Contrasting mechanisms for CO₂ absorption and regeneration processes in aqueous amine solutions: Insights from density-functional tight-binding molecular dynamics simulations

CO₂ chemical absorption and regeneration processes in aqueous amine solutions were investigated using density-functional tight-binding molecular dynamics simulations. Extensive analyses of the structural, electronic, and dynamical properties of 100 independent trajectories supported the contrasting mechanisms in the absorption and regeneration processes. In the CO₂ absorption process, bicarbonate formed where the hydroxyl anion migrated through the hydrogen-bond network of water molecules, namely, by a Grotthuss-type mechanism. On the other hand, direct proton transfer from the protonated amine to the hydroxyl group of bicarbonate, which is called the ion-pair mechanism, was the key step to the release of CO₂.