Applying choline chloride-based hydrophilic deep eutectic solvents for separation of acetonitrile-water solutions:...

In this study, the effects of two hydrophilic choline chloride-based deep eutectic solvents (DESs) on the liquid-liquid extraction of water from acetonitrile-water (ACN-W) mixtures were investigated. Both studied DESs comprising choline chloride:ascorbic acid (ChCl:AA) (2:1) and choline chloride:glucose (ChCl:Glu) (1:1) exhibited strong water affinities. The liquid-liquid equilibrium (LLE) data for the ternary systems of (ACN + W + DES) were measured at 298 K for each system. The calculated distribution coefficients and selectivity values revealed that both DESs significantly enhance water extraction, while ChCl:Glu shows a slightly better performance in a wider feed composition range. The hydrogen bond accepting abilities and polarities of both DESs are higher than those of ACN, which enables them to establish hydrogen and polar bonds with water. The studied hydrophilic DESs showed superior selectivities in the separation of water from ACN-W mixtures in comparison to those of hydrophobic DESs in literature for the separation of ACN. Moreover, as water can be separated directly by the hydrophilic DESs, it allows enrichment of ACN through lower separation stages. The density functional theory (DFT) calculations were performed to investigate electron density distribution, hydrogen bonding, and intermolecular stabilization between DES components and water. The results confirm that hydrogen bonding is the dominant factor driving the water extraction, while all the analyses confirmed that ChCl:Glu can form stronger bonds with water than ChCl:AA. The combination of experimental and computational analyses suggests that hydrophilic DESs with a tunable performance are promising green extractants for the dehydration of acetonitrile mixtures.