Adsorption of CO2, CH4, N2 and He on MFI, CHA and DDR zeolites

The adsorption equilibrium isotherms of the common components of natural gas and biogas, CO2, CH4, N2, and He were experimentally measured over wide temperature ranges on all-silica MFI, CHA, and DDR zeolite crystals. First, large zeolite crystals, suitable for adsorption measurements, were synthesized and characterized by XRD and SEM. In the next step, gas adsorption data was recorded and the Toth equation was fitted to the measured adsorption data, and the adsorption capacity at saturation (Csat), affinity constant (b), and Toth heterogeneity parameter (t) were estimated. Finally, the van't Hoff equation was used to calculate the isosteric enthalpy of adsorption and adsorption entropy for all gases on each zeolite. The results reveal that the Toth equation can accurately predict the adsorption of gases on the studied microporous zeolite crystals in the investigated temperature range. To the best of our knowledge, the saturation adsorption capacity and adsorption enthalpy for helium on CHA and DDR zeolites have been determined experimentally for the first time in the present work. The estimated adsorption parameters presented in this work are accurate, primarily due to the large crystals used for the adsorption measurements and the recording of low-temperature adsorption equilibrium isotherms over broad temperature ranges. These factors are crucial for the reliability of our results, which are invaluable for understanding adsorption and mass transfer in zeolite materials, as well as for advancing the development of zeolite materials for gas separation.