R obert E. Treybal, Lawrence D. W eber1, and Joseph. F. Daley2
method is described for estim ating the position o f the plait point. Densities, refractive indices, and viscosities at 25° C. as well as vapor-liquid equilibria at 755 m m . Hg were determined for the binary system acetone-trichloro- cthanc. Vapor pressures o f trichlorocthane were measured over the range 73.5° to 113.5° C. The data indicate that 1,1,2-trichloroethane would m ake an acceptable sol
vent for extracting acetone from its aqueous solutions.
I
N CONNECTION with a program for determining the characteristics of liquid-liquid extraction equipment, it was found desirable to have rather complete data on equilibrium and other physical properties for the ternary system acetone-water- 1,1,2-trichloroethane. These data were accordingly determined, and are reported in this papier.
Reagent grade acetone, dried over Drierite, was fractionated in a laboratory column equivalent to approximately 20 theoreti
cal plates, and a central portion of the distillate amounting to about 75% of the still charge was retained for this work. The fraction had a normal boiling point of 56.1° C. over its entire range, a density dip = 0.7840, and a refractive index n2D5 = 1.3556; these values agree with the accepted characteristics (10).
’ A t present in the United States Navy.
5 Present address, The Flintkote Company, East Rutherford, N. J.
The 1,1,2-trichloroethane, purchased from the Carbide and Carbon Chemicals Corporation, was distilled by a method similar to that used for acetone, and the central portion of the distillate had a normal boiling point of 113.5° C. over its entire range.
Determinations were made at 25° C. of the limiting solubility and the tie lines in the ternary system, according to the cus
tomary procedures. Mixtures of acetone and trichloroethane of known concentration were held in a water bath at 25.0° ± 0 . 1 ° C., and were titrated with water until the appearance of a slight turbidity indicated the limiting solubility concentrations. The refractive index (by Abbe refractometer) and density (by pycnom- eter) of the solutions were determined after the turbidity had settled from the solution by standing for a short time in the water bath. Similar measurements were made by titration of acetone- water solutions with trichloroethane.
The solubility of trichloroethane in acetone-free water (Table I) is in agreement with the data of van Arkel and Vies (I). Al
though the solubility of water in trichloroethane has appar
ently been measured {16), the present determination could not be checked because the published data were unavailable.
A C E T O N E
Since the slopes of these lines are so nearly unity, the value 14.58 should nearly equal the initial slope of the mole fraction distri
bution curve of Figure 2 {17), and this is the case.
A convenient method of estimating the position of the plait point can be developed in connection with this diagram. At the plait point, the distinction between the water-rich and trichloro- othane-rich layers disappears. Consequently
/ X y \ _ ( X n \ _ fX z \ ( X n \ _ _ / X ,\
\ x J P ~ \ x j p \ x j p \ x J P \ x j „ \ x j p
To determine the tie lines, known mixtures of all three compo
nents, of such compositions as to ensure the formation of insoluble liquid solutions, were agitated in the water bath for a minimum of 3 hours. Samples of the settled layers were withdrawn, and their refractive indices measured. Reference to a large scale plot of refractive index against concentration of acetone for saturated solutions gave the analysis of the equilibrium layers.
Data for the tie lines are listed in Table II. Solubility and tie line data are plotted in Figure 1 on the usual triangular coordi
nates. The crosses near the centers of the tie lines represent the over-all composition of the two-liquid-phase mixtures used in determining the individual tie lines; it is necessary, if a material balance is truly established, that the tie lines pass through these points.
T I E L I N E C O R R E L A T IO N S
A simple curve of the distribution of acetone between two im
miscible solvents can be obtained by plotting the concentration of acetone in the water-rich layer against its concentration in the trichloroethane-ricli layer. This is presented in Figure 2, in both weight and mole fraction units. The acetone favors the trichlorocthane-rich layers; consequently this solvent can be recommended (at least from the point of view of liquid equilib
rium) for extracting acetone from aqueous solutions.
Using the notation previously presented {17), the weight frac
tions of components o, 6, and c of the ternary mixtures are X h
The same type of plot was later developed in terms of mole frac
tions, and its significance was discussed {17). The present data plot well in this manner, and the equations of the straight lines can be extrapolated until it intersects the limiting solubility curve. The plait point for the present system has been determined in this manner; the corresponding concentrations are listed in Table II.
Othmer, White, and Treuger {14) discussed the importance of another factor which influences the choicQ of solvent in an ex
traction process. They point out that in the extraction of a sol
ute such as acetone from an aqueous solution, it is important that the high relative immiscibility of . solvent and water be main
August, 1946 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y 819 graphically by the use of effective concentration
curves; the present data are plotted in this manner in Figure 4. It is evident that the curve remains high over great ranges of acetone concentration.
AD DITION AL SOLUTION PRO PE RTIE S In order to make more complete the available data on such mixtures, additional densities, refractive indices, and viscosities were determined. Those for the binary system acetone-trichloroethane are listed in Table III and plotted in Figure 5. Viscosities were determined with calibrated Fenske-Cannon- Ostwald viscometers. Several densities of the ternary mix'tures in the area of complete mutual solubility were also determined (Table IV). The data were plotted with the densities of solutions along the solubility curve, with densities of acetone-water solu
tions (10), and with densities of acetone-trichloro
ethane (Figure 6). The densities and tie line rela
tionships arc such that, at all parts of the diagram ex'cept the-plait point, the water-rich layers arc less dense than the corresponding equilibrium trichloro- ethane-rich layers.
V A PO R-LIQ U ID DATA FOR ACETONE- TR ICH LO RO ET H A N E
In order for a solvent to be satisfactory for ex
traction purposes, it must be-easily separable from the extracted solute. In this connection vapor-liquid equilibria at a pressure of one atmosphere (755 mm.
Hg) were determined with a standard Othmer still ( / / , 12) fitted with a barostat. The barostat was capable of holding the pressure constant within 0.5 mm. of mercury. Samples from the still and con
densate receiver were analyzed by refractive index with the help of the previously determined data for
ponents were necessary. Adequate data were avail
able for acetone {15), but considerable discrepancy was found between the published vapor pressures for trichloroethane {10, 15) and similar data made avail
able by the manufacturers (S). Consequently some additional measurements were made with a Wash
burn-Read apparatus {18) fitted to the barostat used
T an i,k II. E q u i l i b r i u m T i e L i n e C o n c e n t r a t i o n s f o r
Figure 3. Tie Line Correlation and Determination o f Plait Point
Estimated plait point 14.6 27.4 58.0 Figure 4. Effective Concentrations in the Ternary Liquid
System
T a b l e I I I . P r o p e r t i e s o p A c e t o n e - L 1 , 2 - T r i c i i l o r o e t h a n e
in accordance with the generalizations based on hydrogen bond
ing of Ewell, Harrison, and Berg {5). The general shape of the curves in Figure 9, and the fact that the molar volumes of the components are of the same order of magnitude, indicate that they should be capable of fitting the Margules type of equations (4). The best over-all fit that could be obtained required ter
minal values of activity coefficients equal to 0.437 for acetone and 0.912 for trichloroethane; the corresponding curves are shown as dashed lines in Figure 9. The fit is not good, yet the values of vapor concentration calculated from these curves, as listed in Table V, do not differ greatly from observed data.
The ratio of terminal values of acetone activity coefficients for the binary systems acetone-water and acetone-trichloroethane should equal the coefficient of the mole fraction tie line equation, 14.58, when the exponent in this equation is so nearly unity {17).
If the activity coefficient of acetone at infinite dilution in water is 9.3 (2), this would require that the terminal acetone activity coefficient in trichloroethane solutions be 0.639, which falls near the observed value. An exact check with the Margules equations may be lacking because of slightly incorrect temperatures taken in the Othmer apparatus; incorrect readings may have been made because, although the thermometers were calibrated, no provision was made for wetting the thermometer with both liquid and vapor. It may also happen that the Margules equations do not apply to this system.
For the separation of acetone from trichloroethane solutions containing small amounts of water, as produced by an extraction operation, the flowsheet of Otlimer and Ratcliffe {18) would ap
ply. Their conclusions with respect to the similar system ace- tone-water-chlorobenzene, that the small amounts of water held by saturated solutions will not affect the separation of acetone, seem completely applicable here.
CONCLUSION
The ternary liquid equilibrium data, both for tie lines and effective concentrations, show that acetone is readily extracted from aqueous solu
tions by. 1,1,2-triehloroethane. The density dif
ferences between equilibrium layers in the range of concentration that would ordinarily be en
countered are large, and interfacial tension characteristics, although not measured, are such previously on the Otlimer equilibrium still. The results are pre
sented in Table VI and in Figure 8 on (log p vs. 1/T° K .) coordi
nates. The new data and those made available {8) agree well and are somewhat lower than those previously published.
Activity coefficients w'ere calculated and plotted in Figure 9 (4). Since the activity coefficients are largely fractional, the solutions show negative deviations from Raoult’s law. This is
5 1.39
Properties o f A ceton c-l,l,2-Tricliloroeth an e Solutions at 25° C.
August, 1946 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y 821
Figure 7. V a por-L iq u id E quilibria o f A ceton e- 1, 1 ,2-T rick lorocth an e a t 755 M m . M ercury
that settling of insoluble phases is rapid and complete. In addi
tion the vapor-liquid equilibrium data show that the acetone can be readily separated from trichloroethane solutions by distilla/- tion. This solvent should therefore be acceptable as an extrac
tion agent for removal of acetone from its aqueous solutions.
N O M E N C L A T U R E
a, b c X
x
= relatively immiscible solvents '= distributed solute
= liquid concentration, weight fraction
= liquid concentration, mole fraction
■ y = vapor concentration, mole fraction
Subscripts 1, 2, 3 = components a, b, c, respectively; first sub
script refers to component whose property is indicated, the second to the predominant component of the solution. Thus, xn = mole fraction of c in an a-rich solution
p = plait point
MOLE FRACTION ACETONE IN LIQUID Figure 9. A ctivity Coefficients in the Binary System
(3) Carbide and Carbon Chemicals Corp., private communication.
(4) Carlson, H . C., and Colburn, A . P., In d. En g. Chem., 34, 581 Chemical Rubber Publishing Co., 1941.
(9) Henne, A . L., and Hubbard, D . M .,
J.
A m .Chem. Soc.,
58, 404(19 3 6 ).'
(10) International Critical Tables, New York, M cGraw-Hill Book C o., Inc., 1928.