ZK-5: A CO2-Selective Zeolite with High Working Capacity at Ambient Temperature and Pressure

The increased carbon dioxide concentration in the atmosphere caused by combustion of fossil fuels has been a leading contributor to global climate change. The adsorption-driven pressure or vacuum swing (PSA/VSA) processes are promising as affordable means for the capture and separation of CO2. Herein, an 8-membered-ring zeolite ZK-5 (Framework Type Code: KFI) exchanged with different cations (H+, Li+, Na+, K+, Mg2+, Ca2+) was synthesized as novel CO2 adsorbent. The samples were characterized by SEM, energy-dispersive X-ray spectroscopy (EDAX), XRD, and gas adsorption (CO2 and N-2). The Toth adsorption model was used to describe the CO2 adsorption isotherms, and the isosteric heats of adsorption were calculated. CO2 capture adsorbent evaluation criteria such as working capacity, regenerability and CO2/N-2 selectivity were applied to evaluate the zeolite adsorbents for PSA/VSA applications. The in situ FTIR CO2 adsorption spectra show that physisorption accounts for the largest fraction of the total CO2 adsorbed. The CO2 adsorption analysis shows that Mg-ZK-5 is the most promising adsorbent for PSA applications with the highest working capacity (Delta N-CO2=2.05 mmolg(-1)), excellent selectivity (alpha(CO2/N2)=121), and low isosteric heat. Li-, Na- and K-ZK-5 with good working capacity (Delta N-CO2=1.552.16 mmolg(-1)) and excellent selectivity (alpha(CO2/N2)=103128) are promising CO2 adsorbents for the VSA working region.