INDUSTRIAL A N D ENGINEERING CHEMISTRY
198
Vol. 44, No. 1
AH. = change of enthdlpy in B.t.u. per pound with temperature
LITERATURE CITED
at constant volume J = 0.18506, factor for converting cubic feet, pounds per square inch, pounds to B.t.u. per pound L = latent heat of vaporizatjon in B.t.u. per pound p = pressure in pounds per square inch absolute AST = change of entropy in B.t.u. per pound per O R. .with volume a t constant temperature A S , = change of entropy in B.t.u. per pound pdr O R. with temperature a t constant volume T = absolute temperature, " R. ( " R. = " F. plus 459.69) t = temperature, O F. tc = critical temperature (83.93" F.) v = gas volume in cubic feet per pound VL = liquid volume in cubic feet per pound
(1) Beattie, J. A.,and Bridgeman, 0. C., Proc. Am. Acad. Arts Sci., 63, 229-308 (1928). (2) Benedict, M., Webb, G. B., and Rubin, L. C., J . Chem. Phys., 8, 33445 (1940). (3) Benning, A. F.,'and McHarness, R. C., IND.ENO. CEEM.,31, 912-16 (1939). (4) Ibid., 32, 698-700 (1940). (5)Ibid., pp. 814-16. (6) Henning, F.,2. Instrumentenk., 33, 33 (1913). (7) Kahovec, L.,and Wagner, J., 2. physilc. C h m . , B48, 177 (1941). (8) McNabney, R.,unpublished thesis, Western Reserve University, 1941. (9) Plyler, E.K.,private communication, 1949. (10) Riedel, L.,2. ges. Kttlte-Id., 48,9-13 (1941). (11) Ibid., pp. 89-92. (12) Ruff, O.,and Keim, R., 2. anorg. u. allgem. Chem., 201, 255 (1931). (13) Thornton, N. V., Burg, A. B., and Schlesinger, H. S., J . Am. Chem. Sw., 55, 3177 (1933). (14) Wenner, R. L.,"Thermochemical Calculations," 1st ed., New York, McGraw-Hill Book Co., 1941. (15) Whitney, J. H.,private communication with E. I. du Pont de Nemours & Co., 1948. RECEIVED October 13, 1950.
ACKNOWLEDGMENT
The authors wish to thank E. I. du Pont de Nemours & Co. for its generous financial assistance in this investigation. The suggestions of A. F. Benning and R . C . McHarness of Du Pont Co. are especially appreciated.
Phase Equilibria in Hvdrocarbon N
Systems 4
VOLUMETRIC BEHAVIOR OF THE NITROGEN-ETHANE SYSTEM H. H. REAMER, F. T. SELLECK, B. H. SAGE, AND W. N. LACEY California Institute of Technology, Pasadena 4, Calif.
N
ITROGEN is found in many petroleum reservoirs and may be considered as a component of natural gaa. Since mix-
turea of nitrogen and p a r a f i hydrocarbons do not form ideal solutions ( I f ) at elevated prwurea, a knowledge of the volumetric behavior of such mixtures is of industrial interest. Keyes and Burks (12) investigated the volumetric behavior of mixtures of nitrogen and methane with an accuracy adequate for most purposes. The work has been supplemented by the measure ments of Eilerts, Carlson, and Mullens (9)upon the effect of nitrogen on the volumetric behavior of natural gas. Burnett (7) recently summarized the thermodynamic properties of nitrogen. The volumetric behavior of the nitrogen-ethane system does not appear to have been established a t the higher pressures. The present study is concerned with the volumetric behavior of three mixtures of nitrogen and ethane at pressures up to 10,000 pounds per square inch in the temperature interval between 40" and 460" F.
The influence of temperature and pressure upon the volume of ethane has been investigated in some detail. Beattie and coworkers ( 4 ) determined the volumetric behavior up to approximately 3,000 pounds per square inch with good accuracy. These studies have been extended recenly to somewhat higher pressures (19). Barkelew, Valentine, and Hurd (1) reviewed available experimental information concerning ethane and prepared a tabulation of thermodynamic data. The compressibilities of nitrogen and mixtures of hydrogen and nitrogen were determined over a wide range of temperatures and pressures by Wiebe and Gaddy (18). Volumetric studies of the nitrogen-carbon dioxide system were made by Haney and Bliss (10). The characteristics of nitrogen at pressures near 1 atmosphere were carefully determined by Baxter and Starkweather ( 8 ) . Benedict (6)studied the influence of pressure and temperature
upon the volume of nitrogen a t elevated preasurea. Beattie and Bridgeman established constants for this compound for their equation of state (3). Roebuck and Osterberg (16)and Deming and Deming (8)measured the Joule-Thomson coefficient of nitrogen over an extended range of pressures. The thermodynamic properties of this compound were made available recently (16). This background of experimental information serves to establish the volumetric behavior of the components of the nitrogen-ethane system with an accuracy adequate for present needs. MATERIALS
The nitrogen used in this investigation was obtained from the Linde Air Products Division of the Carbide and Carbon Chemicals Corp. which reported it to contain less than 0.0005 mole fraction of material other than nitrogen. This sample was passed over activated charcoal a t a low temperature and by means of a mass spectrometric analysis, .the purified material was found to contain less than 0.0002 mole fraction of. impurities. Before use the nitrogen was stored in a steel vessel at elevated pressures. The ethane was obtained from the Phillips Petroleum Co. which reported it to contain less than 0.001 mole fraction of impurities. This material was subjected to a single fractionation in a column packed with glass helices a t a reflux ratio of approximately 40 to 1. The central fraction from this distillation yielded less than 0.2 pound per square inch change in vapor pressure as a result of a change in quality-Le., the weight fraction gas of a heterogeneous system, from 0.2 to 0.8 a t a temperature of 70" F. Difficulty in obtaining satisfactory improvement in purity by fractionation had been experienced with other sources of ethane. This behavior may have resulted from the formation of an azeotropic mixture with one of the impurities which would have rendered simple fractionation ineffective as a means of purification. The ethane was stored in a weighing bomb ( 1 7 ) until ready for use.
INDUSTRIAL AND ENGINEERING CHEMISTRY
January 1952
2000
4000
PRESSURE
6000
POUNDS PER SQUARE INCH
Figure 1. Typical Experimental Results for a Mixture of 0.7318 Mole Fraction Nitrogen
199
tem eratures. The volumetric measurements of Wie&e and Gadd (18)and of Benedict ( 5 ) were utilized to relate d e measurements of total volume, pressure, and temperature to the weight of the Sam le employed. As a result of the agreement of t t e two sets of volumetric measurements and the small variation in the weight of the sample as established at a number of pressures, it appears that the quantity of nitrogen was determined with an uncertainty of not more than .0.15%. After the quantity of nitrogen had been established, the ethane was introduced by the use of wei hing bomb techniques (I?'). Experience witf this method of introducing hydrocarbons indicates a probable uncertainty of about 0.1%. The magnitude of this error resulted from the relatively small quantity of ethane involved. The total volume of the system was determined for approximately 15 pressures at each of eight systematically chosen temperatures between 40" and 460' F. Approximately fourfifths of the sample was then withdrawn and the volumetric behavior a t the lower pressures wag established. The total quantity of the sample remaining in the apparatus was determined from the volumetric data obtained with the large sample. Extrapolations of the isotherms to zero pressure yielded values of the compressibility factor of unity within uncertainty. RESULTS
PROCEDURES
Figure 1 presents typical experimental results for a mixture of The data indicate a marked deviation from the behavior mcribed to a perfect gas. A sample of the detailed experimental results is dven in Table I and such information for the three mixtures investigated at eight different temperatures is available (14). The molal volumes of the three
The apparatus has been described in detail ( 1 7 ) . In principle, it consisted of a closed steel vessel mthin which the Sam le was confined over mercury. Mercury was introduced or witgdrawn to control the effective volume of the vessel. Mechanical agitation was rovided and the temperature was controlled by immersing t i e pressure vessel in an agitated oil bath. The oil bath was maintained a t a constant temperature by a modulated electronic circuit. The temperature of the pressure vessel containing the sample was measured by means of a platinum resistance thermometer of the strain-free type. This thermometer was compared with a similar instrument calibrated by the U. S. Bureau of Standards. It is believed that the temperatures yere related to the international platinum scale within 0.01 F. throughout the temperature range of the investigation. The pressure was determmed by means of a balance (17), which in turn was calibrated against the va or pressure of carbon dioxide at the ice point (6). The calgration of the balance' has changed by less than 0.04% in over a decade and it is believed that the pressures were known within 0.06% or 0.16 pound per square inch, whichever is larger. The quantity of nitrogen introduced into the apparatus was established by measurement of the total volume of the sample used at a series of pressures and OF EXPERIMENTAL RESULTS FOR A MIXTUR~ TABLE I. SAMPLE OF 0.7318 MOLEFRACTION NITROQEN
Pressure Lb./S Inih Absaute
Volume Cu. Ft./Lb.
Mole
100°
381.8 480.9 620.9 776.5 947.3 1119.5
Corn ressib h y
Sample Weight = 0.1637680 1399.4 3.9405 1639.8 3.3481 1906 .O 2.8774 2115.9 2.5966 2336 .O 2.3618 2680 .O 2.0827 1.8355 3104.8 1.4910 4054.7 5093.7 1 ,2943 6151,. 6 1.1669 6995.1 1.0972 8103.1 1.0245 9075.0 0.9777 9525.2 0.9599 a Sample weight expressed in pounds.
-
10000
9000
I
1.4
I2
8
1.0
I-
u LL.
Factor
F.
Sample Weight = 0.0422330 15.2298 12.0100 9.2164 7.3014 5.9309 4.9772
0.7318 mole fraction nitrogen.
E 2
0.96809 0.96157 0.95273 0.94388 0.93537 0.92766 0.91805 0.91406 0.91306 0.91468 0.91863 0.92928 0.94878 1,01122 1.09764 1.19509 1.27490 1.38215 1.47717 1.52226
0.8
m
B8 z
8
0.6
0.4
