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

Abstract

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.