Reaction dynamics of in aqueous amines from ab initio molecular dynamics: 2-amino-2-methyl-1,3-propanediol (AMPD) compared to monoethanolamine (MEA)

We present Car-Parrinello molecular dynamics simulations-combined with metadynamics-of the reactions accompanying the capture of in an aqueous amine solution. The selected amine is 2-amino-2-methyl-1,3-propanediol, which has been investigated experimentally in the search for optimum absorbents. In analogy with the empirical search, we use as reference aqueous monoethanolamine (MEA) at 30 wt%, namely the chemical absorbent most frequently used for the removal of from combustion gases. In particular, we refer to our own results which have led to a detailed characterization of several reaction paths for the absorption of and the amine regeneration (Ma et al. in J Chem Theory Comput 11:3189, 2015). Our simulations refer to the zwitterion mechanism leading to the formation of a carbamate or carbamic acid and to the release of the molecule in solution. The scenario established for the reactions in MEA is confirmed, and in particular the role of the zwitterion mechanism also for release. We find that the difference in the structure of the two molecules does not influence the dynamics of either the formation or the dissociation of the zwitterion. However, it affects its interaction with water in a significant way, thus reducing the probability of carbamate formation and its stability in solution.