The study of high pressure vapor-liquid equilibria by gas-liquid partition chromatography
Stalkup, Fred I.
Doctor of Philosophy
A method has been investigated for measuring vapor-liquid equilibrium ratios, or K-values, of a solute distributed between a gas phase and a non-volatile liquid phase. A gas-liquid partition chromatographic technique is employed in which an inert, porous fire-brick is impregnated with the liquid phase, and the resulting liquid-containing solid is packed into a tube. The gas phase is flowed through the tube, and the solute of interest is eluted through the tube by the flowing gas phase. The data taken for the solute elution process is then related to the K-value of this solute in the vapor-liquid system maintained in the column. A previous mathematical solution describing the chromatographic elution process for a one component elution gas and which may be used to relate K-values to retention times for the solute at infinite dilution in the vapor-liquid equilibrium system is reviewed and expanded to include the effect of elution gas solubility in the liquid phase. A new mathematical solution is presented relating K-values to retention times for the case of a solute being eluted by a binary elution gas mixture composed of components soluble in the liquid phase. This solution covers the case of the solute sample being one of the components of the elution gas, in which the calculated K-values would be for the solute present at some finite composition in the system, and the case of the solute not being initially present in the elution gas, in which case the calculated K-value would be for the solute at infinite dilution in the vapor-liquid equilibrium system. Data were taken for ethane, propane, and n-butane solutes at infinite dilution in the methane-n-decane system at 160, 70, 40, 0, and -20°F from 20--2000 psia; for propane at infinite dilution in n-hexadecane at 70°F and 20--225 psia; and propane in the system methane-propane-n-decane at 40°F from 20--460 psia. The chromatographically determined K-values for n-butane at infinite dilution in methane-n-decane were compared over portions of the 40 and 160°F isotherms with published static equilibrium values and found in agreement. Data for all the solute isotherms were compared at atmospheric pressure with the results of the Bronsted-Koefed relation for predicting activity coefficients, and, again, close agreement was found. The applicability of the chromatographic method for determining freezing points was investigated, and the solid-liquid-gas line for the methane-decane system was measured.