Mechanistic Study of CO₂ Absorption in Alkanolamine Solutions Based on Density Functional Theory

Among the various CO₂ capture technologies, chemical absorption is currently one of the most widely applied methods in industrial practice. In this study, density functional theory was employed to investigate the reaction mechanisms of CO₂ absorption by typical alkanolamine solvents. Reaction pathways between CO₂ and four representative alkanolamines—monoethanolamine (MEA), diethanolamine (DEA), triethanolamine (TEA), and methyldiethanolamine (MDEA)—were constructed and analyzed. By evaluating the activation energy barriers of different amines, the thermodynamic characteristics and reaction feasibility of the CO₂ absorption process were systematically elucidated. The results show that the primary amine MEA exhibits the lowest activation energy barrier (32.02 kJ/mol), indicating the most favorable reaction kinetics, while the secondary amine DEA shows a slightly higher barrier of 47.35 kJ/mol. As tertiary amines, TEA and MDEA exhibit significantly higher activation energy barriers, indicating slower reaction kinetics; however, they generally possess higher CO₂ loading capacities and less stable reaction products, which facilitate solvent regeneration. The activation energy barriers of MDEA and TEA were calculated to be 54.53 kJ/mol and 94.17 kJ/mol, respectively, indicating that MDEA reacts more readily with CO₂ than TEA.