INDUSTRIAL AND ENGINEERING CHEMISTRY
1116
Vol. 21, No. 11
Vapor Pressure Chart for Lower Aliphatic Hydrocar bons‘ R. L. Copson and Per K. Frolich DEPARTMENT OF CHEMICAL ENGINEERING, MASSACHUSETTS INSTITUTE OF TECHNOLOGY, CAMBRIDGE, MASS.
H E literature contains a large amount of data on Curves for the members of the olefin series above ethylene the vapor pressures of the simpler hydrocarbons. have been omitted in order to avoid confusion in plotting These data, however, are widely scattered, since they the data. These vapor pressure curves fall above and close have been obtained by a great number of experimenters, to those for the corresponding paraffins. I n preparing the chart a logarithmic pressure scale has no one of whom has covered the entire range of temperature or worked with more than one or a few members of any been used, and the temperature scale is proportional to given series. ( - l / T ) . This temperature scale results in very nearly I n order to present the vapor pressure curves of the mem- a straight line for the vapor pressure of methane, the curvabers of the hydrocarbon series on a single chart, various ture increasing for the higher members of the series. This empirical methods have been proposed (1, 8, 9, 27, 28). is the opposite of the effect observed with the temperature However, all the charts so prepared have been applied scale adopted by Cox (9) and by Calingaert and Davis (6), chiefly to the higher hydrocarbons and are inaccurate for in which case it will be remembered that the lower members of the paraffin series show the greatest deviation from a the lower members. The method of presenting vapor pressure data originally straight line. The tendency of the curves for these lower proposed by Cox (9) and later improved by Calingaert hydrocarbons to become parallel a t the higher temperatures, and Davis (6) is perhaps the one which is now most widely rather than to intersect in a common point, is quite proused. This method consists in plotting the logarithm of nounced. the vapor pressure against an arbitrary temperature scale Acknowledgment which is proportional to l / ( t 230), where t is the temperature in degrees Centigrade. This choice of temperature The determinations on isobutane around atmospheric scale results in the vapor pressure-temperature curves bepressure were obtained from 0. Maass by private communicoming essentially straight lines, which also appear to intercation, and the data contributed by the Research Laboratory sect in a common point. On a Cox’s chart, however, the of Applied Chemistry are the outcome of investigations curves for the lower members of the paraffin series deviate considerably from a straight line. Furthermore, it follows made by various staff members during recent years. that the curves for the various compounds cannot actually References intersect in a common point, but must rather tend to become Methane: 14, 7, 24, 21, 29, 11 parallel since from .studies of the solubilities of gases HildeEthylene: 20, 2, 6, 24, 25 Ethane: 22, 20, 19, 2, 17, 6, 16, 15, 21 brand (IS) has shown that the hypothetical vapor pressure Propane: 22, 20, 4, 10, 12, 21 of a gas above its critical temperature has a real significance Isobutane: 22, 18. 23, 4, 10 %Butane: 22. 23. 3. 10. 26 and it cannot be supposed that a temperature should exist Isopentane: 30 n-Pentane: 22, 30 a t which pentane, for example, should have a vapor pressure, even a hypothetical one, equal to that of methane. Bibliography The chart presented in this paper has been prepared to represent accurately the vapor pressures of the lower (1) Ashworth, J . Inst. Petroleum Tech., 10, 787 (1924). members of the paraffin series: methane, ethane, propane, (2) Burrell and Robertson, J . A m . Chem. Soc., 37, 1893 (1915). (3) Burrell and Robertson, Ibid., 37, 2188 (1915). normal and isobutane, and normal and isopentane. I n (4) Burrell and Robertson, Ibid., 37, 2482 (1915). addition, ethylene has been included. The range covered (5) Calingaert and Davis, IND.ENG.CHEM.,17, 287 (1925). is from the critical down to vapor pressures of less than (6) Cardoso, J. Chem. Soc., 11, 104, 210 (1912). 0.001 atmosphere, except in the case of methane. The (7) Cardoso, J. chim. fihys., 13, 322 (1915). (8) Carr and Murphy, J . A m . Chem. Soc., 51, 116 (1929). chart has been found useful in connection with solubility E N D .CHEM.,16, 592 (1923). (9) Cox, IND. determinations and purification of these hydrocarbons, and (10) Dana, Jenkins, Burdick, and Timm, RefYigerating Eng.,12, 387 (1926). particularly in their analysis by low-temperature fractionation. (11) Dewar, Phil. M a g , [SI 18, 210 (1884). The data used in preparing the chart have been obtained (12) Hainlen, Ann., 282, 229 (1894). chiefly from the literature, and it is believed that nearly all (13) Hildebrand, “Solubility,” Chemical Catalog Co., 1924. Taylor, and Smith, J . Math. Phys. Moss. Inst. Tech., 1, 211 the available figures have been included. In addition, (14) Keyes, (1922). hitherto unpublished data (22) obtained in this laboratory (15) Kuenen, Proc. Roy. SOC.Edinburgh, 21, 433 (1897). have been used in the lower temperature ranges. Deter- (16) Kuenen and Robson, Phil. >Mag., [6]3, 149 (1902). minations made a t McGill University (18) on isobutane (17) Loomis and Walters, J . A m . Chem. Soc., 38, 205 (1926). (18) Maass and Coffin, Private communication. around atmospheric pressure have also been included. (19) hfaass and McIntosh, J . A m . Chem. Soc., 36, 737 (1914). I n spite of the large number of sources, the data are in very (20) hlaass and Wright, Ibid., 43, 1098 (1921). good agreement. The only discrepancies of any magnitude (21) Olszewski, Compt. rend., 100, 940 (1885). are found in the case of methane, where the data of Olszewski (22) Research Laboratory of Applied Chemistry, Unpublished data. (23) Seibert and Burrell, J . A m . Chem. Soc., 57, 2683 (1915). (21) differ from the more accurate but not generally accessible (24) Stock, Henning, and Kuss, B e y . , 64, 1119 (1921). determinations of Keyes and co-workers (14); and in the (25) Villard, A n n . chim. phys., 7 , 10, 395 (1897). case of isobutane, where the data of Burrell and Robertson (26) Visser, Verslag. A k a d . Wetenschafipen, 22, 330 (1913). (27) Wilson, IND.EXG.CHEM.,20, 1363 (1928). (4) appear to be out of line with the results of other in- (28) Wilson and Bahlke, Ibid., 16, 115 (1924). vestigators. (29) Wroblewski, Comfit. rend., 102, 1010 (1886).
T
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1 Received
July 26, 1929.
(30) Young, Sci. Proc. Roy. Dublin Soc., 12, 374 (1910).
November, 1929
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