Role of hydrogen bond capacity of solvents in reactions of amines with CO2: A computational study.

Various computational methods were employed to investigate the zwitterion formation, a critical step for the reaction of monoethanolamine with CO2, in five solvents (water, monoethanolamine, propylamine, methanol and chloroform) to probe the effect of hydrogen bond capacity of solvents on the reaction of amine with CO2 occurring in the amine-based CO2 capture process. The results indicate that the zwitterion can be formed in all considered solvents except chloroform. For two pairs of solvents (methanol and monoethanolamine, propylamine and chloroform) with similar dielectric constant but different hydrogen bond capacity, the solvents with higher hydrogen bond capacity (monoethanolamine and propylamine) facilitate the zwitterion formation. More importantly, kinetics parameters such as activation free energy for the zwitterion formation are more relevant to the hydrogen bond capacity than to dielectric constant of the considered solvents, clarifying the hydrogen bond capacity could be more important than dielectric constant in determining the kinetics of monoethanolamine with CO2.