189 .034 .596 .091 .121 .424 .661 .131 .093 .113 .502 .892 .469 .914 .177 .518 .862

.166 .237 .039 .181 .399 .211 .124 .092 .486 .194 .046 .037 .342 .267 .169 .181 .062 .409 .787 .197 .607 .665 .287 .374 .051 .279 .409 .208 .064 .587 .213 .678 .005 .000 .000 .000 .000 .029 .048 .092 .315 .064 .383 .058 .103 .368 .101

Two-phase run.

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

10.

LYBARGER

Activity

AND

GREENE

Separation

of

Mixtures

Coefficients

XTHF

y

water

fMEK

y

THF

.273 .276 .094 .313 .224 .329 .553 .212 .140 .298 .369 .095 .279 .226 .324 .381 .867 .548 .103 .686 .209 .054 .275 .338 .653 .220 .422 .197 .074 .321 .598 .288 .399 .909 .879 .577 .339 .840 .859 .796 .184 .044 .149 .028 .721 .113 .037

Temp. °C.

mole fr. 2.021 1.710 1.343 2.065 2.497 1.925 2.577 1.267 2.608 1.846 1.598 1.088 2.463 2.157 1.876 2.143 7.289 8.396 5.933 5.455 4.274 3.385 2.188 2.994 3.101 1.244 4.588

1.722 1.891 8.008 1.878 1.379 1.612 1.352 3.058 1.353 1.723 2.045 7.152 1.375 1.611 1.661 1.476 1.057 0.980 0.962 0.989 1.050 1.167 1.481 1.186 1.318 1.791 1.060

1.946 1.752 6.582 1.738 1.362 1.587 1.306 2.794 1.421 1.777 2.005 6.462 1.343 1.570 1.706 1.483 1.022 1.041 1.182 1.035 1.136 1.407 1.492 1.242 1.204 1.968 1.173

64.7 65.3 61.6 64.0 67.9 65.8 63.5 64.9 68.8 65.3 63.6 64.2 67.4 67.5 65.5 65.5 62.9 67.4 72.2 64.8 69.6 70.5 67.0 67.1 62.9 67.7 65.7 67.4

5.872 4.179 8.089 1.558 6.745 5.455 2.321 1.375 5.186 6.412 5.343

1.020 1.108 0.966 1.845 0.000 0.000 0.000 0.000 1.054 1.087 1.065

1.099 1.086 1.086 2.038 1.052 1.022 1.465 2.467 1.025 1.010 1.036

68.8 64.7 71.5 63.1 61.4 62.7 62.0 62.7 63.1 63.1 63.5 68.3 68.8

4.738

1.162

1.063

63.1 70.3

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

152

EXTRACTIVE

AND

AZEOTROPIC

DISTILLATION

h y d r o c a r b o n v a p o r is m a i n t a i n e d at the b o i l i n g t e m p e r a t u r e of the l i q u i d s a m p l e i n t h e contactor. T h e s t i l l is t h o r o u g h l y i n s u l a t e d so that the l i q u i d a n d v a p o r i n the c o n t a c t o r are m a i n t a i n e d at a d i a b a t i c c o n d i t i o n s . S t a n d a r d i z e d p r o c e d u r e s for o b t a i n i n g e q u i l i b r i u m a n d for s a m p l i n g t h e r e s u l t a n t v a p o r a n d l i q u i d , as o u t l i n e d b y L y b a r g e r ( 7 ) , w e r e f o l l o w e d . A l l v a p o r - l i q u i d e q u i l i b r i u m d a t a w e r e o b t a i n e d at a constant pressure of 730 m m of m e r c u r y w h i c h w a s a c h i e v e d b y a p p l y i n g v a c u u m or n i t r o g e n pressure to the s t i l l ( d e p e n d i n g o n a t m o s p h e r i c pressure) u n t i l the d e s i r e d differential w a s o b t a i n e d . A f t e r the v a p o r was r e c i r c u l a t e d , a constant pressure c o u l d b e m a i n t a i n e d i n the s t i l l w i t h o u t further adjustments. A l l l i q u i d a n d v a p o r samples w e r e a n a l y z e d o n a V a r i a n A e r o g r a p h M o d e l 202-1B t h e r m a l c o n d u c t i v i t y gas c h r o m a t o g r a p h . A 12-foot c o l u m n p a c k e d w i t h P o r a p a k Q , w h i c h g a v e a c l e a n s e p a r a t i o n for water, was u s e d , b u t it c a u s e d the peaks for m e t h y l e t h y l ketone a n d t e t r a h y d r o f u r a n to b e s l i g h t l y m e r g e d . T h e c h r o m a t o g r a p h w a s c a l i b r a t e d u s i n g 11 solvent b l e n d s of k n o w n c o m p o s i t i o n s . A r e a c o r r e c t i o n factors w e r e d e t e r m i n e d f r o m the s t a n d a r d samples, r e l a t i n g w e i g h t f r a c t i o n to a r e a f r a c t i o n . A l l samples w e r e a n a l y z e d t w i c e , a n d the results w e r e a v e r a g e d . C a l i b r a t i o n of the c h r o m a t o g r a p h w i t h k n o w n w a t e r - M E K - T H F samples i n d i c a t e d accurate d e t e r m i n a t i o n to w i t h i n ±0.002-0.005 m o l e f r a c t i o n , d e p e n d i n g o n composition. Results and

Discussion

Vapor—Liquid Equilibrium Data.

F o r t y - f o u r pairs of v a p o r - l i q u i d

e q u i l i b r i u m d a t a w e r e d e t e r m i n e d for the t e r n a r y system; l i q u i d c o m p o sitions i n the s i n g l e a n d two-phase regions w e r e s t u d i e d . Results of these runs are s u m m a r i z e d i n T a b l e

I a l o n g w i t h the l i q u i d phase

activity

coefficients a n d b o i l i n g p o i n t s o b t a i n e d at a pressure of 730 m m of mercury.

Tabulated

compositions

are averages of t w o

analyses for

each

sample. C a l c u l a t e d l i q u i d p h a s e a c t i v i t y coefficients are b a s e d o n R a o u l t ' s and Dalton's laws:

Pi =

Piji

=

tiPiXi

(1)

a s s u m i n g v a p o r phase i d e a l i t y . The

v a p o r — l i q u i d e q u i l i b r i u m d a t a for the single-phase

r u n s are

g r a p h i c a l l y s h o w n i n F i g u r e 2 w h e r e the two-phase r e g i o n at 60 ° C

is

also p l o t t e d to i n d i c a t e the extent of p a r t i a l m i s c i b i l i t y at the b o i l i n g point.

A l i n e connects e a c h p a i r of v a p o r - l i q u i d e q u i l i b r i u m c o m p o s i -

tions. T e m p e r a t u r e results for the v a p o r - l i q u i d e q u i l i b r i u m d a t a i n d i c a t e a l o w b o i l i n g v a l l e y c o n n e c t i n g t h e b i n a r y azeotropes of (66.2

mole

%

M E K , normal boiling point 73.4°C)

and

water—MEK water-THF

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

10.

L Y B A R G E R

A N D

Separation

G R E E N E

of

Water

0.00 THF

0.10

0.20

0.30

0.40

0.50

153

Mixtures

KEY

0.60

0.70

0.80

030

100 MEK

Figure 2. Ternary vapor-liquid equilibrium data for the one-phase region at 730 mm mercury absolute pressure with the solubility envelope for 60° C

(81.7 m o l e

%

T H F , normal boiling point 64.0°C).

The

dashed line

s h o w n i n F i g u r e 2 indicates the a p p r o x i m a t e l o c a t i o n of this v a l l e y . Results for the two-phase r u n s are p l o t t e d i n F i g u r e 3 a l o n g w i t h the s o l u b i l i t y e n v e l o p e at 60 ° C .

A l t h o u g h the e q u i l i b r i u m s t i l l w a s n o t

d e s i g n e d for two-phase o p e r a t i o n , it was p o s s i b l e to o b t a i n the necessary d a t a for this solvent system since t h e v a p o r i n e q u i l i b r i u m w i t h the t w o phase l i q u i d was a l w a y s single-phase w h e n c o n d e n s e d . S e v e r a l two-phase samples w e r e a n a l y z e d after c o o l i n g h a d o c c u r r e d , a c c o u n t i n g for t h e fact t h a t the ends of the l i q u i d - l i q u i d tielines i n this r e g i o n d o n o t q u i t e e x t e n d to the s o l u b i l i t y c u r v e .

E q u i l i b r i u m vapor compositions

corre-

s p o n d i n g to the l i q u i d c o m p o s i t i o n s are also p l o t t e d i n F i g u r e 3 a n d , except for R u n 42 w h i c h e x p e r i e n c e d

severe b u m p i n g d u r i n g b o i l i n g ,

f a l l a l o n g a n a l m o s t straight l i n e . F o r a t e r n a r y system the c o m p o s i t i o n of v a p o r i n e q u i l i b r i u m w i t h a heterogeneous l i q u i d m i x t u r e c a n b e r e l a t e d to the l i q u i d c o m p o s i t i o n s b y two relationships (5).

F i r s t , the same v a p o r c o m p o s i t i o n w i l l result

f r o m a n y l i q u i d c o m p o s i t i o n o n a g i v e n l i q u i d - l i q u i d tieline. S e c o n d , a

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

154

EXTRACTIVE

AND

AZEOTROPIC

DISTILLATION

s m o o t h c u r v e c a n be d r a w n t h r o u g h the v a p o r c o m p o s i t i o n s i n e q u i l i b r i u m w i t h heterogeneous

liquid

c o m p o s i t i o n s . T h i s c u r v e extends

f r o m the v a p o r i n e q u i l i b r i u m w i t h the b i n a r y heterogeneous azeotrope to v a p o r i n e q u i l i b r i u m w i t h the h o m o g e n e o u s l i q u i d w h e r e t h e c o m p o sitions of t h e t w o l i q u i d phases b e c o m e c o i n c i d e n t ( t h e p l a i t p o i n t ) . W i t h these t w o r e l a t i o n s h i p s , one c a n .closely a p p r o x i m a t e t h e c o m p o s i t i o n o f v a p o r i n e q u i l i b r i u m w i t h a g i v e n t w o - p h a s e l i q u i d f r o m F i g u r e 3.

Wottr

0.00

0.10

0.20

0.30

0.40

0.50

0.70

O60

030

0.90

THF

1.00 MEK

Figure 3. Ternary vapor-liquid equilibrium data for the two-phase region at 730 mm mercury absolute pressure with the solubility envelope for 60° C Thermodynamic and Ellis (6)

Consistency.

T h e test d e v e l o p e d b y M c D e r m o t t

w a s u s e d to d e t e r m i n e t h e t h e r m o d y n a m i c c o n s i s t e n c y of

the v a p o r - l i q u i d e q u i l i b r i u m d a t a . T h i s test i n v o l v e s c a l c u l a t i o n of the deviation, ( D

c d

) , b e t w e e n p a i r s of p o i n t s (c, d)

as d e f i n e d b e l o w :

η D

cd

=

Σ i=l

(x

ic

+ x) id

(log y id

-

log y ) ic

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

(2)

10.

L Y B A R G E R

Separation

A N D G R E E N E

155

of Mioctures

T h i s d e v i a t i o n is d e r i v e d f r o m t h e i s o t h e r m a l - i s o b a r i c f o r m of t h e G i b b s D u h e m e q u a t i o n a n d c a n b e a p p l i e d to i s o b a r i c e q u i l i b r i u m d a t a b y m i n i m i z i n g t h e c o m p o s i t i o n a n d t e m p e r a t u r e differences b e t w e e n p a i r s of points. T h i s w a s d o n e b y c h o o s i n g d a t a paths t h r o u g h t h e ternary e q u i l i b r i u m d i a g r a m so that differences i n c o m p o s i t i o n a n d t e m p e r a t u r e b e t w e e n pairs o f p o i n t s w e r e m i n i m i z e d . A p o i n t w a s c o n s i d e r e d to b e inconsistent i f i t d e v i a t e d m o r e t h a n 0.02 w i t h b o t h o f its n e i g h b o r s . T h i s d e v i a t i o n w a s chosen since i t a p p r o a c h e d t h e a p p r o x i m a t e l i m i t of t h e d e v i a t i o n c a u s e d b y a n a l y t i c a l i n a c c u r a c y . R u n s 1, 4, 5, 13, 15, 2 3 , 27, a n d 28 w e r e d e t e r m i n e d to b e inconsistent o n this basis. Correlation of Liquid Phase Activity Coefficients. F o r a c t i v i t y c o efficients to b e u s e d i n d i s t i l l a t i o n c a l c u l a t i o n s , t h e y are n o r m a l l y repre sented as a f u n c t i o n o f c o m p o s i t i o n . H e r e a m u l t i p l e regression c o m p u t e r p r o g r a m w a s u s e d to d e t e r m i n e t h e coefficients f o r a n e q u a t i o n o f t h e form lny.i

= α + a&i + a x 0

2

aaXz

2

+

α 7Χ&2

+ a3 X 3 + a X i + 2

4

2

+

a&ix

z

+

a&

2

2

+

(3)

a& x 2

z

w h e r e x x , a n d x a r e t h e l i q u i d m o l e fractions of water, m e t h y l e t h y l ketone, a n d t e t r a h y d r o f u r a n , respectively. l9

2

s

T e r m s w e r e d e l e t e d f r o m t h e regression e q u a t i o n u n t i l a n e q u a t i o n c o n t a i n i n g o n l y terms h a v i n g a confidence l e v e l of greater t h a n 8 0 % to i m p r o v e fit ( i n terms o f s u m o f squares e r r o r ) w a s o b t a i n e d . Coefficients (α/s) f o r t h e r e s u l t i n g s i m p l i f i e d equations a r e s u m m a r i z e d i n T a b l e I I w i t h a n estimate o f fit. Table II.

Regression Analysis Coefficients Used in Equation 3 an

ai

en

a5

-4.5041

2.4778

—

-0.0426

—

2.0063

- 0.1641

-0.0017

—

2.0828

0.1995

a

W a t e r (1) ( R = 0.996) MEK

(2)

( R = 0.983) THF

(3)

( R = 0.997) a

2.2301

All a{'8 not listed above were determined to be zero.

F o r m i x t u r e s c o n t a i n i n g m o r e t h a n 0.95 m o l e f r a c t i o n o f either w a t e r o r M E K , respective a c t i v i t y coefficients f o r w a t e r o r M E K a r e r e c o m m e n d e d to b e chosen as 1.0 rather t h a n t h e v a l u e p r e d i c t e d b y t h e regression equations since insufficient d a t a i n these regions cause a c t i v i t y coefficients to d e v i a t e s o m e w h a t f r o m t h e r e q u i r e d t e r m i n a l v a l u e o f u n i t y .

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

156

EXTRACTIVE

A N DAZEOTROPIC

DISTILLATION

THF

WATER

f~~®

© IV

20 Plates

WATER

Figure 4.

Feed 5 th

15 Plates

15 Plats»

L/D« 9

Feed 5 th

Feed β*

L/D* 3

L/D»3

1

MEK

Schematic diagram of solvent separation

T e r n a r y Separation B y Distillation.

scheme

T o design a recovery

system,

a s t a r t i n g c o m p o s i t i o n o f 85 m o l e % w a t e r , 7.5 m o l e % t e t r a h y d r o f u r a n , a n d 7.5 m o l e % m e t h y l e t h y l k e t o n e w a s chosen. T h i s assumes 1.5 p o u n d s of steam p e r p o u n d o f solvent are u s e d for r e g e n e r a t i o n a n d a b l e n d o f e q u a l a m o u n t s o f the solvents for t h e p o l y v i n y l c h l o r i d e processing. F i g u r e 2 shows b y t h e r e l a t i v e l e n g t h o f t h e c o n n e c t i n g Unes that i n t h e r e g i o n o f w a t e r - r i c h l i q u i d m i x t u r e s r e c t i f i c a t i o n to p r o d u c e v a p o r s r i c h i n T H F is easily o b t a i n e d . H o w e v e r , the existence o f a m i n i m u m b o i l i n g v a l l e y e x t e n d i n g across the d i a g r a m f r o m the T H F - w a t e r b i n a r y a z e o t r o p e t o t h e M E K - w a t e r b i n a r y azeotrope m a k e s i t i m p o s s i b l e t o r e m o v e a l l w a t e r f r o m the o v e r h e a d b y a single d i s t i l l a t i o n . T h e

best

that c a n b e d o n e i n t h e i n i t i a l d i s t i l l a t i o n is a n o v e r h e a d p r o d u c t i n the l o w b o i l i n g valley a n d a bottom product of substantially pure water. S e v e r a l alternatives exist t o treat f u r t h e r the o v e r h e a d stream. A s e c o n d d i s t i l l a t i o n , u s i n g t h e o v e r h e a d f r o m t h e i n i t i a l d i s t i l l a t i o n as feed, w o u l d y i e l d a n o v e r h e a d close t o the T H F - w a t e r b i n a r y a z e o t r o p e a n d a b o t t o m i n t h e r e g i o n o f the M E K - w a t e r b i n a r y azeotrope.

These

two

streams c o u l d t h e n b e d r i e d b y r e m o v i n g w a t e r p h y s i c a l l y — b y m o l e c u l a r

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

LYBARGER

10.

AND

Separation

GREENE

of

157

Mixtures

sieve o r c a l c i u m c h l o r i d e treatment, e t c . — t o y i e l d r e l a t i v e l y p u r e T H F and M E K . A s e c o n d alternative, u s i n g o n l y d i s t i l l a t i o n m e t h o d s , is c o n s i d e r e d here. T h i s m e t h o d , s h o w n s c h e m a t i c a l l y i n F i g u r e 4, involves t r e a t m e n t of t h e o v e r h e a d f r o m the first c o l u m n ( c o m p o s i t i o n i n t h e l o w b o i l i n g v a l l e y ) b y a d d i n g to it sufficient d r y T H F to b r i n g t h e n e w f e e d c o m p o s i t i o n across the l o w b o i l i n g v a l l e y . D i s t i l l a t i o n of this n e w f e e d y i e l d s the T H F - w a t e r azeotrope as o v e r h e a d a n d a b o t t o m c o n s i s t i n g of d r y M E K or an M E K - T H F mixture. T h i s T H F - w a t e r azeotrope may then b e d r i e d b y extractive d i s t i l l a t i o n w i t h d i m e t h y l f o r m a m i d e , as has b e e n p r e v i o u s l y d i s c u s s e d (4).

T h e b o t t o m p r o d u c t , as a n M E K - T H F m i x -

ture, is easily p u r i f i e d b y a n a d d i t i o n a l d i s t i l l a t i o n , b u t w i t h r e g u l a t i o n of f e e d c o m p o s i t i o n i n t h e p r e v i o u s c o l u m n , this stream m a y b e

made

to a p p r o a c h p u r e M E K , e h m i n a t i n g the n e e d for this s u b s e q u e n t d i s t i l l a t i o n . F i n a l l y , a s m a l l c o l u m n u s e d t o separate the solvent, d i m e t h y l f o r m a m i d e ( D M F ) , f r o m the w a t e r is necessary to c o m p l e t e the separat i o n scheme. Multicomponent Computer Methods for Sizing Required Columns. A modified Thiele-Geddes

m e t h o d , p r o g r a m m e d for a n I B M 370-155,

w a s u s e d to p e r f o r m t h e c a l c u l a t i o n s n e e d e d to size e a c h r e q u i r e d c o l u m n . E x p e r i m e n t a l a c t i v i t y coefficient d a t a w e r e u s e d to a l l o w for n o n ideal l i q u i d phase

behavior

while

e n e r g y balances, u s i n g

estimated

e n t h a l p y d a t a , w e r e u s e d to c o r r e c t for non-constant m o l a l overflow. T h e t a M e t h o d w a s u s e d for convergence, a n d a l l p l a t e efficiencies

The were

a s s u m e d to b e 1 0 0 % . ( See R e f e r e n c e 7 for a d d i t i o n a l c a l c u l a t i o n a l details a n d a program listing. ) Table III.

Stream No. Flow Rate (moles/hr) Composition (mole fraction) THF MEK H0 DMF 2

1

2

Column Specifications 3

4

5

100 20.0 80.0 34.3 26.8

.075 .374 .075 .369 .002 .850 .258 .998

6

7

7.5 21.6

.635 .799 .016 .215 .011 .984 .150 .190 —

8

9

10

15.2

5.2

10.0

.999 — —

—

—

.660 .999 .001

.340

—

.001 .999

Column Specification and Flowsheet. A s c h e m a t i c d i a g r a m of

the

solvent s e p a r a t i o n scheme a n d t h e results of the c o m p u t e r analysis for e a c h c o l u m n a r e s h o w n i n F i g u r e 4 a n d T a b l e III, respectively.

Feed

p l a t e locations are g i v e n w i t h respect to the b o t t o m of e a c h c o l u m n . P l a t e

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

158

EXTRACTIVE AND AZEOTROPIC DISTILLATION

requirements for columns III and IV, which contain dimethylformamide, are based on an extension of a previous design analysis by Shah and Greene (4). Literature Cited 1. "Recovery of THF du Pont Tetrahydrofuran," Ε. I. du Pont de Nemours and Co. (Inc.), Electrochemicals Department, Wilmington. 2. Methyl Ethyl Ketone, Shell Chemical Corporation, Technical Publication SC: 50-2, New York. 3. Shnitko, V. Α., Kogan, V. B., "Liquid-Vapor Equilibrium in the Systems Tetrahydrofuran-Water and Tetrahydrofuran-Ethylene Glycol and a Method for Dehydration of Tetrahydrofuran,"J.Appl. Chem. USSR 4 (6) 1236-1242. 4. Shah, C. S., Greene, H. L., "Vapor-Liquid Equilibrium for the Ternary System Tetrahydrofuran-Water-Dimethylformamide," J. Chem. Eng. Data 15 (3) 408-411. 5. Hala, E., Pick, J., Fried, V., Vilim, O., "Vapor-Liquid Equilibrium," pp. 107-109, Pergamon, 1967. 6. McDermott, C., Ellis, S. R. M., "A Multicomponent Consistency Test," Chem. Eng. Sci. (1965) 20, 293-296. 7. Lybarger, Η. M., "Ternary Vapor-Liquid Equilibrium Data Applied to the Separation of a Mixture of Water, Methyl Ethyl Ketone, and Tetrahydro furan," Thesis, The University of Akron (March 1972). RECEIVED February 14, 1972.

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

11 Prediction of Vapor Composition in Isobaric Vapor-Liquid Systems Containing Salts at Saturation D. JAQUES and W. F. FURTER Department of Applied Chemistry, Royal Melbourne Institute of Technology, Melbourne, Victoria, Australia, and Department of Chemical Engineering, Royal Military College of Canada, Kingston, Ontario, Canada A method is described for calculating equilibrium vapor compositions from boiling point vs. liquid composition data in ternary systems composed of two liquid components and a salt added to saturation. The procedure is tested on the ethanol-water system containing each of a wide range of inorganic salts at saturation. The results suggest that good quality Τ-Π-x data will yield y values of comparable accuracy.

* T * o o b t a i n v a p o r — l i q u i d e q u i l i b r i u m d a t a for b i n a r y systems, i t is n o w w e l l e s t a b l i s h e d that u n d e r

certain circumstances

it can be

more

accurate a n d less t i m e c o n s u m i n g to m e a s u r e the b o i l i n g p o i n t , the t o t a l pressure, a n d the l i q u i d c o m p o s i t i o n a n d t h e n use the G i b b s - D u h e m r e l a t i o n s h i p to p r e d i c t v a p o r c o m p o s i t i o n ( I ) r a t h e r t h a n to m e a s u r e it. T h e d i s a d v a n t a g e is that there is n o w a y o f c h e c k i n g the t h e r m o d y n a m i c consistency o f the e x p e r i m e n t a l data. F o r systems c o m p o s e d o f t w o l i q u i d s a n d a salt at saturation, this p r o c e d u r e is e s p e c i a l l y attractive because there are c o n s i d e r a b l e e x p e r i m e n t a l difficulties i n o b t a i n i n g accurate x - t / - T - I I d a t a a n d the

process

is m o r e t i m e c o n s u m i n g t h a n i n the absence o f salts. A p r o c e d u r e is presented w h i c h is b a s e d u p o n B a r k e r s m e t h o d for c a l c u l a t i n g v a p o r c o m p o s i t i o n s f r o m the

k n o w n temperature

(2) de

p e n d e n c e o f the v a p o r pressure of the p u r e constituents, w i t h s u i t a b l e m o d i f i c a t i o n for the presence o f salt, a n d f r o m the d e p e n d e n c e

o f the

b o i l i n g p o i n t o f the m i x t u r e w i t h c o m p o s i t i o n o f the e q u i l i b r i u m l i q u i d phase.

159 In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

160

EXTRACTIVE

AND AZEOTROPIC DISTILLATION

Procedure A c o m p u t e r p r o g r a m is u s e d w h i c h m i n i m i z e s 2 ( Π - Π ) 0

2

where the

t o t a l pressure is g i v e n b y : n

= x p '

c

+ (ΐ-χ)ρ' γ,

m

(1)

2

U s i n g ρ Ί a n d p ' i n s t e a d o f t h e s a t u r a t i o n v a p o r pressures o f t h e p u r e 2

l i q u i d components

a l l o w s f o r t h e presence

o f salt.

F o r salt-saturated

systems i t i s p r o p o s e d t o base t h e a c t i v i t y coefficients o n a s t a n d a r d state of e a c h l i q u i d c o m p o n e n t s a t u r a t e d w i t h salt. T h e a c t i v i t y

coefficients

are r e l a t e d t o t h e l i q u i d c o m p o s i t i o n b y u s i n g t h e two-constant W i l s o n e q u a t i o n ( 3 ) except f o r systems w h i c h s h o w a r e g i o n o f i m m i s c i b i l i t y w h e n t h e three-constant f o r m is necessary. O n e a d v a n t a g e o f t h e W i l s o n e q u a t i o n o v e r other s e m i - e m p i r i c a l a p p r o x i m a t i o n s f o r i n t e g r a t i n g t h e G i b b s - D u h e m e q u a t i o n is t h a t i t h a s a d e g r e e o f b u i l t - i n dependence form

f o r t h e l i q u i d - p h a s e a c t i v i t y coefficients.

temperature

T h e two-constant

gives:

mη -

-W-AM-*))

in y, -

+ (i-x) { - ^

- H i - Α * ,

-

-

W h e n t h e best values o f A i a n d A s i t i o n is c a l c u l a t e d : 2

ln(l-y)

= Ζη((1-χ)ρ' /Π) j(l-x) X

2

j,^}

12

\ 1-A x

(2b)

have been found, the vapor

2 2

A 12

1

ïT^fb)} <*>

(£ -V )(II-p' )/RT -

2

_

-

2

_

2

xA

21

1-A

21

compo

ln(l-A x) 12

)

<> 3

(l-x)f

T h e t e r m i n v o l v i n g t h e m i x e d s e c o n d v i r i a l coefficients

was not used

because o f t h e u n c e r t a i n t i e s i n t h e values o f t h e s e c o n d v i r i a l

coefficients

of t h e p u r e c o m p o n e n t s . Application T h e m e t h o d d e s c r i b e d a b o v e is a p p l i e d t o t h e e t h a n o l - w a t e r

system

w h i c h has b e e n s a t u r a t e d i n t u r n w i t h e a c h of a w i d e r a n g e o f i n o r g a n i c salts. T h e v a p o r pressure o f w a t e r s a t u r a t e d w i t h salts o v e r a t e m p e r a t u r e range is a v a i l a b l e f o r m a n y salts (4).

F o r e t h a n o l these d a t a a r e

u n a v a i l a b l e , a n d a c o r r e c t i o n to t h e saturation v a p o r pressure is a p p l i e d b y m u l t i p l y i n g b y t h e r a t i o o f t h e v a p o r pressure o f e t h a n o l s a t u r a t e d

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

11.

J A Q U E S

A N D

Prediction

F U R T E R

of Vapor

161

Composition

w i t h salt to the v a p o r pressure of p u r e e t h a n o l at the salt s o l u t i o n b o i l i n g T h i s r a t i o , c,

point.

is a s s u m e d to

be

independent

of

temperature.

I n t e r p o l a t i n g l i t e r a t u r e d a t a y i e l d e d the r e q u i r e d v a l u e s of the v o l u m e s of the t w o l i q u i d s ( 5 )

molar

at the a p p r o p r i a t e temperatures a n d the

s e c o n d v i r i a l coefficients of w a t e r ( β )

and ethanol (7).

A n example

of

the fit is s h o w n i n T a b l e I. Table I. Calculated Vapor Compositions from Fit of Isobaric D a t a Ethanol—Water—Saturated Ammonium Chloride (14)

X .034 .074 .124 .170 .284 .446 .633 .759 .858 .938

G*/RT-x

Τ—χ fit

y

Τ

.495 .595 .646 .674 .696 .720 .752 .807 .869 .936

93.8 87.2 84.2 82.5 81.7 80.8 79.4 78.5 77.7 77.9

fit

(y-y»)

(y-yc)

.000 -.012 -.007 -.005 -.001 -.003 -.019 -.012 -.006 .001

.003 -.007 .000 .004 .009 .005 -.016 -.014 -.011 -.003 .0098

.0098

Sample deviation

A s a n alternative, these d a t a w e r e also fitted to W i l s o n s free e n e r g y equation: (? /RT = E

-x

ln(l-A (l-x)) 21

-

(l-x)

(4)

ln{\-A x) l2

a n d the v a p o r c o m p o s i t i o n w a s a g a i n c a l c u l a t e d b y u s i n g E q u a t i o n 3.

A

d i r e c t c o m p a r i s o n c a n b e m a d e b y e x a m i n i n g the s a m p l e d e v i a t i o n of the v a p o r c o m p o s i t i o n f r o m b o t h

fittings.

T a b l e II presents the t w o sets

of s a m p l e d e v i a t i o n s b a s e d u p o n v a p o r c o m p o s i t i o n s . a n d σο /κτ Ε

T h e values of σπ

i n d i c a t e that some of the d a t a are of d u b i o u s a c c u r a c y — i . e . ,

l o w consistency a n d / o r h i g h e x p e r i m e n t a l scatter. of the o b s e r v e d Ύ-χ

G r a p h i c a l smoothing

d a t a w o u l d have r e d u c e d the values of the s a m p l e

deviations b y r e m o v i n g the e x p e r i m e n t a l scatter c o m p o n e n t , b u t i t w a s c o n s i d e r e d d e s i r a b l e to use the r a w d a t a . T h e v a l i d i t y of the Ύ-χ

e s t i m a t i o n for

the e t h a n o l - w a t e r

binary

w i t h o u t salt was c h e c k e d u s i n g three sets of l i t e r a t u r e d a t a . T h e results are i n c l u d e d i n T a b l e II, a n d O t s u k i s d a t a ( S )

are s h o w n i n F i g u r e 1.

C a l c u l a t e d a n d e x p e r i m e n t a l y-values agree satisfactorily. A d d i t i o n of a salt i n m a n y cases results i n a c o n s i d e r a b l y w i d e r b o i l i n g range, a n d this w o u l d affect the heat of m i x i n g t e r m a n d l e a d to a p o o r e r fit of the d a t a . H o w e v e r , this is u n l i k e l y to be a n i m p o r t a n t factor because

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

162

EXTRACTIVE

AND AZEOTROPIC

DISTILLATION

it has b e e n s h o w n ( 9 ) that a g o o d fit i s o b t a i n e d w i t h i s o b a r i c d a t a f o r the m e t h a n o l - a n i s o l e system w h i c h has a 64 ° C b o i l i n g range.

Comparing

the t w o sets o f results i n T a b l e I I i n d i c a t e s that the G /KT-x

fit

i s gen

e r a l l y superior, b u t f o r t h e better d a t a as i n d i c a t e d b y s m a l l

sample

E

deviations o f pressure a n d free energy, t h e differences c o n c l u s i o n is not u n e x p e c t e d . In y = Ζ τ φ ρ Ί / Π ) -

However, if the following

(Bu-VOffl-p'O/RT

ttl-x)A \ l-A x l2

+

U

X )

are s m a l l .

12

-

This

equation

ln(l-A {l-x)) 2l

xA ) l-A (l-x)f

<> 5

21

21

is u s e d to c a l c u l a t e the v a p o r c o m p o s i t i o n i n s t e a d o f E q u a t i o n 3, i n every case except f o r b a r i u m nitrate t h e opposite is true. m a r g i n a l , a n d a n e x p l a n a t i o n is offered Table II. Salt — — —

NH CI 4

tNaCl t NaBr t NaN0 tKCl KBr KI K S0 Ca(N0 ) Ba(N0 ) CuCl HgCl HgBr Hgl LiCl" t NaCl » t Na S0 tKCl» ΚΙ" BaCl KN0 (NH ) S(V 3

2

4

3

3

2

2

2

2

2

2

4

2

3

4

d

e

2

6

T h i s effect i s n o t

below.

Comparison of the T - * Fit and the G^/RT-x the Wilson Equation σΠ

«y

<sG RT

4.88 6.24 9.69 13.66 18.82 27.42 30.06 31.40 28.09 19.48 3.95 33.69 20.20 10.31 5.10 8.40 13.69 6.07 20.96 23.95 22.90 3.65 11.42 4.94 24.9

.0079 .0068 .0045 .0098 .0119 .0471 .0260 .0301 .0109 .0234 .0118 .0078 .0152 .0092 .0138 .0273 .0142 .0062 .0184 .0264 .0180 .0058 .0110 .0099 .0358

6.45 4.48 6.34 5.84 11.79 60.27 31.75 28.74 10.72 14.08 6.23 28.12 15.45 7.54 3.55 17.47 13.98 12.54 14.64 19.63 10.14 4.00 4.34 7.70 35.3

Fit Using Reference

E

.0082 .0064 .0059 .0098 .0054 .0375 .0187 .0200 .0150 .0098 .0082 .0096 .0130 .0096 .0119 .0261 .0146 .0056 .0143 .0132 .0088 .0045 .0085 .0078 .0320

Data of limited range: x = 0.3-1.0. Data of limited range: x = 0-0.8. Data of limited range: x = 0.2-1.0. Data of limited range: x = 0-0.6. Partially miscible systems-use of three constant Wilson equation, t See text.

a

6

c

d

e

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

8 12 18 U

14 15 u U

15 15 U

11 u η π η u 16 17 18 17 16 U

19 14

11.

J A Q U E S

A N D

Prediction

F U R T E R

of Vapor

163

Composition

χ Figure 1. Comparison of the experimentally de termined vapor compositions for the ethanol-water system (8) with two constant Wilson T - x fit Observed

Ο

Calculated

A n i n t e r e s t i n g a n o m a l y o c c u r r e d for the seven systems m a r k e d w i t h a d a g g e r i n T a b l e II.

T h e o r i g i n a l c o m p u t e r p r o g r a m w h i c h was b a s e d

u p o n first o r d e r l i n e a r i z a t i o n of the n o r m a l e q u a t i o n s f a i l e d to find a s o l u t i o n for the G V R T - x fit for these systems. A s e c o n d p r o g r a m u s e d a more powerful

t e c h n i q u e w h i c h u s e d a n e w a p p r o a c h to

m e t r i c a l g o r i t h m s (10).

variable

B e c a u s e the t w o constants i n the W i l s o n e q u a

t i o n c a n n o t be greater t h a n u n i t y , a constraint is p l a c e d u p o n the p l a n e w h e r e a s o l u t i o n is sought. A i w a s r e p l a c e d b y 1-A 2

2

T o free the p r o g r a m f r o m this constraint,

and A

12

b y 1-B . 2

This program found a solu

t i o n , b u t it d i d n o t represent a true m i n i m u m . T h e s o l u t i o n o c c u r r e d at a wall—i.e.,

where

A i =

1, a n d analysis s h o w e d that this w a s

2

lowest p o i n t of the A i - A i 2

2

the

p l a n e . A n a l y z i n g the r e m a i n i n g systems of

T a b l e II s h o w e d that a g e n u i n e m i n i m u m — i . e . , a least v a l u e w h e r e the first derivatives of the object f u n c t i o n v a n i s h — w a s f o u n d i n a l l of these cases. T h e t w o systems c o n t a i n i n g p o t a s s i u m nitrate a n d a m m o n i u m s u l fate e a c h h a v e a r e g i o n of p a r t i a l m i s c i b i l i t y . A d d i n g a t h i r d constant to the W i l s o n e q u a t i o n allows c o r r e l a t i o n of s u c h systems. T h e results are s h o w n i n T a b l e II a n d F i g u r e 2. ( T h e b r o k e n l i n e of F i g u r e 2 is a feature of systems w h i c h s h o w m a t e r i a l i n s t a b i l i t y . A g r a p h of m o l a r free energy

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

164

E X T R A C T I V E

A N D

A Z E O T R O P I C

DISTILLATION

of m i x i n g as a f u n c t i o n of l i q u i d m o l e f r a c t i o n shows a c o n v e x u p w a r d s p o r t i o n w h e r e a r e g i o n o f p a r t i a l m i s c i b i l i t y exists (20).

The

vapor-

l i q u i d e q u i l i b r i u m c u r v e s h o u l d , of course, b e h o r i z o n t a l i n the r e g i o n of t w o l i q u i d phases, b u t the f o r m of the e q u a t i o n m u s t g i v e a c o n t i n u o u s c u r v e a n d h e n c e c a n n o t p r e d i c t a h o r i z o n t a l l i n e , w h i c h w o u l d a m o u n t to a r e g i o n of d i s c o n t i n u i t y i n the e q u a t i o n . ) T h e t w o - c o n s t a n t W i l s o n e q u a t i o n w a s c h o s e n as t h e c o r r e l a t i n g e q u a t i o n r a t h e r t h a n t h e three-constant R e d l i c h - K i s t e r e q u a t i o n (21)

for

t w o reasons. I n a m a j o r i t y of the systems the s a m p l e d e v i a t i o n of v a p o r c o m p o s i t i o n w a s smaller, a n d i n c e r t a i n cases the R e d l i c h - K i s t e r e q u a t i o n e r r o n e o u s l y p r e d i c t e d phase s e p a r a t i o n . F i g u r e 3 shows s u c h a n e x a m p l e . T a b l e I I I gives a c o m p l e t e l i s t i n g of m , c, c, A21,

A , a n d C values i 2

w h i c h a l l o w us to estimate the v a p o r c o m p o s i t i o n s of e t h a n o l - w a t e r m i x tures c o n t a i n i n g a w i d e r a n g e of i n o r g a n i c salts. Discussion D i f f e r e n t object functions ( Π, y, In 72/71, etc. ) h a v e b e e n u s e d for m a n y years; w h e n d i s c r e p a n c i e s h a v e a r i s e n , at least one a u t h o r

2 LAYERS H .1

.2

.3

.4

.5 X

.6

.7

.8

.9

Figure 2. Comparison of the experimentally de termined vapor compositions for the ethanol-watersaturated potassium nitrate system (19) with the three constant Wilson T - x fit Observed

Ο

Calculated

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

(22)

11.

J A Q U E S

A N D

Prediction

F U R T E R

.1

.2

.3

.4

of Vapor

.5 X

.6

.7

Composition

.8

165

.9

Figure 3. Comparison of experimentally deter mined vapor compositions for the ethanol-watersaturated potassium sulfate system (14) with (a) two constant Wilson T-x fit and (b) three constant Redlich-Kister T-x fit Observed Calculated

Ο (a)

(b)

has a t t r i b u t e d t h e m to errors i n d a t a . A c t u a l l y , there are three possible sources of e r r o r : 1. T h e W i l s o n e q u a t i o n is a n i m p e r f e c t m o d e l . I n t h e i s o b a r i c case the effect of n e g l e c t i n g the t e m p e r a t u r e d e p e n d e n c e of A i a n d A and i n u s i n g the G i b b s — D u h e m e q u a t i o n , w h i c h w a s d e r i v e d for constant t e m p e r a t u r e a n d pressure, a d d to the i n h e r e n t i m p e r f e c t i o n . 2

12

2. A l l the e x p e r i m e n t a l d a t a are subject to error, a n d i n t h e salt effect field a n a d e q u a t e e s t i m a t i o n of e x p e r i m e n t a l errors is r a r e l y m a d e . F o r e x a m p l e , w i t h o u t d o i n g a statistical treatment of the error i n the m e a s u r i n g of t e m p e r a t u r e , a s i m p l e e s t i m a t i o n of r a n d o m e x p e r i m e n t a l error b a s e d u p o n the g r a p h i c a l s m o o t h i n g of b o i l i n g p o i n t - c o m p o s i t i o n d a t a for eight systems c o n t a i n i n g w a t e r , m e t h a n o l o r e t h a n o l , a n d a n acetate salt at s a t u r a t i o n [ t a k e n f r o m the literature ( 2 3 ) ] suggested a n o v e r a l l average error of ± 0 . 9 ° C o n the b o i l i n g p o i n t s . 3. T h e w h o l e p r o c e d u r e , w i t h o r w i t h o u t salts, m a y n o t b e b a s e d u p o n s o u n d statistical p r i n c i p l e s . R a t h e r t h a n u s i n g v a r i o u s object f u n c tions, i t appears better t o use a r e l i a b l e statistical t e c h n i q u e s u c h as t h e m e t h o d of m a x i m u m l i k e l i h o o d (24) o r the B a y e s i a n a p p r o a c h (25), b o t h of w h i c h take i n t o a c c o u n t the errors i n a l l e x p e r i m e n t a l o b s e r v a tions i n a l o g i c a l l y justifiable f a s h i o n . T h e v a r i o u s d i s c r e p a n c i e s a n d anomalies n o t e d i n the present w o r k w o u l d b e m o d e r a t e d b y u s i n g either

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

166

EXTRACTIVE

Table III.

m

const.

ε

—

—

—

—

—

—

—

—

—'

—

.9294 .9935 .9174 .8853 .9547 .9572 .9383 .9962 1.0712 1 1 1 1 1 .9659 .9935 1.019 .9640

3

2

4

3

2

2

2

2

2

2

4

BaCl

2

KN0 (NH ) S0 3

4

2

4

AZEOTROPIC

DISTILLATION

Constants for the Τ—χ Fit Using the Wilson Equation

Salt

NH4CI NaCl NaBr NaN0 KC1 KBr KI K S0 Ca(NO,) Ba(N0 ) CuCl HgCl HgBr Hgl LiCl NaCl Na S0 KC1 KI

AND

—

A M

—

I

2

.8140 .7899 .8526 .8829 .9476 .9138 .9420 .9198 .9214 .8433 .9188 .8531 .8208 .8486 .8314 .8428 .8267 .7926 .9332 .9349 .9307

.1325 .1813 .0848 .4154 .3692 .5005 .5592 .4314 .2744 .4000 .0802 .0090 .1780 .0565 .0791 .1263 .1095 .5457 .3308 .1633 .3226 .3285 .2142

-.0032 .1109 .0776 -.0704 -.0037 .0360 .0719 .0105 .9368 0 0 0 0 0 .9199 .1109 .0969 .0235

1.013 1.019 0.912 1.020 1.000 0.983 0.886 1.023 0.747 1.027 1.042 .892 .965 1.010 .492 1.019 1.000 1.000

.9383

.0719

.9275

.9906 .8570

.0348

.975 1

-.2250 .0487

1.000 1.011

.7515 .9409

.9731

A

.9170

C

Refere

— —

8 12 13

—

U

—

—

14

—

15

—

14 14

— —

15 15

—

U

—

11 11

—

—

14 14 14 14

— — — —

—

16 17 18 17

—

16

—

11

— —

—

- . 3 9 0 8 2.959 .0449 1.250

19

14

estimate w i t h the o n l y sources of error b e i n g i n the observations a n d i n the p h e n o m e n o l o g i c a l m o d e l . Conclusions A

method

has b e e n

d e v e l o p e d for c a l c u l a t i n g e q u i l i b r i u m

vapor

c o m p o s i t i o n s , b a s e d o n b o i l i n g p o i n t vs. l i q u i d c o m p o s i t i o n d a t a ,

for

systems saturated w i t h a salt. S u c h ternary systems i n effect h a v e b e e n treated as b i n a r i e s (26)

i n w h i c h the s t a n d a r d state of e a c h of t h e t w o

l i q u i d c o m p o n e n t s is that of b e i n g saturated w i t h salt i n s t e a d of b e i n g p u r e and w i t h the pure-component example,

v a p o r pressures b e i n g so adjusted.

i n the e t h a n o l - w a t e r - s a l t

t e r n a r y systems

b e e n c o n s i d e r e d as b i n a r i e s c o m p o s e d

tested, t h e y

For have

of w a t e r s a t u r a t e d w i t h salt as

one c o m p o n e n t a n d e t h a n o l saturated w i t h salt as t h e other

component.

I n the testing to w h i c h i t has b e e n subjected so far, the m e t h o d seems encouraging.

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

11.

J A Q U E S

A N D F U R T E R

Prediction

of Vapor

Composition

167

Acknowledgment T h e r e s e a r c h f o r this p a p e r w a s s u p p o r t e d b y t h e D e f e n c e R e s e a r c h B o a r d o f C a n a d a , G r a n t n u m b e r 9530-40. T h e authors are g r a t e f u l t o F . M . L a r k i n o f t h e C o m p u t e r C e n t r e at Queen's U n i v e r s i t y , K i n g s t o n , for m a n y h e l p f u l discussions. Lest of

Symbols

Subscripts: 1 = ethanol 2 = water c = calculated value A21, A12, C = e m p i r i c a l constants i n W i l s o n e q u a t i o n A,B = e m p i r i c a l constants f o r use w i t h F l e t c h e r s s u b r o u t i n e Bu = s e c o n d v i r i a l coefficient o f c o m p o n e n t i G = excess free e n e r g y o f m i x i n g In = natural logarithm log = l o g a r i t h m t o the base 10 m, const. = e m p i r i c a l constants i n the e q u a t i o n : l o g p'2 = τη l o g p ° 2 — const, p'i = v a p o r pressure o f c o m p o n e n t i s a t u r a t e d w i t h salt R = gas constant Τ = absolute t e m p e r a t u r e Vi = molar volume of component i x = m o l e f r a c t i o n o f e t h a n o l i n the l i q u i d phase, c a l c u l a t e d o n a salt-free basis y = mole fraction of ethanol i n the vapor phase 7i = a c t i v i t y coefficient o f c o m p o n e n t i e = r a t i o o f v a p o r pressure o f e t h a n o l s a t u r a t e d w i t h salt to t h e v a p o r pressure o f p u r e e t h a n o l at t h e salt s o l u t i o n boiling point Π = t o t a l pressure σσ /κτ = s a m p l e d e v i a t i o n o f t h e excess free e n e r g y i n E q u a t i o n 4 σ = s a m p l e d e v i a t i o n o f the v a p o r c o m p o s i t i o n c o r r e s p o n d i n g to E q u a t i o n 4 σπ = s a m p l e d e v i a t i o n o f the t o t a l p r e s s u r e i n E q u a t i o n 1 σ = s a m p l e d e v i a t i o n o f the v a p o r c o m p o s i t i o n c o r r e s p o n d i n g to E q u a t i o n 1 E

Β

ν

ν

Literature Cited 1. MacKay, D., Salvador, R. T., Ind. Eng. Chem. Fundamentals (1971) 10, 167. 2. Barker, J. Α., Australian J. Chem. (1953) 6, 207. 3. Wilson, G. M.,J.Amer. Chem. Soc. (1964) 86, 127. 4. International Critical Tables, pp. 362-374, Vol. III, McGraw-Hill, New York, 1929. 5. Prausnitz, J. M., Eckert, C. Α., Orye, R. V., O'Connell, J. P., "Computer Calculations for Multicomponent Vapor-Liquid Equilibrium," Appendix B, Prentice-Hall, 1967.

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

168

EXTRACTIVE AND AZEOTROPIC DISTILLATION

6. Rowlinson, J. S., Trans. Faraday Soc. (1949) 45, 974. 7. Lambert, J. D., Discussions Faraday Soc. (1953) 15, 226. 8. Otsuki, H., Williams, F.C.,Chem. Eng. Progr. Symp. Ser. 6 (1953) 49, 55. 9. Cukor, P. M., Prausnitz, J. M., Intern. Symp. Distillation, Inst. Chem. Eng (London), Section 3B, p. 73 (1969). 10. Fletcher, R., U.K. At. Energy Authority Kept. TP383 (1969). 11. Rius Miró, Α., Alvarez Gonzalez, J. R., Uriante Hulda, Α., Anales Real. Soc. Espan. Fis. Quim. (Madrid) (1960) 56B, 629. 12. Rieder, R. M., Thompson, A. R., Ind. Eng. Chem. (1949) 41, 2905. 13. Furter, W. F., Ph.D. Thesis, University of Toronto, 1958. 14. Johnson, A. I., Furter, W. F., Can. J. Chem. Eng. (1960) 38, 78. 15. Meranda, D., Furter, W. F., A.I.Ch.E. Journal (1972) 17, 38. 16. Rius Miró, Α., Otero de la Gandara, J. L., Alvarez Gonzalez, J. R., Anales Real. Soc. Espan. Fis. Quim. (Madrid) (1957) 53B, 185. 17. idem., ibid. (1957 53B, 171. 18. Tursi, R. R., Thompson, A. R., Chem. Eng. Progr. (1951) 47, 304. 19. Rieder, R. M., Thompson, A. R., Ind. Eng. Chem. (1950) 42, 379. 20. Rowlinson, J. S., "Liquids and Liquid Mixtures," p. 144, 2nd ed., Butterworth, 1969. 21. Redlich, O., Kister, A. T., Ind. Eng. Chem. (1948) 40, 345. 22. Newton, Α., Intern. Symp. Distillation, Inst. Chem. Engrs. (London), Section 3B, p. 82 (1969). 23. Meranda, D., Furter, W. F., A.I.Ch.E. J. (1971) 17, 38. 24. Kendall, M. G., Stuart, Α., "The Advanced Theory of Statistics," Vol. II, 2nd ed., Griffin, London, 1967. 25. Lindley, D. V., "Introduction to Probability and Statistics from a Bayesian Viewpoint," Cambridge, 1965. 26. Jaques, D., Furter, W. F., A.I.Ch.E. J. (1972) 18, 343. RECEIVED January 11, 1972.

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

INDEX

A Acetone 43 azeotrope, methanol 47 -methanol separation 48 system acetic a c i d 136 Acid, Lewis 50 Activity coefficients 17,124,140 dilution 49 liquid phase 2,3,150,151 paraffin 20 selectivity and 27 ADP -ADPLLE 91 simplified calculations by subprogram 68 A D P P L L E , subprogram 69 Agent, separating 37 Air pollution 148 Alcohols, mixtures of water and simple 93 Algorithm, modification of correction 131 Alternate solvent recovery 32 Analysis economic 24 regression 155 venture 24 Applications 43 Aqueous ethanol calculated azeotropic distilla tion results compared for dehydrating 65 dehydrating 14 mixtures, dehydration of . . . . 2 systems 41 Aromatics 58 Association complexes 17, 42 factors, vapor, and liquid 138 Automated feature, use of the . . . . 69 Azeotrope 38,110 methanol-acetone 47 of water and entrainers 112 Azeotropic column 115 distillation 14,65 batch 115 column 12 comparison of extractive with 12 modified 115

Azeotropic (Continued) distillation ternary wo, ADP/ADPLLE results compared for dehydrat ing aqueous ethanol, calculated or extractive distillation columns

ι* 65 65 93

Β Barker's method 159 Base, Lewis * 50 Basic flow 114 Basis cost calculation 25 design 23 Batch azeotropic distillation 115 Benzene 65, 89 and diethyl ether, comparison for the entrainers, n-pentane 87 Binary system 99 Boiling point 107 Bonding solvents, hydrogen 21 Bottom product 12 1,3-Butadiene recovery 33 Butanol HI

C Calcium chloride Calculated azeotropic distillation results compared for dehydrat ing aqueous ethanol Calculation basis, cost computer design distillation for the extractive distillation of aqueous ethanol mixtures . . sequence by subprogram A D P , simplified . tray-to-tray Changing the molecular environ ment Chemistry of the salt effect Choice of an entraîner C3 hydrocarbon mixtures C4 hydrocarbon separations

171

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

39

65 25 64 91 122 4 125 68 70 1 40 87 34 33

172

E X T R A C T I V E

Circulation rate 17 solvent 24 Clay, colloidal 120 Coefficient activity 17,124,140 dilution activity 49 distribution 64 fugacity 97 imperfection-pressure 2 liquid phase activity 3,150,151 paraffin activity 20 selectivity and activity 27 Cohesive density, polar 51 energy, polar 48 Coke 119,120 Colloidal clay 120 Column 35 azeotropic 115 distillation 12 or extractive distillation 93 efficiency 24 extractive distillation 6 profiles 84 solvent recovery 10,11 Comparison for the entrainers, n-pentane, benzene, and diethyl ether 87 of extractive with azeotropic distillation 12 Complexes, association 17, 42 Components, feed 1,17, 22, 40 Composition 7, 35, 94,125,146 liquid 107 vapor 41,159 phase 97 Computer calculations 64 methods, multicomponent 157 Concentration molal salt 40 saturation 39 solvent 19 Condenser temperature 131 Consistency test 146 Content, water 110,114 Cooler, solvent 17 Correction algorithm, modification of 131 matrix, Jacobian 126 Cost calculation, basis 25 extractive distillation 30 utility 26 Cracking 119 Criteria, solvent selection 18

D Dalton's law 152 Data, isobaric vapor-liquid equilibrium 96,124,136 Debye, electrostatic theory of . . . . 42 •Décantation 114

A N D

A Z E O T R O P I C

DISTILLATION

Dehydrating aqueous ethanol 14 calculated azeotropic distillation results 65 process, demulsifying 114 Dehydration of aqueous ethanol mixtures 1,118 Demulsification of crude oils 108 Demulsifying, dehydrating process 114 Density, polar cohesive 51 Design basis 16,23 calculations 91 process 16,106 of separation processes 2 Diethyl ether 65,89 comparison for the entrainers, n-penane, benzene, and diethyl ether 87 Digital computers 2 Dilution activity coefficients 48 relative volatilities through G L C , infinite 59 Dipole-induced dipole 49 Dispersion 49 Dissolution, feed 117 Dissolved salt 37 Distillation of aqueous ethanol mixtures, calculations for the 4 azeotropic 14, 65 batch azeotropic 115 calculations 122 column azeotropic 12,13, 93 extractive 6,13,93 continuous 115 costs, extractive 30 extractive 1,12,14,16,148 modified azeotropic 115 program A D P / A D P L L E , azeotropic . . 65 ternary azeotropic 68, 72 results compared for dehydrating aqueous ethanol, calculated azeotropic 65 solvents ethylene glycol as the extractive 2 extractive 58 screening of extractive 46 using dissolved salts as separating agents, extractive 40 Distribution coefficients 64

Ε Ease of separation Effect chemistry of the salt magnitude of salt mixed solvents

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

40, 46 35, 40 41 52

173

INDEX

Effect (Continued) of solvent and solute concentration 50 Efficiency, column 24 Electrolytes, solution theory of . . . 40 Electrostatic theory of Debye . . . . 42 Energy, Gibbs free 95 Energy molar free 163 polar cohesive 49 Enthalpies for liquid and vapor . . 4,124 Entraîner 12,64,65,110 azeotropes of water and 112 choice of 87 n-pentane, benzene, and diethyl ether, comparison for the . . 87 solvent 116 Entrainment 37 Environment, changing the molecular 1 Equation Gibbs-Duhem 155 modified van Laar 3, 66 non-random, two liquid 93 nonlinear 122 NRTL Redlich-Kister 164 van Laar 132 vapor pressure 3 Wilson 95,160 Equilibria data 124 isobaric vapor-liquid 93,136 prediction of three-phase 65, 66 relative volatilities for three phase 67 relation, modified 139 salt effect on vapor-liquid 40 separation system 123 stage requirements 28 three-phase 67 vapor-liquid 35, 67,148 Ethanol 13,39, 86, 89,93 calculated azeotropic distillation results compared for dehydrating aqueous 65 calculations for the extractive distillation of aqueous 4 mixtures dehydration of aqueous 1,2 recovery of 7 -water 38,41,97,160 Ethylene glycol 1, 2,12 -water 41 Extraction, primary 119 Extractive distillation 1,12,14,16,132,148 of aqueous ethanol mixtures, calculations for the 4 columns, azeotropic or 6, 93 costs 30 solvent 58 ethylene glycol as the 2

Extractive distillation (Continued) solvent screening of using dissolved salts as separating agents

46 40

F Factor, separation 17, 59 Factors, vapor and liquid associations 138 Feed 5 components 17, 22, 40 dissolution 117 Feedstock 113 Flow basic 114 vapor 129 Flowsheet 18,111,157 Foaming 114 Fraction, naphtha Ill Fractionation, reverse 28 Free energy 95,161 molar 163 Fugacity coefficients 94,97

G G C O S process 118 Gibbs-Duhem equation . . . 146,155,159 Gibbs energy 42,95 GLC infinite dilution relative volatilities through 59 screening solvents through . . . . 58 Great Canadian Oil Sands, Ltd. ( G C O S ) Process 118

H Heat loads 14 recovery system 30 Hydration 43 Hydrocarbon 55,93,109 C 4 mixtures 48 separations, C4 33 Hydrogen bonding solvents 21 Hypothetical saturation vapor pressure 138 3

I Imperfection-pressure coefficients . 2 Infinite dilution relative volatilities through G L C 59 Internal pressure 42 Isobaric vapor-liquid equilibrium data 93,136 systems 159 Isothermal-isobaric system 155 Iteration variables 125,127

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

174

E X T R A C T I V E

J Jacobian correction matrix

126,128

Κ Κ values Kerosene Knockback section, solvent

9 117 37, 44

L Law, Raoult's 18,101 Layer, top bitumen 121 Lewis acid 50 base 50 and Matheson technique 70 Limit, miscibility 22 Liquid associations factors, vapor and . 138 composition 107 equation, non-random, two . . . . 93 equilibrium data, isobaric vapor35,93,136,148 -liquid tieline 153 phase activity coefficients . . . 2,3,150,151 miscibility 107 systems, isobaric vapor159 and vapor, enthalpies for 4 phases, relative distributions between the separable . . 2 Loading, solvent 24 Lowest water content 89

M Matrix, Jacobian correction . . . . 122,126 Matheson technique, Lewis and . . 70 Mercuric chloride 41 Methanol -acetone azeotrope 47 separation, acetone48 Method Marquardt's 134 non-hydrocarbon mixtures: The Schiebel 47 Parachor 56 Weimer-Prausnitz ( W P ) 57 multicomponent computer 157 Newton 134 3-Methyl-l-butanol-water 100 Methyl ethyl ketone, water148 Miscibility limit 22 liquid-phase 107 Mixed solvents effect 52 Mixture THF-MEK 149 C3 hydrocarbon 34, 48 nonideal 122 ternary 96 of water and simple alcohols . . . 93

A N D

A Z E O T R O P I C

DISTILLATION

Mixture (Continued) the Scheibel Method, nonhydrocarbon 47 Modification of correction algorithm 131 process 29 Modified azeotropic distillation 115 equilibrium relation 139 Redlich-Kister test 140 van Laar equations 3, 66 Molal salt concentration 40 Molar free energy 163 Molecular environment, changing the 1 Multicomponent systems 13,17,157

Ν Naptha fraction HI Newton's methods 122,134 Non-hydrocarbon mixtures: the Scheibel Method 47 Nonideal mixtures 122 Nonideality 1,95 Nonlinear equations 122 Non-random, two-liquid equation . 93 Notation, matrix 122 N R T L equation 96

Ο Octane Oil wet sludge demulsification of crude Olefins Operating temperature Optimum design Othmer recirculation still

HI 115 108 58 24 16 43

Ρ Parachor method 56 Paraffin activity coefficient 20 -olefin system 19 n-Pentane 1,12,65,89 benzene and diethyl ether, comparison for the entrainers 87 Petroleum crudes 108 P° P°, 47 Polar cohesive density 51 energy 49 solvent 20 Pollution, air 148 Potassium acetate 37 Prediction of three-phase equilibria 66 Pressure 94,107 coefficients, imperfection2 equations, vapor 3 t

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

175

INDEX

Pressure (Continued) hypothetical saturation vapor . . 138 vapor 110 Process demulsifying, dehydrating 114 design 16,106 Great Canadian Oil Sands, Ltd. ( G C O S ) process 118 of separation 2 modifications 29 Product, top 5,12, 86 A D P / A D P L L E , azeotropic distillation 65 ternary azeotropic distillation... 68, 72 Propane 33 separation of propylene— 16 Propylene 33 propane, separation of 16

R Raoult's Law 18,101,152 Rate circulation 17 solvent circulation 24 Reboiler temperature 131 Recirculation still, Othmer 43 Recovery alternate solvent 32 1,3-butadiene 33 column, solvent 10,11 ethanol 7 and recycle step 37 system, heat 30 Recycle step, recovery and 38 Redlich-Kister equation 164 test, modified 140 Regression analysis 155 Relation, modified equilibrium . . . 139 Relationship, Gibbs-Duhem 146 Requirements, equilibrium stage . . 28 Reverse fractionation 28 Runs, two-phase 153

S Salt 35,159 concentration, molal 40 dissolved 37 effect 35 chemistry of the 40 magnitude of 41 on vapor-liquid equilibrium . 40 free 39 molecules, undissociated 41 as separating agents, extractive distillation using dissolved . 40 Saturation 159 concentration 39 vapor pressure, hypothetical . . . 138 Scheibel method, non-hydrocarbon mixtures: the 47

Screening of extractive distillation solvents 46 solvents through G L C 58 Section, solvent knockback 37 Selection criteria, solvent 18 Selectivity 18,47 and activity coefficients 27 Separating agent 37 C4 hydrocarbon 33 extractive distillation using dissolved salts as 40 Separation 91 acetone-methanol 48 ease of 40, 46 factor 17,59 of propylene-propane 16 solvent 156 system, equilibrium 122 Silt 108 Simplified calculations by subprogram A D P 68 Sludge, oil-wet 115 Solubility 113 Solute concentration, effect of solvent and 50 Solution theory of electrolytes . . . . 40 Solutions, ideal 47 Solvent 35,47,114 circulation rate 24 concentration 19 cooler 17 effect, mixed 52 ethylene glycol as the extractive distillation 2 evaluating 19 extractive distillation 58 through G L C , screening 58 hydrogen bonding 21 knockback section 37 loading 24 polar 20 Solvent recovery column 10,11,32 screening of extractive distillation 46 Selection criteria 18 separation 156 and solute concentration, effect of 50 volatility 22 Stage requirements, equilibrium . . 28 Step, recovery, and recycle 38 Still, Othmer recirculation 43 Stripping trays 11 Submatrices, Jacobian 128 Subprogram A D P , simplified calculations by . 68 ADPPLE 69 System acetic acid-acetone 136 aqueous 41 binary 99 equilibrium separation 122 ethanol-water 97,160

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

176

E X T R A C T I V E

System (Continued) isobaric vapor-liquid multicomponent paraffin-olefin ternary

159 17,93 19 103

Τ Temperature . . . .7, 54, 94,110,125,161 denser 131 operating 24 reboiler 131 Ternary azeotropic distillation program . 69 mixtures 96 separation by distillation 156 system 103 Test consistency 146 modified Redlich Kister 140 Tetrahydrofuran 148 Theory of Debye, electrostatic 42 of electrolytes, solution 40 T H F - M E K mixture 149 Three-phase equilibria 66 relative volatilities for 67 Top bitumen layer 120 Top product 5,12, 86 Transport 119 Tray-to-tray 70,71 Trays, stripping 11 Two liquid equation, non-random . . . 93 phase runs 153

U Undissociated salt molecules U N I V A C 1108 computer Use of the automated feature

41 4 69

A N D

AZEOTROPIC

DISTILLATION

Utility costs phase composition

26 2 97

van der Waal forces 42 van Laar equation 95,132 Vapor composition 41,159 enthalpies for liquid and 4 flows 129 relative distributions between the separable liquid and 2 -liquid equilibria 35,67,148 and liquid associations factors . . 138 pressure 110 equations 3 hypothetical saturation 138 Variable, iteration 127 Vector differentiation 126 Venture analysis 24 Viscosity 108 V L E data 96 Volatilities 17, 40,47, 89,104,145 through G L C , infinite dilution relative 59 profiles 7 solvent 22

W Water content 11,110,114 lowest 89 and entrainers, azeotropes 112 ethanol38,41,160 ethylene glycol41 methyl ethyl ketone 148 and simple alcohols, mixtures of 93 Weimer-Prausnitz ( W P ) method . 56 Wilson equation 95,160

In Extractive and Azeotropic Distillation; Tassios, D.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.