Ab Initio Study of CO_2 Capture Mechanisms in Monoethanolamine Aqueous Solution: Reaction Pathways from Carbamate to Bicarbonate

摘要

Ab initio calculations combined with the continuum solvation model have been conducted to obtain complete reaction pathways involved in the CO_2 capture into monoethanol (MEA) aqueous solution. We have investigated the reaction pathways for the decomposition of MEA carbamate into bicarbonate. Although the already known pathways invoke a generation of free CO_2(aq), we are concerned with another mechanism which does not involve such an intermediate. The neutral hydrolysis of the MEA carbamate was found to be a slow reaction that has an essentially two-step nature. We propose an alternative pathway that involves the carbamic acid as an intermediate that undergoes an alkaline hydrolysis leading to the formation of bicarbonate. Taking account of the novel reaction pathways elucidated here as well as the established routes for the formation of carbamate and bicarbonate may lead to a comprehensive understanding and a better prediction of the chemical CO_2 capture process under specific conditions including pH (concentration of amine) and partial pressure of CO_2.