Vapor-Liquid Equilibria at Subatmospheric Pressures BINARY SYSTEM ACETONE-CARBON TETRACHLORIDE KENNETH C. BACHMAN' AND EDWARD L. SIMON9 Rutgers University, New Bricnswick, N . J .
A
elsewhere (2). The distillations carried out for the purpose of determining the azeotropic compositions by the method of successive approximations were performed in the same still used for the purification of the carbon tetrachloride.
COMPLETE study of the vapor-liquid equilibria in the binary system acetone-carbon tetrachloride has never been reported, and what data exist concerning this system are very limited. In 1890Haywood (If)presented boiling point data for the system a t 777 mm. and reported that a solution containing 80 to 85 weight % (91.4 t o 93.7 mole %) acetone distilled unchanged at a temperature only 0.05" C. below that of pure acetone. Atkins ( 1 ) in 1920 reported the existence of an azeotrope boiling a t 59.8" C. a t 763 mm. but presented no composition data. The only definite report of an azeotrope at 760 mm. was made by Lecat ( I S ) who listed a boiling point of 56.01 C. a t 88.5 weight yo(95.3 mole %) acetone. In this investigation complete vaporliquid equilibrium data have been determined a t 760, 450, and 300 mm.
VAPOR PRESSURE MEASUREMENTS
Calculations of activity coefficients require vapor pressure data for the pure components. For carbon tetrachloride the data of Dreisbach and Shrader (8)were found to be satisfactory. They may be represented by the equation Carbon tetrachloride: loglop(mm.)=
O
- 1627.23/T '+7.53127 (1)
For acetone the data of these authors could not be used because they led t o a boiling point of 56.20 C. at 760 mm. which is 0.12 O C. higher than the value obtained in this investigation. This difference was felt to be significant both because it is greater than the error in the experimental measurements herein reported and because i t is almost the same as the difference observed in this investigation between the boiling points of pure acetone and the azeotrope. The boiling points of acetone were carefully determined in the Othmer still a t the four operating pressures. Although the plot of log p us. 1/T showed a slight curvature, the data could be represented satisfactorily by the equation O
MATERIALS USED
The carbon tetrachloride (Eimer and Amend Technical Grade) was purified by distillation at atmospheric pressure through a column packed with 6-nun. glass Raschig rings. The column waa 130 cm. long and 38 mm. in diameter, and with t.his packing and a reflux ratio of 6 to 1, it was equivalent to 8 theoretical platea (IS). The acetone (Eimer and Amend C.P. Grade) was purified by t.he method of Bramley (4). A 5% solution of potassium permanganate in distilled water was used as the oxidizing agent, and the material was distilled twice through a 25-plate Brunn column at, atmospheric pressure and a reflux ratio of 5 to 1. The purified liquids were stored in brown glass bottles, and all experimental work involving the acetone was carried out in apparatus protected from light to prevent any photolytic decomposition (6). The physical constants of the purified liquids are listed in Table I along with previously published values.
Acetone: logl~p(mm.) = -1633.65/T
4- 7.84311
(2)
I n Table 111 are listed the boiling points obtained in this investigation, those obtained from the data of Dreisbach and Shrader and those calculated using Equation 2. VAPOR-LIQUID EQUILIBRIUM DATA
The experimehtal results obtained for the various isobars are presented in Table I V along with the values of the activity coefficientscalculated from the relationships:
ANALYTICAL METHOD
Equilibrium samples of liquid and vapor condensate were analyzed by specific gravity measurements, using a standingtvDe Drecision 10-ml. Dvcnometer of b"irosificate glass (Eck axid Krebs, Cataiog No. 4154). Analytical checks using this apparatus never exceeded and were TABLE I. PHYSICAL CONSTANTS O F hzATERIALS USED usually less than f0.2mg. Values of the Refractive Index Speci5c Gravity Boiling Point, C. Rpecific gravitie.; of known mixtures w e Liquid Exptl. Llt. Exptl. Lit. Exptl. Lit. Ref. presented in Table TI along with refracAcetone 66 08 66 08 0.78508as 0.7850S2: l.35606s6 1 . 3 5 6 0 9 y 4,7 tive index data on the same solution obt 4 n e d with a dipping refractometer. Carbon tetrachloride 76.74 76.75 1 5844': 1.58472': 1.45706%' 1 45704%' 8, 7 The constant temperature bath used in these measurements was controlled to 10.01O C. by a mercury-toluene reguAND REFRACTIVE INDEXES OF TABLE 11. SPECIFICGRAVITIES Intor. MIXTURES OF ACETONEA N D CARBON TETRACHLORIDE O
Acetone, Mole % 0 00 10 22 19.73 30 10 40 07 50 04 59 95 69 90 79 96 89 97 100 00
EXPERIMENTAL METHODS
The vapor-liquid equilibrium data were determined by the
u& of a glass Othmer still ( 1 5 ) connected to a vacuum manifold in which the pressure regulation was accomplished by means of a Cartesian diver-type hanostat (9, IO). A detailed description of the complete assembly and its operation has been reported 1
Present address, M.W. Kellogg Co., Jersey City, N. J. address, General Electric Reaearch Laboratory, Schenectady,
* Present N.Y.
202
1 58440
1 5204% 1 45851 1 38771 1 31587 1 24000 1 1601s 1 07520 0.98409 0 88758 0 78508
ng 1 45706 1 44926 1 44158 1 43260 1 42356 1.41401 1 40359 1.39300 1 38147 1 36916 1 35606
INDUSTRIAL A N D ENGINEERING CHEMISTRY
January 1952 I
I
I
I
I
I
I
l
T A B L111. ~ BOILING POINTS O F ACETONE AT VARIOUS
o LIQUID
d VAPOR
P~~~:SSURES
Pressure Mm. Merchry 760.0 612,5 600.0 510.5 507.5 450.0 421.5 346.4 315.5 300.0
m-
$
w- 52-
a
2a 502 481
e 4e-
44 42 -
Ix)
“8.0
0.;
0,;
0; Old 0:s ole 0; ole COMPOSITION MOLE FRACTION ACETONE
203
ole
I
Boiling Point, C. Equation 2 Dreisbach and Snyder 56.04 56.20 49.94 49.37 44.96 44.81 44.81 41.81 39.89 34.86 32.53 32.55 31.28
Exptl. 56.08
49.36 41.56 31.29 I
t
1
1
1
1
ib
Figure 1. Boiling Point-Composition Curve for the Binary System Acetonecarbon Tetrachloride at 450 Mm.
in which y = mole fraction in the vapor phase x = mole fraction in the liquid phase po = vapor pressure of pure component at the boiling point of the solution P = total still pressure Subscript 1 refers to the more volatile component acetone. Subscript 2’refers to the less volatile component, carbon tetraohloride. The data at 450 mm. are presented in Figure 1, which is the boiling point-compositiondiagram, and in Figure 2, which is the distribution diagram. The corresponding curves for the other
TABLEIV. EQUILIBRIUM DATA FOR
69.16 49.26 49.27 49.36
Acetone, Mole % Liquid Vapor 760 Mm. 0.00 0.00 5.90 20.25 27.10 8.70 40.75 17.90 48.95 26.40 56.55 37.40 61.26 45.10 65.50 52.55 61.65 70.65 75.80 69.60 79.85 76.20 84.60 82.95 89.80 89.50 91.40 91.50 95.30 95.20 100.0 100.00 600 Mm. 0.00 0.00 90.48 90.85 90.50 90.90 100.00 100.00
60.40 55.29 52.80 49.50 47.96 46.26 44.88 44.06 43.65 43.05 42.68 42.42 42.11 41.92 41.82 41.73 41.58 41.54
450 Mm. 0.00 18.90 27.95 39.30 45.30 51.50 57.35 61 .OO 63.55 67.70 69.90 72.80 75.90 78.40 80.00 82.90 89.45 90.15
Boiling Point, C.
0.00 4.90 8.75 16.25 22.00 29.70 38.30 44.70 49.30 66.50 60.40 65.25 70.25 74.10 76.30 80.45 88.90 89.56
THE
SYSTEM ACETONE-CARBON TETRACHLORIDE AT VARIOUS PRESSURES
Activity Coefficients
ri
MOLE FRACTION ACETONE IN LlOUiD
Figure 2. Distribution Diagram for the Binary System Acetone-Carbon Tetrachloride at 450 Mm.
79
Boiling Point, C.
41.58 41.57 41.53 41.53 41.52 41.49 41.48 41.50 41.56
1.008 1.008
1.000
2.34 2.11 1.80 1.82s 1.457 1.324 1.244 1.198 1.136 1.111 1.08: 1.060 1.046 1.040 1.028 1.007 1.009
1.000 1 .& 1.8s
48.77 43.95 40.58 38.60 38.80 a5.46 34.33 34.20 33.36 33.33 33.18 32,74 32.21 31.89 31.90 31 ..63 ai.52 31.33 31.28 31.27
...
3i:27 31.24 3i:25 31.22 31.25 31.20 31.23 31.25 31.29
Aoetone, Mole 5% Liquid Vapor 450 Mm. (Contd.) 90.45 90.90 91.25 91.65 92.00 92.25 92.60 92.70 92.75 92.80 93.60 93.60 94.50 94.50 96.85 96.75 100.00 100.00
0.00 5.10 11.20 16.60 23.45 31.10 38.25 39.90 49.35 48.50 51.50 56.30 65.55 70.10 71.65 76.75 78.80 86.50 90.85 93.40 94.40 94.60 94.70 95.10 95 20 95: 50 95.85 96.15 96.80 97.95 99.40 100.00
Activity Coefficients 71
n 1.81 1.87 1.90 1.91 1 .9, 1 .9, 1.97 2.01
2.41 2.01 1.80 1.60
1.436 1.321 1.28r 1.187 1.197 1.15r
1.135 1.075
1.05: 1.044 1.036 1.02B
1 .ooo 1.005 1.028 1.050
1.085
1.134 1.191 1.228 1.288 1.291 1.331 1.355
1.455
1.00,
1.56 1.57 1.64 1.65 1.79 1.84 1.90
1.000 1.002
1.96 1.9,
1.010 1.006
... ...
:
1 00,
1 .OO¶ 1.001
1.008
1 .ooz 1.001 1.000
... ... ...
1.91 1.96 1.9, 1.96 2.01 1 .9s
‘
Vol. 44, No. 1
INDUSTRIAL A N D ENGINEERING CHEMISTRY
204
isobars are of the same form displaced only slightly from the 450 mm. curves. DETERMINATION 0F A ZEOTROPIC COMPOSITION S
The method most commonly used for establishing the azeotropic composition is to determine the point at which the distribution curve crosses the 45O diagonal. In this system the distribution curve approaches this line with a slope so close to 45” that the crossing cannot be determined accurately. The azeotropic composition was therefore determined independently a t
relationship between the constants in either the Margules or van Laar equations which may be used to represent the variation with composition of the logarithm of the activity coefficient of each component. The final forms of the Margules and van Laar equations may be represented as follows: Quantity
Margules
van Laar
R
2.4
e
I 3.0
CARBON TETRACHLORIDE
I
0.1
0.2
I
I
I
0.3 0.4 0.5 0.6 0.7 0.6 MOLE FRACTION ACETONE IN LIQUID
I
I
0.9
1.0
Figure 3. Variation with Composition of the Activity Coefficients of the Binary System Acetone Carbon Tetrachloride at 450 Mm.
For these data the observed variation of the activity coefficient with composition could be more satisfactorily represented by a van Laar equation with A and B values somewhat different from those obtained from the terminal values of the activity coefficientcomposition plots, as suggested by Carlson and Colburn. In Figure 3 the variation of activity coefficient with composition is shown, circles representing the data for the 450 mm. isobar, and solid lines the van Laar equations with A equal to 0.470 and B equal to 0.320. Redlich and Kister have expressed the Gibbs-Duhem equation directly in terms of experimental data ( P , t , 2,y) and arrive a t a set of equations from which it is possible to calculatc the slopes of the boiling point-omposition curves a t various points. For all composition values except the limiting ones of x equal to zero and one, the slope may be calculated from the equation
-
dt/dy = 4x1
Circles represent experimental data Solid lines represent the van Laar equations
Y1)/Yl(l
- Yl)
(5)
where the slope factor, s, is defined by
approximations (20). The azeotropic boiling points were then determined from a large scale plot of the boiling point as a function of composition. The azeotropic data are shown in Table V.
0.$343/[~1 d log p?/dt
s
760, 600,450, and 300 mm. by Young’s method of successive
+ (1 -
21)d
log p!/dt]
(6)
When x is zero and unity the following relationships apply: x = o
Slope dt/dzl
e(l
dt/dz
s(1 .-
- a)/a a)
TABLEV. AZEOTROPIC COMPOS~TIONS AND BOILING POINTS where CY is defined by pressure, Mm. Mercury 760 600 450 300
Acetone, Mole % ’ 94.85 94.90 95.20 96.40
Boiling Point, 55.98 49.26 41.47 31.22
C.
Several attempts have been made empirically t o relate the change in azeotropic composition with pressure (12, 14, 16, 19), but in all these cases the variation of composition with pressure has been many times larger than that observed in this investigation. A change of only 1.55% in the azeotropic composition brought about by a change of 460 mm. pressure is much too small to be represented by any of the methods suggested. The variation with pressure of the azeotropic boiling point parallels the vapor pressure-temperature relationship’of pure acetone as seen from the fact that for each isobar the difference between the aaeotropic boiling point and that of acetone is essentially constant a t 0.09’ f 0.02 ’C. THERMODYNAMIC CONSISTENCY OF THE DATA
The internal consistency of the data was tested by the methods of Carlson and Colburn (5) and of Redlich and Kister (17). Both are based upon the Gibbs-Duhem equation, which, for any homogeneous system at constant temperature and pressure, defines the relationship between the composition of the system and the values of any partial molar quantities of the components. Carlson and Colburn have utilized this equation to establish a
ff
=
(9)
P:rl/P,0rz
For calculations herein reported the limiting values of yJy2 were obtained by extrapolation of the log ( y ~ / y z )us. x curve. In Equations 6 and 9 the vapor pressures, py and pg, have been used instead of Redlich and Kister’s PI and Pz functions which include correction terms for nonideal gas behavior and for the variation with temperature of the activity coefficients. In Table VI are tabulated the data necessary for these cal-
TABLEVI. COMPARISON O F CALCULATED AND GRAPRICALLY DETERMINED VALUES O F d t / d y AXD THE LIMITINGSLOPES FOR ACETOXE-CARBON TETRACHLORIDE AT 450 MM.
THE S Y S T E M
dt /du I
Temp 0
C.”
52.80 49.50 46.26 43.65 42.42
$1
211
8.75 16.25 29.70 49.30 65.25
27.95 39.30 51.50 63.55 72.80
51
8
a
0.00 100.00
29.79 26.29
4.99 0.948
”
Graphidlog d log Calcd. by cally from py/dt p?Jdt 8 Equation 5 Figure 1 -27.0 -28.9 0.0154 0.0153 2 8 . 3 7 -27.8 -27.0 0,0156 0,0155 27.99 -23.8 -24.6 0 , 0 1 5 9 0,0159 2 7 . 3 1 -16.6 -16.4 0.0163 0.0162 2 6 . 7 3 -10.8 -9.6 0,0165 0.0164 2 6 . 3 8 LIMITINGSLOPES dt/dx dt/du GraphiGraphiCslcd, by cally from Calcd. by cally from Equation 8 Figure 1 Equation 7 Figure 1 -118.9 -132.0 -23.8 -22.7 +1.44 +l.6 f1.37 +l.4
January 1952
INDUSTRIAL AND ENGINEERING CHEMISTRY
culations along with a comparison of the experimental and calculated slopes. This test, like the former, was applied only to the data for the 450-mm. isobar. Sample calculations showed that the activity coefficient data were virtually temperature independent over the range of this investigation. The satisfactory fit of the data with the van Laar equation and the agreement between the calculated and observed boiling point curve slopes indicate that the data of this investigation are thermodynamically consistent. ACKNOWLEDGMENT
The authors gratefully acknowledge the support given t o this investigation by the Research Council of Rutgers University. LITERATURE CITED
(1) Atkins, W.R.G., J . Chem. SOC.,1920,218. ( 2 ) Bachman, K.C., thesis, Rutgers University, 1950. (3) Beilstein, “Handbuch der Organischen Chemie,” 2nd supplement, Vol. 1, p. 22,Ann Arbor, Mich., Edwards Bros., 1941. (4) Bramley, A.,J. Chenz. SOC.,1916,lO.
20s
(5)Carlson, H. C., and Colburn, A. P., IND.ENG.CHEM.,34, 581 (1942). (6) Davis, W., Jr., Chem. Revs., 40,201 (1947). ENG.CHEM.,41,2875 (7) Dreisbach, R. R., and Martin, R. A,, IND. (1949). (8) Dreisbach, R. R.,and Shrader, S. A., Zbid., 41,2879 (1949). (9) Gilmont, R.,Anal. Chem., 23,157 (1951). (10)Gilmont, R.,IND. ENG.CHEM.,ANAL.ED., 18,633 (1946). (11)Haywood, J. K.,J . P h y 8 . Chem., 3,317 (1899). (12)Horsley, L.H.;AnaZ. C h a . , 19,603 (1947). (13)Lecat, M., “Tables Azeotropiques,” Tome Premier, 2nd ed., p. 194,Ucole-Bruxelles, published by the author, 1949. (14)Nutting, H.8.,and Horsley, L. H., A n d . Chem., 19, 602 (1947). ENG.CHEM.,35,614 (1943). (15)Othmer, D. F.,IND. (16)Othmer, D.F.,and Ten Eyck, E. H., Jr., Ibid., 41, 2897 (1949). (17)Redlich, O.,and Kister, A. T., Ibid., 40,341 (1948). (18) Robinson, 5. R.,‘and Gilliland. E. R., “The Elements of Fractional Distillation,” 3rd ed., p. 221,New York, McGraw-Hill Book Co., Inc., 1939. (19) Skolnik, H., IND. ENG.CHEM.,43, 172 (1951). (20)Young, S.,“Distillation Principles and Processes,” p. 61, London, Macmillan and Co., Ltd., 1922. RECEIVED April 12, 1961. Presented before the Division of Industrial and CHEMICAL Engineering Chemistry at the 119th Meeting of the AMERICAN SOCIETY, Boston. Mass.
Vapor-Liquid Equilibria in Methanol Binary Systems N
METHANOL-PROPANOL, METHANOL-BUTANOL, AND METHANOL-PENTANOL WILLACE D. HILL’ AND M. VAN WINKLE University of Texas, Austin, Tex.
V
APOR-liquid equilibrium studies of the low molecular weight, oxidized hydrocarbons have been restricted largely to the first and second members of homologous series. This investigation is the first of a series of projects to develop data for the possible evaluation of some correlating factors for vapor-liquid equilibrium data based on the type of oxidized hydrocarbon. With the growing commercial importance of the direct oxidation process, accurate data for the design of separator units has become necessary. T o the authors’ knowledge, no complete data have been reported on any of the systems investigated. All vapor pressures used in calculating the activity coefficients were obtained from the literature. MATERIALS
The source and the physical constants of the purified materials are presented in Table I. The pentanol was fractionated for purification in a glass column, which had a &foot height and a */,-inch diameter, and was packed with glass helices. Approximately 200 ml. of a constant boiling center cut were obtained for use in the investigation. The other compounds were considered to be sufficiently pure when received. Because of the tendency of anhydrous methanol to absorb moisture from the atmosphere, the material was exposed to the atmosphere only momentarily while chargisg the equilibrium still. Periodic refractive index checks were made on all materials to detect any change in purity. Present addreaa, Monsanto Chemioal Co., Texas City, Tex.
APPARATUS
A Bausch and Lomb recision refractometer was used to determine the cornposition ofliquid and vapor Sam les taken from the equilibrium still and the purity of the chemicaE used in the investigation. Prism temperature was maintained a t 20’ C. (68’ F.) i 0.05” C. (0.09’ F.) with a Precision Scientific Co. constant temperature circulator. Monochromatic light for the optical system was obtained from a sodium vapor lamp. A Cottrell boiling point apparatus was used to check urity and to calibrate the equilibrium still thermocouple (4). &e boiling temperatures were obtained with a thermometer graduated in 0.2” C. (0.36’F.)divisions, and the temperaturedata were re orted to f0.1’ C. (0.18’ F.). Either pressure or vacuum o o u l d t e applied to the system and it could be controlled manually or with a Cartesian manostat. The boiling temperatures were transposed from the temperature at the pressure in the still to the temperature a t 760 mm. pressure, usrng the vapor pressure data for t h e pure materials as reported in the literature (8,9). The va or-liquid equilibria were determined in a Colburn still (6) modifed with respect to size and the addition of an extra
TABLE I. REFRACTIVE INDEX AND BOILINGPOINTS FOR Amonom Compound Methanol
Propanol Butanol Pentanol
Source J. T.Baker Chem. Co. Eastman KOdak Co. J. T. Baker Chem. Co. J. T.Baker Chem. Co.
Normal Refractive B.P., O C. Index Temp., Exptl. Lit. Exptl. Lit. C. 64.7 64.7 1,32870 1.32875 20.5
97.0
97.8 1.38581 1.38543
20
117.0
117.5 1.39911 1.39931
20
137.0
137.8 1.41146 1.40994
20
