Reversible Ionic Liquid Stabilized Carbamic Acids: A Pathway Toward Enhanced CO2 Capture

Abstract

Capturing CO2 from flue gas streams under near ambient conditions—e.g. coal-fired power plants—has traditionally involved the use of aqueous alkanol amine solutions. Aqueous solvent-based processes are energy intensive, as solvent regeneration can be costly. With growing concern over climate change, alternative CO2 capture technologies that are energy and cost efficient are required. We have established that nonaqueous silylamines can be used to efficiently and reversibly capture and release CO2 via the formation of reversible ionic liquids. We now report their unique, enhanced CO2 uptake at room temperature under 1 atm of CO2, as silylamines exhibit CO2 capture capacities greater than that expected from the conventional stoichiometry of a 2:1 amine to CO2 mole ratio. Experimental evidence is presented supporting the formation of a carbamic acid species in equilibrium with an ionic liquid network of ammonium–carbamate ion pairs to give a 3:2 amine to CO2 mole ratio. This is the first report of the stabilization of carbamic acid by reversible ionic liquids. Stabilization of carbamic acid leads to a significant increase in CO2 capacity (30% on average) over conventional amine solutions for CO2 capture.