Investigating the role of water on CO₂ capture by amine-based deep eutectic solvents through a combined experimental-molecular modeling approach

To investigate the effect of water on key physicochemical properties of novel amine-based deep eutectic solvents (DES) for CO₂ capture, neat binary and aqueous ternary amines (i.e., 2.5–12.5 wt% water) using choline chloride ([Ch][Cl]), and amines including monoethanolamine (MEA), diethanolamine (DEA), and methyldiethanolamine (MDEA) were prepared. Experimental results shed light on the unique role of water in reducing the viscosity of the ternary amine-based DESs by 25%, while leading to peculiar changes in CO₂ solubility and heat of absorption, depending on the water content. The experimental data were used to develop molecular models for the soft-statistical association fluid theory (soft-SAFT) to reliably predict their thermophysical properties at a wide range of conditions than those experimentally measured. Quantum chemistry calculations were also used to identify the role of water on the interactions in the amine-based DESs, assisting in the development of the soft-SAFT molecular models. The models provided excellent agreement with the experimental data, while predicting the effect of water on solvents’ properties at other conditions, and effectively modeling the CO₂ chemisorption process. This allowed identifying the optimal water content for the ternary amine-based DESs that minimized viscosity and heat of absorption, while maximizing CO₂ solubility, with the addition of 11, 12, and 16 wt% water for MEA, DEA, and MDEA-based DESs, respectively. These results pave the path for developing alternative solvents to accelerate the deployment of CO₂ capture technologies.