Study of the Liquid–Liquid Equilibrium and Extraction Properties of Deep Eutectic Solvents Based on Choline Chloride for the Separation of the Ethanol–Ethyl Formate System for Potential Use in Biofuel Production

The separation of the azeotropic mixture ethanol–ethyl formate by various deep eutectic solvents (DESs) based on choline chloride was investigated. The liquid–liquid equilibria (LLE) for the systems ethanol–ethyl formate–DES were studied at 293.15 and 313.15 K and atmospheric pressure. 1H NMR spectroscopy was used for the quantity analysis system under study. Density and dynamic viscosity were measured for the investigated DESs in the temperature range 293.15–323.15 K. The efficiency of separation of the system ethanol–ethyl formate by the DESs formed by choline chloride with various hydrogen bond donors (glycerol, urea, glutaric acid, and ethylene glycol) was evaluated by calculating the distribution coefficients and selectivity values. Dependences of the obtained selectivity values on ethanol mass fractions were discussed. A comparison of these data with the separation efficiency of other ethanol–ester systems by the same DESs was made. A correlation of experimental LLE data by the nonrandom two-liquid (NRTL) equation was carried out. Calculated data showed a good agreement with experimental compositions