Combined experimental and computational study on elucidating steric effects in amine-based CO2 capture

This study systematically investigates how steric architecture governs CO 2 absorption kinetics by analyzing six sterically modulated amines in aqueous and ethanol solutions. The stopped-flow apparatus was employed to determine pseudo-first-order kinetic constants (k 0 ) for CO 2 absorption by six sterically hindered amines with varying spatial configurations in aqueous and ethanol solutions within 293.15–308.15 K. The kinetic model based on the zwitterion mechanism outperforms the base-catalyzed hydration mechanism in predictive accuracy, with average absolute relative deviations (AARD) of 1.45–3.31 % in aqueous solutions and 2.28–2.58 % in ethanol solutions. Density functional theory (DFT) calculations reveal that increased molecular steric hindrance diminishes the nucleophilicity of amine-N atoms; the strengthened interactions of –OH groups concurrently facilitate the formation of intramolecular hydrogen bonding, which collectively amplify steric hindrance and thereby diminish reaction kinetics. In addition, ethanol’s strong solvation effects further diminish amine reactivity toward CO 2 , resulting in significantly lower absorption rates in ethanol-based systems compared to aqueous environments. These findings elucidate the complex interplay between steric hindrance, solvent dependence and CO 2 absorption kinetics, providing theoretical guidelines for optimizing design of CO 2 absorbent.