The measurement and application of free gas volumes in a gas-liquid chromatographic column methane K-values and liquid molar volumes in the methane-n-octane system
Alyea, James Ivan
Master of Science
The purpose of this research was to investigate an experimental method for determining the free gas volumes in a gas-liquid chromatographic column. Methane K-values and liquid molar volumes in the methane-n-octane system were obtained and compared with known values. Infinite dilution K- values for helium, neon, and argon were also calculated and reported. All data were taken for a system temperature of -25°C and for a pressure range of 40 to 1028.7 psia. For a given system temperature the free gas volume inside the column was a function of the system pressure or the methane gas dissolved in the liquid phase. For each pressure, the retention volumes of helium, neon, argon, and tritium-tagged methane were determined. These volumes, measured at atmospheric conditions, were converted to column conditions and were corrected for system dead volume outside the column and for the response of the electronic equipment. The logarithms of the corrected retention volumes of helium, neon, and argon were plotted against the reciprocals of the reduced temperatures of the respective components. This plot, which was almost linear, was extrapolated to a value of zero for the reciprocal of the reduced temperature. The corresponding value of retention volume was taken to be the free gas volume in the column. The K-value of methane and the infinite dilution K- values of helium, neon, and argon in the methane-n-octane system were readily calculated. As the pressure was increased, the free gas volume decreased as a result of the swelling of the liquid phase upon dissolution of methane. The molar volume of the pure liquid at its vapor pressure and the composition of the liquid phase at each experimental pressure were obtained. It was then possible to calculate the liquid molar volumes at the various experimental pressures. The methane K-values and the liquid molar volumes compared very favorably with literature values. The helium, neon, and argon K-values appear to be reasonable, but no literature values are available for comparison. This method for determining the free gas volume in a gas-liquid chromatographic column appears to be the most reasonable method devised to date.