Reaction Mechanism and Kinetics Study of CO₂ Absorption into [C₂OHmim][Lys]

In this work, a novel hydrophilic ionic liquid (IL) 1-hydroxyethyl-3-methylimidazolium lysine ([C 2 OHmim][Lys]) with a considerable CO 2 absorption capacity of 1.68 mol CO 2 /mol IL was synthesized. Three reaction products between CO 2 and neat [C 2 OHmim][Lys] were successfully separated and detected by 13 C NMR. Meanwhile, the absorption capacity of [C 2 OHmim][Lys] aqueous solutions with an initial conentration of 1mol/L was 1.2604 mol CO 2 /mol IL. The reaction mechanism and kinetic study of CO 2 adsorption into an aqueous solution of [C 2 OHmim][Lys] were also investigated by using 13 C NMR and wetted wall column. In the early stage of absorption, the dominant chemical reaction was the formation of carbamate and belonged to the fast reaction. The reaction order was found to be an average value of 1.862 with respect to [C 2 OHmim][Lys]. At high CO 2 loading (more than 0.95 mol CO 2 /mol IL), the hydrolysis of carbamate was the main reaction, and it was between the fast reaction and the medium-speed reaction. Also, the two amino groups on the lysine anion have different reaction behaviors in the hydrolysis stage, suggesting that the carbamate linked to carboxyl in lysine anion participates in the hydration reaction while the other carbamate does not.