Extraction of ethanol from mixtures with n-hexane by deep eutectic solvents of choline chloride + levulinic acid, + ethylene glycol, or + malonic acid

The separation of azeotropic mixtures is a great challenge for concentrating a desired chemical compound because it cannot be attained by a simple distillation process. Liquid-liquid extraction can be an alternative process to resolve the separation problem if an appropriate solvent is selected to effectively partition the mixture. In this work, the feasibilities of three different deep eutectic solvents (DESs) for breaking azeotropes of n-hexane and ethanol mixture were examined by means of liquid-liquid extraction. Choline chloride (ChCl) was chosen as a base compound and three hydrogen bond donors (HBDs) of levulinic acid, ethylene glycol, and malonic acid were added at their eutectic ratio to form DESs. Liquid-liquid equilibrium experiments for an azeotropic n-hexane + ethanol system were carried out to determine binodal compositions and, then, evaluate the compositions at both liquid phases at 298.2 K and atmospheric pressure by employing the prepared DESs. Refractive index, density, and viscosity at the binodal compositions were measured to provide properties required for extraction process establishment. The measured tie-lines were compared with the predicted results calculated by COSMO-SAC model. Moreover, the ability for extracting ethanol was evaluated with distribution coefficient and selectivity. It was found that the distribution coefficient and selectivity values are high enough to support a scaling-up process by a liquid–liquid extraction.