Reversible Reaction of CO2 with Superbasic Ionic Liquid [P66614][benzim] Studied with In Situ Photoelectron Spectroscopy

Ionic liquids (ILs) are of significant interest as CO2 capture agents, and one subgroup of ILs that has shown particular promise is that of superbasic ILs. They can absorb large quantities of CO2 in the dry state, but some will have a diminished CO2 capacity when pre-wetted. In the work presented here, the superbasic IL trihexyl-tetradecylphosphonium benzimidazolide, or [P66614][benzim], was exposed to 3 mbar CO2, 2 mbar H2O vapor, and a CO2 + H2O gas mixture; and investigated using near-ambient pressure X-ray photoelectron spectroscopy. The results show that the IL reacts with CO2 to form carbamate, and that the reaction is reversible through reduction of the surrounding gas pressure. Regardless of whether the IL was exposed to CO2 or H2O vapor first, the presence of H2O under these experimental conditions does not significantly hinder the IL’s ability to absorb and react with CO2. Furthermore, the IL appears to preferentially react with CO2 over H2O vapor.