Thermal oxidation degradation mechanism under the rust-catalyzed condition of CO2 absorbent monoethanolamine and the DFT analysis of pathway

The study of the degradation mechanism of MEA is of great significance for developing anti-degradation agents for MEA to achieve long-term stable operation of CO₂ capture. In this paper, the effects of air, CO₂, and rust on the long-period degradation behavior of MEA were investigated under simultaneous thermal and oxidative degradation. Based on a systematic analysis of the long-cycle degradation products of MEA, new degradation products such as glycyl-L-alanine and pentetic acid were identified, which enriched the degradation pathways of MEA (18 degradation pathways of MEA were constructed), and DFT analysis was performed. The results showed that CO₂ can promote the degradation of MEA. Rust makes it easier for MEA to move in the direction of generating zwitterionic, thus greatly inhibiting the generation of compounds in other pathways, leading to fewer degradation products. The DFT analysis showed that the degradation process of MEA involved endothermic and exothermic reactions, where the highest energy was absorbed for degradation to 1-Piperazinecarboxaldehyde (170.561 kcal/mol) and the highest energy was released for degradation to 4-Hydroxyisovaline (397.483 kcal/mol). In the process of CO₂ capture technology with MEA, adding appropriate rust or lowering the reaction temperature can enhance the long-term operation of CO₂ capture technology, as well as reduce the cost of the capture technology and improve the capture efficiency.