Binary mixtures of choline chloride-based deep eutectic solvents as green extractants for the extraction of benzene from n-hexane

A suitable green solvent for extraction of aromatics from aliphatics must possess good solvation and physicochemical properties, a rare occurrence in a single deep eutectic solvent (DES). Mixture of DESs could enable synergy and provide a good candidate extractant. In this study, DESs of glyceline, ethaline, and reline were synthesized and their binary mixtures (glyceline/ethaline, reline/ethaline, and glyceline/reline) produced by blending in various volume proportions. Twelve of such mixed solvents were prepared and their extraction efficiency for separating benzene from n-hexane investigated in a batch equilibrium process. Liquid–liquid equilibria (LLE) data for the pseudo-ternary systems of n-hexane + benzene + mixed DESs were measured at 303 K and 101.3 kPa. The distribution coefficient (D) and selectivity (S) of each pseudo-ternary system were determined to elicit extraction efficiency. The physicochemical properties of the mixed DESs were also measured. The results show that generally the distribution coefficients, selectivities, and physicochemical properties of the mixed DESs lie between the corresponding values for the constituent DES. The best performance was given by the mixed solvent of glyceline and ethaline in the 80:20 volume ratio, respectively, with D = 0.75 and S = 422.485. This assertion was further corroborated by higher percent recovery of benzene obtained from the said mixed DES (57.88%) relative to other mixed DESs (≤ 49.11%) examined in this study. Furthermore, its separation efficiency is superior to sulfolane but lower than glyceline, though there was a 9.4% reduction in its viscosity relative to glyceline.