Thermal degradation of tertiary amine for CO2 capture: Structure–activity relationships and density functional theory calculations

Aqueous amine solution is a promising absorbent for CO₂ capture, yet irreversible reaction, that is, degradation can happen for amine and leads to performance decrease and many operating difficulties. Despite numerous research on reaction between amine and CO₂ for absorption, the reaction of amine degradation is not fully understood, especially for tertiary amine which is a vital component in constructing high-performance CO₂ absorbent. Considering the variety of tertiary amines, this article studied the thermal stability of five tertiary amine solutions at different temperatures to mimic the regeneration condition. The density functional theory (DFT) calculation was applied to reveal the degradation mechanism. The alkylation reaction that triggered the degradation of tertiary amine was deemed as the limiting step. Then the molecular simulation method was extended to 12 tertiary amines, aiming to further illustrate the influence of molecular structure on the alkylation reaction. These results provide basic data and theoretical guidance for developing the anti-degradation CO₂ absorbent.