Evaluation of cation-exchanged zeolite adsorbents for post-combustion carbon dioxide capture

Zeolite adsorbents were evaluated for potential application in post-combustion CO2 capture using a new high-throughput gas adsorption instrument capable of measuring 28 samples in parallel. Among the zeolites tested, Ca-A exhibits the highest CO2 uptake (3.72 mmol g-1 and 5.63 mmol cm-3) together with an excellent CO2 selectivity over N2 under conditions relevant to capture from the dry flue gas stream of a coal-fired power plant. The large initial isosteric heat of adsorption of -58 kJ mol-1 indicates strong interactions between CO2 and the Ca-A framework. Neutron and x-ray powder diffraction studies reveal the precise location of the adsorption sites for CO2 in Ca-A and Mg-A. A detailed study of CO2 adsorption kinetics further shows that the performance of Ca-A is not limited by slow CO2 diffusion within the pores. Significantly, Ca-A exhibited a higher volumetric CO2 uptake and CO2/N2 selectivity than Mg2(dobdc) (dobdc4- = 1,4-dioxido-2,5-benzenedicarboxylate; Mg-MOF-74, CPO-27-Mg), one of the best performing adsorbents. The exceptional performance of Ca-A was maintained in CO2 breakthrough simulations.