Kinetics of CO2 absorption into ethanolamine + water + ethanol system—mechanism, role of water, and kinetic model

Abstract

The kinetics of CO2 absorption in ethanolamine (MEA) + H2O + ethanol systems was investigated using stopped-flow apparatus. The first-order reaction rate constant (k0) values were tested with varying H2O and MEA concentrations. Transiting from the aqueous to non-aqueous solvents, the k0 decreases and the reaction order for MEA shifts from 1.05 to 1.88. The zwitterion mechanism with the rate-limiting step of deprotonation was used to explore the role of water and its effect. Results showed that water could impact reactions through direct involvement and changing solvation environment. An improved kinetic model based on the zwitterion mechanism was obtained to indicate the quantitative influence of H2O concentration on the reaction kinetics of MEA + H2O + ethanol systems. The predicted values from the model well agreed to the experimental data with the average absolute relative difference of 6.73%. This study highlights the important effects of water on the reaction kinetics of CO2 absorption into water-lean amine solutions.