Effect of Polar Components on Relative Volatility of the Binary System: Normal Octane-Ethylcylohexane P. S. PRABHU and MATTHEW V A N WINKLE University of Texas, Austin 12, Tex.
Vapor liquid equilibrium data are presented for the binary systems n-octane-ethylcyclohexane, n-octane-butyl Cellosolve, n-octane-2-propanol and ethylcyclohexane2-propanol at 400 mm. Hg pressure. To determine the effect of additions of butyl Cellosolve and 2-propanol to selected compositions of the n-octane-ethylcyclohexane system on the relative volatility partial ternary data were determined at 400 mm. Hg. The butyl Cellosolve increased the relative volatility of the n-octane relative to the ethylcyclohexane to a greater extent than the 2-propanol.
THIS
RESEARCH is a part of the program being conducted to study experimentally the character and the effect of polar components on the relative volatility of binary systems. Houser ( 8 ) , Lyvers (IO), Murthi ( I I ) , Roberts (17), and Quozati (15) have completed portions of this over-all study. Some other pertinent investigations in this area have been reported by Gerster ( 4 ) , Pierotti ( 1 3 ) , Prausnitz ( 1 4 ) ,Ralf Anderson (16),and Updike ( 2 4 ) . Vapor liquid equilibrium data for the n-octane-ethylcyclohexane, n-octane butyl Cellosolve, n-octane-2-propanol, and ethylcyclohexane-2-propanol systems have been determined a t 400 mm. Hg absolute. The results are presented in tabular and graphical form. In addition the effect of the quantity of butyl Cellosolve and 2-propanol added to mixtures of varied compositions
of n-octane-ethylcyclohexane in modifying their relative volatilities has been investigated a t 400 mm. Hg absolute. Butyl Cellosolve was found more effective than 2-propanol in changing relative volatility. EXPERIMENTAL Materials. The experimental and literrture values of physical properties of the materials used in this investigation are given in Table I . They were of reagent or pure grade. As the physical properties of these materials checked with the literature values with the exception of 2-propanol, no attempt was made to purify them further. The maximum possible error in composition introduced by the difference in refractive index of 2-propanol is 0.0004 mole fraction.
Table I. Properties of Materials
Ethylcyclohexane
Normal Octane Exptl.
Lit.
Exptl.
Lit.
R.I. C. 30
nD
Density d,
30 31 B.P., 400 mm. Antoine Constants A
1.39287
1.39268(2)
0.694943
0.69438 (2)
104.1
104.0(23)
1.428369 0.77832 109.2
0.77865 (2) 109.1 (23) 6.87041 1384.036 215.128
6.92374 1355.126 209.517
B C
1.42859(2)
2-Propanol
Butyl Cellosolve Exptl.
Lit.(3)
Exptl.
1.41746 1.41943
1.4172 1.4193
1.37672
Lit.
R.I. C. nD
25 20
1.37757(9) 1.37711(25)
Density dr 25 0.89565 B.P., 400 mm. 149.2 Antoine Constants A B C Log P = A - B / ( C + t ) , where P = mm. Hg and t = C.
14
0.8958 149.3 7.16462 1538.7 188.0
0.780709 67.8
0.7810(7) 67.8(23) 6.7392 846.79 137.4
JOURNAL OF CHEMICAL AND ENGINEERING DATA
Apparatus. The equipment used in obtaining the vapor liquid samples was a modified Colburn still similar to that described by Haynes and Van Winkle ( 5 ) . Pressure was measured to *0.5 mm. Hg By using a calibrated mercury manometer. A copper constantan thermocouple and a Leeds & Northrup type K potentiometer were used to measure temperature to within *0.05" C. This arrangement was calibrated by deasuring the boiling points of pure compounds. A Bausch & *Lomb precision refractometer maintained a t 30" C. was used to determine the index of refraction of the vapor and liquid samples. The accuracy of the refractometer was tested by the standards supplied by Bausch and Lomb. Procedure. The procedure for determination of vaporliquid equilibrium was essentially that described by Haynes ( 5 ) . For each of the binary hydrocarbon systems, refractive index calibration curves were obtained with samples of different known concentrations at 30° C. The composition of vapor and liquid samples were read from the calibration curves. I n the ternary systems, three mixtures of n-octaneethylcyclohexane in the mole ratios of 25 to 75, 50 to 50, 75 to 25 were used; 2-propanol was added to each of the above mixtures to give equivalent mole fractions of 0.33, 0.50, 0.67, 0.75, and 0.80 in the ternary mixture. These mixtures were subjected to equilibrium distillation in the Colburn still, and vapor and liquid samples were obtained. Another set of experiments were conducted similarly using
butyl Cellosolve as solvent. These samples were extracted with water to remove the added agent. After several washings, the hydrocarbon layer was transferred to 10-ml. sample bottles. T o these bottles were added crystals of Drierite, which removed any traces of water remaining in the hydrocarbon mixture. The washed samples were kept overnight, and the added agent-free samples were analyzed by refractometer. DISCUSSION OF RESULTS
Experimental activity coefficients for the components in the binary mixtures were calculated using the following equation:
The fugacity coefficient v = ( f / p ) is equal to unity where the ideal gas law is valid. Fugacity coefficient was assumed to be unity in all of the work reported here. The validity of the assumption was checked using the generalized f / p charts. The vapor-liquid equilibrium data for the five binaries are reported in Table I1 and in Figures 1 to 4. The data were correlated by Carlson and Colburn modified van Laar equations ( 1 ) :
I I I I I I I -CALCULATED ( EQUATION.2.) EXPERIMaTAC I
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EQUATION 2.)
-CALCULATED.(
EX PER1MENTAL
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MOLE % NORMAL OCTANE
Figure 1 . N o r m a l octane-butyl Cellosolve system a t 400 mm. pressure
VOL. 8, No. 1 , JANUARY 1963
t
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MOLE%
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ETHYLCYCLOHEXANE
Figure 2. Ethylcyclohexane-butyl Cellosolve system a t 400 mm. pressure
15
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