Hydrogen-bond-engineered solvent microstructure enhances COS removal in MEA-MDEA systems

Understanding the structure-property-performance relationship of mixed amine solvents is essential for developing high-efficiency Carbonyl sulfur (COS) removal technologies. In this work, the thermophysical properties, intermolecular interactions, and COS capture performance of monoethanolamine (MEA) and N-methyldiethanolamine (MDEA) binary aqueous systems were systematically investigated. The density ( ρ ) and viscosity ( ν ) of MEA - MDEA mixtures were measured over a temperature range of 293.15–318.15 K with varying MDEA mole fractions. Key thermodynamic parameters, including viscosity deviation (Δ η ), excess molar volume ( V m E ), and excess Gibbs free energy of activation (Δ G *E ), were subsequently calculated. The results reveal that within an MDEA mole fraction range of 0.35–0.60, Δ η reaches a maximum while V m E remains negative, indicating stronger intermolecular attraction and denser molecular packing. Spectroscopic characterizations combined with quantum chemical calculations further confirm the formation of directional O—N–H hydrogen bonds between the hydroxyl groups of MDEA and the amino nitrogen of MEA, which stabilize the solvent microstructure. Based on these findings, COS absorption-desorption experiments were conducted. Notably, the mixed amine systems with MDEA mole fractions of 0.3852 and 0.5446 exhibited a significant synergistic effect, maintaining over 95 % COS removal efficiency throughout the 120 min absorption process, along with excellent regeneration performance characterized by higher and more stable desorption rates during the 60 min regeneration phase. This work establishes a clear structure-property-reaction correlation, providing valuable molecular-level insights for the rational design of efficient amine-based absorbents for industrial COS capture.