Effect of water on eutectic solvents: Structural properties and physical interactions with CO2

Deep eutectic solvents (DESs) are versatile solvents for various applications including CO2 separations due to their good solvent strength, low volatilities, high thermal stabilities, and tunable properties. Properties of DESs alter with the presence of water and especially in applications where the solvent is in direct contact with air such as CO2 removal from the atmosphere. This study employs classical molecular dynamics (MD) simulations to examine the impact of water (0 to 70 wt%) on the liquid structure and physical interactions in a eutectic solvent composed of an ionic liquid (IL) 1-ethyl-3-methylimidazolium 2-cyanopyrrolide, [EMIM][2CNPyr], that functions as a hydrogen bond acceptor (HBA) and with three different hydrogen bond donors (HBDs): ethylene glycol (EG), propylene glycol (PG), and monoethanolamine (MEA). It is found that water preferentially solvates HBDs and weakens the hydrogen-bonding interactions between [2CNpyr] and the HBDs, thus resulting in significant structural changes that lead to enhanced interactions between CO2 and [EMIM], [2CNpyr], and MEA. Although these systems represent CO2-chemisorbing solvents in practice, the physical interactions in the presence of water as examined herein provides guidance on their phase behavior and tuning of physical properties by composition for targeted applications including CO2 separations.