Thermal Degradation Mechanism of 2-(Ethylamino) Ethanol Aqueous Solution within a Postcombustion CO₂ Capture Process

An amine-based aqueous solution is considered a promising absorbent for postcombustion CO2 capture. The novel amine 2-(ethylamino) ethanol (EMEA) presents better absorption and desorption performance compared to the benchmark amine monoethanolamine (MEA), giving it more potential for CO2 capture. However, with the lack of in-depth research on the thermal degradation of EMEA, it remains uncertain whether it can operate stably over the long term in industrial CO2 capture processes. Therefore, a comprehensive computational study combined with experiments was employed to figure out the thermal degradation of EMEA with CO2. The results indicate that the key reaction intermediate 3-ethyl-1,3-oxazolidin-2-one (EOZD) is formed in the thermal degradation process. EOZD can be formed through the ion pair reactions of protonated EMEA (EMEAH+) and ethyl (2-hydroxyethyl) carbamate (EMEACOO–) or through the water-catalyzed self-cyclization–dehydration reaction of ethyl (2-hydroxyethyl) carbamic acid (EMEACOOH). Additionally, EOZD can be formed through a unique reaction between EMEAH+ and protonated 2-diethylaminoethanol (DEEAH+), with DEEAH+ being formed by the methylation and demethylation reactions of EMEAH+ and EMEA. Then, the formed EOZD can be further transformed into the stable product N,N-ethyl-N′-(2-hydroxyethyl) ethylenediamine (DEHEED). The revealed thermal degradation mechanism of EMEA serves as a foundation for understanding the thermal stability of other structurally analogous secondary amines. Through comparison of EMEA and MEA degradation, it was found that EMEA is more prone to thermal degradation due to the existence of an ethyl group as an electron-donating substituent. This insight can offer theoretical guidance for regulating and reducing amine degradation and the development of more thermally stable amine-based solvents for CO2 capture.