Adsorption of CO2, CH4, C3H8, and H2O in SSZ-13, SAPO-34, and T-Type Zeolites

Single-component adsorption isotherms for CO2, CH4, C3H8, and H2O on SAPO-34, SSZ-13, and zeolite T were measured, and isosteric heats of adsorption were estimated. Long equilibration times were required for C3H8 adsorption in SAPO-34 and SSZ-13 because C3H8 diffuses slowly in these zeolites, but C3H8 isotherms were obtained quickly on zeolite T. Thus, when CO2 and C3H8 coadsorption loadings were measured by temperature-programmed desorption on SSZ-13, CO2 loadings were higher than C3H8 loadings at short times, whereas at long times, C3H8 loadings were higher as C3H8 displaced adsorbed CO2. In contrast, adsorption of CO2/C3H8 mixtures equilibrated quickly in zeolite T because of the fast C3H8 diffusion. These adsorption measurements may explain previously reported zeolite membrane behavior where C3H8 decreased CO2 permeances for SAPO-34, SSZ-13, and zeolite T membranes under most conditions, and steady state was only slowly obtained for SAPO-34 and SSZ-13 membranes in the presence of C3H8.