SUPERSCRIPTS E = excess = infinite dilution
co
=
U
vaporization
literature Cited
American Petroleum Institute Project 44, “Selected Values of Properties of Hydrocarbons and Related Compounds,” 1953. Anderson, R., Ph.D. dissertation, Department of Chemical Enrineerinc. Universitv of California. Berkelev. 1961. BaikeYr, J. A.,”J. Chem. Phis. 20, 1526 (1952). Black, Cline, Znd. Eng. Chem. 50,403 (1958). Bondi, A., Simkin, D. J., J . Chem. Phys. 25,1073 (1956). Carlson. H. C.. Colburn, A. P., Znd. Ene. Chem. 34. 581 (1942). Deal, C. H., Derr, E. ‘L.. IND. EN;. CHEM.‘PROCESS DESIGN DEVELOP. 3. 394 (1964). DreGbach, R.’R., ‘(P-V-T Relationships of Organic Compounds,” 3rd ed., Handbook Publishers, 1958. Dreisbach, R. R., Adv. Chem. Ser., Nos. 15, 22, 29 (1955, 1959, /
I
1 oh1 ’i
Dreisbach, R. R., Znd. Eng. Chem. 41, 176 (1949). Dreisbach, R. R., “Physical Properties of Chemical Substances,” Dow Chemical Co., Midland, Mich., 1953.
Flory, P. J., J . Chem. Phys. 9, 660 (1951). Gerster, J. A,, Gorton, J. A,, Eklund, R. B., J . Chem. Eng. Data 5 , 423 (1960). Hildebrand, J. H., Scott, R. L., “Regular Solutions,” Prentice Hall. Endewood Cliffs. N. J.. 1962. Hildebrandv, J. H., Scott, R. L., “Solubility of Nonelectrolytes,” 3rd ed.. Dover Publications. New York. 1946. Huggins, ’M. L., J . Chem. Phys.’9,440 (1941). Orye, R. V., Prausnitz, J. M., Znd. Eng. Chem. 57, 18 (May 1965). Perry, J . H., “Chemical Engineer’s Handbook,” 4th ed., McGrawHill, New York, 1963. Pierotti, G. J., Deal, C. H., Derr, E. L., Znd. Eng. Chem. 51, 95 (1959). Reid, R. C., Sherwood, R. K., “Properties of Gases and Liquids,” McGraw-Hill, New York, 1958. Scatchard, G., Chem. Revs. 8, 321 (1931). Stull, D. R., Znd. Eng. Chem. 39, 517 (1957). Suryanarayana, Y. S., Van Winkle, Matthew, J. Chem. Eng. Data 11, 7 (1966). Van Laar, 1906. Weimer, R. F., Prausnitz, J. .M., Hydrocarbon Process. Petrol. Refiner 44, 237 (1965). Wilson, G. M., J.Am. Chem. SOC.86, 127 (1964). RECEIVED for review March 16, 1967 ACCEPTED October 13, 1967
LIQUID-LIQU ID AND VAPOR-LIQUID EQUILIBRIA FOR BINARY AND TERNARY SYSTEMS WITH DIBUTYL KETONE, DIMETHYL SULFOXIDE, n=HEXANE, AND 1-HEXENE H. RENO“ AND J. M. P R A U S N I T Z Department of Chemical Engineering, Uniuersity of California, Berkeley, Calif.
To facilitate a study of extractive separation using a mixed solvent, phase equilibrium data were obtained for mixtures of dibutyl ketone and dimethyl sulfoxide (DMSO) with n-hexane and with 1 -hexene. To characterize the binary solvent mixture, total vapor pressure data were obtained at 60”,70°,and 80” C.; to characterize ketone-hydrocarbon interactions, total vapor pressures were measured over the same temperature range for the binary systems ketone-hexane and ketone-hexene. Mutual solubilities with DMSO were obtained for both hydrocarbons. Liquid-liquid equilibrium measurements at 25” and 60” C. were made for the two ternary systems containing two solvents and one hydrocarbon. Data reduction utilized the nonrandom, two-liquid (NRTL) equation for excess Gibbs energy. While addition of dibutyl ketone to DMSO decreases the solvent-hydrocarbon ratio required for separation, the corresponding decrease in solvent selectivity is too large for any signifrcont economic advantage.
EQurD-liquid extraction and extractive distillation processes usually utilize only one solvent. I n the separation of olefins from paraffins, solvents which are highly selective unfortunately dissolve only small quantities of hydrocarbon and as a result, large solvent-hydrocarbon ratios are required to operate separation process equipment (Stephenson and Van Winkle, 1962). To lower this undesirably large ratio, one may add another solvent having more favorable solubility characteristics; however, such solvents tend to lower solvent selectivity. 1 On leave of absence from Institut F r a n p i s d u Pttrole, Rueil-Malmaison, 92, France
220
I&EC PROCESS DESIGN A N D DEVELOPMEN1
To obtain increased understanding of phase relations in a mixed-solvent system, we have studied the separation of nhexane-1-hexene mixtures with dimethyl sulfoxide (DMSO) and dibutyl ketone. Experimental Apparatus and Procedure
Vapor-Liquid Equilibria. STATICMETHOD.The apparatus, shown schematically in Figure 1, consists of an isothermal bath containing the vapor-pressure cell and a differential manometer, a mercury manometer, a sampling section, degassing equipment, and a high-vacuum system. I n part, it is similar to the equipment used by Hermsen and Prausnitz (1963) and Orye and Prausnitz (1965). A glass cell is used, and the contents of the cell are: transferred to a sampling
CONICAL JOINT
Figure 1 .
Static still for vapor-liquid equilibria
vessel after the pressure measurements. T h e operation of this apparatus is similar to that described by Scatchard, Wilson, and Satkiewicz (1964). The temperature is controlled to 2~0.01" C. and is read on a mercury thermometer with 0.05" C. divisions. The pressure is read on mercury manometers with a Wild-Heerbrugg K M 274 cathetometer with a n accuracy of 1 0 . 0 2 mm. of H g ; the estimated error in pressure is therefore 0.08 mm. Good results with this type of apparatus require that the pure substances be thoroughly degassed. Details of operation are given by Renon (1966). The static method was used to obtain total pressures for the dibutyl ketone-DMSO system at GO', 70°, and 80" C. DYNAMIC METHOD.The dynamic still used is described by Scatchard and Ticknor (1952). T h e advantages of this type of still are: simple operation, high accuracy at low pressure, absence of stopcocks in contact with the liquid, and small sample size (40 cc.). T h e apparatus is shown in Figure 2 . A modification in the original design was a longer Cottrell pump, P, obtained by adding a helicoidal glass tube between the boiler, B, and the thermometer well, T. A small bulb, b , was put into the feed line in order to avoid fluctuations of liquid level. T h e coiled Cottrell pump, a feature of the still described by Ellis (1952), minimizes overheating of the liquid without a hydrostatic head effect. Around the top of the still insulation, I, was placed; it was possible to heat this part of the still with a heating tape in order to prevent condensation of vapor when operating at the highest temperature. T h e pressure was kept constant within 1 0 . 0 5 mm. of Hg with a manostat consisting of a large surge tank made of three 25-liter stainless steel bottles immersed in a water bath; the pressure was read on a mercury manometer as in the static method. T h e temperature was read on a mercury thermometer with 0.05' C. divisions. A test run of the stills was made with the mixture benzenen-heptane; the measurements were in good agreement with those of Brown and Ewald (1951). T h e dynamic method was used to obtain total pressures for the systems 5-nonanonen-hexane and 5-nonanone-1-hexene at 60' and 80" C. Liquid-Liquid Equilibria. Tie lines and binodal curves were determined simultaneously by chromatographic analysis of the two liquid phases at equilibrium. The two-phase liquid mixture was stirred for at least 30 minutes in a 50-cc. Erlenmeyer flask immersed in a water bath regulated within 1 0 . 0 1 " C. with a Hallikainen Thermotrol Model 1053A. After the phases separated and appeared completely clear, 4-cc. samples were withdrawn from each layer with a preheated syringe and hypodermic needle and were immediately transferred to 10-cc. Erlenmeyer flasks. They were weighed, and a weighed amount of one of the components of the mixture was added in order to avoid phase
splitting due to cooling. T h e homogeneous mixture obtained was analyzed by chromatography. Mutual solubilities of D M S O and each hydrocarbon were also measured by the cloud-point method because the solubilities are small; in that event, the chromatographic method is not adequate for precise analysis. Chemical Analysis. A Wilkens Aerograph 1520 gas chromatograph equipped with thermal-conductivity cells was used for analysis. T h e column, made of 5-foot X '/c-inch stainless steel, was packed with Chromosorb T impregnated with 10% Carbowax 1540. The carrier gas was purified helium. T h e operating conditions were selected in order to separate DMSO, 5-nonanone, and either n-hexane or 1-hexene. T h e temperature of the column was 166' C. The electric signal was recorded on a Honeywell Electronik 15 recorder equipped with a disk-chart integrator, Model AND MANOSTAT
I
VAPOR S A M P L E LIQUID SAMPLE
-
0 2 4 6 8 CM.
Figure 2. equilibria
Dynamic still for vapor-liquid
VOL 7
NO. 2 A P R I L 1 9 6 8
221
201B. Areas under the peaks were read on the integrator trace. T h e chromatograph was calibrated with seven ternary samples for each of the systems n-hexane-5-nonanone-DMSO and 1-hexene-5-nonanone-DMSO. Materials. Anhydrous dimethyl sulfoxide was obtained from Matheson, Coleman & Bell. 5-Nonanone was obtained from K & K Laboratories; it was purified by distilling twice and keeping each time only the middle fraction. n-Hexane and 1-hexene (pure grade) were obtained from Phillips Petroleum Co. Table I compares measured indices of refraction, nD, at 25 ' C., densities, d, a t 25' C., and vapor pressures at 60' C. with literature values.
Experimental Results
Vapor-Liquid Data. I n the static method, corrections were made to the readings of mercury levels for mercury density and gravity. I n the system dibutyl ketone-DMSO, no correction in the composition of the liquid phase was found necessary in order to take into account the amount of material in the vapor phase. At higher temperatures DMSO is unstable but no significant decomposition was observed at 80' C. Experimental liquid compositions and pressures are listed in Table I1 and shown in Figure 3. Taking into account an error of 0.1 mm. of H g in the pressure and 0.05' C. in the temperature, the experimental relative error in pressure is 1.5% at 60' C., 1.0% at 70' C., and 0.7% at 80' C. I n the systems containing hexane or hexene, for mole fractions of 5-nonanone larger than 0.72 at 60' C. and 0.90 at
Table 1.
Properties of Pure liquids
n$ Liquid
Obsd.
Lit.
Ref.
Obsd.
d26, G./MI. Lit.
Vapor Pressure at 60' C., Mm. Hg Obsd. Lit. Rq.
Rd.
Dimethyl sulfoxide 1.47726
1 ,0947
.0946 (Clever, 1963)
5-Nonanone n-Hexane
0.8171 0.6538
,8270 (Hodgman, 1963) 5.22 ... .65481 (American Petroleum 572.77 572.74 (American Petroleum Institute, 1964) Institute, 1964) .66848 (American Petroleum 678.96 679.57 (American Petroleum Institute, 1964) Institute, 1964)
1-Hexene
,4783a ( Crown-Zellerbach Co., 1964) 1.41796 ,421b (Hodgman, 1963) 1,37238 ,37226 (American Petroleum Institute, 1964) 1.38511 ,38502 (American Petroleum Institute, 1964)
80' C., it was difficult to operate the dynamic still; the operation of the Cottrell pump became irregular, initiation of the boiling became difficult and there was poor mixing between the liquid coming from the condenser and that in the boiler. Consequently, the temperature did not stay sufficiently stable to allow good measurement. At the higher temperature a second limitation in the concentration range where operation was possible was encountered: I t was not possible to operate at low concentration in 5-nonanone because the still was not equipped to work at pressures above atmospheric. Because it was impossible to operate the still at high concentration in 5-nonanone, and because of the large difference in volatility between the hydrocarbons and the ketone, the vapor-phase mole fraction of 5-nonanone in the vapor phase was always small (most often lower than 2%, with an average of 0.5%). For these low concentrations, chromatographic analysis with thermal conductivity cells becomes inadequate, and we do not report experimental vapor-phase mole fractions but only the equilibrium pressure. Tables I11 and I V present the experimental results. Liquid-Liquid Data. T h e results are expressed in weight fractions. Table V gives the cloud-point determination of binary mutual solubilities. Tables VI and VI1 give the ternary data for the systems n-hexane-5-nonanone-DMSO and 1-hexene-5-nonanone-DMSO obtained by the analytical method. Ternary diagrams are given in Figures 4 and 5 . Data Reduction. An expression for the excess Gibbs energy recently introduced by Renon and Prausnitz (1968) was used for binary data reduction and for prediction of multicomponent phase equilibria. The nonrandom two-liquid (NRTL)
0.6680
5.15 (Crown-Zellerbach Co., 1964)
5.12
d41a.
Table 11.
Liauid Mole Fraction of 5Nonanone 0.0 0,0607 0.0897 0.2254 0.3307 0.3742 0.3834 0.4311 0.4588 0.4639 0.5288 0.6241 0.6602 0.8408 1.o
222
Vapor-liquid Equilibria for Binary System 5Nonanone-Dimethyl Sulfoxide
I Measured Total Pressure, Mm. Hg 60" C. 70' C. 80' C. 5.12 8.98 14.99 6.94 11.93 19.66 7.24 12.51 20.75 7.94 13.68 22.45 7.98 14.02 23.20 8.20 14.15 23.17 8.01 13.88 23.06 8.05 13.98 23.19 8.18 14.05 23.05 8.22 14.01 23.27 8.07 13.99 23.20 7.89 13.83 22.90 7.85 13.67 22.73 7.12 12.43 20.70 5.22 9.43 16.26
Calcd. Vapor Mole Fraction of 5-Nonanone 60' C. 70' C. 80' C. 0.0 0.0 0.0 0.2910 0.2816 0.2729 0,3413 0.3323 0.3240 0.4219 0.4178 0.4144 0.4399 0.4395 0,4400 0.4456 0.4468 0,4489 0.4469 0.4484 0.4508 0.4537 0.4569 0.4611 0,4581 0.4624 0,4677 0.4589 0.4634 0,4689 0.4715 0.4786 0.4867 0.4980 0,5092 0.5214 0.5115 0.5244 0,5382 0.6355 0.6564 0,6772 1 .o 1.o 1 .o
l & E C P R O C E S S DESIGN AND DEVELOPMENT
--
W
I
I
I
I
I
I
I
I
I
I
I 0.3
I
I
I
I
I
I
/I
01 0
Figure 3.
I
0.1
0.2
0.4 0.5 0.6 0.7 0.8 0.9 x , LIQUID MOLE FRACTION 5-NONANONE
1.0
Total pressures for 5-nonanone-DMSO mixtures
Vapor-Liquid Equilibria for Binary System 5Nonanone-n-Hexane Calcd. Vapor Measured Total Liquid Mole Mole Fraction Pressure, Fraction of 5-Nonanone Mm. Hg 5-.Vonanone 60' C. 0 572.77 0
Table 111.
0.0291 0.0495 0.0552 0,1268 0.1395 0.1982 0.2035 0.2538 0.3067 0.3573 0.3614 0.3850 0.4903 0.5310 0.5856 0.6083 0.6433 0.7137 0 0.2976 0.3496 0.5001 0.6322 0.7524
555.53 545.05 541.87 507.93 499.59 474.52 472.19 448.21 428.53 402.93 405 .43 391.66 339.35 323.22 291.53 278.60 260.66 216.29 70" C.
592.79 562.00 465.10 363.82 256.64 80" c.
0.0006 0.0009 0.0010 0.0022 .. . 0.0024 0.0033 0.0034 0.0041 0,0049 0.0058 0.0059 0.0063 0.0085 0.0096 0.0114 0.0122 0,0138 0.0179 ~~~
0 0.0062 0.0073 0.0114 0.0174 0.0281 0
0
0.3704 0.5181 0.6030 0.6188 0,7546
743.56 608.48 521.32 505.15 339.37
o
no97
0.0152 0.0201 0.0213 0.0370
Vapor-liquid Equilibria for Binary System 5Nonanone-1-Hexene Measured Liquid Mole Total Calcd. Vapor Pressure, Mole Fraction Fraction of of 5-Nonanone 5-h'onanone Mm. Hg 60" C. 0 678.96 0
Table IV.
0.0897 0.2675 0.3720 0.3905 CI ,5294 0,6422 0,6928 0.7220 0.4416 014712 0.7002 0,7660 0.8556 0.8800 0,8875
Table V.
619.73 515.55 455.85 443.75 356 .OS 281.09 246.83 222.67 80' C . 744.92 718.59 433.91 347.89 220.07 186.32 179.38
0.0011 0.0034 0.0049 0.0052 0.0083 0.0125
9 . oiS3
0.0173 0.0109 0.0118 0.0272 0 . d370 0.0636 0.0771 0.0824
Mutual Solubilities of n-Hexane and 1-Hexene with Dimethyl Sulfoxide
Hydrocarbon +Hexane
1-Hexene
Cloud point determinations Weight Fraction X 7000 D M S O in HydroT p., hydrocarbon in C. carbon DMSO 25 15 18 60 23 37 25 14 48 60 42 90
Table VI.
Equilibrium Compositions in Ternary Liquidliquid Equilibria
n-Hexane-5-nonanone-dimethyl
sulfoxide (tie-line data). Weight fractions x 1000 n-Hexane Phase D M S O Phase n-Hexane ' 5-Nonanone n-Hexane 5-Nonanone 25' C. 0 10 994 0 44 11 8 948 800 180 16 22 624 17 343 59 18 508 419 83 390 499 19 108 301 543 25 135 21 1 561 27 176 161 557 31 207 60' C. 984 0 29 0 841 121 36 34 745 203 40 56 78 257 41 667 .547 337 52 1l o 528 347 56 122 408 400 65 159 240 400 107 258 233 397 117 266 ~~
Table VII.
Equilibrium Compositions in Ternary Liquidliquid Equilibria
1-Hexene-5-nonanone-dimethylsulfoxide (tie-line data), Weight fractions >( 1000 7-Hexene Phase D M S O Phase I-Hexene 5-Nonanone 7-Hexene 5-Nonanone 25' C. 982 0 44 . 0 45 41 7 .. 925 86 42 883 17 48 134 26 829 44 198 748 36 699 237 51 46 589 317 50 66 436 409 60 97 369 443 62 120 288 464 62 155 236 460 66 190 159 445 87 258 60' C. 0 81 951 0 9 904 820 32 717 56 637 70 531 271 120 105 445 288 152 143 ~~
equation for the molar excess Gibbs energy of a multicomponent liquid mixture is: N
k=l
where x is the mole fraction, N is the number of components of the system and rjt
=
k j 1
- g11)/RT
Gj1 = exp (-
(2)
(3)
a j t 7ji)
Properties of the NRTL equation are discussed by Renon (1966, 1968). It can be used for representation of vaporliquid and liquid-liquid equilibria with two adjustable paramg r l ) and (gi5 g j j ) , for each binary liquid eters, ( g j l
-
(e)
-
VOL 7
NO. 2
APRIL 1 9 6 8
223
------
-a
/
CALC. 25'C 60'
80' EXPTL.
\
95'
( W E I G H T FRACTIONS)
Figure 4. Liquid-liquid equilibria for system n-hexane( 1)5-nonanone(2)-dirnethyl sulfoxide(3)
------
CALC. 25.C
60' 80' EXPTL.
I
( W E I G H T FRACTIONS)
Figure 5. Liquid-liquid equilibria for system 1 -hexane( 1 )5-nonanone(2)-dimethyl sulfoxide(3)
mixture; a third parameter, ai$,which represents the nonrandomness of the mixture, can be selected according to rules based on the type of mixture. Prediction of multicomponent vapor-liquid and liquid-liquid equilibria is possible with binary parameters only. The parameters are linear functions of temperature, allowing extrapolation over a reasonable range of temperature.
First, we determine the binary parameters from the binary data. The system 5-nonanone-DMSO is strongly nonideal. Fitting the data was found insensitive to a12 with a best value of a12 = 0.40. The high degree of nonideality of this completely miscible mixture also indicates such a high 0112. The parameters obtained from the data at 60°, 70°, and 80' C. are listed in Table VI11 with the linearly extrapolated values at 25' C. The r.m.s. relative deviations in pressure are 1.25% at 60' C., O.6y0at 70' C., and 0.570 at 80' C. Calculated vapor mole fractions are listed in Table 11. For the systems n-hexane-5-nonanone and I-hexene-5nonanone, a12 was set at 0.30, which is suitable for moderately nonideal mixtures. T h e parameters from fitting the data at 60°, 70°, and 80' C. are listed in Table V I I I with linearly extrapolated values at 25' C. T h e r.m.s. relative deviation in pressure for all data is 0.5%. Calculated vapor mole fractions are listed in Tables I11 and IV.' The vapor pressures of the pure hydrocarbons used for the reduction of the data were taken from API Project 44 (1964). Mixtures of hydrocarbons with DMSO are not totally miscible; the binary mutual solubilities provide the two parameters when a12 is chosen. T o select a value for a12, one could consider vapor-liquid data at some higher temperature, but this is not practical because of thermal instability of DMSO; on the other hand, detailed correlations for a12 are not yet available for this type of system. Therefore, we considered the ternary liquid-liquid data and found that prediction of the solubility curve depends on the value of a12 chosen for the immiscible binary; an increase in a12 decreases the domain of immiscibility. We therefore selected the values of a12 to obtain a good representation of the ternary liquid-liquid data at 25' and 60' C. with parameters calculated from binary data or from linear extrapolations with respect to temperature. Table VI11 gives the parameters calculated from the arithmetic average of the cloudpoint and analytical determination of the mutual solubilities of n-hexane and DMSO with a12 = 0.355, and I-hexene and DMSO with a12 =I 0.375, at 25' and 60' C. and from the extrapolated values at 70" and 80' C. Liquid mixtures containing n-hexane-1-hexene are nearly ideal. Suryanarayana and Van Winkle (1 966) measured isobaric vapor-liquid equilibria for this system at atmospheric pressure and these data are suitable for calculation of the parameters because the difference between the boiling points of the pure substances is small. For a12 we use 0.30. T h e r.m.s. relative deviation in pressure is 0.2070 and in vapor mole fraction, it is 0.5%. T h e cy12 parameters, listed in Table V I I I , are assumed to be temperature-independent. Process Application. With the parameters (Table VIII) obtained by direct fitting of data or by linear extrapolation, we can calculate all the phase equilibria (vapor-liquid and liquid-liquid) which we need to evaluate the usefulness of solvents in the temperature range 25' to 80' C. We now
Parameters in NRTL Equation 60" C. g12-g*zb g21-g11 g12-gz2 g21-&?11 31 31 31 31 - 270 793 256 54 -381 - 269 780 605 2100 1942 2199 2263 1511 1753 1672 2057 1163 447 1111 646
Table VIII.
25' C.
System Component I n-Hexane n-Hexane 1-Hexene n-Hexane 1-Hexene 5-Nonanone a
224
Dimensionless.
Component 2 I-Hexene 5-Nonanone 5-Nonanone DMSO DMSO DMSO b
a12=
0.30 0.30 0.30 0.355 0.375 0.40
gij-gjj, cal./gram mole,
(91%= 921).
I&EC PROCESS D E S I G N A N D DEVELOPMENT
70' C. g12-922 pzl-gll 31 946 830 2054 1676 390
31
- 363
-413 1869 1465 1178
g12-g22 31 1100 880 2007 1599 332
80' C. gzl-gll 31
- 456 -445
1795 1419 1194
c
16b
1
4
DMSO SOLVENT
SOLUBILITY CURVE
‘.
TI21.4 1 .
5 ~ 1 05-NONANONE 0W E% l G H T FRACTION (HYDROCARBON FREE
212
‘.
0.9 0.8
t I
0
I
,20
010
I
I
1
A
I
0.1 0.2 0.3 0.4 ‘ 0.9 1.0 W E I G H T F R A C T I O N HYDROCARBONS
Figure 6. Relative volatility of an equiweight mixture of n-hexane(1)-1 -hexene(2) in a mixed solvent Dimethyl sulfoxide-5-nonanone
consider the feasibility of two extractive processes: solvent extraction and extractive distillation. SOLVENTEXTRACTIOS.D M S O has a good separation factor, 6, for extraction of 1-hexene from its mixture with n-hexane (0 = 2.6 a t 60” C.). I t can dissolve 5% (weight fraction) of paraffin, the least soluble hydrocarbon, a t 80” C. T h e best way to increase the capacity of the solvent is to increase the temperature to the limit where D M S O becomes unstable. The addition of 5-nonanone at a given temperature unfortunately decreases the selectivity strongly without increasing the capacity very much. EXTRACTIVE DISTILLATION. For extractive distillation the capacity of D M S O is also too low. The relative volatility at infinite dilution of pure D M S O compares favorably with that of other solvents: I t is 1.61 for D M S O at 80’ C., 1.21 for trichloropropane at 147” C., 1.14 for butyl glycol at 135” C., 1.17 for 1,4-dioxane at 101” C., and 1.50 for dimethylformamide at 80”C. (But all the other solvents are totally miscible at 80” C.) 5-Nonanone has poor selectivity, not even sufficient to compensate for the lower vapor pressure of n-hexane com-
pared to 1-hexene; the relative volatility at infinite dilution of n-hexane and 1-hexene in 5-nonanone is 0.96. Figure 6 shows how the relative volatility varies with solvent concentration and with the solvent dosage expressed as weight fraction of 5-nonanone in the hydrocarbon-free solvent. I n Figure 6 the solubility curve is also represented; only the points below the solubility curve have physical meaning. Figure 6 shows that the addition of ketone seriously reduces the selectivity without sufficiently increasing the capacity. An addition of 10% weight fraction of 5-nonanone to the solvent brings the selectivity at infinite dilution down to 1.41, lower than that of dimethylformamide, and increases the capacity by 60%, but even then only 8% (weight fraction) of paraffin can be dissolved in the solvent. I t appears that the solvent pair investigated here is not adequate because the high-capacity solvent, 5-nonanone, has too low selectivity by itself and does not sufficiently increase the capacity. Since 5-nonanone is a long, paraffin-like molecule, it forms a nearly ideal solution with the hydrocarbon and in the ternary liquid-liquid system DMSO-5-nonanone-hydrocarbon it goes preferentially into the hydrocarbon phase. Acknowledgment
T h e authors are grateful to the National Institutes of Health and to the National Science Foundation for financial support and to the Computer Center, University of California, Berkeley, for the use of its facilities. literature Cited
.4merican Petroleum Institute Project 44, “Selected Values of Properties of Hydrocarbons and Related Compounds,” A 8( M College of Texas, College Station, Tex., 1964. Brown, I., Ewald, A. H., Australian J . Sci. Res. A4, 198 (1951). Clever, H. L., Snead, C. C., J . Phys. Chem. 67,918 (1963). Crown-Zellerbach Co., Camas, Wash., “Dimethylsulfoxide,” Tech. Bull., 1964. Ellis, S. R. M., Trans. Znst. Chem. Engrs. (London) 30, 58 (1952). Hermsen, R. TV., Prausnitz, J. M., Chem. Eng. Sci. 18, 485 (1963). Hodgman, C. D., ed., “Handbook of Chemistry and Physics,” Chemical Rubber Publishing Co., Cleveland, Ohio, 1963. Orye, R. V., Prausnitz, J. M., Trans. Faraday SOC.61, 1338 (1965). Renon, H., doctoral dissertation, University of California, Berkeley, 1966. Renon, H., Prausnitz, J. M., A.Z.Ch.E. J., in press, 1968. Scatchard, G., Ticknor, L. B., J . A m . Chem. SOC. 74, 3724 (1952). Scatchard, G., TVilson, G. M., Satkiewicz, F. G., J . A m . Chem. SOG.86, 125 (1964). Stephenson, R. FV., Van TVinkle, M., J . Chem. Eng. Data 7 , 510 11962).
S&anarayana, Y. S., Van FVinkle, M., J . Chem. Eng. Data 11, 8 (1966). RECEIVED for review April 24, 1967 ACCEPTED November 15, 1967
VOL. 7
NO. 2 A P R I L 1 9 6 8
225
