DFT Studies on Thermal and Oxidative Degradation of Monoethanolamine

Thermal and oxidative degradation of monoethanolamine (MEA) represents a major problem for modern day carbon capture technologies. Here, we report on a series of density functional theory (DFT) calculations investigating the possible chemical pathways leading to the formation of the most commonly observed degradation products. 2-Oxyzolidinone (OZD) can be formed from ring closure reactions of carbamates, carbamic acids, or isocyanates. The latter, itself, formed by dehydration of MEA. N-(2-hydroxethyl)ethylenediamine (HEEDA), 1-(2-hydroxyethyl)imidazolidone (HEIA), and N-(2-aminoethyl)-N′-(2-hydroxyethyl)imidazolidin-2-one (AHEIA) are all hypothesized to form favorably from degradation reactions of OZD. MEA can undergo oxidative degradation to form imines and hydroperoxides. This work details the mechanistic steps leading to the formation of these species that could help in the location of new compounds that aim to prevent their formation in future systems. Moreover, the thermochemical data will aid in the construction of a chemical kinetic mechanism to rationalize the rate of formation of all the species in real systems.