Phase behavior and extraction mechanism of ethanol in alcohol ester mixture separated by deep eutectic solvents

The production of diclofenac salt involves an azeotropic system consisting of ethanol and isopropyl acetate (IPAc). Owing to their simple preparation, low cost, and non-volatility, deep eutectic solvents (DESs) have attracted considerable attention in the field of azeotrope separation. The σ profiles were constructed using a conductor-like shielding model, and the hydrogen-bonding ability between several common hydrogen-bond acceptors (HBAs) and hetero-azeotropic systems was analyzed. To prepare the three types of DESs, choline chloride (ChCl) was selected as the HBA, while ethylene glycol, urea, and glycerol were selected as the hydrogen-bond donors (HBDs). The liquid–liquid equilibrium (LLE) experimental data of the IPAc, ethanol, and synthetic DES systems were then measured at 101.3 kPa and 298.15 K. The accuracy of the experimental data was verified by correlating the data with the Othmer–Tobias and Hand equations, and the NRTL model was used to fit the experimental results. According to the distribution (D) and selectivity (S) coefficients, ethanol had the highest affinity for the ChCl–ethylene glycol DES, and the experimental data and the molecular dynamics (MD) simulations data were well correlated. The interaction energy, spatial distribution functions (SDFs), radial distribution functions (RDFs), and self-diffusion coefficients were calculated using MD simulations to elucidate the extraction mechanism. The MD simulation results showed that the interaction between the HBA in the DESs and ethanol was dominant in the separation, whereas the interaction of the HBD in the DESs with ethanol played an auxiliary role. Based on the experimental and simulation results, the feasibility and effectiveness of the azeotropic system for the DES separation of ethanol and IPAc were verified, which is important for the sustainable utilization of resources.