Vapor-Liquid Equilibrium in the Ethanol-Water System Saturated with

7 Vapor-Liquid Equilibrium in the Ethanol-Water System Saturated with Chloride Salts

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M. A. GALAN, M. D. LABRADOR, and J. R. ALVAREZ Department of Chemistry (Technical), Faculty of Science, University of Salamanca, Salamanca, Spain

Vapor-liquid equilibrium data at atmospheric pressure (690700 mmHg) for the systems consisting of ethyl alcohol-water saturated with copper(II) chloride, strontium chloride, and nickel(II) chloride are presented. Also provided are the solu bilities of each of these salts in the liquid binary mixture at the boiling point. Copper(II) chloride and nickel(II) chloride completely break the azeotrope, while strontium chloride moves the azeotrope up to richer compositions in ethyl alcohol. The equilibrium data are correlated by two separate methods, one based on modified mole fractions, and the other on devia tions from Raoult's Law.

M

any papers concerning salt effect o n v a p o r - l i q u i d e q u i l i b r i u m have been published. T h e systems f o r m e d b y a l c o h o l - w a t e r mixtures saturated w i t h various salts have been the most w i d e l y studied, w i t h those based on the e t h y l a l c o h o l - w a t e r b i n a r y b e i n g of special interest (1-6,8,10,11). H o w e v e r , other a l c o h o l m i x t u r e s have also been s t u d i e d : m e t h a n o l (10,16,17,20,21,22), 1-propanol (10,12,23,24), 2-propanol (12,23,25,26), butanol (27), p h e n o l (28), a n d ethylene g l y c o l (29,30). O t h e r b i n a r y solvents studied have i n c l u d e d acetic a c i d - w a t e r (22), p r o p i o n i c a c i d - w a t e r (31), n i t r i c a c i d water (32), acetone-methanol (33), ethanol-benzene (27), p y r i d i n e - w a t e r (25), a n d d i o x a n e - w a t e r (26). Although the third component of these systems is usually a single inorganic

salt, mixtures of two or more salts have been studied, a n d some research has been done w i t h t h i r d components of l o w vapor pressure (18,19).

Some qualitative

studies have been done on salt effect i n v a p o r - l i q u i d equilibrium w i t h salts w h i c h are either:

soluble i n only one or both components, hygroscopic or non-hygro-

scopic, etc. 85

In Thermodynamic Behavior of Electrolytes in Mixed Solvents; Furter, W.; Advances in Chemistry; American Chemical Society: Washington, DC, 1976.

86

THERMODYNAMIC BEHAVIOR OF ELECTROLYTES

The present work studies the v a p o r - l i q u i d equilibrium of the ethanol-water system saturated w i t h copper(II) chloride, strontium chloride, a n d nickel(II) chloride. Salts soluble i n ethanol as w e l l as water have been f o u n d to break the azeotrope, while salts w h i c h are very soluble i n water and only slightly soluble i n the alcohol move the azeotrope to richer ethanol regions without b r e a k i n g it.

Fur-

thermore, the salts or compounds w h i c h dissolve more i n one component are found to raise the volatility of the other component.

This finding is i n conformity

w i t h that of previous workers i n the f i e l d (8,11,12,13,18,19,23,24,27).

I n this

work the e q u i l i b r i u m diagrams were obtained at atmospheric pressure (690-700


m m H g ) , a n d under saturation conditions. F r o m experimental data for the ethanol-water system without salt, obtained at 700 a n d 760 m m H g , it c a n be seen that w i t h i n this pressure range the effects of pressure o n the e q u i l i b r i u m data are small enough to be w i t h i n the experimental scatter.

In fact, i n previous works (8,11,12,13,18,19,23,24,27)

there seems

to be no clear difference between the e q u i l i b r i u m data at 700 and at 760 m m H g . Errors obtained i n the determination of l i q u i d a n d vapor compositions are approximately ± 0 . 0 5 wt % for the systems without salt.

F o r salt-saturated systems,

»the same error prevails for the vapor phase, w h i l e the error is between 0.1 a n d 0.2 wt % for l i q u i d phase compositions.

T h e error for the b o i l i n g temperature

is less than 0.1 ° C for the systems without salt, but for saturated solutions the error is m u c h greater:

f r o m 0 . 2 ° C for nonconcentrated solutions to 3 ° C or more for

highly concentrated solutions.

Experimental

Procedure

T h e apparatus and experimental procedure used here are the same as those used i n previous work (8,11,12,13,18,19,23,24,27). A n i m p r o v e d O t h m e r still is used. In the lower part of the still, at five c m f r o m the base, there is a stopcock through w h i c h l i q u i d samples c a n be taken. T h e cock bore is larger than the standard bore, thus preventing sticking b y the salt. A thermometer w h i c h measures the b o i l i n g temperature is i n t r o d u c e d into the vessel through a n inlet on either side of the still, w i t h the b u l b submerged i n the solution. This solution is vigorously stirred magnetically. T h e still neck is covered w i t h nichrome thread through w h i c h an electric current is passed. In this way, the temperature of the vapor can be kept higher than the boiling point, thus avoiding any condensation. T h e recycling tube has a narrow bore section, w h i c h prevents m i x i n g of solution a n d vapor. T h e vapor composition was d e t e r m i n e d b y picnometry. T h e l i q u i d phase was evaporated to dryness; the solubility of the salt and the composition of the l i q u i d on a salt-free basis were determined f r o m the salt and the l i q u i d obtained b y w e i g h i n g a n d picnometry.


7.

GALAN E T AL.

Ethanol-Water

87

Saturated with Chloride Salts

Results and Discussion Figure 1 shows the equilibrium data for the ethanol-water systems saturated w i t h copper(II) chloride, strontium chloride, or nickel(II) chloride.

Figure 2

shows the temperature-compositions diagrams corrected to 700 m m H g . F o r the copper(II) chloride system, a m a x i m u m a n d m i n i m u m were observed.

M a x i m u m a n d m i n i m u m points have also been observed for the 1 -

p r o p a n o l - w a t e r system saturated w i t h copper(II) chloride.

T h e explanation

for these singular points w i l l be made after demonstration of the solubility data. The temperature data for the ethanol-water-strontium chloride system show Downloaded by MONASH UNIV on June 9, 2013 | http://pubs.acs.org Publication Date: June 1, 1976 | doi: 10.1021/ba-1976-0155.ch007

that the curve for the l i q u i d phase cuts the curve corresponding to the salt-free system.

This tends to happen w i t h salts that are very soluble i n water a n d only

slightly soluble or insoluble i n ethanol (8,12).

Figure 1. Vapor-liquid urated with copper(U)

This is because, for a b i n a r y

equilibrium data for the ethanol-water systems satchloride, nickel(II) chloride, and strontium chloride


88



20

40

60

80

x , y

100

% mole

Figure 2. Temperature-composition diagrams, corrected to 700 mmHg, for the ethanol-water systems saturated with copper(II) chloride, nickel(II) chloride, and strontium chloride mixture of a determined composition a n d at a determined pressure, the b o i l i n g point is a fixed temperature. If a salt w h i c h is somewhat soluble i n both water a n d ethanol is a d d e d to a binary mixture, the composition of the l i q u i d phase is m o d i f i e d such that the solution can be considered to consist of a b i n a r y mixture f o r m e d b y free water and ethanol w i t h a composition richer i n ethanol than the initial binary mixture


7.

GALAN ET AL.

Ethanol-Water


89

(without salt), and the salt with fixed water; hence the salt effect is to fix the water, thus raising the alcohol volatility. T h e boiling temperature of the solution w i t h salt w i l l be the sum of: the boiling temperature of free water and ethanol (lower than the b o i l i n g temperature of the initial solution), a n d the temperature increment due to the salt. If this increment is small (as w i t h ions of small activity such as Na+, K , S r ) , the solution w i t h salt m a y have a lower b o i l i n g point than the +

2 +


same solution without salt.

Figure 3.

Salt solubility

data for boiling ethanol-water with copper(II) chloride

mixtures


saturated

90



F r o m the e q u i l i b r i u m composition and temperature, it can be deduced that copper(II) chloride and nickel(II) chloride break the azeotrope, w h i l e strontium chloride moves it toward a richer ethanol concentration. Figures 3 a n d 4 show solubility data for these systems, expressed i n grams of salt per h u n d r e d grams of solvent, plotted against l i q u i d composition i n wt % on a salt-free basis. Solub i l i t y data for the copper(II) chloride system (see F i g u r e 3) show a m a x i m u m

Figure

4.

Salt solubility data for boiling ethanol-water mixtures with nickel(II) chloride and strontium chloride


saturated

7.

G A L A N E T AL.

Ethanol-Water


91

and m i n i m u m for two different compositions of the b i n a r y mixture. This was also observed i n the 1 -propanol-water-copper(II) chloride system (24). These singular points were also f o u n d i n other systems: a m i n i m u m i n the solubility data was f o u n d i n the 1-propanol-water-cobalt(II) chloride system (24), a n d a m a x i m u m was f o u n d for the ethyl alcohol-water system saturated w i t h phenolphthalein (19). T h e solubility m a x i m u m a n d m i n i m u m for the e t h a n o l water-copper(II) chloride system c a n account for the temperature m a x i m u m and m i n i m u m (see F i g u r e 2). O n the other hand, the system shown i n F i g u r e 1 breaks the azeotrope completely.

This means that the vapor phase composition must always be larger


than the l i q u i d phase compositions over the entire range of compositions.

From

this, the b o i l i n g point of the vapor must be lower and the composition of vapor must be higher than those of the l i q u i d .

Therefore, the lines for the l i q u i d phase

and the vapor phase i n this d i a g r a m go through the m a x i m u m a n d m i n i m u m without crossing (cutting) over the entire range of concentrations.

These singular

points are not observed i n the case of nickel(II) and strontium chlorides.

Correlation Equations studied previously (19,27) have been used to correlate the e q u i librium data. Alvarez and Vega (27) correlate the equilibrium data as a function of a m o d i f i e d mole fraction X ' i , and the l i q u i d phase composition on a salt-free basis X i . +

logX

,

i

=

fllogX + i

+ logfe

(1)

In this equation, a and b are constants characteristic of the system. T h e modified mole fraction is the one d e f i n e d by L u (34) f r o m the compositions on a salt-free basis and f r o m the vapor pressure of the pure components and of the salt plus pure l i q u i d solutions. Figures 5 and 6 show the values of X ' j a n d X j corresponding, respectively, to ethanol and water for each of the three systems. F o r nickel(II) chloride and strontium chloride, the experimental data follow a straight line, while for copper(II) chloride the data f o r m three straight lines, as was expected (24) f r o m the m a x i m u m and m i n i m u m i n the temperature d i a g r a m . +

F o r nickel(II) a n d strontium chlorides the experimental data are i n good agreement w i t h data obtained b y A l v a r e z G o n z a l e z and V e g a Zea (27); that is, w h e n the solubility of the salt i n one component increases, the value of X\ decreases for the pure component. Moreover, the decrease is proportional to the solubility of the salt i n this component. A c c o r d i n g l y , a salt that is insoluble i n one component must pass through the point X ' j = 100, X = 100. T h e values obtained for constants a and b of E q u a t i o n 1 are shown i n T a b l e I. +

{

T h e e q u i l i b r i u m data were also correlated b y studying the deviations f r o m Raoult's L a w .

Since the salt-free system obeys this law w h e n the concentration


92


of a specified component is substituted b y its activity, it follows that f o r the salt-free system:

a n d for the system w i t h salt, *yi = F i ° ( X 7 i ) s i

n

where X j is the real concentration of component i i n the salt solution, a n d the salt is considered a t h i r d component w i t h no vapor pressure. X j is the concentration of the salt-free system, a n d 7J° the activity coefficient of the salt-free system for the concentration X i ° corresponding to X . It is interesting to rem e m b e r that X i ° = X i . S

0


s i

+

0.10

0.20

0.30

_L 0.40

J_ 0.50

1.00

Figure 5. Modified molar fraction vs. salt-free base composition referred to ethanol for the systems saturated with copper(II) chloride, nickel(II) chloride, and strontium chloride



7.

G A L A N E T AL.

Ethanol-Water

0.10

93


0.20

0.30

0.40 0.50

1.00

Figure 6. Modified molar fraction vs. salt-free base composition referred to water for the systems saturated with copper(II) chloride, nickel(II) chloride, and strontium chloride T a b l e I.

Experimental Values Obtained for Constants a and b in Equation 1

Reference

Component

E t h a n o l - s t r o n t i u m chloride Water-strontium chloride Ethanol-nickel(II) chloride Water-nickel(II) chloride Ethanol-copper(II) chloride Ethanol-copper(II) chloride Ethanol-copper(II) chloride Water-copper(II) chloride Water-copper(II) chloride Water-copper(II) chloride

Second Component water ethanol water ethanol water water water ethanol ethanol ethanol

a 0.717 0.768 0.794 0.998 0.877 -0.537 1.012 1.164 1.967 1.193


b 3.553 1.613 2.504 0.497 1.407 547.4 0.695 0.240 0.017 0.256


94


•

0.1

0.2

0.3

0.A

0.5

CuCl

2

A NiCl

2

o

2

SrCl

1.0

oc r° s

Figure 7. saturated

Alvarez-Bueno-Galan correlation for the ethanol-water systems with copper(II) chloride, nickel(II) chloride, and strontium chloride

T h e exponent n indicates the deviation of the system w i t h salt f r o m the salt-free system. F i g u r e 7 shows the values of log iryjPp vs. log ( X 7 i ° ) for the ethanol-water system saturated w i t h copper(II) chloride, nickel(II) chloride, and strontium chloride respectively. T h e values for n obtained f r o m the above system are shown i n Table II. si

T a b l e II.

Experimental Values Obtained for Constant n in Equation 2 System

n

E t h a n o l - w a t e r - s t r o n t i u m chloride Ethanol-water-nickel(II) chloride Ethanol-water-copper(II) chloride

0.38 0.53 0.67


7.

GALAN E T AL.

Ethanol-Water

95


A l v a r e z Gonzalez et al. (19) stated that those systems i n w h i c h the value of n is less than unity move the azeotrope to richer ethanol compositions, even to breaking the azeotrope. consideration.

This was also observed for the systems presently under

Reference 19 proposes a correlation of the e q u i l i b r i u m data b y

the e m p i r i c a l equation:

^

= K(X,V)

* R

(3)

n

where F R is the vapor pressure of an ideal ethanol-water system w h i c h obeys Raoult's law, and K is a constant. T h e exponent n gives the deviation of the system, salt-free or not, w i t h respect to the ideal system, w h i c h follows Raoult's law. The log iryjP^ vs. log ( X ^ ) is presented i n Figure 8 for the three systems studied. T h e values obtained for n are presented i n T a b l e III.


0

o

10

ETHANOL - WATER

•

CuCl

2

A

NiCl

2

20

30

40

50

100 x °

r°

Figure 8. Empiric correlation of Alvarez-Bueno-Galan for the ethanol-water system and ethanol-water saturated with copper(II) chloride, nickel(II) chloride, and strontium chloride


96


T a b l e III.

Experimental Values Obtained for Constant n in E q u a t i o n 3 System

n

Ethanol-water E t h a n o l - w a t e r - s t r o n t i u m chloride Ethanol-water-nickel(II) chloride Ethanol-water-copper(II) chloride

1.39 1.03 1.05 1.13


F r o m these it can be deduced that the system w i t h a slope of less than 1.39 moves the azeotrope toward richer ethanol composition, as was also deduced i n Reference 19. T o correlate the temperatures, these same authors (19) proposed the representation of log T R J Y J O / T J V S . log ( T 7 i ) , where T is the boiling temperature R i

0

R i

'R

1

Figure 9. Temperature correlations of Alvarez-Bueno-Galan ethanol-water system and ethanol-water saturated with copper(II) nickel(II) chloride, and strontium chloride

for the chloride,


7.

GALAN E T AL.

Ethanol-Water


97

of the ideal system and T is the b o i l i n g temperature of the real system without salt. F i g u r e 9 shows that a straight line was obtained for each system. x

These correlations allow the p r e d i c t i o n of e q u i l i b r i u m data for systems saturated w i t h salt f r o m only one or two experimental points. Nevertheless, i n all work done on salt effect it seems that what was stated at the beginning of this paper is true, i.e., the effects on the volatilities of components and hence the variation i n relative volatility depend on the solubility of the salt i n both c o m ponents.


Literature Cited 1. Kyrides, L. P., Carwell, T. S., Pfeifer, C. E., Wobus, R. S., Ind. Eng. Chem. (1932) 24, 795. 2. Rieder, R. M., Thompson, A. R., Ind. Eng. Chem. (1950) 42, 379. 3. Tursi, R. R., Thompson, A. R., Chem. Ing. Prog. (1951) 47, 304. 4. Jost, W., Chem. Eng. Tech. (1951) 23 No. 3, 64. 5. Costa, E., Moragues, J., An. R. Soc. Esp. Fis. Quim. (1952) 48B, 397-408; (1952) 48B, 441. 6. Yamamoto, Y., Maruyano, T., Chem. Eng. Jpn (1952) 16, 166. 7. Dobroserdov, L. L., Il'Yina, V. P., Tr. Leningr. Tekhnol. Inst. Pishch. Prom. (1956) 13, 92. 8. Rius Miro, A., Otero de la Gandara, J. L., Alvarez Gonzalez, J. R., An. R. Soc. Esp. Fis. Quim. (1957) 53B, 171; (1957) 53B, 185. 9. Dobroserdov, L. L., Il'Yina, V. P., Tr. Leningr. Tekhnol. Inst. Pishch. Prom. (1958) 14, 147. 10. Johnson, A. I., Furter, W. F., Can. J. Chem. Eng. (1960) 38, 78. 11. Rius Miro, A., Alvarez Gonzalez, J. R., Uriarte, A., An. R. Soc. Esp. Fis. Quim. (1960) 56B, 629. 12. Alvarez Gonzalez, J. R., Artacho, E., An. R. Soc. Esp. Fis. Quim. (1961) 57B, 219. 13. Alvarez Gonzalez, J. R., Uriarte, A., An. R. Soc. Esp. Fis. Quim. (1962), 58B, 145. 14. Proinova, Z. A., Toncheva, G., Khim. Ind. Sofia (1966) 38 (3), 130. 15. Meranda, D., Furter, W. F., Can. J. Chem. Eng. (1966) 44, 298. 16. Meranda, D., Furter, W. F., A.I.Ch.E. J. (1971) 17, 38. 17. Meranda, D., Furter, W. F., A.I.Ch.E. J. (1972) 18, 111. 18. Alvarez Gonzalez, J. R., Galan Serrano, M. A., An. R. Soc. Esp. Fis. Quim. (1973) 69, 545. 19. Alvarez Gonzalez, J. R., Bueno Cordero, J., Galan Serrano, M. A., An. R. Soc. Esp. Fis. Quim. (1974) 70, 262. 20. Jaques, D., Furter, W. F., Ind. Eng. Chem. Fundam. (1974) 13 (3), 238. 21. Meranda, D., Furter, W. F., A.I.Ch.E. J. (1974) 20 (1), 103. 22. Yoshida, F., Yasunishi, A., Hamada, Y., Chem. Eng. (Tokyo) (1964) 28 (2), 133. 23. Rius Miro, A., Alvarez Gonzalez, J. R., An. R. Soc. Esp. Fis. Quim. (1958) 54B, 797. 24. Alvarez Gonzalez, J. R., Galan Serrano, M. A., An. R. Soc. Esp. Fis. Quim. (1974) 70, 271. 25. Ohe, S., Yokayama, L., Nakamura, S., Ishikawajima Harima Giho (1971) 11 (5), 368. 26. Prausnitz, J. M., Targovnik, J. Chem. Eng. Data (1958) 3, 234. 27. Alvarez Gonzalez, J. R., Vega Zea, J., An. R. Soc. Esp. Fis. Quim. (1965) 61B, 831; (1967), 63B, 749. 28. Bogart, M. J. P., Brunjes, A. S., Chem. Eng. Progress (1948) 44, 95. 29. Fogg, E. T., Diss. Abstr. (1953), 13, 739-740. Univ. Microfilm Pub. No. 5589. Univ. of Pennsylvania. EE. UU. 30. Fox, P. M., M.S. Thesis., Univ. of Pennsylvania, 1949.


98

31. 32. 33. 34.

T H E R M O D Y N A M I C BEHAVIOR O F

ELECTROLYTES

Ramalho, R. S., Edgett, N. S., J. Chem. Eng. Data (1964) 9, 324. Baranov, A. V., Karev, V. G., Tr. Sib. Tekh. Inst. (1963) 36, 61. Proszt, J., Kollar, G., Rocz. Chem. (1958) 32, 611. Benjamin, C., Lu, Y., Ind. Eng. Chem. (1960) 52, 871. 1975.


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Vapor-Liquid Equilibrium in the Ethanol-Water System Saturated with

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