ACKNOWLEDGMENT
The authors thank the Phillips Petroleum Co. for the hydrocarbons they provided for this study. A National Science Foundation grant (NSF-G9700) supported in part the experimental phase of this investigation.
NOMENCLATURE
C = composition parameter, x , / (z, + xA
K = vapor-liquid equilibrium constant for j component, y , / x , PI = pressure at point of convergence, p.s.i.a. P, = critical pressure, p.s.i.a. t, = critical temperature, F . xI = mole fraction in liquid phase of component of lowest volatility z, = mole fraction in liquid phase of component of intermediate volatility
x , = mole fraction in liquid phase of j component y = mole fraction in vapor phase of J component A = pressure, p.s.i.a.
LITERATURE CITED (1) Carter, R.T., Sage, B.H., Lacey, W.N., A m . Inst. Mining Met. Engrs., Tech. Publ. 1250 (November, 1940). (2) Grieves, R.B., Thodos, George, Ind. Eng. Chem. (Fundamentals Quarterly) l , 45 (1962). (3) Hadden. S.T.. Chem. Eng. Progr. (Symp. Ser.) No. 7, 49, 53 (19533. (4) Kay, W.B., Ind. Eng. Chem. 32,353 (1940). ( 5 ) Reamer, H.H., Sage, B.H.. Lacey, W.N., J. CHEM.ENG.DATA 5,44 (1960). (6) Rigas, T.J., Mason, D.F., Thodos, George, Ind. Eng. Chem. 50, 1297 (1958). RECEIVED for review October 17, 1961. Accepted March 19, 1962.
Vapor Pressures of Silicon Tetrae hloride-Ca rbon Tetrachloride Mixtures WILLIAM R. KING' and LAWRENCE N. CANJAR Department of Chemical Engineering, Carnegie Institute of Technology, Pittsburgh 13, Pa.
APQR PRESSURE of silicon tetrachloride-carbon tetrachloride systems a t 30", 40°, and 50" C. are presented. The constant of the symmetrical van Laar equation which satisfies the total vapor pressure data is given as a linear regression against reciprocal temperature. Wood (2) obtained data on this system using chemical analysis but his results do not show thermodynamic consistency. The procedure and apparatus have been described previously by Ryder, Kamal, and Canjar ( I ) .
work, the Gibbs-Duhem equation can be assumed valid
a log y
d log
= x'
",!\l
(-c,(2)
and equations which satisfy the Gibbs-Duhem criteria such as the van Laar equations logy, =
Ax:
+ x?]'
(31
+ ( B A ) x?l'
(4)
/ ( A B ) x,
EXPERIMENTAL COMPO UNDS
Baker Analytical Reagent grade carbon tetrachloride and Fisher Scientific Technical grade silicon tetrachloride were used in the experimental work. No attempt was made t o determine purity of the reagents.
log y 3 = -[XI
can be used to describe the variation of log y with composition. I f A = B , the van Laar equations reduce to
VAPOR-LIQUID EQUILIBRIUM THEORY
logy = B(l- x,)Z
At low pressures, the total pressure exerted by a binary mixture may be written as P, = x l y l P , o + x2y2P20
(1)
If log y does not vary much with pressure as in the present
' Present address, FMC Corp., South Charleston, W . Va. VOL. 7, NO. 3, JULY, 1962
Bxlz
(5)
By expressing y bas a sum of an infinite series y =1
+ B ( l - x , ) +~ (B/2) (1- x,)$
(6)
and ignoring all but the first two terms, Equation 1 may be written as P, = X l ( 1
+ Bx:) A + xz(1 + Bx:) p:
(7)
35 1
1
Table I. Experimental Total Vapor Pressure Data for CC14-SiC14 System
EXPERIMENTAL
-VAN LAAR
1
CORRELATION
(Total vapor pressure, cm. of Hg)
60.0
Run No. 7 3
5 8 2-A 2-B 1-A 1-B
50.0
P E
40.0 LL
3
m
a
0. LL
3
Mole Fraction CC1, 1.0000 1.0000
i.oooo
0.6863 0.5244 0.5244 0.5224 0.5224 0.5219 0.3518 0.1279 0.0000 0.0000
30.0" C. 15.25 15.34 i5.40 21.43 23.94 23.92 23.92 23.79 24.14 26.08 29.08 30.37 30.20
40.0" C. 21.23 21.28 21.51 31.02 34.00 33.94 34.40 34.10 33.99 37.86 41.70 43.84 43.91
50.0" C 31.61 31.72 31.85 43.30 47.21 47.41 47.58 47.47 47.25 52.22 57.81 60.98 61.20
30.0
tainty of 10% in the range of experimental temperatures .1.5399+
20.0
I0.C
0.5483 x 10'
(10)
if logarithms to the base e are used in Equation 5 . The vapor-liquid equilibrium distribution ratios for this system can be obtained from the following relation ao
a4
0.2
0.6
ae
1.0
MOLE FRACTION CC14.
Figure 1. Experimental vapor pressure of SIC14-CC14 mixtures vs. mole fraction CC14
yzlx, = Y8PPIPt
(11)
Figure 1 compares the experimental data with the total pressure calculated from the van Laar equations using the value of the van Laar constant predicted by Equation 10. Table I summarizes the results of the experimental work. NOMENCLATURE
or
B=
Pi
- XlPP - x*PS
XIX?(X?E
+ XIp5)
B can be calculated directly from experimental data by Equation 8. Analysis of the experimental data presented here indicates that the assumption A = B in the van Laar equation is justified for this particular system. The maximum error introduced into the calculation by the approximation of the infinite series is about 0.5 mm. Hg. The experimental variance is greater than 0.5 mm. Hg.
A , B = van Laar constants Pi = total vapor pressure of mixture (cm. Hg) R = vapor pressure of pure component i (cm. Hg) T = absolute temperature, K. xi, = mole fraction of component, i, in liquid mixture yz = mole fraction of component, i, in vapor in equilibrium with liquid mixture 7 , = activity coefficient of component i log = natural logarithm, log, LITERATURE CITED
RESULTS
(1) Ryder, G.A., Kamal, M.R., Canjar, L.N., J. CHEMENG.DATA 6, 594 (1961). (2) Wood, S.E., J . Am. Chem. SOC. 59, 1510 (1937).
The variation in B with reciprocal absolute temperature can be represented by an equation with a relative uncer-
RECEIVED for review December 6, 1961. Accepted February 12, 1962.
352
JOURNAL
OF CHEMICAL AND ENGINEERING DATA
