Room-Temperature Ionic Liquid−Amine Solutions: Tunable Solvents for Efficient and Reversible Capture of CO2

Abstract

Solutions of room-temperature ionic liquids (RTILs) and commercially available amines were found to be effective for the capture of CO2 as carbamate salts. RTIL solutions containing 50 mol % (16% v/v) monoethanolamine (MEA) are capable of rapid and reversible capture of 1 mol of CO2 per 2 moles MEA to give an insoluble MEA−carbamate precipitate that helps to drive the capture reaction (as opposed to aqueous amine systems). Diethanolamine (DEA) can also be used in the same manner for CO2 capture in RTILs containing a pendant hydroxyl group. The captured CO2 in the resulting RTIL−carbamate salt mixtures can be readily released by either heating and/or subjecting them to reduced pressure. Using this unprecedented and industrially attractive mixing approach, the desirable properties of RTILs (i.e., nonvolatility, enhanced CO2 solubility, lower heat capacities) can be combined with the performance of amines for CO2 capture without the use of specially designed, functionalized “task-specific” ionic liquids. By mixing RTILs with commercial amines, reactive solvents with a wide range of amine loading levels can be tailored to capture CO2 in a variety of conditions and processes. These RTIL−amine solutions behave similarly to their water-based counterparts but may offer many advantages, including increased energy efficiency, compared to current aqueous amine technologies.