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Vapor-liquid equilibrium of benzene-biphenyl Waldichuk, Michael 1950

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VAPOR-LIQUID EQUILIBRIUM ^ : i GF BENZENE-BIPHENYL BY MICHAEL WALDICHUK - 0 -A t h e s i s submitted i n p a r t i a l f u l f i l m e n t o f the requirements f o r the degree of MASTER OF ARTS IN THE DEPARTMENT OF CHEMISTRY - 0 -THE UNIVERSITY OF BRITISH COLUMBIA OCTOBER, 1950. ' 1 THE UNIVERSITY OF BRITISH COLUMBIA V A N C O U V E R , C A N A D A C H E M I S T R Y September 30, 1950. To Whom It May Concern: This i s to certify that the thesis entitled "Vapour-Liquid Equilibrium of Benzene-Biphenyl" by Mr. Michael Waldichuk measures up to the required standards of the Master's thesis in this Department. Yours truly, -ew ABSTRACT A comprehensive s u r v e y has been made o f vapor l i q u i d e q u i l i b r i u m apparatuses i n the l i g h t o f h i s t o r i c a l development. Two of the b e t t e r types o f u n i t s have been chosen and b u i l t f o r t h i s r e s e a r c h . The vapor l i q u i d e q u i l i b r i a o f benzene-n-butanol and benzene-biphenyl were determined on the G i l l e s p i e - F o w l e r e q u i l i b r i u m s t i l l . Thermo-dynamic c o n s i s t e n c y o f the r e s u l t s was checked w i t h the van Laar and Margules i n t e g r a t i o n s o f the Gibbs Dubem e q u a t i o n . R e s u l t s o b tained on the benzene-n-butanol system appear t o Con4 form t o the o r y w i t h i n experimental e r r o r . However, those o f benzene-biphenyl show v e r y l i t t l e c o n s i s t e n c y . Temperature-Composition diagrams were drawn f o r both systems and f o l l o w the g e n e r a l form f o r non-azeotropic m i x t u r e s ; ACKNOWLBDGEMEIJT The author wishes to express his appreciation of the constructive criticism as well as encouragement given by Dr. L.W. Shemilt under whose supervision this research was carried out. Thanks are also due Mr. Wm. Pye, who carried out the glassblowing on the Gillespie-Fowler equilibrium s t i l l along with other smaller projects; and to Mr. A. Werner, who gave helpful suggestions and hints i n the d i s t i l l a t i o n and general purification of the compounds. Acknowledgement is also made of the National Research Council Summer Scholarship which aided financially in the continuation of this research for the months May to September of 1949 and for May of 1950. TABLE OF CONTENTS TITLE I I n t r o d u c t i o n I I T h e o r e t i c a l " D i s c u s s i o n PAGE 1 7 Gibbs Duhem eq u a t i o n Van Laar E q u a t i o n s Margules Equations Other thermodynamic Treatments of V a p o r - l i q u i d e q u i l i b r i a . I l l H i s t o r i c a l Development of the E q u i l i b r i u m Apparatus 24 A. L i q u i d R e c i r c u l a t i n g Type 1. E a r l y Work Determinations o f B i l i n g Temperatures I n t e r n a l Heaters C o t t r e l l Pump Vapor Trap 2. Modern E q u i l i b r i u m S t i l l s The Othmer e q u i l i b r i u m s t i l l C h i l t o n ' s e q u i l i b r i u m s t i l l S t i l l o f Scatchard, Raymond and Gilmann 3. L a t e s t Developments i n E q u i l i b r i u m S t i l l s F l a s h chamber G i l l e s p i e S t i l l w i t h vapor disengagement chamber Fowler m o d i f i c a t i o n of the G i l l e s p i e s t i l l 4 . S p e c i a l i z e d S t i l l s S t i l l s f o r p a r t i a l l y m i s c i b l e b i n a r y mixtures E q u i l i b r i u m s t i l l s f o r h i g h vacua E q u i l i b r i u m s t i l l s . r ' f o r low temperature B. Vapor R e c i r c u l a t i n g Type E a r l y Forms Constant temperature type of r e c i r c u l a t i n g apparatus C. Other Methods of V a p o r - l i q u i d e q u i l i b r i u m Deter-minations Bomb method Dynamic Plow Method Apparatus A. Vapor R e c i r c u l a t i n g Apparatus High vacuum system P u r i f i c a t i o n o f mercury Main E q u i l i b r i u m apparatus C i r c u l a t i n g pump Commutator f o r c i r c u l a t i n g pump Temperature c o n t r o l Constant temperature baths S t i r r i n g equipment Heating, temperature measurement and c o n t r o l Constant Temperature a i r Thermomostats Constant Temperature O i l bath B. L i q u i d R e c i r c u l a t i n g Apparatus M o d i f i c a t i o n s of Fowler s t i l l C. Refractometer D. P l a t i n u m R e s i s t a n c e thermometer M a t e r i a l s A. Benzene 1. I n i t i a l P u r i f i c a t i o n 2. D i s t i l l a t i o n 3. F r a c t i o n a l R e c r y s t a l l i z a t i o n 4. Check on p u r i t y (a) R e f r a c t i v e index (b) F r e e z i n g p o i n t (c) D e n s i t y B. Butanol C. B i p h e n y l 1. R e c r y s t a l l i z a t i o n 2. D i s t i l l a t i o n (a) D e t e r m i n a t i o n of c o n d i t i o n s (b) B i p h e n y l s t i l l developed Pressure c o n t r o l and measurement E f f i c i e n c y o f Column Improvements f o r tne s t i l l D i s t i l l a t i o n Procedure 3. Check on P u r i t y VI E x p e r i m e n t a l u P r o c e d u r e s A. D e t e r m i n a t i o n o f R e f r a c t i v e Index-Composition Curves Benzene-butanol Benzene b i p h e n y l B. V a p o r - l i q u i d e q u i l i b r i u m d e t e r m i n a t i o n s on the G i l l e s p i e - F o w l e r s t i l l C. Determinations on the vapor r e c i r c u l a t i o n apparatus V I I R e s u l t s A. Benzene-Butanol B. Benzene-Biphenyl V I I I D i s c u s s i o n of R e s u l t s A. Benzene-Butanol B. Benzene-Biphenyl IX B i b l i o g r a p h y TABLES 1. P h y s i c a l data f o r Benzene from the l i t e r a t u r e . 66-7. 2. P h y s i c a l data f o r Butanol from the l i t e r a t u r e . 69. 3. F r e e z i n g p o i n t data f o r b i p h e n y l from the l i t e r a t u r e . 8 l . 4. R e f r a c t i v e Index - Composition data f o r benzene-butanol a t 20°C. . 9 0 . 5 . Experimental y a p o r - l i q u i d e q u i l i b r i u m data f o r benzene-butanol a t atmospheric p r e s s u r e . 91* 6. Vapor p r e s s u r e d a t a f o r benzene. 93. 7. A c t i v i t y c o e f f i c i e n t s of benzene and n-butanol from experimental v a p o r - l i q u i d e q u i l i b r i a . 93. 8. T h e o r e t i c a l a c t i v i t y c o e f f i c i e n t s of benzene and n-butanol. 9J?. 9. R e f r a c t i v e Index-Composition data f o r benzene-b i p h e n y l a t 70QC. ' 9.6. 10. Smoothed R e f r a c t i v e Index-Composition d a t a f o r ben-zene - b i p h e n y l a t 70°C. 97. 11. E x p e r i m e n t a l v a p o r - l i q u i d e q u i l i b r i u m data f o r benzene-biphenyl a t atmospheric p r e s s u r e . 98. 12. Smoothed valu e s f o r the v a p o r - l i q u i d e q u i l i b r i u m of benzene-biphenyl. 99. 13. A c t i v i t y c o e f f i c i e n t s of benzene and b i p h e n y l from experimental d a t a . 101. 14. T h e o r e t i c a l a c t i v i t y c o e f f i c i e n t s of benzene and b i p h e n y l . 101., ILLUSTRATIONS 1 . Vapor pressure - composition diagrams of two component systems. 2 . Equilibrium s t i l l designed by Brown in 18*79. 3 . Carveth's apparatus (18*99). 4 . Zawidski's apparatus (1900). 5 . Cottrell's apparatus with an air l i f t device ( 1 9 1 9 ) . 6. Swietoslawski Ts boiling point apparatus. (1925). 7 . S t i l l of Sameshima incorporating a vapor trap (1918). 8. Original Othmer S t i l l (1928). 9 . Othmer s t i l l of 1 9 3 2 . 1 0 . New, improved Othmer S t i l l ( 1 9 4 S ) . 1 1 . Apparatus of Carey and Lewis ( 1 9 3 2 ) . 1 2 . S t i l l of Rogers, Knight and Choppin ( 1 9 4 7 ) . 1 3 . Chilton's s t i l l ( 1 9 3 5 ) . 1 4 . Apparatus of Scatchard, Raymond and Gilmanvx. 1 5 . Equilibrium s t i l l of ilones, Schoenborn and Colburn ( 1 9 4 3 ) . 1 6 . Gillespie's equilibrium s t i l l ( 1 9 4 6 ) . 17. Othmer's refined s t i l l modified by Smith and Bonner ( 1 9 4 9 ) . IS. Equilibrium s t i l l of Williams ( 1 9 4 7 ) . 1 9 . Equilibrium s t i l l of Perry and Fuguilt ( 1 9 4 7 ) . 2 0 . S t i l l of Gordon and Benson for low temperature equilibria ( 1 9 4 6 ) . 2 1 . Apparatus of Rosanoff, Lamb, and Briethut (1909). 2 2 . High vacuum system. 2 3 . Main equilibrium apparatus. 2 4 . Commutator arrangement. 2 5 . C i r c u l a t i n g apparatus. 2 6 . C i r c u i t diagram of temperature c o n t r o l u n i t s f o r a i r baths. 27. Constant temperature baths i n s e c t i o n and s t i r r i n g u n i t . 28. (a) C i r c u i t diagram of e l e c t r o n i c c o n t r o l u n i t f o r constant temperature i n o i l bath. 26% (b) F i n g e r - t y p e thermor.egulator. 2 9 . F o w l e r - G i l l e s p i e e q u i l i b r i u m s t i l l . 3 0 . (a) Benzene s t i l l . 3 0 . (b) Theimer vacuum adapter. 3 1 . F r e e z i n g p o i n t apparatus. 3 2 . C o o l i n g curve f o r benzene. 3 3 . Vapor pressure curve f o r b i p h e n y l . 3 4 . Semi micro s t i l l . 3 5 . B i p h e n y l s t i l l . 3 6 . Pressure r e g u l a t o r f o r vacuum d i s t i l l a t i o n . 3 7 . C o o l i n g curve f o r b i p h e n y l . 38. R e f r a c t i v e i n d e x - Composition cux^ve f o r benzene -n-butanol at 20OC. 3 9 . Experimental vapor l i q u i d e q u i l i b r i u m curve f o r benzene-n-butanol. 4 0 . Vapor pressure curve f o r n-butanol. 41. Vapor pressure curve f o r benzene. 42. P l o t of l o g a c t i v i t y c o e f f i c i e n t s vs mole f r a c t i o n i n l i q u i d f o r benzene-butanol. 4 3 . Temperature-composition diagram f o r benzene-butanol at atmospheric p r e s s u r e . 44• R e f r a c t i v e index-composition curve f o r benzene-biphenyl at 7 0 ° C 45• Experimental v a p o r - l i q u i d e q u i l i b r i u m curve f o r benzene-b i p h e n y l . 46. P l o t of l o g a c t i v i t y c o e f f i c i e n t s mole f r a c t i o n i n l i q u i d f o r benzene-biphenyl. 47. Temperature-composition diagram f o r benzene-biphenyl. PLATES I Vapor R e c i r c u l a t i o n e q u i l i b r i u m apparatus. I I F o w l e r - G i l l e s p i e E q u i l i b r i u m S t i l l . I I I Benzene s t i l l . IV B i p h e n y l s t i l l . 1 CHAPTER I  INTRODUCTION Vapor l i q u i d e q u i l i b r i u m data are of great impor-tance i n the f i e l d s o f d i s t i l l a t i o n , e x t r a c t i o n , and o t h e r contact p r o c e s s e s . A knowledge of such data i s one o f t h e fundamental requirements i n the q u a n t i t a t i v e d e s i g n c a l c u l -a t i o n s f o r columns i n f r a c t i o n a l d i s t i l l a t i o n . However, t h e experimental work r e q u i r e d t o g a i n t h i s knowledge has been found complicated, o f t e n r e q u i r i n g e l a b o r a t e equipment, and very seldom r e p r o d u c i n g the r e s u l t s o f p r e v i o u s r e s e a r c h e r s . In r e c e n t y e a r s , t h e r e has been an o u t b u r s t o f experimental work and p u b l i s h e d papers on such d e t e r m i n a t i o n s . Many authors have done a gre a t d e a l o f r e s e a r c h i n t o the t h e o r e t i c a l a s pects o f vapor l i q u i d e q u i l i b r i u m . T h i s t h e o r e t i c a l approach has been s t i m u l a t e d by the need f o r c e r t a i n mathematical e x p r e s s i o n s which w i l l r e l a t e the thermodynamic p r o p e r t i e s o f compounds t o the v a p o r - l i q u i d e q u i l i b r i u m . Researchers i n t h i s f i e l d have f e l t t h a t e v e n t u a l l y some r e l a t i o n s should be obt a i n e d which would v i r t u a l l y e l i m i n a t e t h e n e c e s s i t y of e x t e n s i v e experimental work t o determine the vapor l i q u i d e q u i l i b r i u m o f a system. Up to the present, c e r t a i n fundamen-t a l thermodynamic e x p r e s s i o n s have been developed and u t i l i z e d f o r the e f f e c t i v e e x t e n s i o n o f common p h y s i c a l data o f some n o n - i d e a l systems. Vapor l i q u i d e q u i l i b r i u m data c o n s i s t e s s e n t i a l l y o f the composition o f the l i q u i d and vapor phases o f a system when they are i n e q u i l i b r i u m . The x - y diagram (x i s the mole f r a c t i o n o f the more v o l a t i l e component i n t h e l i q u i d phase and y i s the mole f r a c t i o n of the more v o l a t i l e compon-ent i n the vapor phase) i s v e r y common i n books on d i s t i l l a t i o n as w e l l as In p u b l i s h e d papers on vapor l i q u i d e q u i l i b r i a . Experimental d i f f i c u l t i e s i n o b t a i n i n g these data are many. They u s u a l l y stem from the nature of the apparatus used i n the d e t e r m i n a t i o n s . There have been many types o f apparatuses developed f o r e q u i l i b r i u m d e t e r m i n a t i o n s , but fundamentally t h e y can be c l a s s i f i e d under two main groups. There i s the vapor r e c i r c u l a t i o n type which i s o r d i n a r i l y employed under constant temperature and i n an evacuated system. The other i s the l i q u i d r e c i r c u l a t i o n t y p e mainly used f o r e q u i l i b r i u m d e t e r m i n a t i o n s under atmospheric p r e s s u r e . Many r e s e a r c h e r s f e e l t h a t the former i s s u p e r i o r f o r a c c u r a t e d e t e r m i n a t i o n s because i t e l i m i n a t e s most o f the common f a u l t s a t t r i b u t e d t o the l i q u i d r e c i r c u l a t i n g s t i l l s . S i nce the l a t t e r i s e s s e n t i a l l y a d i s t i l l a t i o n type o f apparatus, i t s u f f e r s from r e f l u x i n g of the vapors i n the r e g i o n between the b o i l e r and the vapor s e c t i o n , entrainment of d r o p l e t s o f l i q u i d i n the vapor, f l a s h i n g of the more v o l a t i l e component when the c o l d condensate r e t u r n s t o the hot b o i l e r , and superheating o f the system i n i t i a l l y . However, the apparatus can u s u a l l y be b u i l t v e ry simply i n v o l v i n g v e r y few mechanic'al p a r t s , and d e t e r -minations are r e a d i l y made. On t h e o t h e r hand, the vapor r e c i r c u l a t i o n t y p e of apparatus poses many problems i n con-s t r u c t i o n and o p e r a t i o n . Both types of u n i t s w i l l be d i s -cussed f u l l y i n a l a t e r s e c t i o n . 3 The system, benzene-biphenyl chosen i n t h i s work, has v e r y l i t t l e p r a c t i c a l a p p l i c a t i o n . I t i s one, however, t h a t has c o n s i d e r a b l e t h e o r e t i c a l i n t e r e s t . A complete thermodynamic e v a l u a t i o n o f t h e system c o u l d throw c o n s i d e r a b l e l i g h t on c e r t a i n concepts i n the t h e o r i e s o f s o l u t i o n s . The two components o f the system are so v a s t l y d i f f e r e n t i n t h e i r p h y s i c a l p r o p e r t i e s and c r i t i c a l c o n s t a n t s t h a t c e r t a i n workers i n the f i e l d of s o l u t i o n s have taken a keen i n t e r e s t i n t h e study of benzene-biphenyl. Others have experimented w i t h the system from t h e p o i n t of view of s t a t i s t i c a l thermo-dynamics because of the d i f f e r e n c e i n s i z e of the two compon-ent molecules. The e a r l i e s t work on the system by T y r e r i n 1910 (132) was done i n c o n n e c t i o n w i t h the d e n s i t y o f d i f f e r e n t composition o f the components at 25°C. T h i s was f o l l o w e d by the r e s e a r c h of Washburn and Read who determined the e u t e c t i c p o i n t i n 1915 (13#) and the e l e v a t i o n o f t h e b o i l i n g p o i n t i n 1919 ( 1 3 9 ) . In 1921 G e h l o f f (39) d i d what was probably t h e f i r s t thermodynamic e v a l u a t i o n o f the system when he d e t e r -mined the heat of s o l u t i o n . Some time elapsed b e f o r e any f u r t h e r work was c a r r i e d out on benzene-biphenyl. Warner, Scheib and S v i r b e l y (136) i n 1934 c a r r i e d out d e t e r m i n a t i o n s on the s o l u b i l i t y of b i p h e n y l and benzene. A short p e r i o d l a t e r i n 193&, Gilmann and Gross (44) took an i n t e r e s t i n the system from the p o i n t of view of i d e a l i t y . They determined the vapor p r e s s u r e o f benzene over benzene-biphenyl s o l u t i o n s and found t h a t t h e system obeys K a o u l t ' s Law w i t h i n experimental e r r o r . In a paper p u b l i s h e d i n 194$ (130) Tompa d i s c u s s e s the thermo-dynamics o f t h e benzene-biphenyl system as ev a l u a t e d w i t h Guggenheim's formulae ( 5 2 ) . These formulae are based on t h e l a t t i c e model, and i n t h e i r a p p l i c a t i o n t o the system i t i s assumed t h a t the b i p h e n y l molecule o c c u p i e s twice the volume of the benzene molecule. Experimental d e t e r m i n a t i o n s were a l s o made by Tompa and the r e s u l t s were shown to conform to the s t a t i s t i c a l thermodynamic p i c t u r e . One o f the l a t e s t r e f e r e n c e s to t h e system was made i n a paper read to t h e Manchester S e c t i o n of t h e Chemical S o c i e t y i n October, 1949, by Ward and Brooks (134)• They measured t h e v i s c o s i t i e s o f the system at 5°C i n t e r v a l s of temperature and a t d i f f e r e n t compositions. T h e i r r e s u l t s showed t h a t t h e mixture i s i d e a l and g i v e s n e a r l y a s t r a i g h t l i n e p l o t f o r ITL V a g a i n s t 1. T However, they made no mention o f the e a r l y work c a r r i e d out on the v i s c o s i t y o f the system (66). S i n c e they p u b l i s h e d no v a l u e s , i t was not p o s s i b l e to check the e a r l i e r r e s u l t s . Work on t h e benzene- n- b u t y l a l c o h o l system has been c o n s i d e r e d o n l y o f secondary importance i n t h i s r e s e a r c h . V a p o r - l i q u i d e q u i l i b r i u m data f o r i t was o b t a i n e d p r i m a r i l y as a check on the e q u i l i b r i u m s t i l l ( G i l l e s p i e - F o w l e r ) b u i l t towards t h e l a t t e r p a r t o f t h e i n v e s t i g a t i o n s . More i n t e n s i v e work was c a r r i e d out by Emerson and C u n d i l l ( 3 0 ) , who i n v e s -t i g a t e d the system i n t h e i r r e s e a r c h f o r the B.A .Sc. degree. The system has not been p r e v i o u s l y s t u d i e d f o r i t s vapor l i q u i d e q u i l i b r i u m , and t h e r e s u l t s o b t a i n e d here proved t o be of c o n s i d e r a b l e i n t e r e s t . N-Butanol i s the f i r s t s t r a i g h t c h a i n a l c o h o l o f the a l i p h a t i c s e r i e s forming no azeotrope w i t h benzene, but the behaviour does not appear t o d e v i a t e too f a r from t h a t of s i m i l a r mixtures. R e s u l t s appear t o be c o n s i s t e n t w i t h i n experimental e r r o r when checked thermo-dynami c a l l y . On t h e o t h e r hand, data o b t a i n e d f o r t h e benzene-b i p h e n y l system appear to have no thermodynamic c o n s i s t e n c y whatsoever. Although the x-y curve f o r t h e l a t t e r system seems reasonable i n appearance, a p l o t o f the l o g a r i t h m o f the a c t i v i t y c o e f f i c i e n t a g a i n s t the mole f r a c t i o n i n t h e l i q u i d phase g i v e s very l i t t l e i n d i c a t i o n of a smooth curve. An e f f o r t has been made t o e v a l u a t e the system thermodynamic-a l l y ; but s i n c e c o n s t a n t s i n both the van Loar and Margules i n t e g r a t i o n s of the Gibbs Duhem equation are dependent on experimental v a l u e s , no b r i e f i s h e l d f o r i t s v a l i d i t y . The purpose o f the r e s e a r c h d e s c r i b e d here i s two-f o l d . An endeavour has been made to check b e t t e r forms of t h e two types o f v a p o r - l i q u i d e q u i l i b r i u m apparatus,one a g a i n s t the other, and t o check f o r thermodynamic c o n s i s t e n c y of r e s u l t s i n each case by an a p p l i c a t i o n o f at l e a s t one of the i n t e g r a t e d forms of t h e Gibbs Duhem equ a t i o n . A l s o e q u i l -i b r i u m data f o r the system, benzene-biphenyl, was sought f o r purposes of t h e o r e t i c a l c o n s i d e r a t i o n . U n f o r t u n a t e l y , some of the work o r i g i n a l l y planned has been u n s u c c e s s f u l up t o the p o i n t t o which t h e i n v e s t i g a t i o n s were c a r r i e d . The vapor r e c i r c u l a t i o n apparatus r e q u i r e s f u r t h e r m o d i f i c a t i o n and improvement to g i v e the d e s i r e d r e s u l t s . The G i l l e s p i e - F o w l e r e q u i l i b r i u m s t i l l cannot be c o n s i d e r e d as t h e b e s t t y p e of u n i t f o r the d e t e r m i n a t i o n o f - 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 of benzene-biphenyl. However, those r e s u l t s which were obtained are g i v e n as f u l l y as p o s s i b l e along w i t h t h e i r treatment. In a d d i t i o n , a comprehensive survey of the l i t e r a t u r e i s g i v e n t o a i d those who may co n t i n u e s t u d i e s a l o n g t h e l i n e s o f vapor l i q u i d e q u i l i b r i u m . Much of the m a t e r i a l i s v e r y d e s c r i p t i v e and d e a l s l a r g e l y w i t h apparatus c o n s t r u c t i o n . T h i s was f e l t n e c e s s a r y f o r a s u c c e s s f u l c o n t i n u a t i o n of the work as w e l l as f o r any reasonable r e p r o d u c t i o n of r e s u l t s . 7 CHAPTER I I  THEORETICAL DISCUSSION Y a p o r - l i q u i d e q u i l i b r i u m has been t r e a t e d t h e o r e t -i c a l l y a t g r e a t l e n g t h i n r e c e n t y e a r s . T h i s has been found n e c e s s a r y f o r any k i n d of thermodynamic e v a l u a t i o n of systems where i n v o l v e d experimental d e t e r m i n a t i o n s can be a v o i d e d . E s p e c i a l l y i n the f i e l d o f f r a c t i o n a l d i s t i l l a t i o n where quan-t i t a t i v e r e s u l t s are ne c e s s a r y f o r column d e s i g n c a l c u l a t i o n s has i t been the case. To overcome the complexity o f the q u a n t i t a t i v e r e l a t i o n s h i p s i n v o l v e d i n d e t e r m i n i n g the vapor l i q u i d e q u i l -i b r i u m , c e r t a i n b a s i c thermodynamic r e l a t i o n s have been d e v e l -oped (48) (72). These r e l a t i o n s a p p l y i n a l l cases, but i n most of these t h e r e are unknown f a c t o r s which l i m i t t h e i r u s e f u l n e s s u n t i l s i m p l i f y i n g assumptions are made. The a p p l i c a b i l i t y o f the thermodynamic r e l a t i o n may be due t o the l i m i t a t i o n s o f these s i m p l i f y i n g assumptions. However, even i n such a case the r e l a t i o n s h i p s serve as v a l u a b l e c r i t e r i a f o r e s t i m a t i n g the normal behaviour of a system as w e l l as a check on the thermodynamic c o n s i s t e n c y of experimental r e s u l t s . I f we c o n s i d e r a system o f two m i s c i b l e components, Dalton's Law of p a r t i a l p r e s s u r e s h o l d s t r u e a t o r d i n a r y p r e s s u r e s , i . e . , P-L + P 2 = P ( 1 ) A Most mixtures, however, do not obey R a o u l t ' s Law, which s t a t e s A See the end of d i s c u s s i o n f o r an e x p l a n a t i o n o f nomenclature. 8 t h a t "the f r a c t i o n a l l o w e r i n g o f the vapor p r e s s u r e of the s o l v e n t i s equal t o the mole f r a c t i o n of the s o l u t e i n s o l u t -i o n " , or s t a t e d s y m b o l i c a l l y , ? 1 - xxPi 0 ( 2 ) A system obeying R a o u l t ' s Law can be c o n s i d e r e d as i d e a l , and d e v i a t i o n s from i d e a l i t y may be due e i t h e r t o the vapor phase, the l i q u i d phase or both. These d e v i a t i o n s can be both p h y s i c a l and chemical i n n a t u r e . The important f a c t o r s b e l i e v e d t o be i n v o l v e d are t h a t molecules have volume and t h a t they e x e r t f o r c e s upon each other which may be a t t r a c t -i o n s or r e p u l s i o n s . A c t u a l chemical e f f e c t s may a l s o be i n v o l v e d e s p e c i a l l y where the components are eh e m i o a l l y d i s -s i m i l a r , e.g., b e l o n g i n g t o d i f f e r e n t homologous s e r i e s . I t has been shown e x p e r i m e n t a l l y t h a t substances, s i m i l a r chem-i c a l l y d e v i a t e o n l y s l i g h t l y from R a o u l t ' s Law. Non - i d e a l systems e x h i b i t e i t h e r n e g a t i v e or p o s i t i v e d e v i a t i o n s depending on whether the molecules o f one substance tend t o lower or r a i s e the esca p i n g tendency o f the other oomponent m o l e c u l e s . P o s i t i v e d e v i a t i o n i s the most common, and from F i g u r e 1 i t can be seen t h a t i t r e s u l t s i n the p a r t i a l p r e s s u r e o f the components as w e l l as the t o t a l p r e s s u r e o f the system b«ir»<j g r e a t e r than the p r e d i c t i o n o f Ra o u l t ' s Law. As shown i n the diagram, the t o t a l vapor p r e s s u r e may r e a c h a maximum a t a c e r t a i n c o n c e n t r a t i o n . T h i s i s us u -a l l y the case i f the d e v i a t i o n i s g r e a t and the vapor p r e s s u r e s of the two components do not d i f f e r g r e a t l y . Under such c i r -cumstances, t h e r e e x i s t s a c e r t a i n c o n c e n t r a t i o n a t which the A MOLE. F R A C T I O N B FIG ta - M I N I M U M BOtUNG, S Y S T E M D O T T E D U N C 3 B t P R t a t N T * l D E A L C U R V E S A MOLE. F R A C T I O N E> B R ^ . l b . - M M I M U M B O I U M q S Y S T E M F\a I - VAPOR P R E L S S U R E : COMPOSIT ION DIAGRAMS O F T W O C O M P O N E N T S Y S T E M S total vapor pressure w i l l be equal to the atmospheric pressure at a lower temperature than at any other concentration. In other words, the solution has a minimum boiling point at this concentration. Where the total vapor pressure curve exper-iences a minimum corresponding to a concentration at which the solution exerts a pressure equal to atmospheric at a temper-ature higher than for either of the components, we have a maximum boiling mixture. Systems having either of these properties are known as constant boiling or azeotropio mixtures, Gibbs-Dubem Equation For the general case of a system i n which transfer of material takes place, any extensive property such as free energy, F, w i l l depend not only on pressure and temperature but also on the mass of each component present. Thus F = f (T,P,ni,n2, —-) and the general di f f e r e n t i a l expression for dF can be written as follows: dF F^dT =/e> \ + /-3F\dP V ( - 3 F V L m + / 3 FWg+~ v5"T7Pini,n2 r.— V^y/T,n l fn2 VaaJ P,T , n 2 — p,T,: ^^FNdT + feF\dP + TfarW V¥ T/P,ni,n 2---\dP/T,n 1,n 2 Vd ni/T,P n i (3) T,P The partial differential/"^ F \ is known as the partial molar free energy and i s often written as F'i for convenience. It has also been defined as the chemical potential ju.t . Now, at constant temperature and pressure we obtain the expression, dF = /Uldnt (4) It can be shown that the chemical potential with respect to a change in one component i s independent of the amount of that component p r o v i d e d i t s r e l a t i v e c o n c e n t r a t i o n i s co n s t a n t . Hence 4 can be i n t e g r a t e d w i t h u<L regarded as a con s t a n t , i . e . The i n t e g r a t i o n constant drops out when t h e r e i s no change i n c o n c e n t r a t i o n . F r o m E u l e r ' s Theorem, S i n c e the f r e e energy, F, i s an e x t e n s i v e p r o p e r t y of the phase and, t h e r e f o r e , a homogeneous f u n c t i o n o f the f i r s t degree i n , our e x p r e s s i o n reduces t o Eq u a t i o n 7 i s known as the Gibbs-Duhem e q u a t i o n (72). When a p p l i e d to changes i n composition a t constant temperature and pr e s s u r e , i t i s r i g o r o u s l y e xact. Where o n l y the temperature v a r i e s over a s m a l l range, i t may be approximately v a l i d . When the mass of each component present i s consta n t , F - f (P,T) and (5> (6) (7) (8) By d e f i n i t i o n , H - E + PV (9) F - H - TS (10) Combining 9 and 10, F • E + PV - TS (11) D i f f e r e n t i a t i n g 11 g e n e r a l l y , dF = dE + PdV + VdP - TdS - SdT (12) From the f i r s t and second laws o f thermodynamics, dE = TdS - PdV (13) Substituting 13 into 12, dF - VdP - SdT (14) Comparing equations 8 and 14, we obtain ( H ) T " T l l 5 ) We have already defined ML " (MN (16) If we have only one oomponent in two phases we can have only one degree of freedom, as determined by the Phase Rule, and we can write M - dF 7 dn (17) Rearranging and integrating, we obtain yj&.n = JdF ju. n - F (18) If we have only one mole of component,F = ^ and 15 can be written in the following form for a mole of an ideal gas: by* = dF = VdP = RT dP (19) Integrating 19 we obtain at constant temperature M - RT ln P2 + K ( 20) FT In order that this equation apply to the general case of any non-ideal gas, a new property, fugaoity f, i s defined such that dyU. = RT df (21) If the lower limit of integration is taken as fugaeity i n some standard state denoted by f°, we can integrate 21 as follows: (22) Equation 7 can be expressed as n, djLA, + nxd yu^ + — - = o and since n^ ,n2> are proportional to the mole fractions 2-1»^ 2»"" ' xAju, + y^fX% + = 0 ( 2 3 ) Dividing through hy dxi we obtain x i f ^ / M + x 2 (^tt±S + = 0 ( 24) But from the definition of fugacity we can write dyW = RT d i n f for one mole of gas at constant temperature. Therefore, M • + * 2 + 0 (25) which i s a more useful form of the Gibbs-Duhem equation. Here the fugacity can be considered as the "ideal" partial pressure and i s identical with the partial pressure for conditions under which the gas laws hold. The ratio f can be defined as the activity, a, and a the activity coefficient "tf i x Then a-, = f i ; a 9 - f 2 ( 2 6 ) f j 2 Y . = :i V* = a2 ( 27) x l x2. Combining ( 2 6 ) and ( 27) " ; V - f? fl° xl * f2°x 2 (28) If the vapors.behave ideally f 1 » P X ; f 2 = P2 and f 1°= Pi° ; f 2°= P 2° where Pi° and P 2° are the 13 a c t u a l p r e s s u r e s of the pure components. Under such c o n d i t i o n s we can w r i t e X - Pi > • I - P? ' F p ~ x i 1 (29) From D a l ton's Law, Pi - yiP * ?2 = y 2 p ( ? Q ) Combine 29 and 30 to o b t a i n 1 x ^ P p ; x f ^ o ( 5 1 ) These e x p r e s s i o n s f o r the a c t i v i t y c o e f f i c i e n t s are o f g r e a t value i n the treatment of vapor l i q u i d e q u i l i b r i a . They g i v e d i r e c t l y the d e v i a t i o n f a c t o r s from Raoult»s Law, which when p l o t t e d on semilog paper a g a i n s t mdle. f r a c t i o n of one of the components i n the l i q u i d phase r e v e a l c h a r a c t e r i s t i c curves i f the data are thermodynamically c o n s i s t e n t . I f we can assume t h a t t h e r e i s i d e a l behavious i n the vapor phase, by v i r t u e of e q u a t i o n 28 we can express the f u g -a c i t y o f a component i n terms of the a c t i v i t y c o e f f i c i e n t , p r e ssure of the pure component and i t s mole f r a c t i o n . Thus f l « h*i°*l * f2 = *'2P2°X2 (32) Then s u b s t i t u t i n g these v a l u e s i n t o 23 T n e ( ~S&r\ R° \ and Y ^ (Ln P-THerms are zero since P ^ 0 and P 2 ° are constants at constant temperature, and we are l e f t with xl(a&v'O + + ^ ( 3 ^ ) + x 2 3 x 2 + 0 If we consider a two component system and that x 2 <= (1-x^) and dx 2 = -dx^, our expression reduces to xiJBM.) = x 2 ( i k L ] (33) V 3%. /p,r V 3}U V This form of the Gibbs Duhem equation expressed in terms of activity coefficients i s of immediate value in studying experimental data on vapor-liquid equilibrium. It relates the slopes of the plots of logarithms c$. activity coefficients against the composition of the liquid phase. However, since the magnitudes of such slopes are d i f f i c u l t to obtain, there have been a number of solutions advanced for this differential equation. At least two of these solutions w i l l be considered here since they are to be used later in the treatment of the data. Van Laar Equations J. J. van Laar (68), in a thorough study of the thermodynamics of binary mixtures derived, semi-empirically, solutions to the Gibbs Duhem equation. These expressions have proved to be very useful i n treatment of vapor liquid equil-ibrium data. They have been modified and rearranged by var-ious authors, especially by Carlson and Colburn (13), G i l l i l a n d et a l (43) and White (142). The derivation of the solution w i l l not be attempted here since i t becomes considerably i n -volved. However, the general form of the equations w i l l be 1 5 shown and they can be r e a d i l y proved t o be i n t e g r a t i o n s of t h e Gibbs-Duhem e q u a t i o n . C a r l s o n and Colburn g i v e the van Laar equations i n the symmetrical forms l o g tf, " A ( 5 4 ) (l+ A x i V (35) When x i = 0 and x 2 = 1 l o g ^, = A , l o g K = 0 and ^ = 1 When XT_ = 1 • and x 2 = 0 l o g ^ = E> , l o g >j, » G and = 1 Thus the constants A and B i n the equations can be obt a i n e d from experimental l o g $ vs composition p l o t when the curves are e x t r a p o l a t e d t o x^ = 0 and x i = 1 . I t i s assumed t h a t t h e s e two experimental v a l u e s of l o g % are v e r y n e a r l y c o r r e c t i n order t o check the thermodynamic c o n s i s t e n c y of the remainder. The f a c t t h a t and ^ are equal to 1 when xj_ and x 2 are equal to 1 , r e s p e c t i v e l y j s a t i s f i e s the l i m i t i n g c o n d i t i o n t h a t R a b u l t ' s law ho l d s f o r a component whose c o n c e n t r a t i o n approa-ches 1 0 G mole peroent. Other q u a l i t a t i v e checks on experimental data can be r e a d i l y i n d i c a t e d from the p e c u l i a r p r o p e r t i e s o f equations 34 and 35• When x i = 0.5 l o g % » A g A - AB2 ~ (36) ' /i,+ A\2. IA •+ B)2 TA+BJ? ^ BV B2 l o g 1 = B , - B • ^ = A 2B -? (37) X A + -B\2 (A + B) 2 (A + B)2 ^ 57 A* D i v i d e (36) by B and (37) by A and the two can be equated, l o g £ - AB . = l o g \ 1 (A •+ B ) 2 I (38) Now i f A •» B AB = 1 and as A and B d i f f e r the r a t i o (A + B)2 4~ decreases, e.g., when A = 2B AB - 2B2 m 2 (A + B)2 fgZ 9 From 38, i t can be seen t h a t the h a l f way value on one curve i s approximately equal to one q u a r t e r of the end value on the other curve. Thus, a t x^ = 0 .5, i f the curve of l o g 2(, vs x± should be lower, i t w i l l have a h i g h e r end value than the curve l o g #t vs x i . E q u a t i o n s 34 and 35 can a l s o be w r i t t e n " A x 2 2 . (39) ( x 2 + T | x l ) 2 l 0 e - BXI 2 ( x x + B x 2 ) Z (40) To show t h a t these s a t i s f y the Gibbs-Duhem equation, they can be d i f f e r e n t i a t e d remembering t h a t x i - l - x 2 and t h a t dx^ = d x 2 x l (tUtS - x i { - 2 A x 2 2 ( A x i + x ^ (k-l\- 2Ax2 ] x • x o ( - 2 B X l 2 ( x +B x > 3 ( B - l ) - 2 B x l ] S i m p l i f y i n g ~ ? * \ 1 " 2 A X 2 " 2 - x l x 2 ) x i W ^ ' = ^ y . . ? , A . . . . i v f*^2+ V ^ ' I fa • B x V J \ l j X l 2 (42) Now, i f we m u l t i p l y both the numerator and denomin-a t o r o f (42) by A3 we o b t a i n 2A 2 f x i 2 x 2 + 3 B \ / A x i + x l x 2 3 x 2 13/ X (1 + A x i V (43) v xo / x 2 > 3 : which i s i d e n t i c a l to ( 4 1 ) . Hence the van Laar equations s a t i s f y the Gibbs-Duhem p a r t i a l d i f f e r e n t i a l e q u a t i o n . G i l l i l a n d et a l (43) employ v e r y s i m i l a r e x p r e s s i o n s f o r the van Laar equation, but c o r r e c t e d f o r temperature, i . e . , log If, - B T2 (44) X 1 ; I f (43) i s s o l v e d f o r B, B = T ( l + Ax]V i o g < , (43A) . x 2 ' -then the e x p r e s s i o n f o r B can be s u b s t i t u t e d i n t o (44) and one can s o l v e f o r A. % A = 4 + x ^ 2 l o g ^ log = AB/T ( i + - A a s i y l o g * , (44A) A =/xif 10* Tk (44B) With any s e t of a c c u r a t e data o f a c t i v i t y c o e f f i c -i e n t s corresponding to a c e r t a i n c o n c e n t r a t i o n , the constant i n t he above equations can be e v a l u a t e d . U s u a l l y dependable v a l u e s can be o b t a i n e d from the a z e o t r o p i c composition and the whole vapor l i q u i d e q u i l i b r i u m curve can be e v a l u a t e d . White ( 1 4 2 ) rearranged the van Laar equations some what a g a i n and showed t h a t they c o u l d be used as s t r a i g h t -l i n e forms as f o l l o w s : ( l o g K , ) - ! / ^ ^ ^ . ^ ( W ) (log i , ) - 1 / 2 - B 1/ 2 * ^ 1 / 2 ( 4 6 ) These equations were a p p l i e d t o the system 1-butanol-xvater by Smith and Bonner (113) who p l o t t e d ( l o g $( )'~<">•'5 a g a i n s t x l / x 2 a n c * ( i ° S ^ ) ~ ^ " ^ a g a i n s t X2* The check on t h e exper-x l V i m e n t a l r e s u l t s was not near as c l o s e as i n t h e l o g 0 a g a i n s t x p l o t . Margules Equations. Margules ( 7 6 ) found a s o l u t i o n t o the Gibbs Duhem equation by i n t e g r a t i n g i t i n terms of a p a i r of e x p o n e n t i a l s e r i e s . He d e r i v e d the co n s t a n t s o f one of t h e equations from those o f the other by a p p l y i n g equation 33. Thus t h e two s e r i e s e x p r e s s i o n s o b t a i n e d f o r the a c t i v i t y c o e f f i c i e n t s of the components i n a b i n a r y mixture were as f o l l o w s : l o g o, = a x 2 + bxg + c x 2 l o g a ^ i + b ^ 2 + c l x ^ US) These expressions are s u b s t i t u t e d i n t o equation 33 and we o b t a i n t h e f o l l o w i n g two e x p r e s s i o n s : x i (d-£n V. ) - - x i d £ n V, = - ( a x i + 2bx2_x2 + - 3 0 X 3 X 2 ) 2 (49) x 2 (JI&JQSIA = -x 2 d £ N = -(a 1x 2+2b 1x 1X2+3c : Lx 2x 1 2)' (50) V "d^-L - ' / • dxx I f t he c o e f f i c i e n t s o f 49 and 50 are ev a l u a t e d i n such a way th a t the constant terms i n each case are equal, the c o e f f i c i e n t s of the f i r s t power of t h e mole f r a c t i o n terms are equal and so on f o r t h e high e r power terms, we can put both e x p r e s s i o n s completely i n terms o f x 2 ( f r o m x 2=l-x;j_) and equate. a - a x 2 + 2bx 2 - 2bx 2 2 + 3cx^ 2 - 3cx 2^ = a x x 2 + 2 b 1 x 2 - 2 b 1 x 2 2 + 3 c 1 x 2 - 6 c 1 x 2 2 + 3 c 1 x 2 ^ C o l l e c t i n g terras f o r each power o f x 2 a + (-a+2b)x2 + (-2b+3c)x 2 2 - 3 c x 2 3 (a 1+2b 1+3c 1)x2 + (-2b!-6cl)x 2 2 + 3 c l x 2 Equate c o e f f i c i e n t s a =0 ( i ) -a + 2b = a l + 2bl + 3 c 1 ( i i ) -2b + 3c = -2b 1 - 6 C1 ( i i i ) -3c = 3 c l ( i v ) S o l u t i o n s o b t a i n e d are as f o l l o w s : c l = -c From ( i i i ) 2b = 2 t A - 3c S u b s t i t u t e value f o r b i n t o ( i i ) -a + 2 b 1 - 3c = a 1 + 2 b 1 + 3 c 1 T h e r e f o r e , -a = a 1 and a 1 = 0 From ( i i i ) b 1 = 2b + 3c 2 S u b s t i t u t i n g v a l u e s f o r the co n s t a n t s i n t o 47 and 4#, we o b t a i n .." Irxi, = b x 2 2 + . C X 2 ^ (51) JLrdir* b x i 2 + 1 C X ! 2 - cx-^ (52) Although t h e equations have two independent c o n s t a n t s only-one p o i n t i s needed to e v a l u a t e both o f t h e s e . I f more data are a v a i l a b l e i t i s convenient t o p l o t ^' v s . x n , and Jlr\\x v s . x 2 ; and i f the Margules equation, agrees w i t h the X T * data s t r a i g h t l i n e s should be obtained. The s l o p e of the two l i n e s should be j u s t e q u a l to the constant c, w h i l e the i n t e r c e p t can be used f o r e v a l u a t i n g the constant b. Since the c o n s t a n t s o f the Margules equation are a f u n c t i o n o f the temperature, i f one experimental p o i n t i s used t o e v a l u a t e them, they should be s u i t a b l e f o r other compositions at t h e same temperature assuming the equations t o a p p l y . At ot h e r temperatures, however, a d d i t i o n a l experimental data are r e q u i r e d . C a r l s o n and Colburn (15) s l i g h t l y r e v i s e d t h e constants of the Margules equation i n order t o u t i l i z e t he t e r m i n a l v a l u e s o f the l o g v s . x p l o t as c o n s t a n t s . With the c o n s t a n t s A and B r e p r e s e n t i n g the same v a l u e s as t h e corresponding symbols i n t h e van Laar equation, the Margules two-term equations can be w r i t t e n as f o l l o w s : l o g tf, = ( 2 B - A ) x 2 2 + 2(A-B)x 2 3 ( 5 3 ) l o g ( 2 A - B ) X 1 2 + 2(B-A)x 1 3 ( 5 4 ) where (2B-A) = b and 2(A-B) = c i n 51 and 52. I t can be r e a d i l y seen t h a t at x i = 0, l o g #f = A and l o g 0^= 0; at x i 8 5 1 , l o g tf, = 0 and l o g ^ = B. An i n t e r e s t i n g f e a t u r e o f t h e s e equations i s t h a t at x^ = 0.5, l o g ^ 1 = B/4 and l o g = A r e g a r d l e s s of the v a l u e s o f A and 4 B. When A = B the Morgules equations become i d e n t i c a l w i t h those of van L a a r . As t h e value A d e p a r t s from u n i t y , the B two s e t s of equations r e p r e s e n t i n c r e a s i n g l y d i f f e r e n t c u r v e s . Other Thermodynamic Treatments of Vapor L i q u i d E q u i l i b r i a There have been a c o n s i d e r a b l e number of o t h e r t h e o r i e s put f o r t h i n the l i t e r a t u r e i n r e c e n t years on t h e thermodynamic e v a l u a t i o n of systems. These w i l l be o n l y b r i e f l y mentioned because t h e y have not been used t o any extent i n t h i s r e s e a r c h . Scatchard and Hamer ( 1 0 9 ) extended the methods of van Laar to g i v e the a c t i v i t y c o e f f i c i e n t s i n terms of molar volumes and volume f r a c t i o n s of the components. Scatchard [108) proposed a thermodynamic r e l a t i o n i n which a l l the c o n s t a n t s r e p r e s e n t p h y s i c a l p r o p e r t i e s f o r systems where the change of entropy on mixing i s the same as t h a t f o r an i d e a l mixture. Some time l a t e r , Scatchard, Wood and Mochel ( 1 1 1 ) concluded, a f t e r e x t e n s i v e work on t h r e e systems formed by: ... - . .• • - - - • 22 benzene, cyclohexane and carbon t e t r a c h l o r i d e , t h a t - t h e r e was no agreement between the t h e o r e t i c a l and experimental v a l u e s of the constant i n the Scatchard equation. R e d l i c h and K i s t e r (99)in a r e c e n t paper d i s c u s s the examination of experimental e q u i l i b r i u m data t o e f f i c i e n t l y e valuate the thermodynamic p r o p e r t i e s o f n o n e l e c t r o l y t e s o l u t i o n s . T h e i r main concern was t h e d e s i g n o f columns from l a b o r a t o r y data which r e p r e s e n t s the mole f r a c t i o n s x o f t h e l i q u i d and y of the vapor i n e q u i l i b r i u m as f u n c t i o n s o f the temperature a t constant p r e s s u r e . They appeal t o c e r t a i n equations o f s t a t e i n t h e i r e v a l u a t i o n s and present a v e r y comprehensive study o f the assumptions i n v o l v e d . Gilmont et a l (45) take a somewhat new approach i n the d e t e r m i n a t i o n o f a c t i v i t y c o e f f i c i e n t s . They u t i l i z e t h e r e l a t i v e v o l a t i l i t y which i s independent o f composition and t o t a l p r e s s u r e , being the r a t i o o f the vapor p r e s s u r e o f the pure components at constant temperature. A symmetrical form o f power s e r i e s was a p p l i e d f o r the r e l a t i v e v o l a t i l i t y as a f u n c t i o n of composition. 23 NOMENCLATURE A = A r b i t r a r y constant i n van Laar and Margules equations. B = A r b i t r a r y constant i n van Laar and Margules e q u a t i o n s . Equal t o l o g at x 2 = 0. a a l ) b b | )= A r b i t r a r y constants i n s e r i e s i n t e g r a t i o n s l e a d i n g t o c c )' Margules equations. E = i n t e r n a l energy. F = f r e e energy. f - f u g a c i t y . f° = f u g a c i t y i n the Standard S t a t e . ^ = a c t i v i t y c o e f f i c i e n t . H = enthalpy, n = moles o f component. P = t o t a l p r e s s u r e (atmospheric), mm Hg. ^1^2 ~ P a r t i a l p r e s s u r e s o f components, mm Hg. P l ° > P 2 0 = vapor p r e s s u r e s o f pure components, mm Hg. R m gas constant. S = entropy. T = a b s o l u t e temperature. U= F = ^FT = chemical p o t e n t i a l ( p a r t i a l molar f r e e energy). V = volume. x = mole f r a c t i o n i n l i q u i d . y = mole f r a c t i o n i n vapor i n e q u i l i b r i u m w i t h x. S u b s c r i p t s 1 = l o w - b o i l i n g component (benzene). 2 = h i g h - b o i l i n g component (n-butanol or b i p h e n y l ) . E q u a l CHAPTER III HISTORICAL DEVELOPMENT OF THE EQUILIBRIUM APPARATUS A. Liquid Recirculating Type By far the largest proportion of vapor-liquid equilibrium units used are the d i s t i l l a t i o n types which in their more advanced form are liquid recirculating. One of the earliest investigators in the f i e l d of vapor liquid equilibrium was Brown. In a number of papers published in 1881 (8) he made a c r i t i c a l survey of s t i l l s up to that time. At the turn of the century, Sydney Young (LM">) made an ex-cellent criticism of equilibrium s t i l l s in his classic book on d i s t i l l a t i o n , " D i s t i l l a t i o n Principles and Processes" pub-lished in 1903 and subsequently revised in 1922. Only very recently, a comprehensive treatise was written on the evo-lution of this type of s t i l l by R.T. Fowler (35). An en-deavour w i l l be made here to cover the development of equil-ibrium s t i l l s according to the new devices introduced to improve the accuracy of determinations. The vapor recircul-ating type of apparatus w i l l be discussed as well as some of the specialized types. 1. Early Work After making a complete survey of equilibrium s t i l l s up to his time, Brown designed an apparatus which he describes in a paper in 1879 (7). The s t i l l i s of the dynamic d i s t i l l a t i o n type where the composition of the liquid continuously changes. It is illustrated in Figure 2 which shows a copper vessel A with a long neck surrounded by an outer jacket leading to a condenser and condensate receiver B. The neck of the vessel has numerous holes through which the vapors pass into the outer jacket. This arrangement keeps the neck at the temperature of the vapors and prevents con-densation and r e f l u x . The vapors f i n a l l y condense i n the condenser-and enter receiver B from which a sample can be removed f o r ana l y s i s . Brown f e l t that by having a large quantity of l i q u i d i n the b o i l e r compared to that d i s t i l l e d o f f he could obtain reasonable composition values of the vapor i n equilibrium with the l i q u i d at any given concentration. In 1898 Lehfeldt (71) introduced what he f e l t was an improve-ment and made the b o i l e r smaller. The chief d i f f i c u l t y with t h i s type of apparatus i s , of course, that there i s no pro-f -v i s i o n to prevent super heating and, as a r e s u l t , accurate temperature measurement cannot be obtained. Furthermore, i t i s a case of st r a i g h t d i s t i l l a t i o n with a continuous weakening of the l i q u i d i n the more v o l a t i l e component. Analysis has to be made of successive f r a c t i o n s and a c a l -culation must be resorted to f o r an estimate of equilibrium values. Determination of B o i l i n g Temperatures The f i r s t serious attempt to determine the b o i l i n g temperatures of the l i q u i d and vapors i n equilibrium was made by Carveth i n 1899 (16),. Figure 3 shows some of the d e t a i l s of the apparatus. A large bulb contained a f a i r l y large volume of solvent and solute. Glass beads were added to pre-vent superheating. Into the f l a s k were f i t t e d , by means of a rubber stopper, a thermometer, condenser, and a bulb-shaped tube a l s o c o n t a i n i n g a thermometer. In d e t e r m i n a t i o n s , the bulb-shaped tube was withdrawn from t h e l i q u i d and t u r n e d so t h a t t h e s m a l l f u n n e l was c l e a r of the d r i p t i p of t h e con-denser. The l i q u i d was b o i l e d and i t s temperature was noted on ttiermometer 1. Then the bulb was t u r n e d so' t h a t the con-densed vapor was allowed to d r i p i n t o the f u n n e l and onto the bulb o f thermometer 2. The temperature recorded on t h i s thermometer when i t reached s t a b i l i t y was t h a t of the b o i l i n g vapor phase. In order to prevent superheating i n the bu l b , a p i e c e of platinum w i r e was s e a l e d i n t o i t . B o i l i n g temper- ' a t u r e s , however, were found t o va r y w i t h t h e r a t e of h e a t i n g , and Corveth suggested t h a t the r a t e o f h e a t i n g be s t a n d a r d i z e d f o r a l l s u b s e q u e n t work. I n t e r n a l Heaters A d e f i n i t e s t r i d e i n t h e advance toward b e t t e r e q u i l i b r i u m s t i l l s was the i n t r o d u c t i o n o f i n t e r n a l h e a t e r s t o prevent s u p e r h e a t i n g . Zawidski ( 1 5 0 ) , i n 1900, made a s e r i e s o f det e r m i n a t i o n s on b i n a r y mixtures employing such a h e a t e r - i n h i s s t i l l ( F i g . 4 ) . A smal l thermometer was used and i t was t o t a l l y immersed i n the f l a s k t o e l i m i n a t e stem c o r -r e c t i o n . The condenser was equipped w i t h a s m a l l r e c e i v e r f o r c o l l e c t i o n o f samples of the vapor phase. Although the apparatus had c e r t a i n d e f e c t s , such as no p r o v i s i o n a g a i n s t entrainment o f ' . l i q u i d i n the vapor and nothing t o prevent the changing composition of the l i q u i d phase, Zawidski i n v e s t i g -a t e d about t w e n t y - s i x l i q u i d mixtures i n a l l . FlG 4 - Z A W i D S K l ' S A P P A R A T U S (1900) FIG- fe" S W I E T O S L A W S K I ' S B O I L I N G P O I N T " A P P A R A T U S 0 9 2 5 > FVG.T - S T » L - U OF 5AMELSHIMA I N C O R P O R A T I N G A V A P O R T R A P . C o t t r e l l Pump There have been numerous m o d i f i c a t i o n s i n v a r i o u s types o f e q u i l i b r i u m s t i l l s of t h e a i r l i f t d e v i c e f i r s t r e -por t e d by C o t t r e l l (22) i n 1919 ( F i g . 5 ) . The o r i g i n a l pumping apparatus c o n s i s t e d o f a l e n g t h o f t u b i n g f l a r e d out at the bottom and supported v e r t i c a l l y by means o f a p l a t f o r m A. The vapor p a s s i n g up the tube f o r c e d l i q u i d up w i t h i t and the e f f e c t of super-heating i n t h e f l a s k was;considered almost n e g l i g i b l e . On the p l a t f o r m the vapor and l i q u i d separated, the vapor passi n g upward i n t o a condenser and the l i q u i d r e t u r n i n g t o the b o i l e r by way o f t h e o u t s i d e o f t h e thermom-e t e r . Thus t h e temperature r e g i s t e r e d on the thermometer was tha t of the l i q u i d i n e q u i l i b r i u m w i t h i t s vapor. Swietoslawski (122)(123) i n 1925 and l a t e r was one of the f i r s t to adopt the C o t t r e l l device f o r a ve r y a c c u r a t e apparatus f o r b o i l i n g temperature measurements. The apparatus (Fig.6 ) i s q u i t e simple and c o n s i s t s o f a s m a l l bulb A f i t t e d w i t h t h r e e o u t l e t tubes. Tube 1 i s the e n t r y tube f o r adding more l i q u i d , tube 2 i s the C o t t r e l l pump and tube 3 i s t h e l i q u i d r e t u r n . In o p e r a t i o n the s o l v e n t i s b o i l e d i n bulb A and tube 2 s p u r t s the b o i l i n g l i q u i d w i t h i t s e q u i l i b r i u m vapor i n t o t r a p B which c o n t a i n s a thermometer w e l l . I d e a l e q u i l i b r i u m c o n d i t i o n s are c o n s i d e r e d t o e x i s t s i n c e the l i q u i d and vapor are i n t i m a t e l y mixed and hence the thermometer g i v e s the t r u e e q u i l i b r i u m temperature. The l i q u i d i s r e t u r n e d t o bulb A by way of tube 3 and on condensation the vapor p o r t i o n f o l l o w s a s i m i l a r path. F I G . 5 . - C O T T R E L L ' S A P P A R A T U S W I T H A N A I R L I F T D E V I C E ( 1 9 1 9 ) The Vapor Trap The Japanese scientist, Sameshima (106), in 1918 developed an apparatus for equilibrium measurements incorpor-ating a vapor trap. This was an idea which was f i r s t struck by another Japanese, Yamoguchi ( 1 4 6 ) , in 1913. By means of the vapor trap a relatively small amount of the l i q u i d system could be used without the danger of a continuous change i n composition. Sameshima's s t i l l was the forerunner of many of the modern equilibrium s t i l l s which incorporate similar devices. As shown in Figure 7, the vapors rise from the boiler A con-taining an internal heater and totally immersed thermometer, through a carefully logged and heated exit tube B into a condenser C. The condensate f a l l s back into the vapor trap D and overflows into the downtake to vessel A. The condenser E was used to prevent vapor loss. Vapor and li q u i d samples could be removed with pipettes from A and D when required after equilibrium was reached as indicated by the s t a b i l i t y of the temperature. 2. Modern Equilibrium S t i l l s The Othmer Equilibrium S t i l l Perhaps the one type of s t i l l which deserves a place by i t s e l f in a historical survey i s the Othmer s t i l l . D.F. Othmer reported his f i r s t equilibrium s t i l l in 1928 ( 8 6 ) . Since then there has been a steady stream of modifications by the same author as well as by others who have picked up the idea, but the main features of the apparatus have been retained. The original Othmer s t i l l i s illustrated in Figure 8. The system i s boiled i n container A, and as vapors form and r e f l u x on the cold walls of the container a i r i s displaced through tap x. As the whole f l a s k i s warmed, vapors pass over into condenser B, the condensate f i l l s trap C and over-flows back into vessel A. The equilibrium temperature i s recorded on the thermometer protected by the tube, and samples are removed as simultaneously as possible from the b o i l e r and vapor trap by means of stopcocks. Although i t was claimed that the apparatus was easy to use and equilibrium was reached ra p i d l y , some of i t s f a u l t s are obvious. Re-f l u x i n g takes place on the upper walls of the b o i l e r , f l a s h -ing of the more v o l a t i l e component occurs as the cold conden-sate returns to the hot l i q u i d i n A, superheating occurs,and the thermometer does not l i k e l y r e g i s t e r the true temperature of the l i q u i d i n equilibrium with i t s vapor. A l a t e r modification of the Othmer S t i l l (8?) i n -corporates an i n t e r n a l heater which eliminates some of the superheating. Figure 9 shows how some of the general appear-ance has been altered but the fundamental p r i n c i p l e s remain unchanged. There were many papers published i n subsequent years(88, 90, 91, 92, 93, 94)reporting determinations on Othmer s t i l l s with addi t i o n a l improvements. The l a t e s t modification of his s t i l l was reported by Othmer i n 194# (#9). In t h i s paper he reviewed some of the errors common to the various types of equilibrium s t i l l s and pointed out that these were e s s e n t i a l l y eliminated i n his new, improved s t i l l . Figure 10 i l l u s t r a t e s t h i s apparatus and although a s i n c e r e e f f o r t has been made t o e l i m i n a t e a l l d e f e c t s some o f the sources o f e r r o r i n h e r e n t i n t h i s type of apparatus are s t i l l p r e s e n t . Carey and Lewis (14) took the e s s e n t i a l f e a t u r e s of t h e Othmer s t i l l and made a m o d i f i c a t i o n w i t h an arrange-ment f o r the p r e v e n t i o n o f condensation i n the upper r e g i o n s of t h e b o i l e r . T h e i r s t i l l was made o f copper sheet metal and t u b i n g . The b o i l e r w a l l s were completely i n s u l a t e d as a shown i n F i g u r e 11 except f o r / s m a l l peep s i g h t which was provided to view the end of t h e tube p r o t e c t i n g t h e t h e r -mometer. Thus t h e c e s s a t i o n o f condensation c o u l d be noted. The vapors pass over the thermometer and i n t o chamber B. Any condensation which may take p l a c e here i s caught i n t h e chan-n e l and passes out i n t o the vapor t r a p . The remaining vapor condenses i n the condenser and r e t u r n s to t h e b o i l e r by way of t he t r a p . A simple type of e q u i l i b r i u m s t i l l which i n c o r -porates some o f the f e a t u r e s o f the Othmer s t i l l as w e l l as a C o t t r e l l pump i s t h a t o f Rogers, Knight, and Choppin (102). T h i s s t i l l ( F i g . 12) was p r i m a r i l y designed f o r l a b o r a t o r y d e t e r m i n a t i o n s where r a p i d attainment o f e q u i l i b r i u m i s r e q u i r e d . Consequently, r e s u l t s o b t a i n e d a re c e r t a i n l y not of h i g h accuracy. One of i t s main disadvantages i s the use of one t h r e e way stopcock f o r removal of bot h b o i l e r and condensate samples. I t has p r o v i s i o n , however, f o r a c c u r a t e temperature measurement where a d i f f e r e n t i a l Beckmann thermometer can beused f o r p r e c i s e r e a d i n g s . Hence i t can be F i a i O . - N E W , I M P R O V E D O T H M E R S T I L L . (1948') """ "•• —— F I Q . I 3 . - C H I L T O N ' S S T I L U CI935") FIO. 12.- 5TI L.L O F R O G E R S , KNIGHT AND CHOPPIN 0 9 4 1 ) t u r n e d to m o l e c u l a r weight d e t e r m i n a t i o n from b o i l i n g p o i n t e l e v a t i o n . Yft and Hickman (149) d e s c r i b e the use o f the s t i l l f o r a l a b o r a t o r y d e t e r m i n a t i o n of vapor l i q u i d e q u i l i b r i u m i n the system n i t r o m e t h a n e - t r i c h l o r o e t h e n e . Some of the o t h e r e q u i l i b r i u m s t i l l s which f o l l o w e d Othmer's d e s i g n were those o f M i z u t a (78) i n 1934 and Trimble and P o t t s (131) i n 1935. Baker, Hubbard, Huguet, and M i c h a l -orfski (4) e f f e c t e d m o d i f i c a t i o n s i n t h e Trimble and P o t t s apparatus and r e p o r t e d i t i n a paper i n 1939* However, the apparatus does not i n c l u d e any important development not a l r e a d y d i s c u s s e d . In 1942 Langdon and Keyes (70) m o d i f i e d Othmer 1s s t i l l somewhat and i n c o r p o r a t e d a s t i r r e r t o mix the incoming condensate i n the b o i l e r . T h i s , of course, would a i d i n a c h i e v i n g e q u i l i b r i u m c o n d i t i o n s i n the b o i l e r f o r purposes o f sampling and a n a l y s i s . C h i l t o n ' s E q u i l i b r i u m S t i l l Around the l a t e twenties and e a r l y t h i r t i e s e q u i l -i b r i u m s t i l l s were becoming i n c r e a s i n g l y complicated i n d e s i g n and o p e r a t i o n . An example of t h i s i s the h i g h l y e l a b o r a t e arrangement of Nelson (83), (147) where two C o t t r e l l tubes supply l i q u i d from the b o i l e r t o an e q u i l i b r i u m chamber and a thermometer chamber. The Lansberger p r i n c i p l e i s employed where the e q u i l i b r i u m vapors are bubbled through the l i q u i d t o a c h i e v e e q u i l i b r i u m c o n d i t i o n s . In an e f f o r t t o s i m p l i f y these u n i t s without s a c r i f i c i n g too much accuracy, C h i l t o n (17) i n 1935 r e p o r t e d the s t i l l shown i n F i g . 13. I t i n c l u d e s the Lansberger method o f h e a t i n g as w e l l as the vapor t r a p . As the liquid in the boiler A i s heated, the vapors formed bubble through the liquid i n B past the thermometer and are f i n a l l y condensed and collected i n C. The excess condensate, of course, overflows back into the boiler. Liquid samples are siphoned out of B through a condenser to prevent loss of vapor, while vapor samples are removed by means of the stopcock at the bottom of C. Chilton claimed that his apparatus, as well as being simple to construct and operate, gave results whioh compared favorably with those of previous workers. S t i l l of Scat chard, Raymond, and G-ilmann . . . . . . The equilibrium s t i l l designed by Statchard, et a l (110) about 1935 was a modification of the Swietoslowski appar-atus. They provided i t with Chilton's device i n the boiler along with some of the features of the Rosanoff, Lamb, and Briethut (104) apparatus. In operation, the liquid is placed in both vessels A and B (Fig.14) and that in A i s heated. As vapors form they pass into the inner vessel by way of the inlet tube as shown i n section E-E. Yapors and liq u i d from vessel B pass up the belled bottom C o t t r e l l pump and spurt over the thermocouple well. The vapors r i s i n g from vessel B are considered the equilibrium vapors and they pass into the con-denser to reflux into the trap. By means of an overflow return tube the condensate returns to the boiler A. These researchers were probably the f i r s t i n vapor liquid equilibrium studies who made a serious endeavour to measure the equilibrium temperature accurately. They employed Copper-manganin thermocouples which were standardized carefully ft h S E C T » o t H t - E . F1G.I4-APPARATUS of SCATCHARty RAYMOND and OILMANN. by comparison w i t h a p l a t i n u m r e s i s t a n c e thermometer. L a t e s t Developments i n E q u i l i b r i u m S t i l l s . E l a s h Chamber One of the more important s t i l l s e v o lved r e c e n t l y i s t h a t of Jones, Schoenborn, and C o l b u r n ( 6 4 ) r e p o r t e d i n 1 9 4 3 . They i n t r o d u c e d a f l a s h chamber shown as B i n E i g . lj> i n which the r e t u r n i n g condensate was v a p o r i z e d and passed through the l i q u i d i n b o i l e r A as i n the Lansberger apparatus. L i q u i d i s p l a c e d i n b o i l e r A and U-tube C. The b o i l e r and the tube l e a d i n g t o the condenser are wound w i t h r e s i s t a n c e w i r e and a r e heated t o a temperature j u s t below e q u i l i b r i u m temperature. Chamber B i s kept above e q u i l i b r i u m temperature to promote r a p i d v a p o r i z a t i o n . A thermometer or thermocouple p l a c e d i n t o the w e l l i n A g i v e s the e q u i l i b r i u m temperature. The by-pass and three way stopcock p r o v i d e d are f o r purposes o f m a i n t a i n -i n g the vacuum when samples are being taken and p r e v e n t i n g sucking back i n t o the f l a s h b o i l e r . A lthough t h i s s t i l l i s of simple c o n s t r u c t i o n and appears r e l a t i v e l y easy to operate, i t a c t u a l l y r e q u i r e s con-s t a n t a t t e n t i o n d u r i n g a r u n . T h i s stems from the f a c t t h a t superheating and d i s t i l l a t i o n t r o u b l e s i n the apparatus are not e a s i l y a v o i d e d . The f l a s h chamber h e a t i n g c o i l must be a d j u s t e d so t h a t a s m a l l drop of l i q u i d j u s t remains on the bottom of the tube. T h i s i n d i c a t e s t h a t s u p e r h e a t i n g i s not o c c u r r i n g . G i l l e s p i e S t i l l w i t h Vapor disengagement Chamber. One of the b e t t e r e q u i l i b r i u m s t i l l s which seemed to e l i m i n a t e many of the f a u l t s of p r e v i o u s s t i l l s was t h a t put 54 f o r t h hy G i l l e s p i e i n 1946 ( 4 2 ) . Some o f the newer f e a t u r e s of the apparatus ( F i g . l 6 ) were the i n c l u s i o n o f a vapor disengagement chamber, an i n t e r n a l p l a t i n u m h e a t e r along w i t h an e x t e r n a l niohrome w i r e h e a t e r , and p r o v i s i o n f o r the mixing of the vapor condensate w i t h the l i q u i d r e t u r n before r e a c h i n g the b o i l e r . The C o t t r e l l — t u b e from the b o i l e r t o the vapor disengagement chamber c o n t i n u a l l y "pumps l i q u i d and vapor over the thermometer bulb which a c c u r a t e l y r e g i s t e r s the e q u i l i b r i u m temperature. L i q u i d entrainment i n the vapor i s e s s e n t i a l l y e l i m i n a t e d as shown by G i l l e s p i e and l a t e r by R i e d e r , and Thompson (101). The i n t e r n a l h e a t e r prevents su p e r h e a t i n g as w e l l as p r o v i d i n g a means of pumping the l i q u i d through the C o t t r e l l tube. However, t h i s s t i l l has c e r t a i n disadvantages which i n t r o d u c e e r r o r s i n t o any d e t e r -m i n a t i o n s . The l i q u i d i n the b o i l e r i s a c t u a l l y not the l i q u i d i n e q u i l i b r i u m w i t h the vapor disengaged i n the chamber. The l i q u i d sample should be removed from a t r a p as c l o s e t o t h e disengagement chamber as p o s s i b l e s i n c e i t i s here t h a t e q u i l -i b r i u m between the l i q u i d and vapor a c t u a l l y e x i s t s . Secondly, condensation may take p l a c e i n the C o t t r e l l tube, and t h i s n e c e s s i t a t e s good l a g g i n g . F i n a l l y , t h e r e i s a p r e s s u r e d i f f e r e n c e between A and B which may become s e r i o u s a t low p r e s s u r e s . Fowler M o d i f i c a t i o n of the G i l l e s p i e S t i l l . A f t e r making h i s review of e q u i l i b r i u m s t i l l s w i t h a c r i t i c a l a n a l y s i s of each (35)» Fowler designed and r e p o r t e d (36) a m o d i f i c a t i o n of the G i l l e s p i e apparatus. He made a FIG. IG. - G I L L E S P I E ' S E Q U I L I B R I U M S T I L L (1946). complete e v a l u a t i o n of G i l l e s p i e 1 s s t i l l g i v i n g i t s advantages and disadvantages. H i s f i n a l apparatus, s i m i l a r t o t h a t shown i n F i g u r e 29, i n c l u d e s a l i q u i d t r a p D below the detachment chamber. The l i q u i d from the chamber runs i n t o a U-tube f i t t e d w i t h a tap a t the bottom, overflows i n t o a s m a l l bulb a t the top o f the U-tube and then mixes w i t h the c o l d condensate on the way t o the b o i l e r . L i q u i d and vapor samples a r e removed from the a p p r o p r i a t e t a p s . T h i s apparatus e l i m i n a t e s the e r r o r due t o the r e c t i f i c a t i o n which may take p l a c e i n the C o t t r e l l tube or due t o the change i n composition which may~result from the h y d r o s t a t i c head between the b o i l e r and the disengagement chamber. 4. S p e c i a l i z e d S t i l l s S t i l l s f o r P a r t i a l l y M i s c i b l e B i n a r y M i x t u r e s . The f i r s t r e c o r d e d e q u i l i b r i u m s t i l l used f o r d e t e r -minations on p a r t i a l l y m i s c i b l e components was t h a t of S t o c k -h a r d t and H u l l (118) i n 1931. I t was used on the system butanol-water but was shown l a t e r (113) t o produce vapors too r i c h i n the more v o l a t i l e component. A l a t e r s t i l l designed f o r such e q u i l i b r i u m measure-ments was t h a t of Colburn, Schoenborn and S h i l l i n g (20) i n 1943. An o r d i n a r y e q u i l i b r i u m s t i l l would not f u n c t i o n p r o p e r l y i n t h i s case due t o the s e p a r a t i o n of the components i n the phases. These workers d i s t i l l e d the components s e p a r a t e l y , l e d them i n t o a compartment w i t h an approximate e q u i l i b r i u m mix-t u r e of the two components and allowed the l i q u i d and vapor t o r e a c h e q u i l i b r i u m as i n d i c a t e d by the thermometer. The vapors 36 were condensed and ana l y s e d and the f i n a l l i q u i d i n the v e s s e l was s i m i l a r l y a n a l y s e d . T h e " i n l e t tube was surrounded by a b a f f l e tube t o g i v e a c i r c u l a t i n g motion t o the l i q u i d and ensure i n t i m a t e m i x i n g . R e s u l t s obtained on t h i s apparatus were good. How-ever, s k i l l e d m a n i p u l a t i o n was r e q u i r e d and the arrangement f o r s e p a r a t e l y d i s t i l l i n g and then i n t i m a t e l y m i x i n g the com-ponents was r a t h e r clumsy. R e c e n t l y , Smith and Bonner (113) i n l a t e 1949 pub-l i s h e d d e t a i l s of an e q u i l i b r i u m s t i l l which was used on the system 1-butanol-water. An o r d i n a r y c o n d e n s a t e - r e c i r c u l a t i o n type of u n i t would not be s a t i s f a c t o r y f o r t h i s system s i n c e the h e a v i e r l a y e r would b u i l d up i n the condensate t r a p . The de s i g n of the s t i l l (Fig.17) f o l l o w s the g e n e r a l l i n e o f the Othmer-type (93) and i s s i m i l a r i n p r i n c i p a l t o the u n i t o f Baker, Hubbard, Huguet, and Mic h a l o w s k i . The charge i s p l a c e d i n the d i s t i l l a t i o n f l a s k A and the magnetic a g i t a t o r i s t u r -ned on t o prevent s u p e r h e a t i n g . Heat i s a p p l i e d by means of the i n t e r n a l Nichrome wire r e s i s t a n c e h e a t e r and a l l the a i r i s vented out through the o u t l e t C. When vapors b e g i n t o r e f l u x on the neck w a l l s , the vent i s stoppered and the neck heater c o n s i s t i n g of t u r n s of r e s i s t a n c e wire i s turned on. The temperature o f the neck i s kept a t about 3°C h i g h e r than t h a t o f the l i q u i d t o prevent condensation. Vapors are con-densed i n the r e f l u x condenser a t B and the e q u i l i b r i u m vapor temperature i s measured on the thermometer a t D. During a run, the s t i l l i s allowed t o operate about O 3 FIG.I7 - OTHMER REFINED S T I L L MODIFIED BV SMITH I BONNER 09*9) an hour, the 5°C differential between liquid and vapor tem-peratures being maintained. Then the temperatures are recorded and a condensate sample is drawn off by means of the three way stop-cock and the auxiliary cooler F. By using a dye test, the authors found entrainment to be negligible. Equilibrium S t i l l s for High Vacua C.A. Bishop ( 6 ) , doing work on a Ph.D. thesis, was probably the f i r s t to design and construct an apparatus for the determination of vapor liquid equilibrium at low pressures. Details of his unit are unavailable at this writing. In 1947, at about the same time, two papers were published on vapor-liquid equilibrium at low pressures by different authors. Williams (143) described an apparatus which was a modification of Gthmer's (87) 1932 design. Refer-ring to Fig. 18, the liquid i s put in the s t i l l body and stain-less steel helices are added to prevent bumping. The boiler A, as well as the removable oven body B, are insulated and heated by resistance wire. There i s a condenser tube C mode of large diameter tubing to reduce the pressure difference between the vapor trap and boiler. The condensate oollects in the trap D and returns to the boiler. Williams reported good results at 0.1 mm.Hg. pressure on esters boiling 3*0° apart. Perry and Fuguitt (98) had a somewhat different design for their equilibrium S t i l l (Fig. 19). The s t i l l proper was constructed entirely from Pyrex, while the s t i r r e r shaft and top closure were fabricated of metal. The liquid i s put into the boiler A, which i s heated by an internal heater, and stirred by a paddle on a stem passing through a vacuum gland. F I G - 2 0 . - S T I L L O F G O R D O N A N D B E N S O N F O R L O W T E M P E R A T U R E E Q U I L I B R I A , 0 ^ 4 6 > The upper p o r t i o n of the b o i l e r i s wound w i t h niohrome w i r e f o r h e a t i n g t o prevent condensation. By means of a r o t a t i n g d i s c on the s h a f t , the r i s i n g vapors are d e f l e c t e d onto the w a l l s of the v e s s e l c o o l e d by a water j a c k e t . The condensate i s caught i n a trough and flows i n t o a vapor t r a p B. From there i t overflows back i n t o the b o i l e r . The whole apparatus i s brought t o a p r e s s u r e of 0.1 mm of Hg and the authors r e p o r t good r e s u l t s f o r components b o i l i n g 10°0 apart.. None of these u n i t s , however, have p r o v i s i o n s f o r temperature measurement s i n c e t h i s would i n c r e a s e the complex-i t y of the apparatus c o n s i d e r a b l y . E q u i l i b r i u m S t i l l s f o r Low Temperature Work Work w i t h systems which are n o r m a l l y gaseous at room temperature i n v o l v e s added d i f f i c u l t y i n apparatus d e s i g n . Gordon and Benson (49) were p r o b a b l y p i o n e e r s i n vapor l i q u i d e q u i l i b r i a on substances w i t h low b o i l i n g p o i n t s . They c a r r i e d out vapor l i q u i d e q u i l i b r i a d e t e r m i n a t i o n s on the system hydro-gen cyanide-cyanogen c h l o r i d e a t 15°C, the former component of the system having a b o i l i n g p o i n t of 26°C and t h e other 12.8 GG. The apparatus they employed i s i l l u s t r a t e d very d i a g r a m a t i c a l l y i n F i g u r e 20. The p a r t of the u n i t tothe r i g h t o f the d o t t e d l i n e i s e n c l o s e d i n a constant temperature bath and the o u t l e t F l e a d s to the MoLeod gauge, vacuum pumps and mercury manometer. Bulbs C and D c o n t a i n e d the two components which were d i s t i l l e d i n t o the l i q u i d phase bulb A by means of l i q u i d a i r . A g i t a t i o n was obtained w i t h a s m a l l magnetic s t i r r e r B. A f t e r temperature e q u i l i b r i u m was o b t a i n e d the vapor pressure was measured on the mercury manometer. With g r a v i m e t r i c a l l y determined samples of the components t h i s gave the vapor p r e s s u r e curve f o r the system. The e q u i l i b r i u m v a p o r - l i q u i d composition was o b t a i n e d by slow i s o t h e r m a l d i s t i l l a t i o n of the system from bulb A i n t o pycrometer G. From p r e v i o u s measurements the density-compos-i t i o n curve was determined f o r the system and t h i s was used f o r a n a l y s i s of the phases. Almost w i t h i n the l a s t year, Stutzman and Brown (121) c a r r i e d out v a p o r - l i q u i d e q u i l i b r i u m d e t e r m i n a t i o n s a t c o n s i d e r -a b l y lower temperatures. T h e i r measurements were made on n a t u r a l gas and, of course, had to be made i n a low temperature c r y o s t a t . B. Vapor R e c i r c u l a t i o n Type o f Apparatus An E q u i l i b r i u m apparatus b e l o n g i n g t o t h i s group i s one where the vapor i s c o n t i n u o u s l y c i r c u l a t e d through the system and i s brought i n t o r e p e a t e d c o n t a c t w i t h the l i q u i d . I t i s Considered by many authors t o be f a r s u p e r i o r f o r a c c u r -ate vapor l i q u i d e q u i l i b r i u m measurements to those p r e v i o u s l y mentioned, I t s advantages over the dynamic and continuous d i s t i l l a t i o n types of u n i t s a r e , of course, q u i t e obvious. Vapor r e c i r c u l a t i o n i n the apparatus under proper c o n d i t i o n s should prevent superheating, entrainment o f d r o p l e t s of l i q u i d i n the vapor, and r e f l u x i n the l i n e s . Furthermore, s i n c e t h e r e i s no c o l d condensate t o r e t u r n t o the hot b o i l e r , f l a s h i n g o f the more v o l a t i l e component i s e l i m i n a t e d . However, d e t e r -minations on such an apparatus must be c a r r i e d out a t constant temperature and w i t h some mechanical means of c i r c u l a t i n g the vapor. Very o f t e n these i n v o l v e c e r t a i n c o m p l i c a t i o n s which are not e a s i l y overcome. Consequently t h i s type of apparatus i s only r a r e l y used and i t has had only occasional mention i n the l i t e r a t u r e . Early Forms One of the e a r l i e s t types of apparatus employing the p r i n c i p l e of vapor c i r c u l a t i o n was that of Rosanoff, Lamb, and Breithut (104) i n 1909- They employed a modified Lans-berger device shown i n Figure 21 and bubbled the vapor through the l i q u i d to avoid superheating. The l i q u i d system was placed i n both containers A and B and that i n A was heated by means of the inte r n a l heater. The vapor was led i n t o vessel B by way of the i n l e t tube and was bubbled through the l i q u i d . Vapors coming from B were passed through a disengagement device where any entrained l i q u i d was removed and f e l l back into B. To prevent the steady loss of the more v o l a t i l e component additional material was slowly supplied to the l i q u i d i n A, the rate being determined by the temperature reading i n A. The vapor was then condensed and analysed, and a sample of l i q u i d was removed from B by means of a pipette. Nelson ($3) i n 1932 made an elaborate arrangement of a s t i l l incorporating two C o t t r e l l pumps, a vapor trap, and the Lansberger p r i n c i p l e of bubbling the vapor through the l i q u i d . However, although t h i s apparatus employs the scheme of vapor r e c i r c u l a t i o n to a point, i t cannot be classed en-t i r e l y under t h i s group. Constant .Temperature Type of R e c i r c u l a t i on Apparatus In 1929, Ferguson and Funnell (34) reported a novel apparatus f o r vapor l i q u i d determinations. It was a rather FIG.2I." APPARATUS of ROSANOFF, LAMB and B R I E T H U T 09OQ) . .. . • -• - 41 complicated u n i t f o r the r e c i r c u l a t i o n o f a vapor through i t s e q u i l i b r i u m l i q u i d , and then f o r t h e a n a l y s i s of the two phases. T h i s was the f i r s t apparatus i n which the vapors were r e c i r c u l a t e d through t he system by means of a s p e c i a l l y designed, a l l - g l a s s c i r c u l a t i n g apparatus ( 3 7 ) . The vapor p r e s s u r e s of the l i q u i d phase as w e l l as t h a t of the condensed vapor phase were measured on a mercury manometer. From a p r e v i o u s l y determined vapor p r e s s u r e - c o m p o s i t i o n curve the compositions of t h e two e q u i l i b r i u m phases were determined. A m o d i f i c a t i o n of the Ferguson-Funnell apparatus was t h a t employed by Gordon and Hines (50) on t h e system ethanol-acetone. R e f e r r i n g t o F i g u r e 23, which i l l u s t r a t e s a ver y s i m i l a r apparatus, the l i q u i d system was p l a c e d i n t h e f i l l i n g tube T from which i t was d i s t i l l e d i n t o t he l i q u i d phase bulb A and s e a l e d o f f at x. The constant temperature baths, r e p r e s e n t e d by s o l i d l i n e s f o r the water bath and broken l i n e s f o r the a i r baths, were brought on temperature and c i r c u l a t i n g pump P was s t a r t e d . When p r e s s u r e e q u i l i b r i u m was reached, as shown by the manometer at M, the pressure was read. Then the vapor and l i q u i d phases were separated by s e a l i n g o f f the t u b i n g at y and z, the vapor phase was con-densed i n t o bulb B and se a l e d o f f from the r e s t of the appar-atus a t W-. The baths were brought on -temperature again and the vapor pressure of the vapor phase measured. From a pre s -sure-composition curve determined on the same apparatus the composition of each phase was obt a i n e d . The procedure w i l l be more f u l l y d e s c r i b e d i n one o f the- f o l l o w i n g s e c t i o n s s i n c e an apparatus c l o s e l y r e l a t e d to t h a t of Gordon and Hines was employed i n t h i s r e s e a r c h . C. Other Methods of Vapor L i q u i d E q u i l i b r i u m Determinations. The a d d i t i o n a l methods o f vapor l i q u i d e q u i l i b r i u m are not too w i d e l y used and w i l l be d e a l t w i t h o n l y b r i e f l y i n t h i s review. The Bomb Method The apparatus c o n s i s t s of a c l o s e d evacuated v e s s e l kept at constant temperature i n a constant temperature bath. I t has some p r o v i s i o n f o r a g i t a t i o n such as a r o c k i n g device or shaker. The l i q u i d sample i s p l a c e d i n the v e s s e l , a g i -t a t e d u n t i l e q u i l i b r i u m i s reached between the l i q u i d and the vapor at constant temperature. By withdrawal o f the vapor and l i q u i d samples t h e y can be a n a l y z e d . Some work w i t h t h i s method of d e t e r m i n a t i o n was r e p o r t e d by Ferguson, F r i e d and M o r r i s (-33). C e r t a i n d i f f i c u l t i e s a re i n v o l v e d i n such a d e t e r -mination which may become s e r i o u s . During sampling, p r e s s u r e changes occur t h a t a re l i k e l y t o induce e v a p o r a t i o n or con-d e n s a t i o n thus changing the e q u i l i b r i u m s t a t e . Also the sampling l i n e s o f s m a l l c r o s s - s e c t i o n may f i l l up w i t h l i q u i d d u r i n g t h e i n i t i a l p a r t of the operation- and t h i s l i q u i d may never come'to t r u e e q u i l i b r i u m . Dynamic Flow Method Another procedure which has found a c e r t a i n amount of use i n v a p o r - l i q u i d e q u i l i b r i u m s t u d i e s i s one i n which a vapor i s passed through a s e r i e s of v e s s e l s c o n t a i n i n g l i q u i d s of s u i t a b l e composition. A t r a i n of t h i s type was.used i n the work of Parks and Chaffee (95) i n 1927 and, l a t e r i n 1935 Washburn and Handorf (137) employed t h e same p r i n c i p l e . I f c o n c e n t r a t i o n s o f a l l the v e s s e l s a re made t h e same and a l a r g e number of v e s s e l s are used e q u i l i b r i u m w i l l t e n d to be more n e a r l y approached as the vapor passes through the u n i t . T h i s can dispense with a n a l y s i s o f the l i q u i d because i f the conce n t r a t i o n s i n the v e s s e l s are made up a c c u r a t e l y t h e con-c e n t r a t i o n i n the l a s t one w i l l change on l y s l i g h t l y and can be taken as the l i q u i d composition. The apparatus has the advantage of b e i n g simple and i n v o l v i n g a reasonably s m a l l amount of work. However, a f a i r l y l a r g e amount of the components i s r e q u i r e d ; an exact e q u i l i b r i u m cannot be a t t a i n e d due t o the f a c t t h a t a pr e s -sure drop i s i n v o l v e d i n p a s s i n g the vapor through t h e system and there i s a danger of entrainment. 44 CHAPTER IV  APPARATUS A. The Vapor Recirculation Apparatus The apparatus f i r s t constructed was essentially that of Gordon and Hines (50) with a few small modifications for improved operation. Since the whole apparatus, from the high vacuum arrangement to the constant temperature cabinets, was built almost in i t s entirety in this research, i t w i l l be described here in some detail. High Vacuum System The apparatus for the production and measurement of high vacuum was constructed, assembled, and tested without too much d i f f i c u l t y . Figure 22 shows the arrangement of the manometer,' McLeod gauge, and diffusion pump. A reasonably high vacuum was obtained by introducing a narrow or i f i c e or "jet" into the diffusion pump in i t s construction. Backed by a newj Welch "Duo Seal" mechanical forepump, i t gave a pressure below 10~^ mm. of mercury as measured on the McLeod gauge. The gauge was constructed roughly according to the specifications of Rosenberg (105) and was calibrated by the "squared scale" method (145)' Since the compression ratio of the gauge was calculated to be 2.48 x 10"^, the absolute pressure in the system could be measured accurately to a pressure at least corresponding to that figure in mm. of mercury. The mercury used, i n this McLeod gauge was purified as described below and then d i s t i l l e d into the lower bulb to avoid contamination. P u r i f i c a t i o n of Mercury A commercially pure form o f mercury was f u r t h e r p u r i f i e d by a number of standard procedures (107). F i r s t l y , dry, c l e a n , f i l t e r e d a i r was bubbled through the mercury covered by a d i l u t e s o l u t i o n of approximately 1% n i t r i c a c i d . T h i s procedure o x i d i z e d any of the base metals such as copper, z i n c and l e a d t h a t may have been p r e s e n t . The o x i d i z e d metals appeared a s a scum on the s u r f a c e o f the aqueous s o l u t i o n and were l a t e r removed by " p i n h o l i n g " through a f i n e l y drawn down c a p i l l a r y . T h i s o x i d a t i o n procedure was c a r r i e d on f o r about twenty f o u r hours w i t h f r e q u e n t changes i n the n i t r i c a c i d s o l u t i o n . The mercury was then passed through a "scrubber" which c o n s i s t e d of a column some 150 cm. l o n g t e r m i n a t i n g i n a bent c a p i l l a r y i n the form of a t r a p a t the bottom. I t was f i l l e d w i t h about 5$ n i t r i c a c i d s o l u t i o n . The mercury f a l l s through the s o l u t i o n i n the form of a spray which can be e f f e c t e d by p a s s i n g the mercury through a f u n n e l drawn t o a f i n e j e t . Thus any remaining a l k a l i metals a r e o x i d i z e d and by a r e p e t i t i o n of t h e procedure a number of times, the scum i s removed at the f u n n e l . F i n a l l y , the mercury was sprayed through d i s t i l l e d water t w i c e and c o l l e c t e d i n a w e l l c l e a n e d and d r i e d c o n t a i n e r . A f t e r removing any v i s i b l e t r a c e s of water w i t h f i l t e r paper, t h e mercury was t r a n s f e r r e d to. a d i s t i l l a t i o n apparatus. Here i t was twice d i s t i l l e d under vacuum to remove any t r a c e s o f the noble metals such as g o l d or s i l v e r and t i n . , - . , • 46 Main E q u i l i b r i u m .Apparatus R e f e r r i n g t o Fig. 2 3 , A i s t h e l i q u i d phase bulb of 1G0 ml. c a p a c i t y , B i s a bulb of 50 ml. f o r t h e conden-s a t i o n o f the vapor phase, and C i s a g l a s s h e l i x t o a l l o w the incoming vapor t o reach temperature e q u i l i b r i u m . T h i s p a r t of the apparatus i s enclosed i n a constant temperature o i l bath r e p r e s e n t e d by the s o l i d l i n e s . The p o r t i o n of the apparatus enclosed by the dotted l i n e s , which re p r e s e n t t h e constant temperature a i r baths, c o n s i s t s o f a 5 l i t e r p r e s s u r e e q u a l i z -i n g bulb D and Funnell-Hoover c i r c u l a t i n g apparatus P. L r e p r e s e n t s a l e v e l i n g l i n e on a s m a l l m i l l i m e t e r s c a l e which can be viewed through a double g l a s s window i n the a i r t h e r -m o s t a t ^ . The f i l l i n g tube F i s o u t s i d e t h e constant temp-er a t u r e baths and c o n t a i n s the i n i t i a l charge of t h e l i q u i d system. K i s a separate compartment made o f g a l v a n i z e d sheet metal covered w i t h asbestos paper and having a double-walled, i n s u l a t e d , sheet copper door. T h i s a l l o w s access t o the vapor l i n e s j o i n i n g the c i r c u l a t i n g apparatus w i t h t h e bulbs i n the o i l b a t h without d i s t u r b i n g the e q u i l i b r i u m i n the r e s t of the apparatus. A s m a l l L i e b i g condenser 0 was i n t r o d u c e d i n t o t h e l i n e between the l i q u i d phase bulb A and the vapor phase bulb B. T h i s prevented condensation of the system i n t o the bulb B on i n i t i a l d i s t i l l a t i o n from f i l l i n g tube F. As a p r e c a u t i o n a g a i n s t condensation i n the h o r i z o n t a l l i n e l e a d i n g from A t o F, nichrome r e s i s t a n c e wire was wound about i t f o r h e a t i n g purposes. The manometer M permits measurement of the vapor pressure a c c u r a t e l y w i t h a cathetometer. By means of a l e v e l l i n g b ulb J , mercury can be manipulated i n the manometer f o r any d e s i r e d h e i g h t . A l l connecting g l a s s l i n e s on t h e c i r c u l a t o r y p a r t of the apparatus are made of 10 mm. o u t s i d e diameter g l a s s t u b i n g t o a l l o w f o r r a p i d c i r c u l a t i o n . C i r c u l a t i n g Pump T h i s i s the " h e a r t " o f the whole apparatus (Fig.2 5 ) and was perhaps the most d i f f i c u l t i n d i v i d u a l item t o b u i l d . In the f i n a l c o n s t r u c t i o n o f the g l a s s p a r t s , the s p e c i f i c a t i o n s o f F u n n e l l and Hoover (37) were f o l l o w e d q u i t e c l o s e l y . How-ever, i t was found t h a t more e f f i c i e n t o p e r a t i o n was ob t a i n e d by g r i n d i n g t h e v a l v e s i n t o p l a c e w i t h a v e r y f i n e g r i n d i n g compound c o n s i s t i n g o f 200 mesh carborundum w e l l mixed w i t h g l y c e r i n e . Such treatment was a l s o found h e l p f u l f o r t h e p i s t o n s i n c e the smooth s u r f a c e o f the g l a s s was removed and thus helped t o prevent b i n d i n g . The s o l e n o i d s were made 6 .5 cm. l o n g , but were f i n a l l y wound w i t h 1700 t u r n s of No . 2 2 B&S co t t o n i n s u l a t e d copper w i r e . The e x t r a 500 t u r n s over the o r i g i n a l s o l e n o i d s gave a b e t t e r f i e l d and t h e pump was found t o o p e r a t e f o r l o n g e r i n t e r v a l s without i n t e r r u p t i o n . A s u i t a b l e c u r r e n t f o r the c o i l s i s 1.1 amps u s i n g a 40 v o l t D.C. l i n e . The r e s i s t a n c e o f each i s 16 ohms and a 90 ohm rh e o s t a t i n s e r i e s g i v e s s u f f i c i e n t c o n t r o l over the cu r r e n t i n p u t . As an added a i d t o prevent s t a l l i n g of the p i s t o n , an electromagnet E was i n s t a l l e d j u s t above the c e n t r e o f the c y l i n d e r o f the pump. T h i s was made by winding 1200 t u r n s of c o t t o n - i n s u l a t e d copper w i r e on a s o f t i r o n core 3 cm lo n g which had i r o n f l a n g e s threaded on t h e ends. The f l a n g e s a l s o PISTON "1\ ELECTROMA6N ET L r r — 3 1 • ^ ^^^^ AIR COR IE S( >LENOIDS I VALVES J7 FI6.25- CfRCULATING APPARATUS 4 tend to become h i g h l y magnetized and g i v e the magnet a wider range o f i n f l u e n c e . R e s i s t a n c e of the electromagnet was found t o be 11 ohms by means of a Simpson ohmmeter. With a 99 ohm rh e o s t a t i n s e r i e s the electromagnet, a d j u s t e d f o r a c u r r e n t of 1.3 amp from the 40 v o l t D.C. l i n e , was found t o have a c o n s i d e r a b l e f i e l d o f a t t r a c t i o n . Commutator f o r C i r c u l a t i n g Pump A m o d i f i c a t i o n has been made w i t h regards to the commutator arrangement d e s c r i b e d i n the B.A. t h e s i s 033). In p l a c e o f the a u t o m a t i c telephone commutator, a common r e c o r d p l a y e r motor and t u r n t a b l e have been employed. The motor o p e r a t i n g a t 78 r e v o l u t i o n s per minute was arranged i n t o a simple s e t up as shown i n F i g . 24 t o g i v e the p i s t o n o f the pump 78 c y l e s per minute. T h i s speed produces about the maximum e f f i c i e n c y o f t h e c i r c u l a t o r as evidenced by t e s t s made w i t h t h e p r e v i o u s commutator which c o u l d be v a r i e d f o r speed. Although t h e r e have been e l e c t r o n i c d e v i c e s d e s c r i b e d i n t he l i t e r a t u r e (5) (125) f o r such t i m i n g o p e r a t i o n , t h i s commutator was found t o f u n c t i o n v e r y s a t i s f a c t o r i l y without c o m p l i c a t i o n s . Temperature C o n t r o l The temperature range i n which t h e apparatus can be employed i s from room temperature up to 95°C. Temperatures i n + t h e o i l bath were t o be maintained w i t h i n - 0 . 0 0 2°C. Con-sequently, a s e r i o u s problem was f a c e d i n d e s i g n i n g baths which would completely enclose t h e apparatus and s t i l l permit c e r t a i n m a n i p u l a t i o n on the vapor l i n e s without e x c e s s i v e l y • v . : ' : 4 9 d i s t u r b i n g e q u i l i b r i u m d u r i n g a run. A f u r t h e r c o m p l i c a t i o n i s the .iu.se of f r a g i l e g l a s s t u b i n g and b u l b s i n c o n n e c t i o n w i t h bulky and heavy thermostats on a metal rod frame which does not allow too. much f i r m support. Constant Temperature baths The a i r baths were f a b r i c a t e d o f t h r e e - p l y and were made w i t h double w a l l s , the space between f i l l e d w i t h r o c k wool i n s u l a t i o n . .One u n i t c o n t a i n s both compartments separated by a double w a l l . The w a l l s , i n most cases, a re 1 l/k i n c h e s t h i c k and were found to g i v e e f f i c i e n t i n s u l a t i o n . To o f f e r complete freedom i n working w i t h t h e c i r c u l a t o r y p a r t of the apparatus i n p r e p a r a t i o n f o r runs, the baths were made i n two p a r t s . The back p o r t i o n i s f a s t e n e d f i r m l y to the frame and con t a i n s the apparatus. A cover w i t h access doors and v i s i o n windows s l i d e s over theback p o r t i o n . F e l t packing s u p p l i e s f u r t h e r i n s u l a t i o n i n p l a c e s where the back and cover come together and where g l a s s t u b i n g passes through the p a r t i t i o n i n the baths. The constant temperature o i l b a t h i s a l a r g e r e c -t a n g u l a r g a l v a n i z e d i r o n tank w i t h a c a p a c i t y o f approximately 18 g a l l o n s . Around the o u t s i d e o f the tank i s a plywood con-t a i n e r . The space between sheet metal and plywood i s packed l o o s e l y w i t h r o c k wool i n s u l a t i o n . A d r a i n p l u g o f 1" diameter at the bottom a i d s i n the r a p i d drainage o f the bath.-between runs and when condensation o f the vapor phase i s r e q u i r e d . The bath i s kept i n p l a c e by a st u r d y bench b u i l t e s p e c i a l l y f o r the purpose. P l a t e I shows the constant temperature baths as PLATE! I , - V A P O R R E C I R C U L A T I O N E Q U I L I B R I U M A P P A R A T U S . w e l l as the remainder of the apparatus ready f o r o p e r a t i o n . S t i r r i n g Equipment One d r i l l r o d s t e e l s h a f t runs through t h e t h r e e constant temperature baths and bears the f a n s and p r o p e l l e r s which supply t h e ~ c i r c u l a t i o n o f a i r and o i l . There a r e t h r e e brass bushings s e c u r e l y f a s t e n e d t o t h e frame o f t h e constant temperature baths and serve as b e a r i n g s f o r the s h a f t . The a i r c i r c u l a t o r s a re f i v e - i n c h diameter, f o u r - b l a d e d , aluminum fans f i r m l y secured w i t h keys and set screws s u f f i c i e n t l y near the incandescent lamps and heaters to c i r c u l a t e the heat r a p i d l y . The o i l i s c i r c u l a t e d by two brass p r o p e l l e r s t h r e e i n c h e s i n o v e r a l l l e n g t h and c a r r y i n g s u f f i c i e n t p i t c h i n the two blades to throw the o i l at a c o n s i d e r a b l e r a t e . They are f a s t e n e d to the s h a f t by means o f set screws i n a convenient p o s i t i o n t o g i v e the most e f f i c i e n t s t i r r i n g . The s h a f t i s d r i v e n by a 1/8 h.p. motor and the b e l t i s so arranged on t h e p u l l e y s as t o impart an r.p.m. of 1600 t o t h e s t i r r e r s . I t was made i n two s e c t i o n s t o f a c i l i t a t e d i s m a n t l i n g . The lower p o r t i o n o f the s h a f t c a r r y i n g t h e p r o p e l l e r s f o r the s t i r r i n g of the o i l can be r e a d i l y a t t a c h e d by means o f a c o u p l i n g and set screws j u s t above the lower bushing. T h i s was found convenient when o n l y t h e a i r c i r c u l a t o r s were r e q u i r e d t o operate as i n i n i t i a l p ressure measurement d u r i n g a run. F i g u r e 27 shows the constant temperature baths i n s e c t i o n w i t h the s t i r r i n g apparatus. ^3*0 THERMO REGULATOR E A T E R F\G.2<o- C I R C U I T D I A G R A M O F T E M P E R A T U R E C O N T R O l _ U N I T S FOR AIR B A T H S . 51 Heating. Temperature Measurement and C o n t r o l . A i r Baths The upper a i r both was heated by an "Edison-screw cone" h e a t e r o f 660 watts c o n t r o l l e d by a v a r i a c - t y p e t r a n s -former. A s i m i l a r heater as w e l l as an a u x i l i a r y incandescent lamp h e a t e r maintained the temperature i n the lower a i r b a t h . The temperature i n each compartment was i n d i v i d u -a l l y c o n t r o l l e d w i t h a Cenco, h i g h c a p a c i t y , DeKhatinsky thermoregulator connected to t w o - c o i l r e l a y s . Such a t h e r -moregulator c o n s i s t s e s s e n t i a l l y of a b i - m e t a l l i c c o i l which on expansion o r c o n t r a c t i o n w i t h temperature makes c o n t a c t s to a c t i v a t e e i t h e r one or the other o f the c o i l s i n the r e l a y . The r e l a y c o i l s may open or c l o s e the c i r c u i t t o t h e a i r bath h e a t e r s by t h e i r e l e c t r o m a g n e t i c e f f e c t . To overcome the c h a t t e r of 110 v o l t s A.C. i n the r e l a y s , 40 v o l t s D.C. were a p p l i e d to t h e c o i l s and 110 v o l t s A.C. was l e f t on t h e h e a t e r s . T h i s type o f t h e r m o s t a t i c c o n t r o l was found to be e f f e c t i v e f o r m a i n t a i n i n g temperature t o w i t h i n - 0 . 5°C. F i g u r e 26 g i v e s a c i r c u i t diagram f o r such a u n i t . A l o n g thermometer graduated from - 1 0 to 110°C i n d i v i s i o n s of 0.1°C and s t a n d a r d i z e d a g a i n s t a platinum r e s i s -tance thermometer w i t h Bureau of Standards C e r t i f i c a t e was used f o r temperature measurement i n the a i r b a t h s . Constant Temperature O i l Bath The h e a t i n g i n the o i l bath c o n s i s t e d o f f o u r d i f f e r e n t h e a t e r s . Two blade h e a t e r s , one o f 500 watts and the other o f 250 watts, s u p p l i e d the main heat. They were a d j u s t e d w i t h r h e o s t a t s i n s e r i e s and were kept on f o r a temperature j u s t about a degree below t h a t r e q u i r e d of the bath. The vapor phase bulb B was heated s e p a r a t e l y by a nichrome wi r e heater i n very c l o s e p r o x i m i t y . These t h r e e heaters c o u l d be c o n t r o l l e d by a " m e t a s t a t i c " mercury thermo-r e g u l a t o r used i n c o n j u n c t i o n w i t h a Cenco e l e c t r o n i c r e l a y c o n t r o l u n i t . T h i s u n i t was found t o g i v e temperature c o n t r o l to w i t h i n - 0 . 1°C. For t h e acc u r a t e temperature c o n t r o l an improvised e l e c t r o n i c u n i t was employed. I t i n c l u d e d a t r i o d e f o r c o n t r o l o f the a c t i v a t i n g c u r r e n t o f t h e 3 m i l l i a m p r e l a y . F i g u r e 28(a) g i v e s the c i r c u i t diagram. The f i n g e r - t y p e thermo-r e g u l a t o r was simply c o n s t r u c t e d (Fig.2Sb) o f pyrex g l a s s t u b i n g w i t h a stopcock i n one arm f o r adjustment o f the mercury i n the oth e r arm. A needle f i t t e d i n t o a threaded housing of the c a p i l l a r y o f the l a t t e r gave the f i n e r a d j u s t -ment. T h i s thermoregulator works on the mercury expansion p r i n c i p l e and the mercury was o f the s p e c i a l l y p u r i f i e d grade used f o r t h e McLeod gauge. The heate r c o n t r o l l e d by t h i s u n i t was made o f nichrome r e s i s t a n c e w i r e (No.22 B8S gauge) l o o s e l y wound on a g l a s s t u b i n g framework around the i n s i d e o f t h e bath. The whole heater had a r e s i s t a n c e o f 150 ohms and gave 80 watts on t h e f u l l 110 v o l t s o f the A.C. c i r c u i t . For a g r e a t e r wattage, however, the heater was tapped o f f at two p o i n t s , t h e r e s i s t a n c e between which was 80 ohms. T h i s gave a t o t a l power o f 150 watts and was found more s u i t a b l e f o r the h i g h e r temperatures. A small V o r i a c was used f o r THERMO REGULATOR •O Q HEATER A.C. F I G . 28 C I R C U I T D I A G R A M O F E L E C T R O N I C CONTROL . UNIT FOR C O N S T A N T T E M P E R A T U R E IN OIL B A T H DO KJ jtlCMOfitAC TT L E G E N D FOR F IG . Z&d.. L,- 1 5 WATT TUN^STCN P«I.OT LAMP L J . - 25 W * T r T U N G S T E N U A > H P L» - 15 W A T T T U N G S T E N » _ A M * » R, ~ I04 O H M CAffeOM R P S t j r O R R x - 2-2 .*l° f coHM C A * O O K * sesuroe Rj - 2-Z l l ° 4 O H M C A R B O N R C S I S T O K . Re - 3 m RCUA* T - VARIAO-TVPE. TRA*4SFORN*tR. 50 l_G TRIOOE. FIG.26 6.- F I N G E R - T Y P E T H E R M O R E G U LATOR. adjustment of the he a t e r . When a l l h e a t e r s i n the o i l bath were a d j u s t e d p r o p e r l y , the r e l a y o f t h e s e n s i t i v e c o n t r o l u n i t would switch the c u r r e n t on and o f f to t h e nichrome w i r e at i n t e r v a l s of 5 seconds or even l e s s . Under such c o n d i t i o n s the temperature as noted on a Beckmann thermometer, d i d not vary more than - O.G02°C. The Beckmann was a l s o c a l i b r a t e d w i t h the Platinum r e s i s t a n c e thermometer. B. The L i q u i d R e c i r c u l a t i o n Apparatus The apparatus was designed t o be e s s e n t i a l l y the same as t h a t of Fowler ( 3 6 ) . Some of the s m a l l changes made were intended t o be improvements and are l i s t e d as f o l l o w s : -( i ) A c a p i l l a r y stopcock was i n t r o d u c e d f o r the removal o f a sample from the l i q u i d t r a p . T h i s e l i m i n a t e s the l a r g e r q u a n t i t i e s of l i q u i d which stagnate i n an o r d i n a r y 2 mm stopcock. ( i i ) The drop counter of the G i l l e s p i e s t i l l ( 4 2 ) was r e t a i n e d i n the sm a l l bulb above-the. c a p i l l a r y l e a d i n g t o the b o i l e r . T h i s f a c i l i t a t e s i n a d j u s t i n g f o r a proper r a t e of h e a t i n g i n the b o i l e r . ( i i i ) The vapor condensate t r a p was made s m a l l e r i n order t o ac h i e v e e q u i l i b r i u m more r a p i d l y . T h i s change was suggested as an improvement on t h e G i l l e s p i e s t i l l by Rieder and^Thompson (101). Since o n l y r e f r a c t i v e i n d i c e s were o r d i n a r i l y taken, t h e r e was s u f f i c i e n t condensate trapped f o r measurements. By means o f a sm a l l pynometer d e n s i t y measurements c o u l d a l s o be made. ( i v ) A type o f condenser where dry i c e and acetone or an i c e - s a l t mixture can be used f o r the c o o l i n g m a t e r i a l was i n t r o d u c e d above the vapor condensate t r a p . Fowler suggested such an a d d i t i o n f o r e q u i l i b r i u m measurements under reduced p r e s s u r e . (v) A thermometer w e l l w i t h a 19/38 Standard t a p e r female j o i n t was f i t t e d i n t o the upper u n i t t o accommodate thermometers w i t h ground g l a s s j o i n t s used w i t h the C o t t r e l l -Choppin (102) e q u i l i b r i u m s t i l l . The s t i l l ( F i g . 29) was made e n t i r e l y of Pyrex g l a s s by Mr. W. Pye, g l a s s b l o w e r of the Chemistry Department. Tungsten l e a d s were s e a l e d i n t o the standard t a p e r stopper o f the f i l l i n g tube f o r e l e c t r i c a l i n p u t to the i n t e r n a l h e a t e r . T h i s h e a t e r c o n s i s t e d o f 12 i n c h e s of 28 gauge platinum w i r e , wound i n t o a s m a l l c o i l at the end and b r a z e d to t h e tungsten l e a d s w i t h c o n s t a n t i n as the f l u x . A c u r r e n t of 5 amp. con-t r o l l e d by a s m a l l v a r i a c was found s u i t a b l e f o r proper pumping i n the C o t t r e l l tube. The b o i l e r , C o t t r e l l tube, disengage-ment chamber and thermometer w e l l j a c k e t were wound w i t h a l a y e r of asbestos c o r d f o r i n i t i a l l a g g i n g . T h i s was f o l l o w e d by a l a y e r of asbestos cement. A s m a l l s e c t i o n of t h e C o t t r e l l tube and two s m a l l openings at the j u n c t i o n of t h e tube to the disengagement chamber were l e f t unlagged f o r o b s e r v a t i o n o f the pumping a c t i o n . The e x t e r n a l h e a t e r f o r t h e b o i l e r was wound on the l a y e r of a s b e s t o s cement and c o n s i s t e d o f 28 t u r n s of No. 22 B8S gauge nichrome r e s i s t a n c e w i r e . I t was wound r i g h t from the stopcock a t the bottom of the b o i l e r t o the base of the f i l l i n g tube, the l a s t t u r n s being kept i n p l a c e by a few wrappings of t h i n asbestos c o r d . A p o t e n t i a l of about 3$ v o l t s g i v i n g 2 . 4 amp on a s m a l l v a r i a c was u s u a l l y found s u f f i c i e n t f o r f a i r l y low b o i l i n g m i x t ures. The e x t e r n a l h e a t e r was covered by another l a y e r of asbestos cement t o g i v e i n s u l a t i o n t o t h e w i r e . The whole apparatus was mounted on a s m a l l p l a t f o r m 24" by 16" w i t h u p r i g h t s t e e l rods c o n v e n i e n t l y p l a c e d 14" a p a r t . P l a t e I I shows the apparatus without l a g g i n g C. Refractometer The r e f r a c t o m e t e r employed i n t h i s r e s e a r c h f o r a n a l y s i s was a new instrument of the Spencer Abbe t y p e . A d e s c r i p t i o n o f the p r i n c i p l e s and working p a r t s i s g i v e n i n most textbooks on Organic A n a l y s i s (112) and p h y s i c a l methods i n o r g a n i c chemistry. I t was equipped w i t h Amici compensating prisms so t h a t a white l i g h t source c o u l d be used i n s t e a d o f monochromatic l i g h t . The s c a l e o f the r e f r a c t o m e t e r i s c a l -i b r a t e d d i r e c t l y i n r e f r a c t i v e index as measured w i t h t h e D l i n e of the sodium spectrum. I t may be read a c c u r a t e l y t o the t h i r d decimal p l a c e and the f o u r t h may be estimated with an accuracy of - 0 . 0 0 0 2 . The prisms were kept at the temperature c bath c o n t r o l l e d w i t h i n ± 0 . 0 5°C. The temperature on the r e -fractomet er could be read d i r e c t l y t o 1°C and estimated w i t h i n - 0 . 2°C on a c a l i b r a t e d thermometer. T h i s was about the l i m i t of accuracy i n r e a d i n g the r e f r a c t i v e index s i n c e a change i n temperature of 0 . 2°C changed the r e f r a c t i v e index of benzene by approximately . 0 0 0 1 . Gibson and K i n c a i d (41) g i v e a s i m i l a r v a l u e f o r the experimental change i n the r e f r a c t i v e index o f benzene w i t h temperature. K u r t z , Amor and Sankin (67) have made a thorough review o f the e f f e o t o f temperature on d e n s i t y and r e f r a c t i v e index and summarized a v a i l a b l e d a t a . equation They showed t h a t the Eykman\represents e x p e r i m e n t a l d a t a f o r the e f f e c t o f temperature on the d e n s i t y and r e f r a c t i v e index of o r g a n i c compounds q u i t e a c c u r a t e l y over a wide range of temperature. I t was developed by J.F. Eykman (32) as an empir-i c a l formula n 2 j- 1 x 1 - C (33) n + 0.4 d r e l a t i n g the r e f r a c t i v e index n, the d e n s i t y d (both at the same temperature) and a constant C which was s t a t e d t o be independent o f temperature f o r the same compound. The r e f r a c t -ometer was c a l i b r a t e d before and a f t e r any s e r i e s of r e a d i n g s by means o f a s m a l l p i e c e o f g l a s s f u r n i s h e d w i t h the i n s t r u -ment. This g l a s s main t a i n s a constant r e f r a c t i v e index and i s h e l d i n p l a c e on the r e f r a c t o m e t e r p r i s m by o a p i l l a r y a c t i o n w i t h a very s m a l l q u a n t i t y o f mono-bromonaphthalene. As a f u r t h e r check doubly d i s t i l l e d water was used and i t gave a r e f r a c t i v e index o f 1.3330 a t 20°C as compared t o 1.33299 g i v e n i n the l i t e r a t u r e . D. P l a t i n u m R e s i s t a n c e Thermometer For a c c u r a t e temperature measurement a p l a t i n u m r e s -i s t a n c e thermometer No. 169314 w i t h a N a t i o n a l Bureau o f Standards C e r t i f i c a t e dated August 17, 1937, was used. Where i t was i m p r a c t i c a l t o use t h i s thermometer an a c c u r a t e mercury thermometer was c a l i b r a t e d w i t h i t a t s h o r t temperature i n t e r -v a l s . The principle of the platinum resistance thermometer is based on the change in resistance of platinum with temper-ature. This change i s positive with an increase in temperature and can be very accurately reproduced with pure platinum. The National Bureau of Standards which calibrates this type of thermometer issue a certificate giving the value of the resis-tance of the ice point, Ro; the fundamental interval (the difference in resistance between the boiling and freezing points of pure water), R1G0 - Ro = F; and , the Callendar constant, which-is obtained from the sulfur point. Calculation of the temperature i s made by means of the Callendar Equation (13), t - fHt-Ro\ 1G0 +Sf{ t \ 2 - / t \ l Platinum resistance thermometers should be recalibrated at least every five years i f they undergo a reasonable amount of use. The resistance of the platinum may change somewhat with time - and as a Consequence of handling. The ice point of the ther-mometer should be checked at least once a month and the value for Ro should not vary more than .002 ohms from the N.B.S. value (2). In the case where the deviation i s too great for accurate laboratory resistance thermometry, the bridge should, be checked for calibration. If i t appears to be a l l right, the resistance thermometer should be checked or sent into N.BiS. for recalibration. Measurements of resistance were made on a Leeds and Northrup 5-dial decade bridge. A commutator with mercury contacts was used to overcome the problem of lead resistances. The bridge and commutator are described in the Bulletin of the Bureau of Standards by E.J. Mueller (8l). The ice point of the thermometer was checked by the method given by Busse (11), and found to deviate by + .00045 ohms from that given by N.B.S. This error i s quite insignificant for the higher temperature readings but becomes quite important i n the lower temperature range from 0° to 10°C. Consequently, in the measurement of the freezing point of benzene such deviations were found to be quite significant. CHAPTER V  MATERIALS A. Benzene A commercially pure grade of benzene as supplied by Merck & Co., Inc., was used. .It was thiophene free and eon-formed to A.C.S. specifications with a boiling range from ' 79.5°C to 8l.0°C. The freezing point minimum was given as 5.2°C Lot analyses for i t s maximum impurities were given as follows:-Non-volatile > • 0.001$ Acid or a l k a l i - - - - - - passes test Substanoes darkened by H2SO4.-passes test Sulfur compounds (as S)- * 0,003% Thiophene 0.000$ Water - — - - - - - - - - passes test 1. I n i t i a l Purification The benzene was further purified according to the better features of purification reported in the papers of Gilmann and Gross (44), Glanville and Sage (46), Gornowski et a l (51) and Tompa (130). About 1 l i t e r of the CP. benzene was placed i n a large (2 l i t e r ) separatory funnel and agitated for at least 10 minutes with CP* concentrated sulfuric acid. Only a slight turbidity appeared, the sulfuric acid was allow-ed to separate out for about 20 minutes and was then drained away through the stop-cock at the bottom of the funnel. The benzene was washed twice with 500 ml. portions of d i s t i l l e d water and in each case was allowed to stand for some time in order that oomplete separation take place before drainage. A solution of 0.1 N sodium hydroxide was made up of Baker's CP. NaOH in d i s t i l l e d water. The benzene was washed with two 500 ml. portions of this solution each for- about ten minutes followed by two washings with d i s t i l l e d water. About 150 ml. of mercury, highly purified as previously described, were then added to the benzene and thoroughly agitated. A slight scum of black, powdery material was l e f t on the surface and may have been some combination of meroury and sulfur. The mercury was then removed and the benzene was f i n a l l y washed three times with d i s t i l l e d water. On the f i n a l washing the benzene and water were allowed to separate completely and the water was drained. The benzene was poured out from the top of the fun-nel to prevent contamination with the water which had been drained at the lower outlet. Containers used from this point on were always thoroughly washed, rinsed with d i s t i l l e d water and oven dried. Baker and Adamson sodium metal of commercially pure quality was taken directly from the t i n and ribbon was cut on the sodium press. The ribbon was pressed directly into the benzene in a d i s t i l l a t i o n flask so as to prevent oxidation of sodium metal on standing in the atmosphere. The flask was then stoppered loosely with a ground glass stopper and the ben-zene was allowed to stand for one week. Thus any hydrogen formed from the reaction of sodium with water was freely evolved. 2. D i s t i l l a t i o n of Benzene The s t i l l employed for benzene d i s t i l l a t i o n i s illustrated in Fig. 30a. A is a one l i t e r s t i l l pot with 19/4-2 standard taper joint and heated by a Glas-Col heating BENZENE. ST ILL . mantel c o n t r o l l e d by a s m a l l v a r i a c type t r a n s f o r m e r . The column B i s s i l v e r e d , vacuum j a c k e t e d and packed w i t h a mix-t u r e of g l a s s beads, h e l i c e s , and s h o r t l e n g t h s of t u b i n g . The packed p o r t i o n of the column i s 122 cm (4 f t . ) l o n g and the i n t e r n a l diameter i s 25 mm. C i s a s t i l l head which i s s u i t -a b l e f o r both vacuum and atmospheric d i s t i l l a t i o n . A ground g l a s s j o i n t r educer adapts the base of the s t i l l head to the top o f the column. A t o t a l immersion thermometer graduated i n d i v i s i o n s o f 1.0°C r a n g i n g from -10° t o 110°C was used t o measure temperature of the d i s t i l l i n g vapors. The r e f l u x adjustment was c o n t r o l l e d by a p r e c i s i o n - g r o u n d stop-oock which c o u l d e a s i l y g i v e r e f l u x r a t i o s as g r e a t as 100:1 E (Fig.30b), a new type of vacuum adapter as a d v e r t i s e d by the S c i e n t i f i c Apparatus "Glass~~Co. and a t t r i b u t e d . t o E . Theimer (126) 9was i n c o r p o r a t e d i n t o the system. I t was found extremely convenient i n the e l i m i n a t i o n of stop-cocks and a s s o c i a t e d greases as found i n the o l d e r c o n v e n t i o n a l type o f vacuum adapter (128). The p r i n c i p l e of o p e r a t i o n i s merely the a p p l i c a t i o n of atmospheric p r e s s u r e through a two-way top t o a s m a l l v a l v e ground to f i t a c o n s t r i c t i o n . T h i s v a l v e c l o s e s the a c t u a l d i s t i l l a t i o n system and permits the r e c e i v e r t o be changed without d i s t u r b a n c e of e q u i l i b r i u m w i t h i n the column. The complete s t i l l was mounted i n t o a s t u r d y frame i n which i t c o u l d be assembled or dismantled r e a d i l y . P l a t e I I I i s a photograph of the u n i t s e t up f o r vacuum d i s t i l l a t i o n . The e f f i c i e n c y of the column was determined by the method d e s c r i b e d by Morton (80) and d i s c u s s e d i n d e t a i l i n a l a t e r s e c t i o n . A t t o t a l r e f l u x the column was found t o have 14 P L A T E : HL - BEN2fc~Nk 5 T I L L - t h e o r e t i c a l p l a t e s w i t h an H.E.T.P. o f 8 . 5 6 cm. A vacuum d i s t i l l a t i o n was attempted on the benzene. However, d i f f i c u l t i e s were encountered due to the h i g h v o l a t i l i t y of benzene and the heavy l o s s t o the f o r e pump and atmos-phere. This was found t o be the case even when the r e c e i v e r was kept i n a f r e e z i n g mixture of d r y i c e and acetone and the t r a p i n f r o n t of the forepumpwas s i m i l a r l y immersed. S i n c e benzene i s v e r y s t a b l e and i t s b o i l i n g temperature a t atmos-p h e r i c p r e s s u r e i s q u i t e low ( 8 0 . 1 ° C ) , i t was decided t h a t there i s l i t t l e advantage i n d i s t i l l i n g benzene under vacuum. Hence atmospheric d i s t i l l a t i o n was c a r r i e d out. I n i t i a l l y , the r e f l u x r e g u l a t o r was a d j u s t e d f o r t o t a l reflux»and the benzene was r e f l u x e d over sodium r i b b o n f o r t e n hours. The r e f l u x r a t i o was then set f o r 3 0 : 1 and an i n i t i a l f r a c t i o n of about 1 0 0 ml was c o l l e c t e d and d i s c a r d e d . The middle f r a c t i o n which came over a t a temperature of from 8 0 . 0 ° C to 8 0 . 1 ° C was c o l l e c t e d and saved. 3 . F r a c t i o n a l R e o r y s t a l l i z a t i o n The d i s t i l l e d benzene was p l a c e d i n a l a r g e 1 - l i t e r erlenmeyer f l a s k and was s l o w l y f r o z e n i n a d r y - i c e box. I t was allowed t o melt p a r t i a l l y and the f i r s t 2 5 ml of l i q u i d were d i s c a r d e d . The f r e e z i n g p rocess was r e p e a t e d and the change i n p u r i t y was f o l l o w e d by r e f r a c t i v e index. However, s i n c e there was no d e f i n i t e change i n r e f r a c t i v e i ndex w i t h r e o r y s t a l l i z a t i o n , the m a t e r i a l was c o n s i d e r e d t o be pure and two r e c r y s t a l l i z a t i o n s s u f f i c i e n t . The p u r i f i e d benzene was then s t o r e d over f r e s h l y cut sodium i n a ground g l a s s - s t o p p e r -ed f l a s k . 4. Check on P u r i t y There were three separate d e t e r m i n a t i o n s made on the p u r i t y of the benzene, - r e f r a c t i v e index, f r e e z i n g p o i n t and d e n s i t y . Each checked w i t h i n experimental e r r o r w i t h v a l u e s g i v e n i n the l i t e r a t u r e . (a) R e f r a c t i v e Index The Spencer Abbe-type r e f r a c t o m e t e r was ma i n l y used f o r most of the checks on p u r i t y w i t h r e f r a c t i v e index. Read-ings were taken a t both 20GC and 25°C to compare w i t h l i t e r a t u r e v alues a t the two temperatures, and were found to be 1.5010 and 1.49 79, r e s p e c t i v e l y . The v a l u e s of other authors, a r e g i v e n i n Table I. (b) F r e e z i n g P o i n t The f r e e z i n g p o i n t of benzene was determined on an apparatus s i m i l a r t o t h a t o f Mair, - Glasgow, and R o s s i n i (74). F i g u r e J l i s a diagrammatic i l l u s t r a t i o n of the u n i t which was made s u i t a b l e f o r f r e e z i n g p o i n t d e t e r m i n a t i o n s or both s o l i d s and l i q u i d s by the i n t r o d u c t i o n of a h e a t e r . A i s a s i l v e r e d Dewar f l a s k 18 cm h i g h w i t h an i n t e r n a l diameter of 6.5 cm»B i s a sm a l l u n s i l v e r e d Dewar (JO mm i n t e r n a l diameter) f i t t e d w i t h an o u t l e t and stopcock f o r e v a c u a t i o n . The s m a l l Dewar was lagged w i t h asbestos c o r d and w i r e d w i t h 27 t u r n s of No. 22B S nichrome w i r e . The heater was found t o have a r e s i s t a n c e of 15 ohms and c o u l d be e a s i l y c o n t r o l l e d w i t h a v a r i a c . A t h i n l a y e r of asbestos paste was added as i n s u l -a t i o n f o r the h e a t e r . As f u r t h e r i n s u l a t i o n a g a i n s t the c o o l -ant a copper c o n t a i n e r was s l i p p e d over t h e heat e r and l a g g i n g 110 V. A.C LEGEND A - LARGE DE WAR B " U N S I L V E R E D DEWAR // i TH STOPCOCK C C O P P E R J A C K E T D - INSULATION A N D HEATER WIRES EL - S T I R R E R F- PLATINUM RESISTANCE TH ERMOMETER F I G 3 I - F R E E Z I N G P O I N T A P P A R A T U S and h e l d A i n p l a c e by means of a broad r i m s o l d e r e d on a t the top. The rubber stopper i n B accommodates the p l a t i n u m r e s i s -tance thermometer E and s t i r r e r E . In o p e r a t i o n , the c o o l i n g mixture i s added t o A and, i n the case of benzene, a d r y i c e and acetone mixture i s v e r y e f f e c t i v e . P u r i f i e d benzene i s p l a c e d i n B t o a h e i g h t s u f -f i c i e n t t o cover the c o i l e d p o r t i o n of t h e p l a t i n u m r e s i s t a n c e thermometer. The temperature of the benzene should be around 20°C so t h a t a r e a s o n a b l y l o n g c o o l i n g curve can be ob t a i n e d . The i n n e r Dewar i s evacuated by a vacuum pump and i s then p l a c e d i n the c o o l a n t . A r e s i s t a n c e versus time curve i s ob-t a i n e d by t a k i n g the r e s i s t a n c e r e a d i n g every minute f o r the f i r s t t e n degrees of temperature and then every t h i r t y seconds f o r the l a s t few degrees. The c o o l i n g r a t e should be about 1°C or approx. 0.01 ohms i n 1 to 3 min. i n the range 3° t o 10° above the f r e e z i n g p o i n t . The heat t r a n s f e r can be a d j u s t e d by i n t r o d u c i n g a i r i n t o the j a c k e t of the i n n e r Dewar or ev a c u a t i n g down f u r t h e r . A f t e r r e c o v e r y from u n d e r c o o l i n g i s s u b s t a n t i a l l y complete, the r e s i s t a n c e i s recorded a t i n t e r v a l s of one minute a g a i n and f i n a l l y a t 3 minute i n t e r v a l s . Read-ings are continued u n t i l d i f f i c u l t y i s encountered i n s t i r r i n g . The c o o l i n g curve f o r benzene i s shown i n f i g u r e 32. A value of 3.A3A-°C was obtained f o r the f r e e z i n g p o i n t and checks r e a s o n a b l y w e l l w i t h v a l u e s g i v e n i n the l i t e r a t u r e ( T a b l e I } . Si n c e the platinum r e s i s t a n c e thermometer employed has not been checked by the N a t i o n a l Bureau of Standards s i n c e 1937, some of the constants may be out c o n s i d e r a b l y . A t low temperatures e r -r o r i n the i c e p o i n t c a l i b r a t i o n f o r Rft can be v e r y s i g n i f i c a n t . FOIUA C2 r " c H b±;: IPS ±i:P i u^-pr; '_._,, J ; j . 1 : : ; .J u j . . tfiJjJTLu.Li'......ctpj i i t , - ' - ; ;-TJ-:-. the! " "*"' 3 ^ i - -Hi : * e m : $ f f i : a 5 ^ f e . . . u * i ^ :.::iil.; "c 4^ iJ:;_ ;a:'ni'ji_cLc. ; 1,1*11 n r i j - L u - u - i - u >+iu>-u*ii> . 4 » . U « I , I I I I I I I H I I I I I • • - a r i n i M I I ' l i T t n V ^QlHj^fktt-i *fe-S^. 4 0 . 5 0 6 0 SB 70 (c) D e n s i t y D e n s i t y measurements were c a r r i e d out i n a vacuum-jac k e t e d 25 ml. pycnometer b o t t l e . The pycnometer was c a l -i b r a t e d w i t h c o n d u c t i v i t y water a t 2J?0C. For d e n s i t y d e t e r -minations on benzene the b o t t l e was thoroughly washed w i t h soap and d i s t i l l e d water and d r i e d w i t h warm a i r . A b s o l u t e a l c o h o l was used t o remove any excess water and a r i n s e w i t h ether e l i m i n a t e d the a l c o h o l . The b o t t l e was p l a c e d i n a vacuum d e s s i c a t o r f o r a t l e a s t one hour p r i o r t o weighing. I t was weighed w i t h c a l i b r a t e d weights a c c u r a t e l y to 0.1 mg and then f i l l e d w i t h benzene which was below 25°C. The b o t t l e was then c l o s e d f a i r l y t i g h t l y and p l a c e d i n a constant "temperature water bath. The temperature o f the bath was maintained a t / 25°G - .02 a c c o r d i n g t o a c a l i b r a t e d thermometer. A f t e r one hour, the b o t t l e was removed from the bath, excess benzene was wiped o f f w i t h t i s s u e paper and the b o t t l e and benzene were weighed a c c u r a t e l y as b e f o r e . The value obtained f o r the d e n s i t y of benzene at 25°C was 0.87368 gms f m l . There are o n l y a few values i n the l i t e r a t u r e to compare w i t h and they are l i s t e d i n Table I . TABLE I PHYSICAL DATA FOR BENZENE FROM THE LITERATURE AUTHOR REFRACTIVE FREEZING- DENSITY INDEX POINT Renault (100) 4.45°C Lachowitz ( 6 9 ) 5.42 ± 0.02 Mangold (75) 5.5° Linebarger (73) 5.4 Smith and Manzies(114) 5.40 Washburn and Read (138) 5.48 Timmermans and Martin (127) 5.50 Wojciechowski(144) 25 n D = 1.4981 5.51 O.87366 Gilman and Gross (44) 5.42-5.46 I.C.T. (58) •r- 1.5014 5.49 - 0.001 d|° = O.8788 Scatchard, Woodand Mochel (111) 5.53 Allen, Lingo, and Felsing (1) - 1.4980 5.5 0.8732 Eglof f ( 29) - 1.4977 5.49 Gibbons et al(40) n 2 5  nD - 1.4979 5.50 Glasgow, Murphy, Willingham, and Rossini (47) 5.53 Tompa (130) ,25 nD « 1.4981 5.49 Oliver, Eaton, and Huffman (85) 5.50 Handbook of Chemistry2Q and Physics (55) n. = 1.50142 5.51 d4 - 0.8794 Glanville and Sage (46) 25_ nD = 1.5013 TABLE I (CONT'D) AUTHOR REFRACTIVE INDEX FREEZING POINT 'DENSITY Emerson, and on 2 5 C u n d i l l (30) n£ =1.5011 d 4 = 0.8732 n^p = 1*4979 N a t l . Bur. Stand- PO ards (82) n£ » 1.30II 25 n r / « 1.4979 Pesce (97) n ^ 5 = 1.49825 D ^ = 0.87362 Cohen and B u i j ( l 9 ) D ^ = 0.87378 Smyth and W a l l s oc (116) n£ = 1.49815 Gibson and K i n c a i d 25 25 ( 4 1 ) n D - 1.4983 D4 = 0.87366 * 0.0002 B. Butanol The normal b u t y l a l c o h o l used was of a commercially pure grade s u p p l i e d by F i s h e r S c i e n t i f i c Company. The l o t a n a l y s i s data was g i v e n as f o l l o w s : B o i l i n g Range 116° - 117°C Free A c i d ( a s B u t y r i c ) 0.01% N o n - v o l a t i l e matter 0.01% F u r t h e r p u r i f i c a t i o n was c a r r i e d out by f i r s t r e f l u x i n g two l i t e r s of the bu t a n o l over f r e s h l y i g n i t e d c a l c i u m oxide f o r f o u r hours. A three-necked f l a s k was used and the condensers were h e l d i n p l a c e w i t h ground g l a s s j o i n t s . C a l c i u m c h l o r i d e d r y i n g tubes were att a c h e d to the ends of the condensers i n order t o p r o t e c t the but a n o l from atmospheric m o i s t u r e . The buta n o l was decanted from the lime and r e f l u x e d f o r another f o u r hours w i t h magnesium t u r n i n g s . I t was f i n a l l y d i s t i l l e d i n a vacuum-jacketed, s i l v e r e d column s i m i l a r t o t h a t used i n the benzene d i s t i l l a t i o n . The column was packed w i t h g l a s s h e l i c e s f o r 3^ l / 2 inches (93 cm) of i t s l e n g t h . The d i s t i l -l a t i o n was c a r r i e d on at a reduced p r e s s u r e o f approximately 500 mm as obtained by a water s u c t i o n pump. The r e f l u x r a t i o was s e t a t 30:1 and the r a t e o f d i s t i l l a t i o n was a d j u s t e d j u s t below f l o o d i n g by means of a h e a t i n g mantel c o n t r o l l e d w i t h a v a r i a c . The p u r i t y o f the but a n o l was checked by Emerson and C u n d i l l w i t h r e s p e c t t o r e f r a c t i v e index and d e n s i t y . A t 20°C the r e f r a c t i v e index was found t o be 1.3994 and the den-s i t y was determined as O.8063 a t 25°C A comparison w i t h l i t e r a t u r e v a l u e s i s g i v e n i n Table I I . 69 TABLE H PHYSICAL DATA EOR BUTANOL FROM THE LITERATURE AUTHOR REFRACTIVE INDEX DENSITY B.P. Webb and L i n d s l e y (141) 20 n£ = 1.5990 118°C B r u n e l l , Crenshaw, and Tobin (9) n ^ 5 = 1.5974 d4 E E 0.8057 117.71 Smyth and Stoops (115) 20 n D - 1.39922 25 d 4 S 3 0.8060 Jones and C h r i s t i a n (63) d4 S 3 0.8057 Washburn and Stand-shaw (140) ^ E 3 O.8O649 A l l e n , L i n g o , and F e l s i n g (1) 25 n D - 1.3974 a 2 3  d4 0.8057 Handbook o f Chem. and Phys. (55) 20 Dp - 1.39931 20 V 0.80978 117.71 G. B i p h e n y l 1. R e o r y s t a l l i z a t i o n The b i p h e n y l used was of unknown p u r i t y s u p p l i e d by Eastman Kodak Company. The i n i t i a l p u r i f i c a t i o n c o n s i s t e d e s s e n t i a l l y of r e o r y s t a l l i z a t i o n from a b s o l u t e a l c o h o l . How-ever, t h e r e was a c o n s i d e r a b l e amount o f mechanical i m p u r i t y such as d i r t which c o u l d be o n l y removed by f i l t r a t i o n . About 250 grams of the c r y s t a l l i n e b i p h e n y l were i n t r o d u c e d i n t o a o n e - l i t e r erlenmeyer f l a s k . A b s o l u t e e t h y l a l c o h o l was added u n t i l i t j u s t covered the b i p h e n y l . Then the mixture was heated j u s t t o b o i l i n g u n t i l a l l the b i p h e n y l went i n t o s o l u t i o n . The s o l u t i o n was q u i o k l y f i l t e r e d i n a steam heated f u n n e l w i t h s u c t i o n . The f i l t r a t e was allowed t o c o o l s l o w l y a t room temperature and the b i p h e n y l r e a d i l y c r y s t a l l i z e d out without s e e d i n g . F i l t r a t i o n o f the c r y s t a l l i z e d b i p h e n y l was c a r r i e d out i n a l a r g e BQchner f u n n e l (6.j> i n c h diameter) w i t h s u c t i o n . One l a y e r of Whatman F i l t e r Paper No. 1 was found s u f f i c i e n t v f o r the f i l t r a t i o n . The c r y s t a l s were washed twice w i t h c o l d a b s o l u t e a l c o h o l d u r i n g each f i l t r a t i o n . R e o r y s t a l -l i z a t i o n of the b i p h e n y l was c a r r i e d out t h r e e times and on the t h i r d f i l t r a t i o n the mixture was kept somewhat warmer to e l i m i n a t e the h i g h e r m e l t i n g i m p u r i t i e s . With each subsequent r e o r y s t a l l i z a t i o n the f i l t r a t e was found to be much c l e a r e r than p r e v i o u s l y . When water s u c t i o n had removed a l l the a l -c o h o l , the c r y s t a l s were spread out between s e v e r a l l a r g e sheets of f i l t e r paper and were d r i e d a t atmospheric temper-a t u r e and p r e s s u r e f o r 24 hours. 2. D i s t i l l a t i o n (a) Determination of Conditions Since biphenyl has a melting point of around 69°C and a boiling point of approximately 254°C, i t seemed quite imprac-t i c a l to d i s t i l i t at atmospheric pressure. Gn the other hand, i f the pressure i s reduced sufficiently there might be only sublimation with a resulting clogging up of the lines and other d i f f i c u l t i e s . The ideal d i s t i l l a t i o n temperature appeared t o be at about 125°C when the calculated vapor pressure i s very nearly 14 mm. Fig. 33 gives the vapor pressure curve for b i -phenyl from Garrick (38)*nas calculated from the equation, log P (mm) - 7.0220 - 1723 - 245700 (57) T T ^ which was f i t t e d to the data of Chipman and Peltier (18). These researchers experimentally determined thempor pressure above l62°C and found the equation to f i t within experimental error. There have been very few determinations made on the vapor pressure of biphenyl and those have usually been above 150°€ . (38, 791. The determination of an optimum in temperature and pressure was determined on a small semi-micro s t i l l (Fig.34) designed by Mr. A. Werner and built by Mr. W. Pye of the Chemistry department. In order to maintain a certain constant pressure above that given by a mechanical forepump, a pressure regulator, which w i l l be described, had to be installed. Hot water was supplied to the condenser to prevent the s o l i d i f i c -ation of the biphenyl on i t s way to the receiver. About three grams of biphenyl were introduced into s I Z O I AO TEMPE.RATURE 2 6 0 Fia.34 - SELMJ - MICRO 6 T I L L the s t i l l p o t . A l l ground g l a s s j o i n t s were s e a l e d w i t h a non-v o l a t i l e , s t i f f stopcock grease (6enco. No. 15522-A). The s t i l l pot was heated i n a g l y c e r i n e bath and the column was c a r e f u l l y watched f o r the r i s e of b i p h e n y l vapors. Temperature e q u i l i b r -ium was d i f f i c u l t t o achieve w i t h such a s m a l l q u a n t i t y o f m a t e r i a l , but s u f f i c i e n t d ata was obtained f o r an approximate i d e a o f c o n d i t i o n s r e q u i r e d . At 30 mm of mercury pressure the temperature r e c o r d e d was 141°C. (b) B i p h e n y l S t i l l Developed Although mention i s made i n the l i t e r a t u r e (130) of p u r i f i c a t i o n of such substances as b i p h e n y l by vacuum d i s t i l l -a t i o n , t h e r e appears t o be a g e n e r a l p a u c i t y of the d e t a i l s f o r a s t i l l f o r such a d i s t i l l a t i o n . The l i t e r a t u r e was r e v i e -wed from the e a r l i e s t chemical a b s t r a c t s t o the presen t day. The o n l y mention o f such s t i l l s i s u s u a l l y found i n the case o f p l a n t - s c a l e p r o d u c t i o n , almost i n v a r i a b l y covered by pa t e n t s and not d e s c r i b e d . Haehn (53) i n 1907 d e s c r i b e d a s m a l l s t i l l f o r vacuum d i s t i l l a t i o n o f s o l i d substances. I t appeared r a t h e r i m p r a c t i c a l from the p o i n t of view o f h e a t i n g methods used to prevent s o l i d i f i c a t i o n . R e c e n t l y , a s m a l l s t i l l which c o u l d be used f o r s o l i d s was r e p o r t e d ( 2 5 ) . However, t h i s s t i l l was p r i m a r i l y designed f o r semi-micro q u a n t i t i e s o f a maximum of 20 ml. of m a t e r i a l and would not be s u i t e d t o our purpose. Consequently, i t was de c i d e d to d e s i g n and b u i l d a s m a l l s t i l l s u i t a b l e f o r the d i s t i l l a t i o n of l i t e r q u a n t i t i e s of b i p h e n y l . The s t i l l d e s c r i b e d here can be b u i l t without too much d i f f i c u l t y by one who has had a r e a s o n a b l e amount of experience i n g l a s s blowing. There i s n o t h i n g on the s t i l l 73 which, need be expensive, and i n our p a r t i c u l a r case most of the s t i l l and a c c e s s o r i e s were made from scrap m a t e r i a l s . 1 I t has been cbmpaotly assembled and i s r e a d i l y p o r t a b l e . The s t i l l i t s e l f i s i l l u s t r a t e d i n F i g . 35. The s t i l l pot A i s a 1 - l i t e r round-bottomed f l a s k w i t h a 29/42 standard t a p e r female j o i n t . Heat i s s u p p l i e d by a one l i t e r s i z e g l a s - C o l h e a t i n g mantle which i s c o n t r o l l e d by a s m a l l v a r i a c * The s t i l l pot was i n s u l a t e d from h a l f way up the bulb to the top of the j o i n t w i t h asbestos c o r d and asbestos cement. A column was made e s s e n t i a l l y i n two p a r t s , the lower packed p o r t i o n B which was vaouum-jacketed and s i l v e r e d , and the upper p o r t i o n f o r the thermometer. The packed p o r t i o n i s 25 cm. l o n g , of 20 mm. t u b i n g and the packing c o n s i s t s o f s i n g l e t u r n g l a s s h e l i c e s . A s m a l l p l a t i n u m s c r e e n was p l a c e d i n t o the t a k e o f f from the column t o prevent packing from p a s s i n g over i n t o the condenser and i n t e r f e r i n g w i t h the vacuum adap t e r . The j a c k -eted p o r t i o n of the column i s 15 cm. l o n g and the j a c k e t i s made of 37 mm. t u b i n g . S i l v e r i n g o f the j a c k e t was o a r r i e d out by the R o c h e l l e s a l t p rocess d e s c r i b e d i n the Handbook;of Chem-i s t r y and P h y s i c s (55) and i n Strong's U o d e r n P h y s i c a l Labor-a t o r y P r a c t i c e r t . (119) Two u n s i l v e r e d s t r i p s were l e f t i n the ja c k e t f o r o b s e r v a t i o n of the pa c k i n g . The j a c k e t was evacu-ated on a h i g h vacuum system f o r e i g h t hours and the pr e s s u r e as measured on the McLeod gauge was l e s s than a micron. The upper p o r t i o n of the column which was to e n c l o s e the thermo-meter was a l s o double-walled and equipped w i t h an o u t l e t f o r ev a c u a t i o n . T h i s was u n s i l v e r e d t o g i v e a completely '—"Si L E G E N D A h L l T E R S T I L L P O T B P A C K E D C O L U M N G V A C U U M - J A C K E T E D S T I L L H E A D D T H E I M E R V A C U U M A D A P T E R E E L E C T R I C A L L Y - H E A T E D R E C E I V E R F C O N D E N S A T I O N T R A P G. A S B E S T O S L A G G I N G H E L E C T R I C A L L Y - H E A T E D L A G G I N G T O A T M O S P H E R E A N D V A C U U M \ * -F FIC.35. -BIPHENYL ST ILL . 74 u n o b s t r u c t e d view of tne thermometer. The upper end was f i t -t e d w i t h a 10/30. I t c a r r i e s a broken thermometer w i t h a ground g l a s s j o i n t which was formed i n t o a s m a l l hook j u s t below the j o i n t t o h o l d a t o t a l immersion (0°-150°C) thermometer. The j a c k e t e d p o r t i o n of the upper column was made 23 cm. l o n g w i t h 12 mm t u b i n g i n s i d e and 21 mm t u b i n g forming the o u t s i d e j a c k e t . The whole l e n g t h was made such t h a t the thermometer could hang low enough f o r the bulb to be i n the d i r e c t stream of vapors d u r i n g d i s t i l l a t i o n . The j a c k e t was evacuated i n the h i g h vacuum system and was f i n a l l y degassed by a l a r g e bushy flame before being s e a l e d o f f . I n p l a c e o f a r e g u l a r type of condenser, a combinat-i o n o f vacuum adapter and condenser was employed. The adapter used.here is;, s i m i l a r to; the one on the benzene s t i l l except t h a t the o u t l e t t o the vacuum and atmosphere was made i n the form of a b u l b . I t serves as a t r a p to condense e s c a p i n g b i p h e n y l vapors. Hot water f o r the condenser was produced by means of a copper c o i l e n c l o s e d i n a l a r g e copper tube and heated w i t h a Bunsen flame. The temperature was noted on a thermometer i n a chamber between the h e a t e r and the condenser and was c o n t r o l l e d by a d j u s t i n g the s i z e of flame or the flow of water from the t a p . Those p o r t i o n s o f t u b i n g above and below the adapter condenser were lagged w i t h asbestos cord and asbestos cement. They were a l s o heated by 50 t u r n s o f No. 22 B&S nichrome wire embedded i n the l a g g i n g . The temperature of the lower lagged p o r t i o n was checked by means of a 0°-150° thermometer a l s o embedded in the lagging. Figure 3& shows the lagged and heated portions of the s t i l l in dotted lines. The resistance of the heater as measured by a Simpson ohmmeter was found to be 16 ohms. It was connected in series with the nichrome wire heater of the receiver and the voltage input was controlled by a variac. The receivers were made of 30 mm tubing in 12 inch lengths with "5*24/40 female joints. They were constricted and thickened in the upper portion for sealing under vacuum. In order that the biphenyl f i l l the tube completely, the receivers were wound with a large number of turns of No.22 B&S nichrome wire. Pressure Control and Measurement The d i s t i l l a t i o n of biphenyl was found to be very sensitive to pressure change, a variation of less than a mm Hg causing flooding in the column at lower pressures. Consequen-tl y , a simple as well as easily adjustable pressure regulator was required. Various types of manostats as described by Morton (80) and Williams (143) were reviewed. Pressure control devices with a leak valve as reported by Jacobs ( 6 l ) were con-sidered. Emerson and Woodward (31) describe a pressure control apparatus where any desired pressure can be maintained by the use of a special mercury cut off between the exhausted appar-atus and the vacuum pump. There are the more elaborate devices for automatic pressure regulation i n d i s t i l l a t i o n as f u l l y discussed by Coulson and Warne (23) in the Journal of Scientific Instruments* Theae regulators, i n most cases, are of a too complicated nature for a simple laboratory d i s t i l l a t i o n . A much, si m p l e r device g i v i n g c o n t r o l w i t h i n 0.5 mm was r e p o r t e d by Todd (129). Todd's apparatus i s a refinement of the crude arrangements used by Newman (84) and Donahoe e t a l (27). New-man's r e g u l a t o r was merely a wash b o t t l e so arranged t h a t gas .being pumped out of an apparatus had t o overcome a column o f mercury. Todd, u s i n g the same p r i n c i p l e , developed a r e g u l a t o r which c o u l d be r e a d i l y a d j u s t e d f o r d i f f e r e n t p r e s s u r e s . C e r t a i n m o d i f i c a t i o n s i n the Todd apparatus were found necessary to obviate the f r e q u e n t l o s s of mercury due to v i o l e n t t u r b u l e n c e . P r e s s u r e c o n t r o l was not too s e n s i t i v e when mercury was used, because a c e r t a i n p r e s s u r e had t o be b u i l t up w i t h i n the s t i l l b e fore i t overcame the column of mercury and bubbled out. By i n t r o d u c i n g a t r a p w i t h a s m a l l column of mercury between the r e g u l a t o r and the pump and r e d u c i n g the h e i g h t of the mercury i n the r e g u l a t o r i t s e l f t h i s problem was l a r g e l y overcome. This m o d i f i c a t i o n a l s o g i v e s the r e g u l a t o r a wider range o f u s e f u l n e s s s i n c e the head of mercury i n the t r a p can be v a r i e d . The whole r e g u l a t o r was made lon g e r w i t h an e x t r a annular r i n g on the i n n e r tube and r i g h t angle bends i n the arms l e a d i n g t o the pump and s t i l l t o prevent any l o s s of mercury d u r i n g t u r b u l e n c e . The f i n a l apparatus i s diagrammat-i c a l l y i l l u s t r a t e d i n F i g . 36. The p r e s s u r e i n the s t i l l was measured on a d i f f e r e n -t i a l , m e r c u r y - f i l l e d manometer w i t h a m i l l i m e t e r s c a l e c a l i b -r a t e d a g a i n s t a standard meter bar w i t h Bureau of Standards c e r t i f i c a t e . Atmospheric p r e s s u r e was measured on a C e n t r a l S c i e n t i f i c Co. mercury column type barometer, a c c u r a t e l y to TILTING ROD F I G . 3 6 . - P R E S S U R E R E G U L A T O R F O R V A C U U M D I S T I L L A T I O N . 77 + w i t h i n - 0.1 mm. Press u r e w i t h i n the s t i l l c o u l d he r e g u l a t e d and measured to - 0.2 mm. of Hg. The s t i l l and a l l a c c e s s o r i e s , w i t h the e x c e p t i o n of the forepump were mounted on a s o l i d wooden base covered w i t h a sheet o f t r a n s i t e . The base is. 23.5 by 12.5 inc h e s and has heavy v e r t i c a l rods 23 inches h i g h c o n v e n i e n t l y spaced. A c r o s s bar was put on f o r the attachment o f other clamps. The manometer was f a s t e n e d d i r e c t l y t o the base and i s i n f u l l view a t v ery c l o s e p r o x i m i t y t o the column. The whole apparatus i s compact and i s r e a d i l y dismantled or assembled i f n e c e s s a r y . P l a t e IV shows the apparatus assembled and ready f o r o p e r a t i o n . E f f i c i e n c y of the Column The t h e o r e t i c a l p l a t e e f f i c i e n c y of the column c o u l d not be checked too e a s i l y due t o l a c k of a r e f l u x a d j u s t o r . However, a f a i r l y q u a n t i t a t i v e check was ob t a i n e d by d i s t i l l i n g a mixture o f benzene and carbon t e t r a c h l o r i d e . The vapor l i q u i d e q u i l i b r i u m data f o r the system has been r e c e n t l y r e -p o r t e d by Bushmakin and Voe^kova (10), and i t has been shown t o be without \ an azeotrope a t atmospheric p r e s s u r e , c o n t r a r y t o prev i o u s r e p o r t s (135). I t was decid e d t o check the e f f i c i e n c y g r a p h i c a l l y by the method of McCabe and T h i e l e (77) as w e l l as a l g e b r a i c a l l y by the method of Dodge and Huffman ( 26). The m a t e r i a l s used were of a commercially pure grade without f u r t h e r p u r i f i c a t i d n ; The carbon t e t r a c h l o r i d e was a Baker and Adamson product and gave a r e f r a c t i v e index o f 1.4575 a t 25°C. The benzene used was the C.P. m a t e r i a l sup-p l i e d by N i c h o l s and gave a r e f r a c t i v e index of 1.4980 a t 25°C. PLATE E L - B I P H E N Y L S T I L L 78 The c o r r e s p o n d i n g values g i v e n by I.G.T. ( 60) are n ^ = 1.45734 and,n^= 1.49794, r e s p e c t i v e l y . The procedure employed f o r t h e e f f i c i e n c y check was t h a t des-c r i b e d by Morton (80). The v a l u e s of Bushmakin and "Voeikova were used f o r the v a p o r - l i q u i d e q u i l i b r i u m diagram and the r e f r a c t i v e index v s . composition curve was taken from the a n a l -y t i c a l d a t a g i v e n f o r the system i n the I n t e r n a t i o n a l C r i t i c a l Tables (60). The y - i n t e r c e p t f o r the o p e r a t i n g l i n e was ob-t a i n e d w i t h the e x p r e s s i o n g i v e n by Ward (135)» X C T . = y - i n t e r c e p t (58) P T T T The momenclature i s e x p l a i n e d i n the f o l l o w i n g paragraph. A l a r g e s c a l e graph was drawn f o r a c c u r a t e p l a t e d e t e r m i n a t i o n s . As a check on the g r a p h i c a l method of e f f i c i e n c y d e t e r m i n a t i o n , the equation of Dodge and Huffman f o r p a r t i a l r e f l u x was employed. n+1 - 2.303 2R + B (Log 2 A x c l + B -VB2-4AC . 2Axfi+B+l(B2-4AC _2l|B2-4AC \ 2Axf x + B B^4AC 2Ax c l+B+|B2-4ACJ 2 , + 1 l o g Axf, + B x f l + C 1 AX<£ + B x G 1 •+ C J (59) Where A = \R( 1- ) n = no. t h e o r e t i c a l p l a t e s B • R(<X -1) X f x = mol f r a c t i o n C C/4 i n S t i l l C = - x c i X f 2 = mol f r a c t i o n C^H^in S t i l l x C l - mol f r a c t i o n CCI4 i n d i s t i l l a t e x C 2 = mol f r a c t i o n C£H6 i n d i s t i l l a t e R = R e f l u x r a t i o ( r a t i o of r e f l u x t o product) °^ - r e l a t i v e v o l a t i l i t y For the value o f c ^ t h e r e l a t i o n of Bushmakin and Voeikova. was used, o( = 1.203 + 1.00203* (60) where x = mol p e r c e n t , CCJ&4 i n the l i q u i d . These authors a l s o p o i n t e d out t h a t t h i s r e l a t i o n f i t s the data of Rosanoff and E a s l e y (103) although the l a t t e r o n l y r e p o r t e d t h e i r r e s u l t s to 72 mol percent CC£ 4 . In the x-y diagram the v a l u e s of Rosanoff and E a s l e y were above those of Bushmakin and Voeikova i n d i c a t i n g a h i g h e r CC£4 content i n the vapor phase. A r e f l u x r a t i o : of 3»5 c o u l d be o b t a i n e d i n the column by proper adjustment of heat to the s t i l l p o t . Drops of the mixture r e f l u x i n g i n t o the s t i l l p o t a s w e l l as those going i n t o the r e c e i v i n g tube could be counted. However, t h i s was o n l y approximate s i n c e t h e r e were no c a l i b r a t e d drop counters.; The two methods used cheeked q u i t e c l o s e l y , i n each case g i v i n g about seven t h e o r e t i c a l p l a t e s w i t h an approximate H.E.T.P. o f 3.5 cm. Improvements f o r t h e S t i l l One of the major changes which c o u l d be made i n the s t i l l i s the i n s t a l l a t i o n of a device f o r r e f l u x adjustment. There have been s e v e r a l types f o r a vacuum column d e s c r i b e d i n the l i t e r a t u r e . One of the f a v o u r i t e designs i s t h a t i n c o r -p o r a t i n g a s o l e n o i d - a c t i v a t e d long-stemmed v a l v e , d e s c r i b e d i n simple arrangements by C o l l i n s and L a n t z (21) and D i e h l and Hart ( 2 4 ) , and i n a more complex form by Doty (28). Perhaps one type of r e f l u x r a t i o : head which c o u l d be most e a s i l y adapted t o the s t i l l d e s c r i b e d here i s the one r e p o r t e d by Human and M i l l s (57). They c l a i m t h a t t h e i r s t i l l h e a d i s s u i t -a ble f o r substances which s o l i d i f y above room temperature s i n c e the d i v i d i n g mechanism i s kept at the same temperature as the vapor* The r e f l u x r e g u l a t o r has the advantage i n t h i s case o f being simple w i t h e x t e r n a l manual c o n t r o l . D i s t i l l a t i o n Procedure The r e c r y s t a l l i z e d b i p h e n y l was p l a c e d i n the s t i l l p o t w i t h some b o i l i n g c h i p s (marble c h i p s ) . P r e s s u r e i n the s t i l l was maintained a t about 15 mm to gi v e the most e f f i c i e n t oper-a t i o n . Once d i s t i l l a t i o n commenced the s t i l l p o t h e a t e r was ad j u s t e d so t h a t t h e r e was a steady d r i p p i n g o f b i p h e n y l a t the r a t e : of about one drop every three seconds. The b i p h e n y l was d i s t i l l e d t w i c e , the middle f r a c t i o n b e i n g saved i n each case. On the f i n a l d i s t i l l a t i o n the b i p h e n y l was s e a l e d i n c o n s t r i c t e d r e c e i v i n g tubes so t h a t i t c o u l d be s t o r e d under vacuum. 3. Check on the P u r i t y of the B i p h e n y l The f r e e z i n g p o i n t o f b i p h e n y l was checked on the same apparatus as used f o r benzene. The c o o l i n g curve i s g i v e n i n F i g u r e 37 which g i v e s 69.191°C as the f r e e z i n g p o i n t f o r b i p h e n y l . T h i s value agrees f a v o u r a b l y w i t h v a l u e s g i v e n i n the l i t e r a t u r e as seen i n Table I I I which g i v e s a c h r o n o l -o g i c a l review of the f r e e z i n g p o i n t s found by d i f f e r e n t a u t h o r s . Ul <o V7 ss m ^-W-J-T-f-i-CP-U-^ :klj'fi: FOR B t R i A & N V L ' p - i -1 jjjjjjj l it ftyit'-bTrrht-hki;. H E r i 4 t . - t r t f H "rP-i;;,-:t) Si. tf-H-Witi HiHr Lrt i Era Hit Tf j-'-'H'-::-m i n i m i t : j " : } _ ' • • £>1 ft 20 30 4-0 T I M E - _\»-4 M I N U T E S 7 0 TABLE I I I FREEZING POINT DATA FOR BIPHENYL FROM. THE LITERATURE AUTHOR Jaequerod and Wassamer ( 6 2 ) Washburn and Read ( 1 3 8 ) ( 1 3 9 ) G a r r i c k ( 3 8 ) Chipman and P e l t i e r ( 1 8 ) Badger, Monrad, and Diamond ( 3 ) Huffman, Parks, and D a n i e l s ( 5 6 ) M o n t i l l o n , Kohrbach, and Badger ( 7 9 ) Spaght, Thomas, and Parks ( 1 1 7 ) Gilman and Gross (44) E g l o f f ( 29) Tompa ( 1 3 0 ) P.P. 6 9 . 0°C 6 8 . 9 3 69.O 6 9 . 2 , 1 3 6 . 6°F ( 6 9 . 2 ° C ) 6 9.I 1 3 6 . 6°F ( 6 9 . 2 P C ) 6 8 . 3 6 8 . 9 5 70 69.I CHAPTER VI  EXPERIMENTAL PROCEDURES A. Determination o f R e f r a c t i v e Index-Composition Curve  Ben zene-Butano1 The curve f o r the r e f r a c t i v e index a t 20°C versus mole f r a c t i o n of benzene f o r the benzene-butanol system was determined by Emerson and C u n d i l l (30) and w i l l n ot be d i s -cussed h e r e . I t i s shown, however, i n F i g u r e 38. Benzene-Biphenyl S i n c e b i p h e n y l has a m e l t i n g p o i n t of very n e a r l y 70°C and the system i s s o l i d f o r a wide range of composition at 25°C, i t was de c i d e d to determine the r e f r a c t i v e index at 70°C. C e r t a i n d i f f i c u l t i e s were encountered, however, due to the nature of the system and the r e l a t i v e l y h i g h temperature. The benzene was found t o evaporate v e r y r a p i d l y a t t h i s tem-p e r a t u r e and the b i p h e n y l tended t o s o l i d i f y b e f o r e i t was p l a c e d on the prisms f o r r e f r a c t i v e index r e a d i n g s . Consequen-t l y , a technique had t o be developed whereby e r r o r s due to these d i f f i c u l t i e s would be as n e a r l y e l i m i n a t e d as p o s s i b l e . Weighings a l l had to be made r e p i d l y and r e f r a c t i v e i n d i c e s had to be taken immediately. I t was found t h a t w i t h l a r g e r quan-t i t i e s of the system there was l e s s danger of e r r o r due to the l o s s of the more v o l a t i l e component. The procedure employed f o r the dete r m i n a t i o n s was as f o l l o w s . By c a l c u l a t i o n , the r a t i o by weight o f benzene t o b i p h e n y l was e v a l u a t e d f o r each .1 mole f r a c t i o n benzene from 0 to 1.0. A s e t of c a l i b r a t e d weights was used f o r a l l weighings. Weighing b o t t l e s were kept q u i t e warm on a hot p l a t e before s the l i q u i d , b i p h e n y l was added. A f t e r the weighing b o t t l e was c a r e f u l l y weighed alone, 2 to 1G grams of b i p h e n y l were added. An a c c u r a t e weighing was made of the b i p h e n y l and then the weight of benzene r e q u i r e d t o s a t i s f y a c e r t a i n mol f r a c t i o n was c a l c u l a t e d . The benzene was added w i t h an eyedropper u n t i l an approximate balance was a c h i e v e d . The accurate weight of ben-zene and b i p h e n y l was then o b t a i n e d . I f the c o n c e n t r a t i o n of b i p h e n y l was h i g h and the system s o l i d i f i e d somewhat d u r i n g the weighing,' i t was warmed s l i g h t l y on the hot p l a t e w i t h the cover of the b o t t l e down t i g h t l y . S e v e r a l drops of the s o l u t -i o n were p l a c e d on the lower p r i s m of the r e f r a c t o m e t e r and i t was c l o s e d immediately. Temperature e q u i l i b r i u m was allowed . to be reached and a t l e a s t t h r e e r e a d i n g s of r e f r a c t i v e i ndex were taken. I t was o f t e n found t h a t w i t h a c o l d mixture a change i n r e f r a c t i v e index of ,0030 would take p l a c e from the time the s o l u t i o n was f i r s t clamped i n p l a c e i n the prisms to the time temperature e q u i l i b r i u m was a t t a i n e d . The change i n r e f r a c t i v e index was always negative which i n d i c a t e d t h a t i t was m a i n l y due to the i n c r e a s e i n temperature of the s o l u t i o n . There appeared to be no l o s s of benzene once the prisms were clamped i n p l a c e s i n c e a f t e r about one minute when e q u i l i b r i u m was. reached t h e r e was no f u r t h e r change i n the index. A check was made on the g r e a t e s t p o s s i b l e e r r o r due to l a c k of e q u i l i b r i u m i n r e f r a c t i v e index d e t e r m i n a t i o n . Of the t h r e e readings u s u a l l y taken d u r i n g d e t e r m i n a t i o n there was seldom a g r e a t e r d i f f e r e n c e than .0010 i n r e f r a c t i v e index be-tween the f i r s t and l a s t r e a d i n g . T h i s corresponds t o a maximum e r r o r of 1 .5 mol percent i n the most c r i t i c a l r e g i o n of the curve, t h a t i s , a t a mole f r a c t i o n of between 0 .4 and 0 . 6 . However, s i n c e an average was. u s u a l l y taken, t h i s e r r o r would seldom exceed 1 .0 mol p e r c e n t . B. V a p o r - L i q u i d E q u i l i b r i u m Determination on the G i l l e s p i e - Eowler S t i l l . • ' The procedures used f o r the v a p o r - l i q u i d e q u i l i b r i u m d e t e r m i n a t i o n s i n the two systems s t u d i e d here v a r i e d somewhat due t o the nature of the systems. However, s i n c e the i n i t i a l runs made on the benzene-biphenyl system w i t h a h i g h mole f r a c -t i o n of benzene were s i m i l a r i n method t o those of benzene-butanol o n l y the former w i l l be d i s c u s s e d . The f i r s t f i f t e e n d e t e r m i n a t i o n s up t o a mole f r a c t -i o n o f 0.5 i n benzene were c a r r i e d out a t atmospheric temper-ature c o n d i t i o n s . The apparatus was c a r e f u l l y cleaned, f i r s t , w i t h -soap and water f o l l o w e d by 10% a l c o h o l i c - s o d i u m hydroxide s o l u t i o n ; I t was then r i n s e d w i t h c l e a r water; . 1 N hydro-c h l o r i c a c i d s o l u t i o n , c l e a r water aga i n and f i n a l l y w i t h t h r e e p o r t i o n s o f d i s t i l l e d water. Before being used the s t i l l was d r i e d i n an oven a t 120°C f o r twenty f o u r hours. Stopcocks and standard t a p e r j o i n t s were kept f r e e o f a l l greases or other l u b r i c a n t s . I n i t i a l l y , the b o i l e r was charged w i t h appr-oximately 200 ml of pure benzene-by way of the i n t e r n a l h e a t e r opening. The i n t e r n a l heater was set i n p l a c e and the v a r i a c l e a d s were a t t a c h e d . C o l d water was r u n through the condenser to keep the benzene from v a p o r i z i n g . The two h e a t e r s were turned on and a p o t e n t i a l of about 35 v o l t s was g i v e n the ex-t e r n a l heater w h i l e the v a r i a c f o r the i n t e r n a l h e a t e r was kept a t about 12 v o l t s . When the charge i n the b o i l e r had warmed up and pumping i n the C o t t r e l l tube had commenced, the i n t e r n a l h e a t e r was a d j u s t e d so t h a t smooth o p e r a t i o n took p l a c e . I t i s d i f f i c u l t t o p l a c e e x a c t l y the r i g h t q u a n t i t y o f l i q u i d i n the b o i l e r a t the o u t s e t so t h a t when the l i q u i d and vapor con-densate t r a p have f i l l e d adjustments may have t o be made. Gn b o i l i n g , the l i q u i d l e v e l should g e n t l y f l u c t u a t e i n the sm a l l bulb above the c a p i l l a r y tube and i n the s m a l l bulb a t the top of the l i q u i d t r a p . Attainment of temperature e q u i l i b r i u m u s u a l l y took about an hour. I t was found t h a t some mercury i n the t h e r -mometer w e l l helped s t a b i l i z e the temperature c o n s i d e r a b l y . When temperature f l u c t u a t i o n was no g r e a t e r than - ,05°C the b o i l i n g temperature was r e c o r d e d and samples of the l i q u i d and vapor condensate were removed as s i m u l t a n e o u s l y as p o s s i b l e . The o u t l e t s from the two t r a p s were always f l u s h e d out w i t h some of the l i q u i d b efore samples were taken i n order t o remove the stagnant l i q u i d . Samples were put i n t o weighing b o t t l e s w i t h ground g l a s s covers immediately f i t t e d i n t o p l a c e . Re-f r a c t i v e i n d i c e s were taken as r a p i d l y as p o s s i b l e and the same p r e c a u t i o n s were taken as i n the d e t e r m i n a t i o n of the r e f r a c t i v e index-composition curve. Atmospheric p r e s s u r e r e a d i n g s were taken as n e a r l y a t the same time as the o t h e r r e a d i n g s as p o s s i b l e . A Cenco mercury column type of~barometer, l o c a t e d about 15 f e e t above the l e v e l of the vapor l i q u i d e q u i l i b r i u m d eterminations i n the e a r l y p a r t of the runs a t atmospheric temperature and a t the same l e v e l i n the f i n a l runs, was emplo-yed. In subsequent runs benzene was drawn from the vapor condensate trap and pure biphenyl was added to the required height in the boiler to effect changes in composition. This procedure gave points on the x-y curve quite evenly spaced at reasonably close intervals. When the concentration of biphenyl in the system became greater than 0.5 mol fraction s o l i d i f i c a t i o n began to take place in. the liquid trap. Hence a hot air cabinet was required to make the remaining runs. This was found in a large o oven which could be controlled quite well around 70 C. Com-pressed air was run through the condenser and the stream of air was adjusted for whatever amount of cooling was required. It was found that at the temperature of the oven the benzene was vola t i l i z i n g at a tremendous rate. To circumvent this d i f f i -culty the condenser abotfe the vapor condensate trap was con-stantly kept f i l l e d with ice. At the high temperature at which the system had to be boiled a serious problem was faced in the severe bumping which usually accompanies such temperatures with biphenyl. This was .largely overcome by maintaining the internal heater at a maximum potential and providing ample ebullition within the boiler. As a check on equilibrium values taken under the different external temperature conditions, at least one of the determinations made previously at a particular composition was repeated. The two points were found to f a l l very nearly on the same curve as shown at about a mole fraction of 0.5 in Fig. 45. C. Determinations on the Vapor-Recirculation Apparatus About 40 ml of the solution were placed in the f i l l i n g tube J? which was a t t a c h e d t o the main c i r c u l a t o r y apparatus by means.of a ground g l a s s j o i n t . A v e r y l i g h t f i l m of s t i f f stopcock grease was put on the o u t s i d e edge of the j o i n t t o prevent any a i r leakage. Tap 1 to the manometer and h i g h vacuum system was kept c l o s e d and the sample was f r o z e n w i t h l i q u i d a i r . . Then w i t h mercury i n the manometer j u s t above tap J-and taps 1, 2, 4 and 5 open the system was evacuated. When a pressure below 10~^mm, as noted on the McLeod gauge, was reached, tap 1 was c l o s e d a g a i n and t h e sample was allowed to melt a t room temperature. The f r e e z i n g process was repeated a t l e a s t twice i n order t o i n s u r e t h a t the sample was t h o r o u g h l y de-gassed. To d i s t i l the sample i n t o b ulb A i t was f i r s t melted completely a t atmospheric temperature. C o l d water was kept running through the condenser N and bulb A was immersed i n a c o o l i n g mixture of d r y i c e and acetone. A low p o t e n t i a l of about 8 v o l t s was a p p l i e d t o the h e a t i n g tube and con n e c t i n g l i n e h e a t e r s by means of a v a r i a c . When the sample was com-p l e t e l y d i s t i l l e d over i n t o A, the f i l l i n g tube was s e a l e d o f f c a r e f u l l y a t x. Then w i t h the sample f r o z e n s o l i d i n A, t h e a i r baths Tg and T j were brought on temperature, and mercury was r a i s e d i n the manometer t o the l e v e l L. Taps 3 and 4 were c l o s e d and the h e i g h t o f mercury was noted i n the arm M by means of a cathetometer which r e a d a c c u r a t e l y to - 0.01 mm. The oathetometer was c a l i b r a t e d w i t h a standard meter bar having a Bureau of Standards C e r t i f i c a t e . The system i n bulb A was then allowed t o melt; constant temperature bath T-^  was f i l l e d w i t h o i l and brought on temperature. While temperature e q u i l i b r i u m was being reached, the mercury l e v e l was c a r e f u l l y watched a t L so th a t i t was not lowered out of the a i r bath by the i n c r e -a s i n g pressure w i t h i n the system. Such a mishap would cause • vapors of the system t o condense above the mercury and thus i n t r o d u c e e r r o r s i n t o the d e t e r m i n a t i o n s . Water t o condenser 0 was turned o f f and the c i r c u l a t i n g pump B was s t a r t e d . Tem-pera t u r e i n bath T,'was maintained w i t h i n - 0.002°C of t h a t required', w h i l e Tg and T j were kept a t 0.5°C and 2.5°C h i g h e r , r e s p e c t i v e l y . Attainment of e q u i l i b r i u m as noted by the constancy of p r e s s u r e i n manometer M r e q u i r e d about f o u r hours. A t t h i s p o i n t , pump P was stopped, the e q u i l i b r i u m vapor pressure was measured on M w i t h the mercury l e v e l s t i l l a t L i n s i d e the bath. C i r c u l a t i o n was then continued f o r another h a l f hour and the pre s s u r e was a g a i n noted. When the v a r i a t i o n i n p r e s s u r e be-tween s u c c e s s i v e r e a d i n g s d i d not exceed 0.1 mm of mercury, the vapor p r e s s u r e was re c o r d e d as the e q u i l i b r i u m p r e s s u r e . With the c i r c u l a t i n g pump stopped, the l i q u i d phase bulb A was s e a l e d o f f from the r e s t of the system a t y and z. Bath T-j_ h e a t e r s were turned o f f and the o i l was d r a i n e d through the tap a t the bottom. W i t h T 2 and T^ hea t e r s s t i l l on, the vapor phase was condensed i n t o bulb.B u s i n g a d r y ice - a c e t o n e c o o l i n g m i x t u re. Then B was s e a l e d o f f from the remainder of the c i r c u l a t o r y system a t W. The mercury i n the manometer was lowered j u s t above tap 3 and any non-condensable vapors were pumped o f f . Bath Tg was brought on temperature, mercury was r a i s e d t o the l e v e l L, tap 4 was c l o s e d , and the vacuum r e a d i n g was again taken. The condensed vapor phase was 89 melted, o i l "bath f i l l e d and brought on temperature and the p r e s s u r e r e a d i n g was r e c o r d e d . To i n t e r p r e t the readings o b t a i n e d f o r the p r e s s u r e of the two phases i n terms o f composition, a vapor p r e s s u r e -composition curve i s r e q u i r e d . Such a curve f o r benzene-b i p h e n y l was p r e v i o u s l y obtained by Gilmann, and Gross (44-). Of course, the apparatus used here c o u l d be r e a d i l y adapted f o r such r e a d i n g s by i n t r o d u c i n g a s i d e arm to the manometer and checking the vapor p r e s s u r e s of g r a v i m e t r i c a l l y determined samples. 90 CHAPTER V I I  RESULTS A. Benzene-Butanol The v a l u e s obtained f o r r e f r a c t i v e i ndex at 20°C u s i n g d i f f e r e n t compositions of the benzene-butanol system were determined by Emerson and C u n d i l l and a r e shown i n Table 4. E r r o r s due t o v o l a t i l i z a t i o n of the more v o l a t i l e compon-ent d u r i n g weighing and r e f r a c t i v e index d e t e r m i n a t i o n s were c a l c u l a t e d t o be no g r e a t e r than 0.065%. A l a r g e s c a l e p l o t of r e f r a c t i v e index versus composition was made f o r composition d e t e r m i n a t i o n s d u r i n g vapor l i q u i d e q u i l i b r i u m o p e r a t i o n s . F i g u r e 38 shows the curve on a reduced s c a l e . TABLE 4 REFRACTIVE INDEX - COMPOSITION DATA FOR BENZENE-BUTANOL AT 20°C MOLE FRACTION REFRACTIVE INDEX OF BENZENE. AT 20°C e.0000 1.3994 0.1133 1.4093 0.2019 1.4172 0.3020 1.4263 0.4096 1.4368 0.4999 1.4452 0.5992 1.4558 0.6979 1.4662 0.8009 1.4772 0.9005 1.4884 1.0000 1.5011 The vapor l i q u i d e q u i l i b r i u m v a l u e s o f r e f r a c t i v e index, and corresponding composition as determined i n t h i s r e s e a r c h on the G i l l e s p i e Fowler e q u i l i b r i u m s t i l l are ta b u l a t -ed i n Table 5« Values f o r e q u i l i b r i u m temperature and atmos-p h e r i c p r e s s u r e were a l s o r e c o r d e d and are shown. TABLE 5 EXPERIMENTAL VAPOR-LIQUID EQUILIBRIUM DATA FOR  " M Z E i N E . n-BU'TANOL Atf ATMOSPBSRIO PRESSURE • •' Run D u r a t i o n Temp. Atmos. L i q u i d Phase Vapor Phase No. o f Run PC p r e s s . R . I . n * 0 . Mol.Fr. R.I. Mol.Fr, mm. u C 6 H 6 C 6 H 6 1 4.5 79.44 751.6 1.5010 1.0000 1.5010 1.000 2 2.25 79.72 751.6 1.4912 0.9025 1.4959 0.9175 3 3.5 81.40 750.7 1.4665 O.7080 1.4865 0.8720 4 2.75 87.50 750.7 1.4362 0.3935 1.4759 0.7910 5 4.0 9 2.20 752.4 1.425 3 0.2780 1.4679 0.7200 6 3.0 98.70 754.0 1.4137 0.1550 1.4531 0.5750 7 — 117.71 760.0 1.3996 0.0000 1.3996 0.00 A l a r g e s c a l e p l o t was made of the composition o f t h e vapor phase a g a i n s t the composition o f the l i q u i d phase w i t h r e s p e c t to the more v o l a t i l e component. Emerson and G u n d i l l (30) c a r r i e d out e x t e n s i v e i n v e s t i g a t i o n s i n t o the system w i t h both the C o t t r e l l Ghoppin and the G i l l e s p i e Fowler u n i t s . T h e i r e q u i l i b r i u m v a l u e s , obtained on the l a t t e r s t i l l , were a l s o p l o t t e d on the l a r g e graph as a check on the c o n s i s t e n c y of the apparatus. The two curves are shown'in reduced s c a l e i n F i g u r e 39* The l e n g t h o f r u n was v a r i e d f o r each d e t e r m i n a t i o n to note any change i n e q u i l i b r i u m composition v a l u e s . I t was found t h a t under o r d i n a r y c o n d i t i o n s one hour of smooth oper-a t i o n should be s u f f i c i e n t f o r a c c u r a t e v a l u e s . MOL-E FRACTION BENZE .NE . 1 « M UlQUtD 92 The thermodynamic consistency of the system was checked by comparing experimental values of activity coefficients with those obtained theoretically. Experimental activity coeff-icients were evaluated from the expressions P y i and ^ - P 72 Pjx-^ •^ >l^ "2 discussed previously. Values of x± and Xg, mole fractions of respective components in the liquid phase, as well as y^ and yg, mole fractions of the components in the vapor phase, were taken from the experimental equilibrium data. The value of P was taken as the atmospheric pressure under which the deter-minations were carried out. Pressures of the pure components, o o P^ and Pg, at the particular boiling temperature were taken from vapor pressure curves. S t u l l (120) in his review of the vapor pressures of pure organic compounds gave the smoothed vapor pressure values for n-butanol as determined from the work of other researchers (12, 65, 54, 96). The vapor pressure curve i s shown in Figure 40. In the case of benzene, the vapor pressure data for the range of temperature used for both the benzene-butanol system and the benzene-biphenyl system was obtained from various sources. Over the lower temperature region the vapor pressure values are given quite accurately by the equation logitfP (mm) = - 0.0j?223a + b (6l) where T i s the absolute temperature, and a and b are constants having the following values; 0 to 42°C, a = 34,172 42 to 100°C, a •= 32,293 b - 7.9622 b = 7.6546 THJIOlllJ i i L t t f t l 8 % n 40 50 ! T E M P E R A T U R E °C For the r e g i o n of temperature from 100° to 130°C, the e x p e r t -mental va l u e s of Smith and Menzies (114) were drawn upon, while the h i g h e r temperature va l u e s were taken from the work of Gornowski et a l {51}* TABLE 6 VAPOR PRESSURE DATA FOR BENZENE Temp. Pre s s u r e , mm Hg x 10~2 Source of Data 60 0.390 C a l c u l a t e d 2° .548 80 .754 « 90 1.022 tt 100 1.360 11 110 1.751 From Smith and Menzies (114) 120 2.S40 ti 130 2.825 From Gornowski et a l (51) 140 3.518 it 130 4.331 it 160 5.277 it 170 180 6.368 tt 7.621 tt 190 9.050 ti 200 IO.669 it a o 12.495 it 220 14.546 11 230 16.851 11 240 19.425 n 230 22.306 " 260 25.520 tt TABLE 7 ACTIVITY COEFFICIENTS OF BENZENE AND n-BUTANOL FROM EXPERlME^AL VAPOR-LIQUID -EQUILIBRIA T°C P mm H g P i mm Hg Pp-mm Hg x i y i 79.44 751.6 750.0 160.0 1 .000 1.000 1.000 6.30 79 . 7 2 751.6 755.0 1 62.0 0.90 25 0.9175 1 . 0 L 2 3.926 81.40 750.7 778.0 175.5 0 .7080 0.8720 1.188 1.875 87.50 750.7 952.0 230.0 0.3935 0.7910 1.585 1.125 92.20 732.4 I O 9 8.O 281.0 O.278O 0.7200 1.775 I.O38 98.70 754.0 1315.0 367.0 0.1550 0.5750 2.127 1.033 117.71 760 .0. 2125.0 760.0 0 . 0 0 0 0 . 0 0 2.70 1 . 0 0 0 The a c t i v i t y c o e f f i c i e n t s f o r benzene, it, and f o r but a n o l , as e v a l u a t e d from the experimental d a t a are g i v e n i n Table 7« A p l o t was made of l o g a c t i v i t y c o e f f i c i e n t versus mole f r a c t i o n benzene f o r both components i n f i g u r e 42. The curves were e x t r a p o l a t e d to Xj_ = 0 and x-^  = 1 f o r the end v a l u e s of log^.and l o g ^ o . , r e s p e c t i v e l y . Constants A and B i n the van Laar and Margules equations were taken as these t e r m i n a l v a l u e s , A =? l o g ^ , = 0.4J1 and B = l o g $ A - 0 . 799. The t h e o r e t i c a l v a l u e s f o r a c t i v i t y c o e f f i c i e n t s were c a l c u l -ated from the symmetrical forms of the van Laar e q u a t i o n s : l o g = A and l o g = B A-+-AX-JA2 / l + B x 2N 2 k BxT 1 Sg/ As a check, the a c t i v i t y c o e f f i c i e n t s were a l s o c a l c u l a t e d w i t h the Margules e x p r e s s i o n s rearranged i n t o the two-term forms: l o g % f « ( 2B-A) x | + 2(A-B)X2 l o g 5z= (2A-B) xf + 2(B-A)xJ Table 8 g i v e s the t h e o r e t i c a l v a l u e s of the a c t i v i t y c o e f f i c i e n t s as c a l c u l a t e d w i t h both the van Laar and the Mar-gules equations. The t h e o r e t i c a l curves f o r the l o g a c t i v i t y c o e f f i c i e n t s versus mole f r a c t i o n are shown a l o n g w i t h the experimental curve i n F i g u r e 42. LOq A C T I V I T Y C O E F F I C I E N T 23 WEOJ TABLE 8 THEORETICAL ACTIVITY COEFFICIENTS OF BENZENE AND n-BUTANOL  Van Laar Margules 0 . 0 2.700 1 .000 2.700 1 .000 0 . 1 2.419 1.006 2.563 1.003 0 . 2 2.161 1.026 2.344 1.020 0.3 1.925 I . O 6 7 2.086 1.061 0 . 4 ' 1.7H 1.137 1.824 1.141 0.5 1.520 1.253 1.584 1.282 0.6 1.354 1.445 1.379 1.519 0.7 1.215 1.770 1.217 1.920 0.8 1.105 2.56I I.098 2.613 0.9 1.029 3 .543 1.025 3.869 1.0 1.000 6.300 1 .000 6.300 The temperature-composition diagram f o r benzene-butanol i s shown i n F i g u r e 4 3 . B. Benzene-Biphenyl The r e f r a c t i v e i n dex-composition values f o r the system benzene-biphnyl a t 70°C are g i v e n i n Table 9. A l l the p o i n t s obtained - are t a b u l a t e d , but i t was found t h a t many of those taken i n i t i a l l y showed a h i g h e r r e f r a c t i v e index than those obtained as a check. S i n c e technique was improved toward the l a s t d e t e r m i n a t i o n s , and a g r e a t e r ;speed was a c h i e v e d i n weigh-i n g and m a n i p u l a t i o n , the e a r l i e r r e a d i n g s can be suspected as being i n c o n c e n t r a t i o n e r r o r due to e v a p o r a t i o n o f benzene. Consequently, the b e s t v a l u e s were taken and p l o t t e d on l a r g e mm. graph paper where 1 mm. on the a b s c i s s a was e q u i v a l e n t t o .002 mole f r a c t i o n and 1 mm. on the o r d i n a t e was e q u i v a l e n t t o a change i n r e f r a c t i v e i ndex of .0002. F i g . 44 g i v e s a reduced s c a l e curtfe'with a l l experimental p o i n t s f o r r e -f r a c t i v e index a g a i n s t composition. Values of r e f r a c t i v e index f o r even mole f r a c t i o n s were taken o f f the smoothed l a r g e KAO\_E- F R A C T I O N ftELNZ-ELIME-R EL. F'R ACTIVE-"" m D E . ^ s c a l e p l o t and are g i v e n i n Table 10. TABLE 9 REFRACTIVE INDEX-COMPOSITION DATA EOR BENZENE-BIPHENYL AT 70°C Run Moi F r a c t i o n Moi F r a c t i o n R e f r a c t i v e No. Benzene Bi p h e n y l Index 1 0.00 1.00 1.5904 2 0.1090 0.8910 I.5869 3 0.0813 0.9187 1.5836 4 0.5287 0.4713 1.5618 0.5090 0.4910 1.5506 6 0.5052 0.4948 1.5493 7 0.6000 0.4000 - 1.5378 8 O.6967 0.3033 1.5246 9 0.7232 0.2768 1.5205 10 0.9075 0.0925 1.4903 11 1.0 0.0 1.4697 12 0.0 1.0 1.5904 13 1.0 0.0 I.4694 14 0.2870 0.7130 1.5733 15 0.4942 0.5058 1.5463 16 0.1732 0.8268 I.5800 X2 O.3092 0.6108 I.5605 18 0.0701 Q.,9299 I.5856 19 0.6119 0.3881 1.5380 k Values 12 to 19 were taken as a check on rea d i n g s 1 t o 11. TABLE 10 SMOOTHED REFRACTIVE INDEX COMPOSITION DATA FOR BENZENE-BIPHENYL . AT 70PC. . Moi Fraction Moi Fraction Refractive Index Benzene Biphenyl at 70°C 0.0 1.00 1.5904 0.05 0.95 1.5869 0.10 0.90 1.5835 0.15 O.85 1.5799 0.20 0.80 1.5762 0 . 25 0.75 1.5 7 24 0.30 0.70 I.5685 0.35 O.65 1.5642 0.40 0.60 1.5597 0.45 0.55 1.5549 0.50 0.50 1.5497 0.55 0.45 1.5440 0.60 0.40 1.5379 O.65 0.35 1.5314 0.70 O.30 1.5245 0 . 75 0 . 25 1.51 70 0.80 0.20 1.5091 O.85 0.15 1.5006 0.90 0.10 1.4916 0.95 0.05 1.4809 1.00 0.0 1.4697 In a l l , twenty six runs were made on the Gillespie-Fowler S t i l l for the determination of vapor-liquid equilibrium of benzene-biphenyl. The f i r s t f ifteen runs were taken at atmospheric temperature while the remainder were•obtained in an oven kept at 70°C. Table 11 gives a l l the experi;---yAe.nS<aA data obtained with temperatures corrected for calibration with the platinum resistance thermometer. TABLE 11 EXPERIMENTAL VAPOR LIQUID EQUILIBRIUM FOR BENZENE-BIPHENYL AT ATMOSPHERIC PRESSURE.  „ „ , ; m „ , ...... l i q u i d Phase ' Vapor Phase Run Duration Temp. Atmos. — nn ."," •' " 7Q'. " No of Run PC Press. R.I. n^ Moi Fr. R.I. n^ Moi Fr. Hours C£H6 C 6 H 6 1 2 80.10 760.3 1.4700 1.000 1.4700 1.0 2 1.5 80.28 759.9 1.4716 0.991 1.4696 1.0 3 1.5 80.94 758.3 1.4772 .966 1.4700 1.0 4 2.0 8I.8I 759.2 1.4820 .945 1.4700 1.0 5 2.0 83.65 760.7 1.4912 .902 1.4700 1.0 6 2.5 84.54 760.5 1.4932 .891 1.4700 1.0 7 2.5 85.98 760.7 1.5025 .838 1.4700 1.0 8 3.0 87.IO 760.4 1.5100 .794 1.4700 1.0 9 2.0 88.80 76O.6 1.5170 .750 1.4700 1.0 10 5.0 91.85 755.0 1.5235 .706 1.4700 1.0 11 2.0 9 3.65 754.0 1.5265 .685 1.4700 1.0 12 2.5 95.57 754.3 1.5322 .644 1.4700 1.0 13 2.5 97.53 754.2 1.5376 .602 1.4700 1.0 14 1.5 98.98 754.4 1.5425 .563 1.4700 1.0 15 2.5 101.06 757.0 1.5500 .497 1.4700 1.0 16 1 102.26 757.2 I.5482 .504 1.4714 0;992 17 1 104.36 757.7 1.5569 . 430 1.4718 .990 18 1 126.2 757.7 1.5741 .228 1.4714 .992 A 19 1 132.6 757.2 1.5748 . 218 , 1.49 1 2 . 99 2 A 20 1 141.8 757.4 1.5790 .162 I.4787 .960 21 1.5 151.6 75 7.3 1.5 809 .135 1.4 7 29 .985 22 1 167.3 757.3 1.5845 .085 1.4870 .922 it 23 1 187.8 756.7 1.5873 .045 1.4877 .919 24 1.5 199 . 6 756.2 1.58 75 . 041 1.5076 .809 25 2 211.4 757.2 1.5893 .016 1.5493 .503 / 26 2 143.3 757.9 1.5802 .145 1.4782 .962 A Runs were definitely not at equilibrium when refractive indices' were taken. / Run was taken primarily as a rough check on the particular region of concentration. A large scale plot was made of a l l the experimental points with the exception of three which were obtained when the system was definitely not at equilibrium. Figure 45 shows the general form of the curve obtained. Smoothed values were taken from the large graph and are tabulated in Table 12 for even intervals of concentration in the liquid phase. TABLE 12 SMOOTHED VALUES FOR THE VAPOR-LIQUID EOJILIBRIUM OF BENZENE-BIPHENYL.: Moi.Fr. C 6 H D i n Mol.Fr.C6H6in Liquid Phase Vapor Phase Temp.°C. 0.00 0.000 255.3°0 4 0.01 0.308 0.624 230.7""' 0.02 211.2 0.03 0.745 202.6 0.04 0.803 195.9 0.05 0.844 189.6 0 .06 0.875 133.5 0.07 0.899 178.2 0.08 0.920 0 .936 171.6 0 . 0 9 167.7 0.10 0 .950 I 6 2 . 4 0.12 0 .971 151.5 0.14 0.9S4 140.6 0.16 0.96*9 133.3 0.18 0.990 129.8 0.20 0.991 I 2 6 . 5 0.25 0.992 121.4 0.30 0.993 116.4 0.35 0.994 112.2 0.40 0.995 108.4 0.45 0 .996 105.6 0 .50 0.997 102.7 0.55 0.998 99.4 0 .60 0.999 97.3 . O.65 1.000 95.0 0.70 1.000 92.9 0.75 1.000 90.7 0.80 1.000 88.6 0.85 1.000 8 6 . 5 0.90 1.000 34.3 0.95 1.000 82.2 1.00 1.000 80.1 A Temperature f o r the b o i l i n g point of pure biphenyl at 760 mm. taken from the l i t e r a t u r e (79) (18). For c a l c u l a t i o n of a c t i v i t y c o e f f i c i e n t s from the experimental d a t a , p r e s s u r e s o f pure benzene were taken from F i g u r e 41 w h i l e those f o r b i p h e n y l were ob t a i n e d from F i g u r e 22. The experimental a c t i v i t y c o e f f i c i e n t s f o r a l l vapor l i q u i d e q u i l i b r i u m data are t a b u l a t e d i n Table 13. Only the s t a r r e d v a l u e s were p l o t t e d s i n c e they are the o n l y ones which appear r e a s o n a b l e . Curves were drawn through these v a l u e s and are shown i n F i g u r e 46. They were e x t r a p o l a t e d t o 3 0 and x-j_ = 1 and the v a l u e s of A and B o b t a i n e d were .415 and .393, r e s p e c t i v e l y . The v a l u e s of t h e o r e t i c a l a c t i v i t y c o e f f i c i e n t s are t a b u l a t e d i n Table 14, and the curves are drawn i n F i g u r e 46. The temperature-composition data f o r benzene-b i p h e n y l are p l o t t e d i n f i g u r e 47. A smooth curve has been, drawn through the best p o i n t s . L O G A C T I V I T Y C O E F F I C I E N T 0 4 O 5 O YiOJFS o 5 n »+• 4 ^ " 0 3 b-4 O.5- O'fc M O L E . F R A C T I O N B E N Z E N E . 0 7 TABLE 13 ACTIVITY COEFFICIENTS OF BENZENE AND BIPHENYL FROM EXPERIMENTAL DATA T°C P mm Hg P i mm Hg P 2 mm Hg x-j_ v l do. 10 8 0 . 2 8 8 0 . 9 4 8 1 . 8 1 33.65 3 4 . 5 4 3 5 . 9 3 3 7 . 1 0 3 3 . 3 0 9 1 . 3 5 93.65 9 5 . 5 7 9 7 . 5 3 9 3 . 9 3 101.06 102.26 IO4.36 126 .2 1 3 2 . 6 1 4 1 . 3 151.6 I67.3 1 3 7 . 3 199 .6 2 1 1 . 4 143 .3 & P l o t t e d v a l u e s . xx E x t r a p o l a t e d v a l u e s . 7 6 0 . 3 7 6 0 1 . 5 0 1 . 0 0 0 1 . 0 7 5 9 . 9 7 6 3 1 . 6 0 0 . 9 9 1 £ 1 . 0 7 5 3 . 3 7 7 7 1 .75 . 9 9 6 1 . 0 7 5 9 . 2 300 1 . 9 0 . 9 4 5 1 . 0 7 6 0 . 7 345 2 . 0 0 . 9 0 2 t 1 . 0 7 6 0 . 5 365 2 . 0 5 . 3 9 1 1 . 0 7 6 0 . 7 905 2 . 1 5 . 3 3 3 t 1 . 0 7 6 0 . 4 9 3 6 2 . 2 5 . 7 9 4 1 . 0 7 6 0 . 6 9 9 0 2 . 4 0 . 7 5 0 t 1 . 0 7 5 5 . 0 1037 2 . 5 0 . 7 0 6 1 . 0 7 5 4 . 0 . 1 1 4 5 3 . 2 0 . 6 8 5 1 . 0 7 5 4 . 3 1203 3 . 6 0 . 6 4 4 1 . 0 7 5 4 . 2 ' 1 2 7 3 4 . 0 0 . 6 0 2 1 . 0 7 5 4 . 4 1 3 2 2 4 . 2 0 . 5 6 3 1 . 0 7 5 7 . 0 1 3 9 3 4 . 5 0 . 4 9 7 1 . 0 7 5 7 . 2 1 4 3 3 4 . 9 0 . 5 0 4 A 0 . 9 9 2 7 5 7 . 7 1514 5 . 4 0 . 4 3 0 A . 9 9 0 7 5 7 . 7 2 5 3 5 1 4 * 7 0 . 2 2 3 A . 9 9 2 7 5 7 . 2 3 0 0 0 . 1 9 . 0 0 . 2 1 3 . 9 0 2 7 5 7 . 4 3 6 6 4 2 6 . 7 0 . 1 6 2 t . 9 6 0 7 5 7 . 3 4492 3 7 . 2 0 . 1 3 5 . 9 3 5 7 5 7 . 3 6020 6 5 . 3 0 . 0 3 5 $ . 9 2 2 7 5 6 . 7 3470 1 2 9 . 2 . 0 4 5 . 9 1 9 7 5 6 . 2 10270 1 3 4 . 2 . 0 4 1 A . 3 0 9 7 5 7 . 2 1 2 6 1 0 2 5 7 . 0 . 0 1 6 . 5 0 3 7 5 7 . 9 3740 2 3 . 0 . 145 ft . 9 6 2 1 . 0 0 0 1.005 0 . 9 3 0 1.003 1 . 0 0 7 0 . 9 9 4 1 . 0 2 2 1 . 0 2 3 1 . 0 3 2 0 . 9 3 4 0 .961 0 . 9 6 3 0 . 9 3 4 1 . 0 1 3 1 . 0 9 2 1.039 1.151 1 .273 1 . 0 4 3 1.226 1 . 2 3 2 1.363 1 .545 1.456 1 . 3 3 7 1 . 3 4 4 2 . 5 0 xx t» tt tt tt tt tt tt tt n tt tt tt tt ' tt 2 . 4 9 1 2 . 4 6 I 0 . 5 3 4 0 . 4 9 9 1 . 3 5 4 0 . 3 5 3 0 . 9 3 9 0.313^ 1 . 4 9 0 1 . 2 0 3 TABLE 14 THEORETICAL ACTIVITY COEFFICIENTS OF BENZENE AND BIPHENYL Van Laar Margules x l i. V . a . 0 . 0 0 1 . 5 7 0 1 . 0 0 0 ~ " T : 5 W " 1 . 0 0 0 0 . 1 1 . 5 0 0 1 . 0 0 2 1 . 5 5 4 1 . 0 0 1 0 . 2 1 . 4 3 0 1 . 0 1 1 1 . 5 0 3 1 . 0 0 7 0 . 3 I . 3 6 O 1 . 0 2 3 1 . 4 2 9 1 . 0 2 4 0 . 4 1 . 2 9 2 1 . 0 5 3 1 . 3 4 5 1 . 0 5 9 0 . 5 1 . 2 2 5 1 . 1 0 5 1 . 2 5 7 1 . 1 1 9 0 . 6 1 . 1 6 1 1 . 1 3 0 1 . 1 7 5 1 . 2 1 6 0 . 7 1 . 1 0 3 1 . 2 9 9 1 . 1 0 4 1 . 3 6 7 0 . 3 1 . 0 5 2 1 . 4 9 6 1 . 0 4 9 1 . 5 9 6 0 . 9 1 . 0 1 5 1 . 3 4 0 1 . 0 1 3 1 . 9 4 3 1 . 0 1 . 0 0 2 . 5 0 0 1 . 0 0 0 2 . 5 0 0 102 CHAPTER V I I I  DISCUSSION OF RESULTS A. Benzene-Butanol From the p l o t of l o g o f t h e experimental a c t i v i t y -c o e f f i c i e n t s versus mole f r a c t i o n , t h e p o i n t s o b t a i n e d appear t o f a l l on smooth curves. Although t h i s i n i t s e l f i s not a c r i t e r i o n o f thermodynamic c o n s i s t e n c y i t does g i v e a c e r t a i n amount o f i n d i c a t i o n i n t h a t d i r e c t i o n ( 1 5 ) . A check on t h e two curves' at x = 0 . 5 shows t h a t t h e l o g ^ curve f a l l s lower than t h a t o f l o g . T h i s i s f u r t h e r evidence o f c o n s i s t e n c y s i n c e the l o g tf^curve has the h i g h e r end v a l u e , as p o i n t e d out i n the t h e o r e t i c a l d i s c u s s i o n . A thermodynamic check on the c o n s i s t e n c y o f the experimental curve shows a c e r t a i n amount o f d e v i a t i o n . The t h e o r e t i c a l curves are completely dependent on the-accurate,-e x t r a p o l a t e d end v a l u e s o f the experimental curves. I t may be o n l y f o r t u i t o u s t h a t the experimental t e r m i n a l v a l u e s are c o r r e c t and have been a c c u r a t e l y e x t r a p o l a t e d . However, s i n c e the system does not form an azeotrope, these a r e about the o n l y v a l u e s upon which a thermodynamic check can be based. The van Laar and Margules curves do not c o i n c i d e too c l o s e l y . T h i s can be expected s i n c e A, t h e r a t i o o f the c o n s t a n t s , B d e v i a t e s c o n s i d e r a b l y from u n i t y . The temperature-composition curves i n both t h i s r e s e a r c h and t h a t of Emerson and C u n d i l l conformed v e r y w e l l t o the types of curves o b t a i n e d f o r common non-azeotropic mixtures. The experimental p o i n t s o b t a i n e d d e v i a t e d v e r y 103 l i t t l e from smooth curves, but i n the h i g h benzene concen-t r a t i o n end o f the diagram t h e y showed c o n s i d e r a b l e i n t e r e s t . I t i s here t h a t the system appears t o come very c l o s e t o forming an azeotrope. B. B eh z en e- B i ph en v l E v a l u a t i o n o f the a c t i v i t y c o e f f i c i e n t s from ex-p e r i m e n t a l data f o r benzene and b i p h e n y l gave o n l y a few v a l u e s f a l l i n g above u n i t y . When p l o t t e d , the p o i n t s f o r benzene were w i t h i n reason o f a curve. However, those f o r b i p h e n y l were o f f c o n s i d e r a b l y , and o n l y a v e r y few had v a l u e s above u n i t y . T h i s i n c o n s i s t e n c y may have been due t o v a r i o u s reasons. In t h e e xperimental work, the temperature readings c o u l d have been taken too h i g h r e s u l t i n g i n a h i g h vapor p r e s s u r e f o r the pure components i n c a l c u l a t i o n s . Then i n the e x p r e s s i o n •= Py2 the v a l u e o f ^would be c o n s i d e r a b l y too low. I t appears 2 . X 2 t h a t almost i n a l l cases of b i p h e n y l the r a t i o J2. was s m a l l e r than i t should have been. T h i s would i n d i c a t e t h a t the vapor phase was not e x h i b i t i n g a l a r g e enough c o n c e n t r a t i o n of b i p h e n y l . In the lower tem-per a t u r e s of d e t e r m i n a t i o n any e r r o r s i n the vapor p r e s s u r e would manifest themselves t o a h i g h degree i n the a c t i v i t y c o e f f i c i e n t s . I t might be concluded from the r e s u l t s t h a t more s p e c i a l i z e d type o f equipment i s necessary f o r v a p o r - l i q u i d e q u i l i b r i u m d e t e r m i n a t i o n s o f benzene-biphenyl. Perhaps the vapor r e c i r c u l a t i o n type of apparatus with constant temper-a t u r e c o n t r o l would be b e t t e r s u i t e d f o r t h i s system. A more s e n s i t i v e means of a n a l y s i s i s r e q u i r e d s i n c e up to X]_ = 0.5 i t was i m p o s s i b l e t o detect b i p h e n y l i n the vapor phase u s i n g the r e f r a c t o m e t e r . L a s t l y , i t may be necessary t o r e s o r t to other mathematical r e l a t i o n s t o check the system thermodynam-i c a l l y . 105 CHAPTER IX BIBLIOGRAPHY 1. 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