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.