Adsorption of CO2, CH4, and N2 on Gas Diameter Grade Ion-Exchange Small Pore Zeolites

We prepared several different surfaces and pore volumes on small pore zeolites by hydrothermal synthesis and ion exchange (Li+, Na+, and Ca2+) based on three basic gas diameter grade structures of zeolites: KFI (0.39 × 0.39 nm), CHA (0.38 × 0.38 nm), and LEV (0.36 × 0.48 nm), which were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and elemental analysis. The surface area and microporous volumes were calculated using the Dubinin–Radushkevitch (D-R) equation based on CO2 adsorption at 273 K. The CHA was synthesized with a lower Si/Al ratio, and the surfaces and microporous volumes were changed greatly by ion exchange. KFI had a higher Si/Al ratio, and the scope of the surface could be kept smaller. Focusing on the CO2, CH4, and N2 adsorption isotherms at high pressure (1 MPa), we found that the samples were exchanged by Li+ and Na+ with bigger surfaces and greater adsorption volumes. The orifice diameter was very important in the sieving of CO2 and N2 or CO2 and CH4, while Na-LEV had an excellent sieving effect because N2 and CH4 could not diffuse into its structure like CO2. From the viewpoint of the separate adsorption equilibria: Na-zeolites had the highest data adsorption equilibrium selectivity for CO2 and N2 or CO2 and CH4, followed by Li-zeolites, which only had a strong adsorption potential of CO2; K-zeolites with high SCO2/N2 and SCH4/N2, based on the strong adsorption of CO2 and CH4. We conclude that the adsorption potential order was K-zeolites > Na-zeolites > Li-zeolites, so the bigger ions had a stronger affinity.