Continuous production of O2-free enriched CO2 from ambient air using moisture swing sorbents

Abstract

Herein, we report the production of O2-free CO2 from a CO2/O2/N2 mixture using moisture swing sorbents in two parallel reactors under isothermal conditions, wherein CO2/O2/N2 and H2O/N2 are alternately fed into the reactors. The CO2/O2/N2 mixture was fed into the reactor containing the water-pre-adsorbed metal oxide sorbent to capture CO2. After changing to an H2O/N2 gas mixture, moisture-promoted CO2 desorption took place. Sorbent-screening tests showed that Rb-loaded Al2O3 (Rb/Al2O3) was the most effective sorbent material for this process. Thus, Rb/Al2O3 sorbents with different Rb loadings were tested for continuous CO2 separation using two parallel reactors. Various structural analyses revealed that the highly dispersed Rb(I) species were responsible for CO2 capture/desorption. The formation and desorption of surface carbonates on Rb/Al2O3 under working conditions were then studied using in situ Fourier transform infrared spectroscopy (FTIR) with online gas composition analysis (operando FTIR). Finally, we demonstrate the continuous production of O2-free and ca. 5 times enriched CO2 from ambient air.