Reversible and robust CO2 capture by equimolar task-specific ionic liquid–superbase mixtures

Abstract

Integrated sorption systems consisting of 1 : 1 mixtures of an alcohol-functionalized ionic liquid and a superbase were found to be effective for CO₂ capture under atmospheric pressure, eliminating the use of volatile n-alkanols or water. Conversely, by using the current approach, there is no longer a requirement for maintaining scrupulously dry conditions. The effect of ionic liquid structure, choice of superbase, their relative ratios, the sorption temperature, and the reaction time on the absorption and release of CO₂ were investigated. Our results demonstrate that (i) this integrated ionic liquid–superbase system is capable of rapid and reversible capture of nearly one mole of CO₂ per mole of superbase, (ii) the captured CO₂ can be readily released by either mild heating or bubbling with an insert gas (N₂, Ar), and (iii) this novel CO₂ chemisorption platform can be recycled with minimal loss of activity. This efficient and fully reversible catch-and-release process using non-volatile, task-specific ionic liquids provides an excellent alternative to current CO₂ capture technologies, which are based largely around volatile alkanols or alkylamines. Furthermore, our integrated ionic liquid–superbase system can be used as a novel medium for supported liquid membranes, for which they demonstrate both good selectivity and permeability in model CO₂/N₂ gas separations.