ADSORPTION IN CARBON MICROPORES AT SUPERCRITICAL TEMPERATURES

Nonlocal density functional theory and grand canonical Monte Carlo simulations are used to investigate the adsorption behavior of gases of simple spherical molecules in model carbon micropores at temperatures above the critical value for the gas. In most of the calculations the parameters are chosen to model methane as the adsorbed gas, but some calculations are reported for a model of ethylene. The excess adsorption isotherms (which measure the increased density in the pore, relative to that of the bulk fluid) show a maximum at a particular value of the bulk gas density (pressure). Near the capillary critical temperature these maxima have a cusplike nature, similar to that observed experimentally. We investigate the effect of temperature and pore size on the excess adsorption isotherms and on the maximum excess adsorption. Heats of adsorption for an ideal gas phase are also calculated. © 1990 American Chemical Society.