Divide-and-conquer density-functional tight-binding molecular dynamics study on the formation of carbamate ions during CO₂ chemical absorption in aqueous amine solution

Divide-and-conquer-type density-functional tight-binding molecular dynamics simulations of the CO₂ absorption process in monoethanolamine (MEA) solution have been performed for systems containing thousands of atoms. The formation of carbamate anions has been widely investigated for neutral systems via ab initio molecular dynamics simulations, yet the present study is aimed at identifying the role of hydroxide ions in acidbase equilibrium. The structural and electronic analyses reveal that the hydroxide ion approaches, via Grotthuss-type shuttling, the zwitterionic intermediates and abstracts a proton from the nitrogen atom of MEA. We also estimated the fraction of reacted CO₂ and carbamate formed at different initial CO₂ concentrations that confirm a high absorbed CO₂ concentration decreases the fraction of MEA(C) formed due to the abundance of MEA(Z) in the solution.