Vapor-Liquid Equilibria of Binary Hydrocarbon Systems J
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J. M. HARRISON AND LLOYD BERG
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Gulf Research & Development Company, Pittsburgh, P a .
A
number of close-boiling binary hydrocarbon systems has been investigated. Minimum azeotropes exist between 2,2,3-trimethylbutane-benzene, boiling at 75.6' C. at 736 mm. and containing 56.7 mole % benzene; between 2~2,3-trimethylbutane-cyclohexane,boiling at 79.45' C. at 744 mm. and containing 47.8 mole % 2,2,3-trimethylbutane; and between benzene-cyclohexene boiling at 78.9' C. at 740 mm. and containing 65.7 mole % benzene. N o azeotrope was found in the systems 2,2,4-trimethylpentane-methylcyclohexane and cyclohexane-cyclohexene.
P
0.0001. Refractive indices were obtained on weighed mixtures of the hydrocarbons so that mole fractions of the samples could be read from a refractive index-composition curve for each system. The vapor temperature in the still was determined by a calibrated 75-mm., immersion precision thermometer accurate t o 0.1 O c. AZEOTROPIC SYSTEMS
The experimental and calculated data for the 2,2,3-trimethylbutane-benzene system are shown in Table 11. An azeotrope is formed a t 75.6" C. a t 736 mm. (76.6' C. a t 760 mm.) and con' aromatic. The equilibrium diagram is illustains 56.7 mole % trated in Figure 1; the temperature-composition curve (temperature corrected to 760 mm.) is given in Figure 2. Figure 3 is B plot of the relative volatility as calculated from the data. The consistency of the data is shown t o be satisfactory upon inspection of the activity coefficient curves of Figure 4,as suggested by Carlson and Colburn ( I ) . The equations of Smith (8) which were used t o obtain the vapor pressures of the pure hydrocarbons a t various temperatures were:
RECISION fractionation of petroleum demands a thorough knowledge of the behavior of the constituent hydrocarbons upon distillation. The constantly increasing demand for pure hydrocarbons makes it necessary that vapor-liquid equilibrium data for such systems be known. Furthermore, present-day methods of design calculation for handling nonideal systems indicate that, with the determination of more vapor-liquid equilibrium data, it will be possible to design equipment for azeotropic and extractive operations with as much precision as is now obtain1211.215 able for the distillation of regular mixtures. Benzene: loglo p = 6.905216 - 220.870+ Various hydrocarbon types have been discussed and their d a t a tabulated ( 3 , 4,7 , 9 ) , but the number of binary hydrocarbon systems for which equilibrium data are known remains relatively small. The difficulty or impossibility of obtaining certain closePROPERTIES OF HYDROCARBONS TABLE I. PHYSICAL boiling pure hydrocarbons will of necessity limit the extent of a n Boiling Point Refractive Index, investigation designed t o secure desirable distillation data. O C. a t 760 M&. , n .a There are some hydrocarbons, however, which are obtainable in Hydrocarbona Obsvd. Doss ( 8 ) Obsvd. Doss (9) the pure state and for which there is no published information 80.87 1.3893 1.3895 2 2 3-Trimethylbutane 80.8 99.2 99.23 1.3913 1.3914 2:2:4-Trimethylpentane concerning distillation behavior. Some of these compounds 1.4263 1.4262 80.8 80.80 Cyclohexane have been investigated and are reported in this paper. Included 100.8 100.8 1.4230 1.4230 Methylcyclohexane are the following close-boiling systems: 2,2,3-trimethylbutane1,4467 1.4467 83.19 Cyclohexene 83.2 80.1 80.09 1.5010 1.5012 Benzene cyclohexane, 2,2,3-trimethylbutane-benzene, benzene-cyclohexene, 2,2,4-trimethylpentane-methylcyclohexane, and cyclohex5 All were obtained from Eastman Kodak Co. except benzene, from Merck & Co. ane-cy clohexene. Each of the hydrocarbons was purified by refractionation in a glass laboratory column 4 TABLE 11. DATA FOR SYSTEM 2,2,3-TRIMETHYLBUTANE-BENZENE A T 736 MM. feet long, 1 inch in diameter, and packed Mole Fraction Mole Fraction Vapor Pressure,, Activity with 1/4-inch stainless steel carding teeth, Coefficient in Vapor iMm. H g in Liquid 2,2,3-Tri2,2,3-Tri2 2 3-Tri2 2 3-Tricalibrating about forty theoretical plates at r$&hyl&hylRelative methylTemp., methyltotal reflux. With a reflux ratio of 25 to 1, a C. butane Benzene butane Benzene butane Benaene butane Benzene Volatility heart cut was made of each hydrocarbon; the 736 0.000 0.000 79.1 1 :866 1:ooo 0:547 764. :3 718.8 0.050 0.028 78.3 properties are shown in Table I as compared 705.5 691.8 1.683 1,008 0.611 0,087 0.055. 77.7 692.4 1.632 1.007 0.629 679.4 0.143 0.095 77.1 t o values from the literature. 1.006 0.662 681.6 669.3 1.548 0.200 76.6 0.142 The vapor-liquid equilibrium data were ob1.025 0.754 673.0 1.385 661.2 0.255 0.205 76.2 0.868 1,244 1.062 664.1 653.3 0.319 0.289 7 5 . 8 tained in a modification of the apparritus de1 069 0.897 662.4 651.3 1.210 0.378 0.353 75.7 1,110 0.987 1.143 660.3 649.3 0.413 0.410 75.6 scribed by Othmer ( 6 ) . A 50-ml. sample of 1.115 1.000 1.134 660.3 649.3 0.433 0.433 75.6 one hydrocarbon was charged to the still, 1.130 1.029 1.117 660.3 649.3 0.461 0.468 75.6 1.159 1.087 662.4 651.3 1.084 0.499 0.520 75.7 and mixtures with various successive additions 1.190 1.134 664.1 653.3 1.065 0.539 0.570 75.8 1.260 1.256 1.019 673.0 661.2 0.586 0.640 76.2 of the other hydrocarbon were allowed about 1.281 1.294 681.6 669.3 1.016 0.662 0.717 76.6 2 hours to reach equilibrium. Vapor and 1 311 1.318 692.4 1.013 679.4 0.730 0.781 77.1 1.306 1.320 1,010 712.1 698.1 0.822 0.859 38.0 liquid samples were removed, and their com1,512 1.472 732.4 0.993 717.0 0.902 0.933 78.9 ... ... 736 ... 1,000 1,000 79.9 positions were determined by refractive index in a Valentine refract$meter, reading to
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I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
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MOL FRACTION BENZENE IN LIQUID
0.2
MOL
MOL FRACTION
Vol. 38, No. 1.
2 2 3-TRIMETHYLBUTANE Ik ' LIQUID
OA 0.6 0.0 1.0 FRACTION BENZENE IN LIQUID MOL FRACTION
2,2,4-TRIMETHYLPENTANE I N LIQUID
Figure 1 (Left and Above). Equilibrium Diagrams
The following vapor pressure equations for cyclohexane and cyclohexene, derived from data obtained in this laboratory, were used for the pressure range of this investigation: 1505.15 273.18 t 1503.04 Cyclohexene: log10 p = 7.09845 273.18 t
Cyclohexane: loglo p = 7.13289
-
+
+
D a t a for benzene-cyclohexene system are presented in Table
I V and the equilibrium diagram, relative volatility plot, and ac-
2,2,3-Trimethylbutane: log,, p
=
1204.997 6.799682 - 226.615 +
Table I11 contains the data for the 2,2,3-trimethylbutanecyclohexane system. An azeotrope is formed between these two hydrocarbons a t 79.45" C. at 744 mm. (80.15" C. a t 760 mm.) and contains 47.8 mole % paraffin. The vapor-liquid equilibrium diagram, the temperature-composition diagram, the relative volatility plot, and the activity coefficient curves are included in Figures 1, 2, 3, and 4, respectively.
tivity coefficient curves are shown in Figures 1, 3, and 4, respectively. An azeotrope is formed between these two hydrocarbons at 78.9" C. st 740 mm. (79.8" C. a t 760 mm.) and contains 65.7 mole % aromatic. This composition is somewhat lower than that previously reported by Lecat ( 5 ) . I n order to verify the compositions of the azeotropes, three samples of each system were run in a Podbielniak Heli-Grid column at a reflux ratio of about 200 to 1. A sample corresponding to a composition slightly below the approximate azeotrope and then a sample with a composition just above the azeotrope were run in the column. A small overhead sample was removed from each distillation and analyzed by refractive index. The change in composition between the charge and the overhead was plotted against the charge composition. A straight line connecting these two points indicated the azeotropic composition a t the line of zero composition change. A third sample was then made up to the indicated composition and charged t o the column. An
INDUSTRIAL AND ENGINEERING CHEMISTRY
January, 1946
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- 2,2,3-TRIMETHYtBUTANE 60.9
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VS.
80.7
80.5
803
80.1
0 MOL FRACTION BENZENE Figure 2.
MOL FRACTION
2,2,3-TRIMETHYLBUTANE
Boiling Point-Composition Diagrams
overhead of the ssme composition as the charge proved the existence of the azeotrope a t the given composition. The assumption of a straight-line relation for hydrocarbons appears t o be valid; provided the total range of composition change is not greater than 6-10%. Table V contains the data from the distillations which establish the azeotropes between 2,2,3-trimethylbutane and benzene, 2,2,3-trimethylbutane and cyclohexane, and benzene and cyclohexene. Figure 5 illustrates the method of locating the true composition of the azeotrope between 2,2,3-trimethylbutane and cyclohexane.
TABLE111. DATAFOR
S Y S T E M 2,2,3-TRIMETHYLBUTANE-cYCLOHEXANE AT
Mole Fraction Mole Fraction Vapor Preesure, in Liquid in Vapor Mm. H g ’ 2 2 3-Ti-i2,2,3-Tri2 2 3-TriTemp., hbthyl- Cyclo- methyl- Cyclo- hbthyl- CycloC. butane hexane butane hexane butane hexane 80.1 1,000 1.ooo 744 80.0 0.934 740.8 0.958 738.6 0.882 79.9 0.851 0.775 79.75 0.745 735.3 0.721 79.7 0.694 734.2 79.55 0.604 731.0 0.6Zi 729.9 79.5 0.557 0.566 728.8 79.45 0.509 0.616 0.482 728.8 79.45 0.483 728.8 0.478 0.478 79 * 45 728.8 0,346 0.335 79.45 729.9 0.252 0.243 79.5 732.1 0.177 0.166 79.6 734.2 0.140 0.129 79.7 736.4 0.100 0,088 79.8 738.6 0.073 79.9 0.060 740.8 0.048 80.0 0.037 0.000 0.000 80.1
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TABLEIV.
0 0.2 0.4 0.6 0.8 la MOL FRACTION 22.3-TRIMETHYLBUTANE tN LIQUID I
1.3
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Mole Fraction in Vapor CycloBenzene hexene 1.000 0.875 0.841 0.830 0.727 0.680 0.657 0.611 0.595 0.669 0.518 0.487 0.363 0.085 0.000
Vapor Pressure, Mm. H g CycloBenzene hexene 740 6i6:1 733.5 676.1 733.5 676.1 733.5 675.2 732.4 675,2 732.4 675.2 732.4 679.0 737.9 679.0 737.9 679.0 737.9 680.9 740.0 684.6 743.8 692.3 753.1 705.9 769.7 740
...
tMOL FRACTION BENZENE IN LIQUID
Figure 3.
0:iis 0.972 0.972 0.974 0.989 1.004 1.007 1.007 1.007 1.054 1.058 1.083 1.099 1.147 1.226 1.303 .
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1:i i o 1.268 1.142 1.106 1.058 1.033 1.031 1.019 1.016 1,000 1.003 0.999 0.996 0.994 0.990 0.990
...
744 MM.
Relative Volatility 0 : 620
0.764 0.848 0.877 0.930 0.968 0.973 0.996 1.000 1.061 1.049 1.081 1.100 1.152 1.233 1.313
...
DATAFOR SYSTEM BENZENE-CYCLOHEXENE AT 740 MM.
Mole Fraction in Liquid Temp., Cyclo0 C. Benaene hexene 1.000 79.2 0.885 78.95 0.851 78.95 0.842 78.95 0.730 78.9 0.683 78.9 0.657 78.9 0.597 79.1 0.583 79.1 0.553 79.1 0.496 79.2 0.466 79.4 0.330 79.8 81.5 0.068 0.000 82.1
BENZENE VS. CYCLOHEXENE
Activity Coeffcient 2,2,3- Trimethyl- Cyclobutane hexane
Relative Volatility-Composition Diagrams
Activity Coefficient CycloBenzene hexene 0 : 997 0.997 0.995 1.006 1.006 1,010 1.026 1.023 1.032 1.044 1.040 1.081 1.202
...
1:i i o 1.168 1.178 1.108 1.106 1.096 1.052 1.058 1 051 1.039 1.038 1.016 1.029
Relative Volatility 0 : 9io
0.926 0.917 0.985 0.986 1.000 1.060 1.051 1.067 1.093 1.088 1.157 1.272
voi. 38. N ~ 9.
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
li 20
2 2 W
2,23-TRIMETHYLBUTANE VS CYCLOHEXANE
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2 2 + 0.02 E2 J$
26
0.00
f af
y t -0.02 z m-
2:
”
-0.04
0.42 MOL
0.46 0-50 0.54 FRACTION 2 2.3-TRIMETHYLBUTANE I N CHARGE
Figure 5.
D e t e r m i n a t i o n of Azeotropic Composition
MOL F R A C T l O N BENZENE I N L I Q U I D TABLEVI. D 4TA
FOR
SYGTEX
2,2.-1-TRIMETHYLPCNT.4N~-
METHYLCYCLOHEXANE AT 741 Mu.
ILIole Fraction in Liquid 2,2,4-Tnrnethyl- Meths Icypentane clohexane
T:mp , C. 98.2 98.3 98.4 98.55 98.85 98.96 99.1 99.3 99.4 99.6 99.65 99.8 99.9
Mole Fraction in Vapor2,2,4-TiimethylRIethJlcypentane clohexane
0,000
1,000 0,879 0.794 0.695 0.476 0,407 0.340 0.245 0.190 0.140 0.088 0 040 0.000
1.000 0.888 0.809 0.707 0.490 0.416 0.350 0.257 0.204 0.163 0.107 0.048 0.000
0.121 0.208 0.306 0 524 0.593 0.660 0.755 0.810 0.860 0.902 0.960 1,000
0.000 0.112 0.191 0.293 0 510 0,684 0.650 0,743 0,796 0.837 0,893 0.952 1,000
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TABLEVII. DATA FOR
2
3Iole Fraction in Liquid Cyclohexane Cyclohexene
Temp.,
MOL FRACT 1 O N 2,2,3-TRI METHYLBUTANE I N LIQUID
= BENZENE CYCLOHEXENE 1.6
c.
80.0 80.1 80.15 80.3 80.4 80.5 80.66 80.75 80.9 81 .? 82.0 82.1 82.2
SYSTEM CYCLOHEXAXE-CYCLOHEXENE AT 741 M x ,
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1 000 0,940 0.904 0.832 0.742 0.705 0.663 0.578 0.540 0.199 0,099 0 015 0.000
Mole Fraction in Vapor Cyclohexane Cyclohexene
0.000 0.060 0,096 0.168 0 258 0.295 0.337 0 422 0.460 0.801 0,901 0.985 1 000
1 000 0.955 0,919 0.845 0.760 0.735 0.680 0.600 0.565 0.200 0.135 0.035 0.000
0.000 0,046 0 081 0.156 0.240 0.265 0.320 0 400 0.435 0.800 0.866 0.965
1.000
1.4 NONAZEOTROPIC SYSTEMS
0’.g0
0.2 *
0.6 O
0.4
MOL F R A C T I O N BENZENE F i g u r e 4.
0.8
I .o 2
IN LIQUID
Activity Coefficient-Composition Curves
Data for the systems 2,2,4-trimethylpentane-methylcyclohexane and cyclohexane-cyclohexene are given in Tables VI and VII, respectively, and the equilibrium diagrams are included in Figure 1. S o azeotropes were detected in these systems. The system 2,2,3-trimethylbutane-cyclohexene was investigated, but the results were inconclusive. It could not be ascertained definitely whether an azeotrope existed although the data seemed t o indicate none. LITERATURE CITED
TABLE v. No. 1
PODBIELNI.4K-COLUMN
vERIFICATIOK O F
AZEOTROPIC
CONPOSITIONS Hydrocarbon
Benzene
No. 2 2 , 2 3-Trimethyldutane
2,2,3-TrimethyIbutane
Cyclohexane
Benzene
Cyclohexene
Mole Fraction, Run Hydrocarbon 1 Composition No. Charge Distillate Change 0.532 0.567 $0.035 1 2 3 1
2
3 1
2 3
0,615 0.567 0,424 0,525 0.478 0.626 0.698 0.657
0,567 0.567 0.460 0.491 0.478 0.657
-0.048 0.000
$0.036
0.657 0.657
-0.041 0.000
-0.034 0.000
$0.031
(1) Carlson, H. C., a n d Colburn, A. P., IND. ENG.CHEM., 30, 581 (1942). (2) Doss, M. P., “Physical Constants of t h e Principal Hydrocarbons”, New York, T e x a s Co., 1943. (3) Ewell, R.H., Harrison, J. M., a n d Berg, L., Petroleum. Engr., 16, 255, Oct.; 259, Nov.; 227, Dec. (1944). (4) Griswold, J., a n d Ludwig, E. E., IND.ENQ.CHEM., 35, 117 (1943). ( 5 ) Lecat, M., “La tension de vapeur des melanges de liquides. L’azeotropisme”, Brussels, 1918. ( 6 ) Othmer, D. F., IXD.EKQ. CHEM.,35, 614 (1943). (7) Richards, A. R., a n d Hargreaves, E., I b i d . , 36, 805 (1944). ( 8 ) Smith, E. R.,J . Research Natl. Bur. Standards, 26, 129 (1941). (9) Stage, H . , a n d B a u m g a r t e n , I. S., Oel Kohle, 40, 126 (1944)
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