Zwitterionic "Solutions" for Reversible CO2 Capture

The zwitterions resulting from the covalent attachment of 3- or 4-hydroxy benzene to the 1,3-dimethylimidazolium cation represent basic compounds (pKa of 8.68 and 8.99 in aqueous solutions, respectively) that chemisorb in aqueous solutions 0.58 mol/mol of carbon dioxide at 1.3 bar (absolute) and 40 & DEG;C. Equimolar amounts of chemisorbed CO2 in these solutions are obtained at 10 bar and 40 & DEG;C. Chemisorption takes place through the formation of bicarbonate in the aqueous solution using imidazolium-containing phenolate. CO2 is liberated by simple pressure relief and heating, regenerating the base. The enthalpy of absorption was estimated to be -38 kJ/mol, which is about 30 % lower than the enthalpy of industrially employed aqueous solutions of MDEA (estimated at -53 kJ/mol using the same experimental apparatus). The physisorption of CO2 becomes relevant at higher pressures (>10 bar) in these aqueous solutions. Combined physio- and chemisorption of up to 1.3 mol/mol at 40 bar and 40 & DEG;C can be attained with these aqueous zwitterionic solutions that are thermally stable and can be recycled at least 20 times. A new class of basic aqueous sorbents for CO2 based on zwitterions that present environmental and safety advantages that significantly reduce the risks of possible human and environmental contamination and they may be used in the nowadays employed amine scrubbing industrial plants with little or no modifications.image