Extractive Distillation of the Acetonitrile–Water Azeotrope Using an Ethylene Glycol–Choline Chloride Deep Eutectic Solvent: Vapor–Liquid Equilibrium and Separation Performance

Growing demand for sustainable solvents has considered deep eutectic solvents (DESs) as promising alternatives to conventional organic solvents. In this work, a DES composed of ethylene glycol and choline chloride at a molar ratio of 2:1 (EC2:1) was synthesized and studied as an entrainer for the separation of the acetonitrile (ACN)-water azeotrope. VLE measurements were carried out using an improved Othmer recirculation still under ambient conditions. First, measurements were carried out for the pseudobinary systems comprising EC2:1 + water and EC2:1 + ACN. Subsequently, for the pseudoternary system EC2:1 + ACN + water at 5%, 10% and 12 mol % DES concentrations. Increasing EC2:1 concentration progressively enhanced the relative volatility of ACN by lowering water activity through preferential EC2:1–water interactions and a salting-out effect, the azeotrope persisted at 5 mol % EC2:1 but was eliminated at 10 mol %. The experimental VLE data were validated using the NRTL activity coefficient model. The low mean absolute deviations of 0.17–0.44 K in equilibrium temperature and 0.006–0.008 in vapor-phase ACN mole fraction demonstrate good agreement between the experimental data and the NRTL model predictions. Moreover, the systematic evaluation of recovery and reusability of EC2:1 confirmed its high effectiveness and recyclability for the separation of the ACN-water azeotropic mixture.