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

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.