(431a) A Quantitative, Molecular Simulations Based, Kinetic Model of Acid Gas Absorption in Aqueous Amines

The removal of acid gases like CO₂ and H₂S is an essential process in a natural gas plant. The state-of-the-art technology for acid gas treatment is the chemical absorption with aqueous alkanolamines. The same technology is also increasingly used to capture CO₂ from flue gases in the fight against climate change. Despite this technology existing for almost a century, many basic questions remain unanswered, preventing major progress in identifying more efficient solvents for acid gas removal and CO₂ capture.

It would, for example, be efficacious to have a quantitative and predictive model of the rate-controlling processes of acid gas absorption by aqueous tertiary amines. Despite numerous attempts to date, there is no quantitative relationship between the amine structure and the rate of absorption of acid gases (CO₂ and H₂S).

The present computational study achieves this goal by focusing on the reaction of CO₂ and H₂S with OH^- forming HCO₃^- and HS^-. The performance of the resulting model is demonstrated for a consistent experimental dataset of the absorption rates of CO₂ and H₂S for a dozen of amines. The key to the new model’s success is that the reaction free energy barriers are evaluated from the solvation free energies of the reactants and the products, obtained from molecular dynamics simulations. Those simulations include subtle solvation effects of reactants and products, which turn out to be essential to understand the kinetic properties of the amines.

[1] Rozanska, X., Wimmer, E. & de Meyer, F. Quantitative Kinetic Model of CO₂ Absorption in Aqueous Tertiary Amine Solvents. J. Chem. Inf. Model. 61, 1814–1824 (2021)