Adsorption of light hydrocarbon gases on alkene-selective adsorbent

Equilibrium adsorption isotherms of ethylene (C2H4), ethane (C2H6), propylene (C3H6), and propane (C3H8) were measured on a Ag+-impregnated clay-based alkene-selective adsorbent, Olesorb-1, in the temperature range of 293-363 K. The heats of adsorption estimated with the Clausius-Clapeyron equation were higher for ethylene (13.5 kcal/mol) and propylene (14.3 kcal/mol) than for the corresponding alkanes, indicating pi-bond interactions. A sharp decrease in the ethylene and propylene heats of adsorption was observed with increasing coverage. The isotherm data correlated well with the Langmuir-Freundlich isotherm model for all of the systems. Predicted mixture adsorption for ethylene/ethane and propylene/propane systems showed high adsorption selectivity for the alkenes over the corresponding alkanes. The selectivity decreased with increasing alkene composition in the gas phase. The diffusion of the alkenes was rapid compared to that of the corresponding alkanes. Twenty percent of the alkene was irreversibly adsorbed. The adsorbent was evaluated for its performance in a four-bed vacuum swing adsorption process. Ethylene could be separated from ethane with over 85% recovery and 99.8% purity.