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Effect of differing Si/Al on the adsorption and separation of CH4/CO2 over Na-CHA zeolites

Authors: Halamek Jakub | Essid Safaa | Bulánek Roman

Year: 2022

Type of publication: ostatní - přednáška nebo poster

Page from-to: nestránkováno

Titles:

Language	Name	Abstract	Keywords
eng	Effect of differing Si/Al on the adsorption and separation of CH4/CO2 over Na-CHA zeolites	In this work, several Na-exchanged commercially available CHA zeolite materials (Si/Al ratios 8 – 16) were studied as potential adsorbents for the separation of CO2/CH4 mixtures. Their separation performance was evaluated by measurement of single-component volumetric adsorption isotherms of CO2 and CH4 and subsequent analysis of the data by numerical methods (IAST, calculation of adsorption enthalpy). It was found that the uptake of CO2 and ideal selectivity of CO2/CH4 on Na-CHA materials depend significantly on the Si/Al ratio, with the material Na-CHA-8 showing slightly better CO2/CH4 ideal selectivity and comparable uptake as the benchmark 13X zeolite material, as well as slightly lower values of the adsorption heats (by about 4-5 kJ/mol), as reported in literature, suggesting a potential lower cost for the regeneration of the adsorbent. In order to shed more light into the interaction of CO2 with Na-CHA, variable pressure (0 – 1.5 mbar) FTIR spectroscopy was used. Three vibrational bands (2365, 2355 and 2348 cm-1) were observed in the region of the CO2 asymmetric stretch mode, corresponding to different species of physisorbed CO2. The first band (2365 cm-1) was attributed to CO2 molecules interacting with two Na+ cations (dual-site), while the second and third bands (2355 and 2348 cm-1) were attributed to CO2 molecules interacting with two different Na+ cation single-sites. Different distribution of the site population was observed with differing Si/Al ratio, the strength of the band corresponding to the dual-sites correlating with low pressure CO2 uptake, as well selectivity. It should be pointed out, that complete desorption of CO2 molecules at ambient temperature, as observed by FTIR spectroscopy, was achieved in 2-3 min under dynamic vacuum for all studied samples, further suggesting a low energy cost of regeneration of the adsorbents.	zeolite; catalyst; adsorption; CO2; CH4