Selective adsorption of simple mixtures in slit pores: a model of methane-ethane mixtures in carbon

Abstract

The authors report a study of Lennard-Jones mixtures in model carbon pores having parallel walls. The fluid potential parameters were chosen to model methane and ethane, and the 10-4-3 model was used for the solid-fluid potential. A density-functional theory with the nonlocal density approximation was used for the calculations. The authors focused on the selectivity of ethane relative to methane for a wide range of system parameters. Different types of selectivity isotherm were found, which can be explained microscopically in terms of intermolecular and surface forces. Macroscopically, each type of isotherm corresponds to a certain range of temperature in relation to the capillary critical temperatures. At very low temperatures where layering transitions occur, the selectivity isotherm is steplike. The density profiles show a strong surface segregation of ethane from methane. 48 refs., 23 figs.