Dual Effect of Steric Hindrance in Non-Aqueous Amine Absorbents: Navigating the Trade-Off Between Kinetics and...

Sterically hindered amines (SHAs) offering high theoretical capacity and reduced regeneration energy, yet their molecular mechanism, especially in non-aqueous solvents, remains unclear. This study bridges this gap by combining computational and experimental approaches. This involved a systematic investigation of diverse amine classes. We introduced a set of molecular descriptors to quantify the steric hindrance effect, correlated them with key structural features, and rigorously linked these descriptors to the absorption performance through Quantitative Structure-Activity Relationship (QSAR) analyses, encompassing capacity, rate, and reaction thermodynamics. A systematic investigation reveals that the molecular features, including of substituent type and number, hydrogen bonding, and ring structures, affect steric hindrance. More importantly, a dual effect of steric hindrance was proposed: Steric hindrance alters the conventional zwitterionic mechanism, shifting the reaction toward an alcoholysis pathway. This substitution enhances the thermodynamic process by promoting the conversion of carbamate into alkyl carbonate, thereby raising the theoretical CO₂ loading to 1 mol/mol. At the same time, it suppresses the kinetic process by reducing the collision efficiency of CO₂. These fundamental understanding provide design principles for novel absorbents based on SHAs with high CO₂ capacity and low regeneration energy requirements, paving the way for more efficient carbon capture technologies.