Unraveling the Role of Glycine in K2CO3 Solvent for CO2 Removal

Abstract

Carbon dioxide (CO2), a main composition of greenhouse gases, is believed to be responsible for global warming. Both potassium carbonate (K2CO3) and amino acids have been studied for CO2 removal. In this study, for the first time, carbamate formation in the absence of CO2 was discovered in K2CO3 solvents when small amounts of amino acids like glycine were added, and the mechanism of carbamate formation and CO2 absorption in such solvents are detailed and supported the observed fast CO2 absorption in the presence of amino acids. In the mixed solvent of K2CO3 and glycine, bicarbonate and hydroxide were formed from carbonate hydrolysis, and the deprotonated amino acid reacted with bicarbonate to form carbamate in the absence of CO2 and, in the presence of CO2, reacted with CO2 to form carbamate which could subsequently hydrolyze into bicarbonate. As a result, amino acid (even with a small amount) significantly enhanced the CO2 absorption kinetics in the mixed solvents, and a high CO2 loading (0.62 mol CO2/mol K2CO3) was achieved in multiple (e.g., 10) cycles. Such mixed solvents of K2CO3 and amino acid therefore may overcome the limitations of each individual component and may be ideal candidates for CO2 removal.