Optimized cesium and potassium ion-exchanged zeolites A and X granules for biogas upgrading

Partially ion-exchanged zeolites A and X binderless granules were evaluated for CO(2) separation from CH(4). The CO(2) adsorption capacity and CO(2)-over-CH(4) selectivity of binderless zeolites A and X granules were optimized by partial exchange of cations with K(+) and Cs(+), while retaining the mechanical strength of 1.3 MPa and 2 MPa, respectively. Single gas CO(2) and CH(4) adsorption isotherms were recorded on zeolites A and X granules and used to estimate the co-adsorption of CO(2)–CH(4) using ideal adsorbed solution theory (IAST). The IAST co-adsorption analysis showed that the partially ion-exchanged binderless zeolites A and X granules had a high CO(2)-over-CH(4) selectivity of 1775 and 525 respectively, at 100 kPa and 298 K. Optimally ion-exchanged zeolite X granules retained 97% of CO(2) uptake capacity, 3.8 mmol g(−1), after 5 breakthrough adsorption–desorption cycles while for zeolite A ion-exchanged granules the reduction in CO(2) uptake capacity was found to be 18%; CO(2) uptake capacity of 3.4 mmol g(−1). The mass transfer analysis of breakthrough experimental data showed that the ion-exchanged zeolite X had offered a higher mass transfer coefficient, (κ) through the adsorption column compared to zeolite A; 0.41 and 0.13 m s(−1) for NaK(4.5)Cs(0.3)X and CaK(2.5)Cs(0.2)A, respectively.