Thermal degradation of differently structured blend amines used in CO₂ capture studies

High thermal stability amine solvents are critical for post-combustion CO₂ capture. For this, two novel ternary blended amine systems, AMP-AEP-MDEA and AMP-HMDA-MDEA were developed to overcome the limitations of traditional monoethanolamine (MEA) due to its poor thermal stability. The results demonstrated that both the chosen ternary systems exhibited superior CO₂ absorption-desorption performance compared to 30 wt% MEA due to synergistic kinetic effects and high molar amine density, emphasizing the importance of environmental management. To rigorously evaluate long-term durability, accelerated thermal degradation tests were conducted at 150 °C for 28 days to demonstrate AMP-AEP-MDEA had the highest thermal stability with a degradation rate of 25.1%, significantly lower than those of AMP-HMDA-MDEA (29.4%) and MEA (39.6%). Mechanistic investigations using ¹³C NMR and GC-MS elucidated distinct degradation pathways. AMP undergoes independent intramolecular cyclization to form oxazolidinones, while stability of the activators dictates the overall system robustness. Rigid heterocyclic nature of AEP that restricts deep fragmentation, limiting the degradation of the side-chain cleavage. In contrast, flexible linear HMDA chains are susceptible to C-C bond breakage and dehydrogenation, leading to the formation of irreversible aromatic byproducts such as methylpyridine. The research highlights the critical role of molecular topology in solvent stability, suggesting AMP-AEP-MDEA as a promising candidate for large scale CO₂ capture to provide clean environment.