Effect of water on CO2 capture and phase change in non-aqueous 1,4-butanediamine/ethylene glycol biphasic absorbents: Role of hydrogen bond competition

[Display omitted] •Water impacts CO2 capture and phase changes in non-aqueous absorbents.•Water catalyzes and enhances CO2 absorption efficiency in reactions.•Water-induced H-bond competition significantly weakens species interactions.•Enhanced solvation limits key product aggregation, reducing phase changes.•Controlling the water content in flue gas is essential for efficient CO2 capture. Non-aqueous liquid–solid biphasic absorbents show significant potential for reducing energy consumption in CO2 capture. However, the high hygroscopic nature of amine compounds and the approximately 10 % to 20 % water vapor in natural gas plants’ flue gases challenge their efficiency and stability. This study investigated water’s effects on the CO2 absorption/desorption performance, phase-change behavior, and products of the non-aqueous absorbent 1,4-Butanediamine (BDA)/ethylene glycol (EG). Experimental results show that water significantly impacts absorption/desorption performance. The maximum CO2 loading and regeneration efficiency were 1.4199 mol·mol−1 and 89.85 %, respectively. Water leads to the gradual disappearance of phase changes, with solid-phase CO2 loading decreasing from 0.008 to 0.004 mol·g−1. Quantitative NMR demonstrates that carbamates and CO32-/HCO3- are the main CO2-related products in aqueous systems, with their relative proportions affected by water content. Quantum chemical calculations and molecular dynamics simulations reveal that water enhances absorption efficiency by participating in the catalytic environment and reaction process. Water-induced hydrogen bonding competition is the leading cause of weakened interactions between species. Specifically, H-bonds between carbamate/protonated amines were decreased by 23.94 %. The enhanced solvation effect reduces aggregation of the key products, contributing to the gradual disappearance of phase changes. This study provides insights into water’s effect on non-aqueous biphasic absorbents at the molecular level, offering a theoretical foundation for the development and optimization of absorbents suitable for use with steam-containing flue gases.