Separation of n-hexane-ethanol azeotropic mixture using choline chloride +1,4-butanediol deep eutectic solvents

Abstract

For an environmentally friendly and economical separation process of ethanol from n-hexane which is hard to handle due to the azeotrope, the liquid-liquid extraction was carried out by using choline chloride (ChCl) based deep eutectic solvents (DESs) in different molar ratios with 1,4-butanediol: DES1 (ChCl:1,4-butanediol=1:3), DES2 (ChCl:1,4-butanediol=1:4), and DES3 (ChCl:1,4-butanediol=1:5). The liquid-liquid phase equilibrium was performed on the n-Hexane (1) + Ethanol (2) + DES (3) systems at 298.15 K and atmospheric pressure. The binodal curve is determined by using the turbidity method. The various physico-chemical properties such as refractive index, viscosity, and density were measured for compositions in the binodal point. The equilibrium compositions of liquid-liquid phase equilibrium were determined from the refractive index value at the binodal points, and were predicted by COSMO-SAC model. The miscibility area predicted by COSMO-SAC model became larger as the molar ratio of 1,4-butanediol in DES increased, that is, DES3 shows the most miscible area. While in the experimental results, the miscibility depending on DES-type does not show a large difference. The experimental values for PI shows the order of DES2 (ChCl:1,4-butanediol=1:4)> DES1 (ChCl:1,4-butanediol=1:3)> DES3 (ChCl:1,4-butanediol=1:5) at less 3 wt% concentration of ethanol, but at higher concentration range (>3 wt%) DES3 shows the best value. Both of DES2 and DES3 are profitable to adopt in the extraction process of ethanol from n-hexane owing to the high performance index, high distribution coefficient, and high selectivity. The experimental results show the possibility of DESs as an alternative to ionic liquids in the separation of azeotropic mixtures, taking into account the properties of DES such as low price, uncomplicated manufacturing methods, environmentally friendly, and low toxicity.