INDUSTRIAL AND ENGINEERING CHEMISTRY
1428
second-order transition point. Another item of general theoretical interest is the fact t h a t interpretation of some of the data seems t o require that segments of the polymer chains be in motion more than 100' below the second-order transition point. Polybutadiene, prepared with sodium as the catalyst, changes in physical properties with baking a t a rate about four times as fast as does the emulsion polymer. Furthermore, the ratio of cross linking to cyclization is higher in the sodium polymer. These differences are believed t o be due t o the higher content of dangling vinyl groups in the sodium polymer LITERATURE CITED
(1) Alfrey, T.,Goldfinger, G., and M a r k , H., ,J. A p p l t e d Phz/s, 14, 700 (1943).
System J
Vol. 44, No. 6
(2) Blokh, G. A., and Zaionchkovakli, A . D., Legkaya Prom., 11-12, 43 (1946); Rubber Chem. and Technol., 21, 727 (1948). (3) Bolland, J. L., and Orr, W. J. C., Trans. Inst. Rubber Id.,21, 133 (1945); Rubber Chem. and Technol., 19, 277 (1946). (4)Boyer, R. F., and Spencer, R. S., "Advances in Colloid Science," Vol. 11, p. 26, Mark, H., and Whitby, G. S., editors, Kew York, Interscience Publishers, 1946. ( 5 ) Marvel, C. S.,Bailey, %', J., and I n s k e e p , 0 . E., J . Polymer Sci.. 1, 275 (1946). (6) Morton, A. A., Patterson, G. H., Donovan, J. J., and Little, E. L., J . Am. Chem. SOC..68. 93 11946). -,(7) Schmidt, O., Schnell,B., and Rleyer, E. (to I. G. Farbenindustrie), U. S.Patent 1,901,044(1933). ( 8 ) Spencer, R. S., and Boyer, K. F., J . Applied Phys., 17, 398 (1946). ~
~
RXCI:IY?.D for review M a y 23, 1951.
ACCEPTED January 19, 1952.
yl Acetate-Ac J
O
c.
SOLVENT EXTRACTION EQUILIBRIUM DATA V. R. SOHONI AND U. E. WARHADPANDE Lamrninarayan Institute of Technology, Nagpur, M . P . , India
E
T H Y L acetate is used as a solvent for the extraction of acetic acid from dilute aqueous solutions. Knowledge of the ternary mutual solubility and distribution of acetic acid between water and solvent is essential for the design of extraction equipment and evaluation of solvent merits. Complete published data of such nature are, however, lacking. The niutual solubility curve was determined by Mion (4)at 30" C., but the tie line data have not been given. Therefore, the complete data nere obtained by the present authors.
GRADES OF MATERIALS USED
A laboratory source of distilled water and analytical reagent grade chemicals were used. The solvent and the acid were tested for purity by density as well as refractive index determination. The acid was purified by fractional crystallization and its purity was also ascertained by titration. Ethyl acetate required no purification. The properties of the purified chemicals a t 30" C. are giwn below. Refractive Index 1.3320 1.3680 1.3700
Substance Water Acetic acid Ethyl acetate
Density,
Yo Purity by
0.9957 1,0392 0.8939
99 FO
G./MI.
Titration
. .
EXPERI-MEYTA L
The data for the binodal curve were obtained by the synthet,ic method ( 8 ) a t 30" C. using a constant temperature bath. The end point was ascertained by the disappearance of turbidity on addition of increasing amounts of acid to water-solvent mixture8 of known composition. The composition of phases in equilibrium for the heterogeneous region was established by analytical estimation of acetic acid in each phase. Hydrolysis during titration was avoided by addition of ice during titration. This furnished the tie line data.
TABLE I.
SOLUBILITY D.4T.i FOR
BINODAL CUR\-t.:
(Composition by weight)
c/o Ethyl Acetate A
Fter 5.30
9.60 17.90
24,60 33.10 41.00
Figure 1.
Phase Diagram for S y s t e m A c e t i c Acid-WaterEthyl Acetate X.
Experimental t i e lines 0. .Extrapolated t i e lines Solubility data 0. Mion (4) A. Present Authors
48.90
41.25 57.00
67,50 80.30 92.90
3.50
Yo Acetic
C 3.9 13.0 17.4
Acid
20.1
22.1 22.0 21.8
21.75
21.00 17.25 11.70 0 0 0 0
INDUSTRIAL AND ENGINEERING CHEMISTRY
June 1952
1429
TABLE 11. EXPERIMENTAL TIELINE DATA
19
Ethyl Acetate Layer Ethyl Acetio acetate, Water, acid, % % %
18 17
93.0 89.3 85.3 81.0 77.5
76
Water Layer Ethyl acetate, %
Water,
%
%
7.95 8.75 10.00 11.20 11.7
89.3 86.0 82.3 79.0 76.5
2.75 5.25 7.70 9.80 11.80
2.5 5.0 7.5 10.0 12.24
4.5 5.7 7.2 9.0 10.26
Acetic acid,
'
75
i 4 13 12 ii
is
il
Figure 2.
17
75
i3
T9
Tie Line Correlation
Othmer (5) and Hand (2)
Experimental data are given in Tables I and I1 and are reproduced in Figure 1. The tie lines are not shown in this figure, but the conjugate line has been drawn on which experimental and extrapolated points are differentiated.
C; z/ ( Figure 4.
b2
c2)-
+
Selectivity Curves (6)
equation discussed by Smith (8) for calculation of partition coefficients in solutropic systems is, however, inapplicable in this case. SOLVENT PROPERTIES
dl Figure 3.
0.2
0.3
0.4
0.5
Equilibrium Distribution Curves TIE LINE CORRELATION
Many equations have been proposed for tie line correlation, two of which have been plotted in Figure 2. The tie lines correlate best by the O t h e r plot (6),and, hence, the O t h e r plot was used for the extrapolation of tie lines.
Certain conclusions of importance in commercial extraction operations can be drawn from the data obtained in these experiments. A plot of the selectivity curve (6) and equilibrium distribution curve is necessary for this purpose. These are, therefore, plotted in Figures 3 and 4 along with those for some other possible solvents (1, 8,7'). The equilibrium curve gives a rough idea of the quantity of the solvent required for extraction. It will be seen from Figure 3 that ethyl acetate has a high dissolving power for acetic acid in comparison with other solvents and, hence, will be required in less amounts than all other solvents for extracting the same amount of acid. NOMENCLATURE
PLAIT POINT
Determination of the plait point presented experimental difficulties and therefore it was located by plotting the conjugate line on either side of the binodal curve and interpolating the point of intersection of the conjugate and binodal curve. The equilibrium values at the plait point are found t o be 32.7% solvent, 45.3% water, and 22% acid by weight in each layer. These values fit the Othmer plot correctly. SOLUTROPY
From the values of equilibrium distribution of acetic acid it will be seen t h a t the system is a solutrope-Le., the selectivity of the acid for the solvent reverses at a certain stage and then becomes selective towards water. Figure 3 shows this more clearly. Below 9.570 acid in the water layer the acid is present in higher concentration in the solvent than in the water layer. For higher concentrations the reverse is the case. The distribution
a = weight fraction of solvent b = weight fraction of water c = weight fraction of acid Subscript 1 = compositions in extract layer 2 = compositions in raffinate layer LITERATURE CITED
(1) Campbell, H., Trans. Am. Inst. Chem. Engrs., 36,593 (1940). (2) Hand, D.B., J . Phg8. Chem., 34, 1961 (1930). (3) Major, C. J., and Swenson, 0. J., IND. ENG.CHEM.,38, 834 (1946). (4) Mion, Compt. rend., 193, 1330 (1931). (5) Othmer, D. F., and Tobias, P. E., IND. ENG.CWEM., 34, 693 (1942). (6) Othmer, D.F.,et al., Ibid., 37,890 (1945). (7) Saletore, 8. A., Mene, P. S.,and Warhadpande, U. R., Trans. I n d i a n Inst. Chem. Engrs.,2, 16 (194849). ( 8 ) Smith, A. S., IND.ENG.CHEM.,42,1206 (1950). (9) Taylor, 9.F., J. Phys. Chem., 1,461 (1897). R E C E I V ~for D review August 17, 1951.
ACCEPTED January 21, 1952.
