Separation of the Isopropanol and Toluene Azeotropic Mixture Using a Deep Eutectic Solvent

The separation of isopropanol and toluene is complicated by the formation of an azeotrope, which limits the efficiency of conventional distillation. In this study, deep eutectic solvents (DESs) are investigated as sustainable entrainers for extractive distillation of the isopropanol–toluene system. A systematic screening of 5720 candidate DESs was performed using the COSMO-SAC model, with caprylic acid–thymol (1:1) identified as a promising solvent due to its moderate selectivity, low viscosity, and favorable physicochemical properties. Experimental bubble-point pressures of binary mixtures (isopropanol + DES and toluene + DES) were measured and correlated with the NRTL model, yielding average relative deviations below 3%. The ternary vapor–liquid equilibrium (VLE) behavior was subsequently predicted, demonstrating that the DES disrupts the azeotrope by forming strong hydrogen-bonding interactions with isopropanol. The results highlight the potential of DESs as sustainable entrainers for azeotrope separation.