Carbon Dioxide Capture by Aqueous Ionic Liquid Solutions

Confined water in aqueous solutions of imidazolium‐based ionic liquids (ILs) associated with acetate and imidazolate anions react reversibly with CO2 to yield bicarbonate. Three types of CO2 sorption in these “IL aqueous solutions” were observed: physical, CO2‐imidazolium adduct generation, and bicarbonate formation (up to 1.9 molbicarbonate mol−1 of IL), resulting in a 10:1 (molar ratio) total absorption of CO2 relative to imidazolate anions in the presence of water 1:1000 (IL/water). These sorption values are higher than the classical alkanol amines or even alkaline aqueous solutions under similar experimental conditions. Trapped, but active: Aqueous solutions of ionic liquids (IL) with basic anions are employed for CO2 capture, resulting in higher values of sorption. The success of these experiments can be attributed to the occurrence of physical and chemical sorption, mainly owing to bicarbonate formation. Our detailed study shows that bicarbonate species are a result of the reversible reaction between water molecules trapped in the IL activated by the contact ion pair and CO2.