Computational study of MEA adsorption on hydroxylated Cr_2O_3 surfaces

摘要

Aqueous alkanolamine solvents are mostly frequently used for the removal of CO_2 from flue gas and natural gas. However, corrosion represents one of the major operational issue of this process. It is therefore essential to evaluate the stability of the protective Cr_2O_3 layer on stainless steels, when it is in contact with different species found in CO_2 capture processes, e.g. water, monoethanolamine (MEA), a well-known CO_2 capture amine, and the reaction products with CO_2 (carbamate, bicarbonate). The adsorption of MEA on the hydroxylated (0001)-Cr_2O_3 surface was investigated by periodic density functional theory (DFT). using both static and dynamics calculations [1]. Two different adsorption modes were investigated: by direct adsorption of MEA onto the surface and by substitution of a surface water molecule by MEA. Several MEA coverages were studied (from 0.25 to 1 monolayer), as well as temperature and solvation effects. The calculations show that MEA adsorption onto the surface with a density up to 2.37 MEA per nm~2 (0.5 ML) is exergonic at 298 K in an aqueous environment, while the substitution process was found to be endergonic at all coverages at temperatures of 298 K and above. We are currently using these DFT-data to develop parameters for a ReaxFF reactive force field [2], allowing us to model larger systems, including the most abundant species in the aqueous phase and to explore larger time scales.