Ion-exchanged ETS-10 adsorbents for CO2/CH4 separation: IAST assisted comparison of performance with other zeolites

ETS-10, the well-known member of titanosilicates, was synthesized, characterized, and then employed to study CO2 and CH4 adsorption on its cation exchanged forms. Equilibrium isotherms of as-synthesized, K-, Mg-, and Sr-ETS-10 were analyzed at 298 K and pressures up to 100 kPa. High selectivities of CO2/CH4 were observed for all the adsorbents. By a closer look at equilibrium isotherms, adsorption selectivity was found to be in the order of K- > as-synthesized- > Sr- > Mg-ETS-10. Analyses of the data revealed that ETS-10 adsorbents containing monovalent cations have more rectangular isotherms and higher CO2/CH4 selectivity. On the other hand, ETS-10 adsorbents exchanged by divalent cations showed lower selectivity but more curvature isotherms which makes the regeneration easier in the pressure swing adsorption process (PSA). High-pressure adsorption experiments at different temperatures up to 348 K were also studied for the most selective adsorbent, i.e., K-ETS-10. Finally, the ETS-10 adsorbents performance in different binary mixtures of CO2/CH4 was investigated by Ideal Adsorption Solution Theory (IAST), and the results were evaluated and compared with the performance of other aluminosilicates and high silica zeolites in CO2/CH4 separation. The comparison led to a new trade-off plot, i.e., adsorption capacity versus CO2/CH4 selectivity, which can be helpful for adsorbent selection.