Liquid–Liquid Equilibrium Behavior for Ternary Mixtures of Methyl Ethyl Ketone and Methanol with Glycerol-Based Deep Eutectic Solvents

Methyl ethyl ketone (MEK) serves as a broadly applied organic solvent in industrial processes. Since MEK and methanol can form an azeotropic mixture, its separation via conventional distillation remains challenging. To recover MEK from a mixture of methanol and MEK via extraction, three DESs (deep eutectic solvents) prepared by glycerol (Gly) combined with choline chloride (ChCl), tetramethylammonium chloride (TMAC), and betaine (Bet) with a molar ratio of 2:1 were adopted as extraction agents. The assumption of DESs as the pseudopure component was performed to investigate liquid–liquid equilibrium phase behaviors for the pseudoternary ternary systems (methanol + methyl ethyl ketone + DESs). Distribution coefficient and selectivity were computed to evaluate the separation performance of the DESs. The results demonstrated that TMAC:Gly showed the best extraction capability compared to Bet:Gly and ChCl:Gly. Correlation of the tie-line data was performed by the NRTL thermodynamic model, and the corresponding root-mean-square deviation lower than 1.00%. In addition, quantum chemical calculations were adopted to quantify intermolecular interactions existing between the DESs and methanol molecules. The results revealed that the DES TMAC:Gly had the stronger binding affinity toward methanol, thereby achieving better extraction performance in separating the azeotropic mixture of MEK and methanol.