PNNL

Abstract

CO2-binding organic liquids (CO2BOLs) chemically bind and release CO2 more energetically and efficiently than aqueous alkanolamine systems. CO2BOLs are comprised of alcohols and organic amidine or guanidine bases, which bind CO2 chemically as liquid amidinium / guanidinium alkylcarbonate salts. CO2BOLs have high CO2 capacities (19% by weight, 147 g CO2/L) compared to 30% monoethanolamine solution in water (7% by weight, 108 g CO2/L) because they are liquid with or without CO2 and do not require any added solvent such as water. The dissolution of CO2 into and out of the liquid phase limits the rate of CO2 capture and release. Absorption of CO2 is selective over nitrogen in both concentrated and dilute gas streams making these systems applicable to post and pre-combustion CO2 capture. The free energy of CO2 binding in these systems is small and is independent on choice of alcohol. The free energies of these systems are however dependent on the choice of base; -9 kJ/mol for diazabicyclo[5.4.0]unced-7-ene (DBU) and Barton’s base and +2 kJ/mol for 1,1,3,3-tetramethylguanidine. The specific heats of the organic CO2BOLs are over 50% lower than that of water, resulting in a 50% reduction in energy to strip out CO2 as compared to aqueous alkanolamine solutions. CO2BOLs have been recycled for five cycles without losing activity or selectivity towards CO2.