Unveiling solvent encapsulation-driven kinetic inversion in CO2 absorption by water-lean amine solvents

Amine-based water-lean solvents serve as energy-efficient absorbents for carbon dioxide (CO 2 ) capture but face paradoxical kinetic challenges, where the mixed solvents inconsistently accelerate or decelerate reaction rates across amine classes. By integrating stopped-flow kinetics, molecular dynamics simulations, and electrostatic potential analysis, we elucidate water modulates CO 2 absorption in mixed absorbents systems via amine-specific solvent encapsulation effect for the first time. For primary amines (e.g., monoethanolamine, MEA), water preferentially hydrates nucleophilic nitrogen atoms, forming steric barriers that impede CO 2 access and suppress kinetics with increasing hydration. Conversely, secondary amines (e.g., methylaminoethanol, MAE) exhibit oxygen-directed hydration, which weakens nitrogen solvation and enhances electrostatic CO 2 -amine interactions, accelerating kinetics. A zwitterion-based kinetic model quantifies these solvent-induced activation energy shifts, revealing a universal mechanism validated across diverse solvent systems. This work establishes molecular design principles for tailoring water-lean absorbents, bridging the critical gap between solvent engineering and reaction pathways to advance energy-efficient carbon capture technologies.