Electronic, steric, and solvent determinants of COS absorption–desorption–hydrolysis by secondary amines: A descriptor-based quantitative study

The removal of carbonyl sulfide (COS) relies on the coordinated interplay of absorption, hydrolysis, and regeneration. In this work, the COS absorption–desorption–hydrolysis behaviors of eleven secondary amines were systematically evaluated under identical operating conditions, and the quantitative contributions of electronic, steric, and solvent effects were elucidated using molecular descriptors and multivariate statistical analysis. Most secondary amines exhibited high initial absorption capacities but showed pronounced differences in desorption and hydrolysis performance. Among them, Diethanolamine (DEA2) and Diisopropanolamine (DIPA2) displayed the most balanced overall behavior, with absorption capacities of 0.7–0.8 g/L, hydrolysis rates of approximately 30%, and desorption efficiencies of 50–70%. Cycling experiments further confirmed their superior long-term stability, evidenced by the lowest sulfur accumulation and amine recoveries exceeding 90%. Molecular interaction analysis indicated that COS interacts with secondary amines predominantly through hydrogen bonds in the initial contact process. Structure–performance correlations identified a characteristic molecular parameter set associated with optimal integrated performance, including Electrostatic Potential (ESP min ) of −1.76 eV, Highest Occupied Molecular Orbital (HOMO) energy of −30 kJ/mol, a Mean Steric Hindrance Index (SHI) of 140 kJ/mol, and a pKa of 9.0, underscoring the essential synergistic contributions of electronic properties, steric environment, and basicity. Multivariate regression models (R 2  = 0.66–0.88) further revealed that electronic effects govern the binding strength underlying absorption–desorption, steric effects primarily regulate hydrolysis kinetics, and solvent effects determine regeneration by modulating solubility and activity coefficients. This study establishes a structure–property–function framework for secondary-amine absorbents and proposes a synergistic molecular design strategy for next generation regenerable absorbents.