A study on reaction mechanism and kinetics of CO2 and MEA/DEA- tertiary amines in non-aqueous and water-lean solutions

The kinetic behavior of the reaction of CO2 with MEA-TREA in ethanol solution was studied using the stopped-flow technique. The results indicate that the zwitterion mechanism successfully correlates the experimentally measured pseudo first-order reaction constant (k0) and that the TREA participated in the deprotonation step of MEA-zwitterion as an alkaline substance after the formation of MEA-zwitterion. Then, the applicability of this proposed mechanism was investigated by using the reaction kinetics of CO2 with MEA-DMEA, MEA-DEEA, MEA-MDEA, DEA-TREA, DEA-DMEA blended amines in non-aqueous ethanol solution, as well as MEA-TREA, MEA-DMEA, DEA-TREA, DEA-DMEA blended amines in water-lean solutions. It was found that the mechanism of the reaction of CO2 with these mixed amines can be expressed by:k0 = KzA_A[A]2 + KzA_B[A][B] + Kz1[A]. The ethanol and water molecules which contribute to Kz1 can be used as proton transfer channels to accelerate proton transfer, but they do not directly par-ticipate in the reaction. In addition, the alkalinity and the steric hindrance effect controlled by the molec-ular structure of tertiary amines affected the reaction rate at the same time. The activation energies in MEA-EtOH and MEA-TREA-EtOH system were estimated by fitting the second-order rate constants to the Arrhenius expression, indicating that TREA can reduce the reaction activation energy and make the reaction more kinetically favorable.(c) 2023 Elsevier Ltd. All rights reserved.