Phase behavior and molecular insights on the separation of dimethyl carbonate and methanol azeotrope by extractive distillation using deep eutectic solvents

Deep eutectic solvents (DESs) exhibit good separation performance as extractants in extractive distillation. In this study, choline chloride (ChCl)-based and tetrabutylammonium bromide (TBAB)-based DESs were prepared using ChCl and TBAB as hydrogen bond acceptors (HBAs) and urea, glycerol (G), malonic acid (MA), and levulinic acid (LA) as hydrogen bond donors (HBDs). Based on the COSMO-SAC model, the possibility of separating the binary azeotropes of methanol (MeOH) and dimethyl carbonate (DMC) using five DESs was verified. The binary azeotropes of MeOH and DMC were separated by extractive distillation using five DESs, and their separation performance was investigated. The experimental results revealed that ChCl-urea had the best separation effect on the binary azeotropes MeOH and DMC. The macroscopic separation phenomenon and microscopic molecular mechanisms were studied systematically. The interaction of the DESs with MeOH and DMC was investigated at the molecular level by quantum chemical (QC) calculations, and the important role of the hydrogen bond of the DESs in extractive distillation was revealed. The experimental and QC results demonstrate that DESs have a significant effect on the intermolecular forces and can effectively separate azeotropes.