Organic liquid CO2 capture agents with high gravimetric CO2 capacity

We report a new class of CO2 binding organic liquids that chemically capture and release CO2 much more efficiently than aqueous alkanolamine systems. Mixtures of organic alcohols and amidine/guanidine bases reversibly bind CO2 chemically as liquid amidinium/guanidinium alkylcarbonates. The free energy of CO2 binding in these organic systems is very small and dependent on the choice of base, approximately −9 kJ mol−1 for DBU and Barton's base and +2 kJ mol−1 for 1,1,3,3-tetramethylguanidine. These CO2 capturing agents do not require an added solvent because they are liquid, and therefore have high CO2 capacities of up to 19% by weight for neat systems, and slightly less when dissolved in acetonitrile. The rate of CO2 uptake and release by these organic systems is limited by the rate of dissolution of CO2 into and out of the liquid phase. Gas absorption is selective for CO2 in both concentrated and dilute gas streams. These organic systems have been shown to bind and release CO2 for five cycles without losing activity or selectivity.