Deciphering the multistage mechanistic landscape of COS removal by tertiary amines through combined experiments and molecular descriptors

Despite their broad use in acid gas treatment, the Carbonyl sulfide (COS) absorption–hydrolysis–desorption behavior of tertiary amines remains unclear. We systematically investigated ten tertiary amines through performance evaluation and descriptor analysis to resolve their stage specific mechanisms. The results reveal pronounced performance heterogeneity among the tertiary amines, with COS absorption capacities of 0.45–0.80 g/L, hydrolysis conversions of 30–90%, and desorption efficiencies of 10–80%, delineating two characteristic behavioral patterns: high uptake coupled with poor desorption and moderate uptake accompanied by strong desorption. Among all candidates, 3-(Dimethylamino)-1,2-propanediol (DMAPD) and N-Methyldiethanolamine (MDEA) exhibit the highest cyclic stability, showing negligible sulfur accumulation and only 5–10% amine loss over five cycles. Their initial association with COS is found to be governed predominantly by weak van der Waals interactions. The constructed molecular descriptor framework synthesizes stage specific performance metrics with electronic, steric, and solvent-related characteristics. It demonstrates that COS absorption is most closely tied to solvent effects, particularly pKa, log 10 x sol , and ln(γ); in contrast, hydrolysis shows a stronger association with electronic factors together with structural accessibility; and for desorption, the dominant statistical signals shift back to log 10 x sol , and ln(γ), while pKa remains a secondary correlate. Overall, the COS removal process is governed sequentially by solvation control, electronic activation, and solvation weakening. This progression provides a coherent design framework for tertiary amines: tuning solvation during absorption, enhancing electronic and structural features during hydrolysis, and attenuating solvation stabilization during desorption, thereby improving uptake efficiency while reducing desorption energy demand.