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 CO2 separation from CH4. The CO2 adsorption capacity and CO2-over-CH4 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 CO2 and CH4 adsorption isotherms were recorded on zeolites A and X granules and used to estimate the co-adsorption of CO2-CH4 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 CO2-over-CH4 selectivity of 1775 and 525 respectively, at 100 kPa and 298 K. Optimally ion-exchanged zeolite X granules retained 97% of CO2 uptake capacity, 3.8 mmol g(-1), after 5 breakthrough adsorption-desorption cycles while for zeolite A ion-exchanged granules the reduction in CO2 uptake capacity was found to be 18%; CO2 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, (k) through the adsorption column compared to zeolite A; 0.41 and 0.13 m s(-1) for NaK4.5Cs0.3X and CaK(2.5)Cs(0.2)A, respectively.