The Reaction of CO2 absorption in Blended alkanolamine Aqueous Solutions: A theoretical Study on the Effect of Neighboring Molecules

The absorption of CO2 in blended alkanolamine aqueous solutions was investigated using theoretical analysis to elucidate the effects of neighboring molecules. Eighteen reaction models were constructed by varying the type (MEA, AEEA, AMP, or water), number, and arrangement of neighboring species. Structural and energetic analyses of individual molecules as well as reactant, transition-state, and product complexes were performed using density functional theory (DFT). The reactant complexes are stabilized as the number of surrounding molecules increases, adopting configurations more favorable for CO2 absorption. Transition-state structures were influenced primarily by whether the proton transferring molecule was an alkanolamine or water, leading to significant differences in activation energies. Proton transfer mediated by alkanolamines markedly reduced activation barriers compared to water, indicating their catalytic role. Among the alkanolamines, the activation energy increased in the order AEEA < MEA < AMP, consistent with experimental absorption rates (MEA+AEEA < MEA < MEA+AMP). All product complexes formed carbamic acids regardless of the molecular environment, with minimal positional change from reactant complex. These results demonstrate that CO2 absorption performance in blended alkanolamine systems can be predicted from computational analyses of transition states and activation energies. Catalytic alkanolamines exert a dominant influence, whereas non-catalytic neighboring molecules play only a minor role.