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

Abstract

A series of zeolite adsorbents has been 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 the presence of 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.