Mechanism and Kinetics Study of CO₂ Absorption into Blends of <i>N</i>-Methyldiethanolamine and 1-Hydroxyethyl-3-methylimidazolium Glycine Aqueous Solution

Abstract

In this work, the blends of 1-hydroxyethyl-3-methylimidazolium glycine ([C2OHmim][Gly]) synthesized by our laboratory and N-methyldiethanolamine (MDEA) in aqueous solution were prepared for CO2 capture, and the maximum absorption performance of the blends was obtained at the mole ratio of 8:2 of MDEA/[C2OHmim][Gly] with a total concentration of 1.0 mol L–1. CO2 loading of the blended absorbent was less adversely influenced by the temperature and O2 concentration than that of MDEA aqueous, and it had a good performance in regeneration ability. The reaction mechanism of the CO2 absorption in MDEA/[C2OHmim][Gly] was investigated by 13C nuclear magnetic resonance. CO2 first reacted with [C2OHmim][Gly] to form carbamate, and then carbamate promoted the reaction between CO2 and MDEA, which could be described as a shuttle mechanism. The kinetics of CO2 absorption was investigated in a double stirred-cell absorber at different temperatures, and some important kinetic parameters were obtained, such as the reaction rate constant (k2) and the overall rate constant (kov). Experimental results indicated that the addition of [C2OHmim][Gly] enhanced CO2 absorption of MDEA under low CO2 partial pressure, which could improve the application of MDEA in industry.