Physical Absorption of Green House Gases in Amines: The Influence of Functionality, Structure, and Cross-Interactions.

Abstract

Monte Carlo simulations were performed in the isothermal-isobaric ensemble (NPT) to calculate the Henry constants of methane (CH4), nitrous oxide (N2O), and carbon dioxide (CO2) in pure H2O, amines, and alkanolamines using the classical Lorentz-Berthelot combining rules (L-B). The Henry constants of N2O and CO2 in water are highly overestimated and motivated us to propose a new set of unlike interactions. Contrarily, the Henry constant of N2O in MEA is underestimated by around 40%, and again, a new reoptimized cross unlike parameter is able to reproduce the constant to within 10%. An analysis is given of the relationship between the physical absorption of these gases and the chemical structure or functionality of 12 molecules including amines and alkanolamines using the anisotropic united atom intermolecular potential (AUA4). Finally, the solubility of N2O in an aqueous solution of monoethanolamine (MEA) at 30% (wt) was also studied. A Henry constant within 7% of the experimental value was found by using the reoptimized parameters along with L-B to account for the MEA + H2O unlike interactions. This very good agreement without additional adjustments for the MEA + H2O system may be attributed to the good excess properties predictions found in previous works for the binary mixture (MEA + H2O). However, further work, including additional alkanolamines in aqueous solutions at several concentrations, is required to verify this particular point.