(202e) Study on the Separation of Cyclohexane-Benzene Azeotrope via Extractive Distillation. I: Selection of Certain Deep Eutectic Solvents as Entrainers

As a new kind of high efficient and environmentally friendly extraction agent, deep eutectic solvents (DESs) have been the focus in the chemistry field. At the present, traditional organic extraction agents have been related with low efficiency, poor selectivity, high toxicity and other problems. Deep eutectic solvents (DSEs), with cheap raw materials, simple synthesis method with 100% atom utilization rate and low toxicity, which indicate they can be used in extractive distillation field as entrainers. In this paper, three different deep eutectic solvents were evaluated as potential entrainers for the extractive distillation of the aromatic/aliphatic mixtures (benzene+cyclohexane). DES1 (tetrabutylammonium bromide+levulinic acid) (molar ratio=1:2), DES2 (tetrabutylammonium bromide+ethylene glycol) (molar ratio=1:2) and DES3 (choline chloride+levulinic acid) (molar ratio=1:2) were selected for this work. Physical properties and structure of the three DESs were characterized. Vapour-liquid equilibrium (VLE) measurements of the binary systems (clohexane+benzene) and the ternary system (benzene + cyclohexane + DES1~3) were realized at atmospheric pressure.. It was found that DES1 can break the azeotrope but DES2 and DES3 can not at constant molar fraction of 0.1. Moreover, all equilibrium data were related to three classical activity coefficient models: nonrandom two-liquid (NRTL), Wilson, and universal quasichemical (UNIQUAC), using Aspen Plus commercial software. (R²) for the three pseudo-ternary systems were calculated using the three thermodynamic models. These results show that DES1 is a good extraction agent for separating the aromatic/aliphatic mixture (benzene+cyclohexane) and NRTL model is fitter the experimental data than Wilson and UNIQUAC. Research on the mechanism showed that there are hydrogen bond and π–π bond interactions between DES1 and benzene but there is no distinct hydrogen bond and π–π bond interaction between DES2/DES3 and benzene. Therefore DES1 can break the azeotrope, DES2 and DES3 cannot. This work provides a green way to separate aromatic/aliphatic mixtures while decreasing the use of toxic organic solvents in industry