Interfacial Tension of the Methane-Normal Decane System

STEGEMEIER, G.L., JUNIOR MEMBER AIME, SHELL DEVELOPMENT CO., HOUSTON, TEX. PENNINGTON, B.F., JUNIOR MEMBER AIME, HUMBLE OIL AND REFINING CO., HOUSTON, TEX., BRAUER, E.B., JUNIOR MEMBER AIME, UNION OIL CO., ABBEVILLE, LA., HOUGH, E.W., U. OF TEXAS, AUSTIN, TEX. Abstract Interfacial tension divided by the difference in density between the liquid and the vapor phases was determined experimentally by the pendant drop method on several isotherms in the two phase region below the critical point for the methane-normal de can e system. The density difference data of Sage and Lacey was used in the calculation of inter facial tension. Both inter facial tension and interfacial tension divided by density difference were found to vanish at the critical point. Interfacial tensions of less than one dyne/centimeter were observed as far as 1,000 pounds per square inch below the critical pressure. EXPERIMENTAL PROCEDURE The interfacial tension divided by the density difference for the methane-normal decane system was determined at the 100 degrees, 130 degrees, 160 degrees and 190 degrees F isotherms, from pressures of about 1,000 psi to the critical pressure, which is more than 5,000 psi for these isotherms. Particular emphasis was placed upon the investigation at pressures slightly below the critical pressure where the interfacial tension is less than 0.5 dyne/cm. Volumetric properties in the two-phase region, including the critical pressures and temperatures, were taken from the work of Sage and Lacey. The experimental pendant-drop technique used for the determination of interfacial tensions at high pressures incorporated the ideas of Michaels and Hauser, Hough, et al, Walker and Heuer. In addition, the technique for determination of extremely small interfacial tension by Jennings was utilized in the region near the critical points. A detailed description of the apparatus is given in a dissertation by one of the authors. Cleaning operations on the stainless-steel sample system included successive washings with chromic acid, tap water and, finally, distilled water. Subsequent cleanings were performed with re-distilled normal pentane, which had an extremely low residue upon evaporation. Specific composition requirements necessitated a fairly precise sample introduction although, for a two-phase, two-component system, the composition of each phase is completely determined if pressure and temperature are controlled. The normal decane was delivered into the evacuated sample system as a liquid from a burette. The methane was then introduced into the system from a calibrated isothermal container, so that pressure differentials could be used to determine the amount introduced. High pressures were obtained by compressing the sample with a mercury injection pump until the critical pressure was reached for the particular isotherm being studied. Experimental data were then obtained for specific pressures by first decreasing the pressure slightly so that two phases would appear, and then photographing a drop at that pressure. Subsequent photographs were made at increments throughout the pressure range. SPEJ P. 257^