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

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