Mechanism and Kinetic Study of Carbon Dioxide Absorption into a Methyldiethanolamine/1-Hydroxyethyl-3-methylimidazolium Lysine/Water System

In this work, the aqueous solutions of 1-hydroxyethyl-3-methylimidazolium lysine ([C(2)OHmim][Lys]) and methyldiethanolamine (MDEA) were developed to obtain an efficient absorbent for CO2 capture. The absorption performance, regeneration performance, reaction mechanism, and kinetic study of the blends were investigated. It was found that, for the blended absorbents, a molar ratio of 8:2 of MDEA/[C(2)OHmim][Lys] was the optimum ratio based on the absorption rate, absorption capacity, and other factors. The CO2 absorption capacity of the blends is 0.75 mol of CO2/mol of ionic liquid, and the absorption rate was higher than that of the aqueous MDEA solution. The regeneration efficiency of the blends was 93% after the third absorption generation cycle, which was higher than the aqueous solutions of 1 mol/L MDEA (88%) or 1 mol/L [C(2)OHmim][Lys] (88%) under the same conditions, indicating a better regeneration performance of the blends. The reaction mechanism and kinetic study of the CO2 absorption into the blends were investigated by C-13 nuclear magnetic resonance and a double stirred-cell absorber, respectively. [C(2)OHmim][Lys] in aqueous solution first formed carbamate with CO2, and the next step was hydrolysis of MDEA and partial carbamate, with the production of bicarbonate. It also found that the influence of the temperature in the CO2 absorption was different in the two steps. Also, [C(2)OHmim][Lys] could promote the hydration reaction of MDEA and CO2 according to the chemical mechanism and kinetic study. The kinetic region was considered to be a fast pseudo-first-order reaction, and the activation energy of the blends was 40.0 kJ mol(-1).