( F'upor- Liquid Equilibria in Binary Systems)
SYSTEMS INVOLVING cis- OR trans-DICHLOROETHYLENE AND A ICETONE OR ESTER XORJIAN ALPERT AND PHILIP J . ELVING
T
HE study of the vapor-liquid equilibrium relations in binary systems of cis- or trans-dichloroethylene with class 111 liquids was continued with esters (ethyl formate and methyl acetate) and ketones (acetone and 2-butanone). EXPERIMIEi3T.i L
PREPARATION OF MATERI.ILS. All liquids were purified by distillation through the 120-em. column a t a reflux ratio of about 20 to 1. The fraction of ethyl formate (Paragon) boiling at 54.0" C. was collected ( n % O = 1.3598); Eastman Kodak yellow label methyl acetate was purified by t)he method of German and Jamsett (f 1 ) ; final purification was achieved by dist,illation,using the fraction boiling a t 57.2" C. (n%o = 1.3614). The fraction of C.P. acetone collected had a boiling point, of 56.4" C. (n? = 1.3586). 2-Butanone (East,man Kodak yellow label) was collected a t 79.8" C. ( n % O = 1.3785).
DATA
V.\POR-LIQL.IO EQT-ILIBRICM D.k,ra. Equilibrium saniplw i ~ e r canalyzed by refractive index measurements at 20' C. (Table 1). The experimental results are presented in Tahles XI11 to X S and are shown graphically iri Figures 9 and 10; the corresponding vapor-liquid equilibrium diagrams are s h o ~ v nirl Figures 11 and 12. Thr apparent isopiestic activit>ycoefficients for each component wcre calculated (Table XITI t o X X ) and plotted (Figure 13). The compositions and boiling points of the azcot ropes iurnicvi tenis, cis-dichloroethylene--niethyl acetLtw aiid ciedichloroethylene-acetone, could not be checked by iractio~ially distilling mixtures approximating the azeotropic compositions, inasmuch as the most efficient column available (60 theoretied plates) did not have sufficient resolving power. Because the vapor-liquid equilibrium relations are such that etartirig 011 eithrr side of the azeotropic composition gave a than the azeotropic composi originally prcsent in excess,
Figure 9. Boiling Point-Composition Diagrams
Figure 10. Boiling Point-Composition Diagrarna
Temperature, C., DS. mole fraction lower boiling compon e n t a t 760 m m . of mercury pressure I. cis-Dichloroethylene-ethyl formate (lower boiling component) 11. trans-Dichloroethylene (lower boiling component)ethyl formate 111. cis-Dichloroethylencmethyl acetate (1ow.e.r boiling component) JV. trans-Dichloroethylene (lower boiling component)methyl acetate
Temperature, O C., 1.s. mole fraction lower boiling coniponent a t 760 m m . of mercury pressure V. cis-Dichloroethyleneacetone (lower boiling coniponent) VI. trans-Dichloroethylene (lower boiling component)acet0ne VII. cis-Dichloroethylene (lower boiling component)-2but anone VIII. trans-Dichloroethylene (low-erboiling component)Z-butanone
1182
INDUSTRIAL AND ENGINEERING CHEMISTRY
May 1951
TABLE XIII. VAPOR-LIQUID EQUILIBRIUM DATAFOR SYSTEM cis-DICHLOROETHYLENE-ETHYL FORMATE AT 760.0 MM. Temp., 0
c.
60.3 60.3 60.3 60.1 59.7 59.2 08.8
58.6 58.2 57.7 57.1 56.7 56.4 55.8 55.3 54.4 54.0 53.9
T-IBLE XIV.
Mole Fraction Ethyl Formate Liquid, Vapor, Xl Y1 0.000 0.000 0.012 0.014 0.039 0.043 0.120 0.129 0.194 0.213 0.283 0.313 0.363 0.398 0.425 0.463 0.505 0.548 0.579 0.624 0.648 0.700 0.718 0.765 0.783 0,825 0.840 0.877 0.886 0.919 0.955 0.970 0.993 0.998 1,000 1,000
Activity Coefficients . DichloroEster, ethylene, Yi
0.930 0.933 0.882 0,864 0.893 0.918 0.918 0.921 0.933 0.940 0.964 0.964 0.968 0.970 0.982 0,987 0,988 1,000
Yl
1,000 0,991 0.990 0.987 0.986 0.989 0.983 0.981 0.975 0.969 0.944 0.937 0.920 0.887 0.836 0.804 0.349 0.760
'
VAPOR-LIQUID EQUILIBRIUM DATAFOR SYSTEM FORMATE AT 760.0 M M .
trans-DICHIBROETHYLENE-ETHYL
Temp., 0 C. 53.9 53.7 53.5 53.0 52.5 51.9 51.3 50.9 50.5 49.9 49.5 49.3 49.0 48.9 48.6 48.5 48.3
Mole Fraction trans-Dichloroethylene Liquid, Vapor, 21 Yl 0.000 0.000 0.067 0.050 0.140 0.110 0.208 0.167 0.282 0.228 0.369 0.312 0.448 0.387 0.512 0.451 0.525 0.583 0.619 0.662 0.727 0.691 0.758 0.784 0.829 0.849 0.868 0.851 0.934 0.938 0.974 0.976 1.000 1,000
Activity Coefficients Dichloroethylene, Ester, Yl YZ 1.13 1.00 1.14 0.985 1.09 0.975 1.08 0.971 1.10 0.976 1.06 0.976 1.06 0.981 1.05 0.976 1.05 0.989 1.02 1.02 1.03 1.03 1.00 1.05 1.01 1.04 1.01 1.05 1.01 1.13 1.01 1.12 1.00 1.14
TABLEXVI.
1183
VAPOR-LIQUID EQLTLIBRIUM DATAFOR SYSTEM ACETATE AT 760.0 MAI.
trUnS-DICHLOROETHYLENE-MET€iYL
T:mC., 57.2 57.0 57.0 56.7 56.4 55.6 54.8 54.1 53.1 52.3 51.3 50.8 50.1 49.4 49.1 48.5 48.3 48.3
Mole Fraction trans-Dichloroethyle~~e Liquid, Vapor, x1 Y1 0.000 0,000 0.014 0.017 0.032 0 039 0.082 0.100 0.131 0.155 0.222 0.265 0.314 0.368 0.392 0.454 0.508 0.581 0.602 0,675 0.690 0.763 0.743 0.808 0.832 0.877 0.903 0.929 0.929 0.949 0.971 0.978 0.984 0,990 1,000 1.000
-4ctivity Coefficients DichloroEster, ethylene , Yl
0.905 0.926 0.930 0.943 0.922 0.954 0.963 0.970 0.986 0.993 1.01 1.02 1.00 1.01 1.01 1.01 1.02 1.000
Y2
1.ona ~ .
.
1.00 1.00 1.00 1.00 1.00 1.01 1 .oo 0.988 0.976 0.949 0.950 0.947 0.980 0.970 1.05 0.870 0.945
EQUILIBRIUM DATAFOR SYSTEAX TABLEXVII. VAPOR-LIQUID cis-DICHLOROETHYLENE-ACETONE A T 760.0 Mal. Temp., O
c.
60 60 60 61 61 61 61 61 61 61 61 61
61
61 60 fiQ 60 59 58 57 57 56
56
3 6 8 0 3 4 5 7
a
9 8 6 3 0 8 5 2 2 6 8 1 7 4
Mole Fraction Acetone Liquid , Vapor, Yl 0.000 0.000 0.023 0.016 0.035 0.032 0.053 0.044 0.095 0.080 0.125 0.110 0.163 0.147 0.233 0.218 0.263 0.251 0.337 0.333 0.357 0.364 0.407 0.393 0.463 0.493 0.516 0.553 0.586 0.548 0.640 0.587 0.697 0.638 0.736 0.799 0,845 0.799 0.915 0.883 0.950 0.926 0.979 0.987 1,000 1.000
Activity Coefficients DichloroKetone, ethylene, Yl YZ 0.640 1.00 0.608 0.993 0.792 0.979 0.711 0.974 0.715 0.973 0.748 0.973 0.764 0.973 0.789 0.969 0.799 0.959 0.832 0.929 0.854 0.934 0.875 0.933 0.906 0.904 0.917 0.891 0.926 0.894 0.953 0.860 0.966 0.835 0.988 0.782 0.985 0.812 0.987 0.781 1.00 0.745 1 .oo 0.694 1.00 0.700
TABLEXV. VAPOR-LIQUID EQUILIBRICM DATAFOR SYSTEN cis-DICHLOROETHYLENE-METHYL ACETATEAT 760.0 MM. Temp., 0
c.
60.3 60.6 61.0
61.2 61.3 61.4 61.5 61.6 61.7 61.7 61.7 61.6 61.5 61.4 61.2 60.8 60.2 59.7 59.2 58.4 57.6 57.3 57.2
Mole Fraction Methyl S c e t a t e Liquid, Vapor, 21
vi
0.000 0.031 0.072 0.112 0.147 0.198 0.224 0.276 0.296 0.326 0.347 0.375 0.395 0.444 0.511 0.583 0.651 0.715 0.772 0,880 0.950 0.988 1,000
0,000 0.027 0.062 0,099 0.133 0.183 0.213 0.266 0.291 0.326 0.351 0.383 0.408 0.465 0.541 0.623 0.696 0.770 0.820 0,907 0.965 0.993 1.000
hctivity Coefficients Dichloroethylene,
Ester, Yl 0.710 0.774 0.753 0.783 0.786 0.799 0.822 0.831 0.844 0.859 0.869 0,880 0.893 0.906 0.925 0.939 0.961 0.991 0.994 0.994 1.00 1.01 1 00
TABLEXVIII.
Y2
1.000 0.984 0.975 0.974 0.973 0.972 0.968 0.963 0.953 0.946 0.941 0.938 0.933 0.917 0,902 0.876 0.863 0.816 0.811 0.820 0.758 0,643 0.750
points were determined from the smoothed vapor-liquid equilibrium data. Care was taken to determine sufficient experimental points in the vicinity of the azeotropes t o permit drawing of a good average curve. In the system cis-dichloroethylene-methyl acetate, a maximum boiling azeotrope, boiling a t 61.7" C. and containing 0.326 mole fraction methyl acetate, was found. I n the system cis-dichloroethylene-acetone, a maximum boiling azeotrope, boiling a t 61.9" C., and containing 0.326 mole fraction acetone, was found.
VAPOR-LIQUID EQUILIBRIUM DATAFOR SYSTEM 760.0 MM.
tTUnS-~lCHLOROETHYLENE-ACETOKE AT
56.4 56.3 56.0 55 8 55.1 54.8 54.2 53.5 52.3 51.4 51.0 50.1 49.6 49.1 48.8 48.5 48.3 48.3 48.3
Mole Fraction tyans-Dichloroethylene Liquid, Vapor, XI Y1 0.000 0.000 0.021 0,032 0.040 0.048 0.070 0.091 0.130 0.172 0.157 0.198 0.207 0.264 0.276 0.346 0.390 0.474 0.469 0.547 0.537 0.620 0.655 0.723 0.726 0.776 0.787 0,820 0.868 0.885 0.909 0.922 0.956 0.962 0.975 0.978 1.000 1 000
Bctivity Coefficients Dichloroethylene, Ketone, Yi
ya
1.00 1.19 0.947 1.03 1.07 1.04 1.06 1.07 1.07 1.07 1.07 1.05 1.05 1.02 1.02 1.02 1.02 1 02 1 .00
1.00
0.991 1.00 0.998 0.994 1.01 0.998 1.00
0.990
1.01 0.985 0.993 1.04 1.09 1.14 1.13 1.15 1.17 1.14
DISCUSSION
An attempt was made to fit the data to the van Laar or Margules equations. The sources of the vapor pressuretemperature relations for the esters and ketones are indicated in Table XXI. I n all cases, the log of the vapor pressure was plotted against the reciprocal of the absolute temperature on a large scale and the best average straight line drawn. The curves were then used in the 'calculation of the activity coefficients. The results of the attempted fits to the van Laar and Margules
INDUSTRIAL A N D E N G I N E E R I N G CHEMISTRY
1184
Vol. 43, No. 5
Figure 11. Equilibrium Mole Fraction of Lower, Mole FracBoiling Component in Vapor, y ~z's. tion in Liquid, X I , at 760 Mm. of Mercury Pressure Roman numerals refer t o same systems
ns
i n Figure 9
equations are shown in Table XXI. In the systems cis-dichloroethylene-methyl acetate and cis-dichloroethylene-acetone, A and B values calculated from azeotropic data did not give as good agreement as A and B values obtained from the end values of the activity coefficient curves. Examination of the data (Figure 13 and Table XXI) and those given previously reveals several points that are worth noting. E n d l and Welch (9) and Enrell, Harrison, and Berg (8) pointed out that conipounds with the structure -CCl--CHCIn-ill form weak hydrogen bonds with suitable donor atoms such as oxygen in esters, ketones, ethers, etc. Both cis- and truns-
T.4BLE
D . 4 T A FOR SYSTEM XIX. \rAPOR-LIQUID EQUILIBRIUM C~S-DICHLOROETHYLENE-2-BUTANOXE AT 760.0 >far.
Temp., 79.6 79.6 79.5 79.4 79.3 79.2 79.0 78.6 78.3 77.9 77.0 75.9 74.0 72.1 70.1 67.6 65.1 62.6 61.6 60.3
Mple Fraction cis-Diohloroethylene Liquid, Vapor,
Activity Coefficients Diohloroethylene, Ketone
Figure 12. Equilibrium Mole Fraction of Lower-Boiling Component in Vapor, yl, US. Mole Fraction in Liquid, XI, at 760 Mm. of Mercury Pressure Roman numerals refer t o same systems as in Figure 10
dichloroethylene would be expected to form hydrogen bonds 111 the presence of such oxygenated molecules. This would be onc factor in explaining the vapor-liquid equilibrium relations. Another factor would be the dipole moments of the cis and trans isomers, and the dipole moments of the hydrogen-bonded complex formed. It has bcen shown that the value of the dipole
TABLEXX. VAPOR-I~IQUIU EQUILIBRILT DATAE O R SYSTEV tranS-DICHLOROETHYLESE-2-BUTlUOUE
Temp., 0
c.
79.6 79.1 77.3 74.9 72.9 70.2 68.4 66.7 65.5 62.9 61.1 59.6 58.1 56.1 53.9 51.8 49.8 49.2 48.3
Mole Fraction trans-Diciiloroethylene -. Liqiiid, Vapor, XI
211
AT
760.0
Activity Coefficients
Dichloro-
ethylene, Yl
Ketone, Yl
1.00
0.976 0.978 0.980 0.987 0.979 0.983 0.988 0.983 0.968 1.00 0.091 0.998 0.967 0,980 1.09 1.31 1.77
...
May 1951
-
INDUSTRIAL AND ENGINEERING CHEMISTRY
moment for cis-dichloroethylene is 1.8 debyes ($1)’ while the trans isomer has a zero dipole moment. Accordingly, the cis isomer would be expected t o show greater departure from ideality than the trans isomer, because the complex formed through hydrogen bonding in the case of the cis isomer would still have an appreciable dipole moment and tend t o associate through electrostatic attraction. A third factor that must be considered is the closeness of the boiling point of the second component t o the cis or trans isomer. This is especially important in predicting azeotrope formation (8-10). The closer the boiling point of the second component, the more likely that a maximum or minimum will occur in the total vapor pressure curve. Thus, in the systems cis-dichloroethylene-methylal and trans-dichloroethylenemethylal, the trans isomer forms a maximum boiling azeotrope, the only maximum boiling azeotrope with the trans isomer observed in these studies. Aside from the fact that methylal boils much closer to the trans isomer than the cis, a steric factor may be involved. Thus, the cis or trans isomer would be expected t o farm chains of the type
azeotropes v e r y readily with cyclic e t h e r s , as compared to other 1.2 ethers. Brown ( 4 ) 1.0 showed that the base strengths of a series of ethers 1.0 were in the order: .8 tetrahydrofuran > methyl ether > leo ethyl ether > isoZ propyl ether, ,,o when boron tri.8 fluoride was the acid. The results .6 were explained on f the basis of steric 54 strain of the re1.0 s u l t i n g addition H H complex, the .8 strain being least CH, .6 in the case of tetA/ rahydrofuran and ’0\ 0 * . . I .4 g r e a t e s t in t h e C1 H ’ CH, ’ H Cl 1.2 case of isopropyl 1.0 e t h e r . Thus, a I/ .8 steric factor may C 0 .2 .4 . 6 .8 1.0 be important in /\ MOLE FRACTION Xa explaining t h e . . .HAC1 CI H large negative deThis ability of either isomer to form long chains with methylal Figure 13. Activity Coefficient US. viations from through hydrogen bonding, plus the proximity of the boiling Fraction Lower-Boiling ideality with ponent in Liquid, XI, at 760 Mm. of point of the trans isomer to methylal, favors the formation of an tetrahydrofuran Mercury Pressure azeotrope with this isomer. A . Activity coe5cient curve for lower boiland the Chain formation through hydrogen bonding is apparently not ing component n e g a t i v e deviaB . Activity c o e 5 c i e n t curve for higher boilthe predominant factor, because the cis system still shows greater ing component tions from ideality Roman numerals refer to same systems as negative deviations from ideality. with isopropyl in Figures 9 and 10 The vapor-liquid equilibrium relations with isopropyl ether ether. Ewe11 and and tetrahydrofuran are interesting Ewe11 and Welch ( 9 ) Welch (9) found a showed that halogenated hydrocarbons form maximum boiling maximum boiling azeotrope in the system, chloroform-isopropyl ether, but here the hydrogen-bonding tendency of chloroform is much greater than with cis- or tram-dichioroethylene. TABLE XXI. FIT OF EXPERIMENTAL DATAFOR BINARY SYSTEMS TO The results of these investigations of cis- and THEORETICAL EQUATIONS trans-dichlorosthylene with liquids of class I11 (8) Molar indicate several principles that may be of use in Volume Ratio Vapor Second Equations Pressure the separation of cis-trans isomers similar to cisComponent %t%$m Value of Checked Data for and trans-dichloroethylene. The cis isomer us(S.C.) CzHzC1z:S.C. A B for Fit Agreement S.C. ually shows the greater negative deviation from I, C ~ B - D I C H L O R O ~ T H Y L E N ~ ideality and the greater tendency to form a maxiEthyl formate 1:1.07 -0.031 -0.119 van Laar Mostlywithin (10, 19) !% mum boiling azeotrope. The entrainer could be a Margules Fair, extreme liquid of class 111 such as an ester, ketone, or ether, 2% Methylacetate I : 1 06 -0.149 -0.125 van Laar Mostlywithin (27. 1 9 ) which forms a maximum boiling azeotrope with the and 1% extreme Mar ules 1 5% cis isomer, thus permitting greater ease in the Acetone 1 03:l -0.194 -0 1B5 van f a a r Mostly within (8,f5’, IS) separation of the cis-trans isomers by increasing and l % ,extreme Margules J 5% the boiling point difference between separable frac2-Rutanone 1:1 06 - 0 233 -0 280 vanLaar V i t h i n 3 % u p (17, 19) and to 0.6 mole tions consisting of the pure trans isomer and the Margules fraction; bemaximum boiling azeotrope formed by the enyond 0.6 poor fit trainer and the cis isomer. After distillation of 11. t r a n s - D I C H L O R O E T H Y L E N E the trans isomer, if the entrainer were waterEthyl formate 1 . 1 04 + O 053 4-0 057 van Laar Poor soluble and the cis isomer water-insoluble, the still and residue could be washed with water t o recover Margules Methyl acetate 1 : 1 04 0 013 - 0 025 van Laar Mostly within the entrainer, and the relatively pure cis isomer M;$es extreme obtained. These principles have not been tried Acetone 1.05:l 0 0 + O 057 Margules Fair to poor with cis- and trans-dichloroethylene because of the 2-Butanone 1 . 1 04 Close to ideal appreciable difference in boiling point (12 ’ C.), between 0.2 and 0.8, end The application t o other systems should be i n values off teresting.
‘.c/
.
‘d
\/
e
4
.
1185
-
;gp
1.0 .8
3
8
INDUSTRIAL AND ENGINEERING CHEMISTRY
1186
SURIMARY
Vapor-liquid equilibrium relations in binary systems of cisor hns-dichloroethylene with ethyl formate, methyl acetate, acetone, and 2-butanone have been determined at atmospheric pressure. Boiling point-composition, vapor-liquid equilibrium, and refractive index-composit,ion relations are presented for all systems. The activity coefficients (logarithmic scale) of the components in the liquid (linear scale) were plotted. The resulting diagrams are presented. In some ca,ses, the da,ta fitted the van Laar and Slargules equations. The observed vapor-liquid equilibrium relations in this and previous work are explained on the basis of hydrogen bonding, boiling points, dipole moments, and steric factors. A method for separating &-trans isomers by azeotropic distillation is suggested.
Beare, W. G., McVicar, G. .1.,and Ferguson, J. B., J . Piiys. Chem., 34, 1310 (1930).
Brown, H. C., and Adams. R . M., J . Am.. Chem. Sac.,
LITERATURE CITED
(1) &pert, K . , and Elving, P. J., IND.ENG.CHEM.,41, 2864 (1949). (2) Baker, E. hI., Hubbard. R. 0 . H., Huguet, J. H., and Michalowski, 8. S., I b i d 31. 1260 (1939). ~
64, 255;
(1942).
Carlson, H. C., and Colburn, -4.P., I x n . ETG. CHEaf., 34, 584 (1942).
Connor, A. Z., Elving, P.J., and Steingiser, S., I h i d . , (19481. DU Pont Electrochemieals News, 27, 1607 (1949).
40, 409
Field Reseal ch Section, Chem. Eng.
Ewell, R. H., Harrison, J. &I., and B a g , L., IND.ENG.CHEM., 3 6 , 8 7 1 (1944).
Ewell, R. H., and Welch, L. XI., J . Am. Cliem. SOC.,63,
2475
(1941).
Fleer, K . B., J . C ‘ h e m ~Eo’wxition, 22, 588 (1943). German, W.L., and Jamsett, It. -1.. J . C h e m Soc., 1940, 1360. Horsley, L. H., A n a l . C‘hewr., 19, 507 (1947); 21, 831 (1949). “International Critical Tables,” Vol. 111, p. 218, S c w ‘iork, McGraw-Hill Book Co.. 1925. Jones, C. A., Schoenborn, E. M., and Colhurn, A. I’., IXD.E s o . CHEY., 35, 666 (1943).
ACKNOWLEDGIbIENT
One of the authors (S.A . ) wishes to thank the Purdue Research Foundation for an XR Fellon-ship upon lvhich the work deecribed in the first paper in this group was done, and the Atomic Energy Commission for an .4EC Predoctoral Fellowship upon which the work described in t’he latter two papers \vas done.
Vol. 43, No. 5
Lange, N. A , , ed., “Handbook of Chemistry,” 4 t h ed., p. 1516,
Sandusky, Ohio, Handbook Publishers,
1941.
Selson, 0. A , , IKD. EKG.CHEM.,20, 1380 (1928). Perry, J. H., ed., “Chemical Engineer’s Handbook,” 2nd cd., p .
381, New York, iVIcGraw-HilI Book Co., 1941. Reilly, J., and Rae, W.N., “Physicochemical Methods,” 1701,11, pp. 9-10, New York, D. Van Nostrand Co., 1939. S t d , R. D., IND.EXG.C H E Y . , 39, 517 (1947). Todd, F., IXD.ENG.CHEM.,ANAL.ED., 17, 175 (1945). T r a n s . F a r a d a y SOC.,30, Appendix (1934). RECEIVED .4ugust 8, 1949. -4bstracted from the doctor’s thesis of S o r i n a n Alpert, -4ugust 1949, a n d t h e n ~ a s t e r ’ sthesis of D. G. Floin, February 1949.
Thermodynamic Properties of Propylene L4WRENGE N. CANJAR, JIAX GOLDJIAN’,
AND
HENRl- .IIARCHMAN2
Ccirnegie Institrite of Technology, P i t t s b u r g h 13, P a . Exact thermodynamic data are gaining great inlportance in present-day industrial calculations. With the appearance of precise pressure-volume-temperature measurements of propylene in the literature i t w-as possible to calculate the thermodynamic properties of this important industrial compound \cry accurately. This has been done and the results are presented here in form of tables and a pressure-enthalpy chart. These properties cover a range from the liquid at the nor-
mal boiling point to a gas at 480” I?. and 200 atmospheres. 4 datum state has been chosen where the enthalpy and entropy of the elements carbon (graphite) and hydrogen in the ideal gas state and at 1 atmosphere and 0’ K. arc equal to zero. Calculations involving the properties reported here will be the most accurate possible in view of present-day experimental technique. For this reason the data were not extrapolated to regions of uncertainty.
ITH the accurate m e a m enient of the pressuie-voluinetemperature (P-V-T) propel ties of pi opylene by Sage ~t uZ. (4)and Marchman et ul (11) enough drita had bern acruinulated t o enable precise ealculationq of the thermodl-namic propel t i r e of this important hydrocarbon Illarchman et al (11) have also fitted the Benedict-Webb-Rubin equation to the data which nixde available a vcrj convenient method for the calculation of the properties in the superheated legion The other data necessar~ for the complete constiuction and check of a pressure-enthalpi diagram and their sources will br described in detail later. The datum state where the enthalpy and mtropy of the elements carbon and hydrogen in the ideal gas state and at 1 atmosphere and 0” K are equal to zeio has been chosen as the most convenient basis fol universal use In these calculations the
enthalpy change and entiopj- change on formation have been included. The propertkc of other compounds based on the same datum state can be added and subtracted from each other without making corrections for differences in the datum state, Throughout this work the fundamental constants and conversion factors were taken exclusivelj- from the -4merican Petroleum Institute (.4.P.I.) tables ( 1 ) . The molecular weight was talrrn a < 42.078. Othei data \vhich were available follow.
1 2
F1a
Piesent address, R C.A Victor Dirision, Camden 2 , K. J Present addre?-, International A‘llneralq and Chemlcal Corp , Mulberlv
CRITIC4L CONSTANT
Values are reported bv S‘aughan and Graves ( I ? ) , Lu, Kewitt, and Ruheman ( 9 ) , Seihert and Burrell (1.5), and Marchman, Prrngle, and JIotard ( 1 1 ) . The constants of Marchman, Prengle. and Illotard ( 1 1 ) were used in this work, for their values were determined by actually measuring the inflection point of th(3 critical isotherm. The other constants were measured by nit,niLC U P method.
