Deep Eutectic Solvent Formed by Imidazolium Cyanopyrrolide and Ethylene Glycol for Reactive CO2Separations

Abstract

Solvents made from a reactive ionic liquid, with an imidazolium cation and pyrrolide anion, and ethylene glycol at a wide compositional range were studied for separations of CO2 at low partial pressures (â0.1 bar up to 1 bar). Thermal analysis and measurements of viscosity and density show compacting of the liquid upon mixing with enhanced stability achieved by hydrogen bonding. A detailed mechanistic study was performed by IR, quantitative NMR, and ab initio calculations that show significant CO2 absorption capacity below 5000 ppm of CO2 in N2. Three reversible routes are found that yield carbonate (major product), carboxylate (moderate), and carbamate (minor) species. With CO2 at 100% RH, bicarbonate along with carbonate species form. The CO2-ethlyene glycol reaction complex, the carbonate anion, is stabilized by the hydrogen bonding and Coulombic interactions, thus preventing evaporation of the solvent during regeneration. This study demonstrates a promising approach to designer green solvents for CO2 separations in open systems such as direct air capture.