Recovery of Acetonitrile from Wastewater Using Green Low-Toxicity Deep Eutectic Solvents as Extractive Distillation Entrainers

Acetonitrile (ACN) is an important organic compound and versatile chemical intermediate. Recovering ACN from pharmaceutical waste liquids can reduce production costs and mitigate environmental hazards. At atmospheric pressure, ACN forms an azeotrope with water, and extractive distillation is one of the most effective separation methods. In this study, the conductor-like screening model–segment activity coefficient (COSMO-SAC) was employed to identify deep eutectic solvents (DESs) prepared using choline chloride (ChCl) as the hydrogen bond acceptor and oxalic acid (OA) and glycolic acid (GA) as hydrogen bond donors for separating the ACN–water azeotrope. Vapor–liquid equilibrium (VLE) experiments demonstrate that adding 25 mol % DESs significantly enhances the relative volatility of ACN to water. The nonrandom two-liquid (NRTL) model was used to correlate the experimental data with satisfactory accuracy. Quantum chemical calculations were performed to analyze the types, sites, and strengths of weak interactions between DESs and azeotropic components. Results confirm that interactions between DESs and water are stronger than those with ACN, thereby reducing the activity coefficient of water in the liquid phase and enabling azeotrope separation.