Reaction Mechanism and Kinetics Study of CO2 Absorption into [C(2)OHmim][Lys]

摘要

In this work, a novel hydrophilic ionic liquid (IL) 1-hydroxyethyl-3-methylimidazolium lysine ([C(2)OHmim]-[Lys]) with a considerable CO2 absorption capacity of 1.68 mol CO2/mol IL was synthesized. Three reaction products between CO2 and neat [C(2)OHmim] [Lys] were successfully separated and detected by C-13 NMR. Meanwhile, the absorption capacity of [C(2)OHmim] [Lys] aqueous solutions with an initial conentration of 1mol/L was 1.2604 mol CO2/mol IL. The reaction mechanism and kinetic study of CO2 adsorption into an aqueous solution of [C(2)OHmim] [Lys] were also investigated by using C-13 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 CO2 loading (more than 0.95 mol CO2/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.