Separation of ethyl acetate and ethanol by imidazole ionic liquids based on mechanism analysis and liquid–liquid equilibrium experiment

Azeotrope of ethyl acetate (EAC) and ethanol (EA) generated in the synthesis of ethyl acetate (EAC), was difficult to separate by general distillation. Liquid-liquid extraction using ionic liquids (ILs) as extractants is a green and efficient method for separating azeotropes. To select the suitable ILs, the σ-profiles of EAC, EA, and different anions of imidazole ILs were obtained through the COSMO-SAC model. Then, the extraction mechanism of ILs in the EAC-EA system was discussed from the micro perspective, the interaction between ILs and EA was analyzed graphically by the interaction region indicator (IRI) using the Multiwfn and VMD, the interaction energy between ILs and EA/EAC were calculated by Gaussian 09. Finally, we selected 1-ethyl-3-methyl-imidazolium dihydrogen phosphate ([EMIm][H2PO4]), 1-butyl-3-methyl-imidazolium dihydrogen phosphate ([BMIim][H2PO4]), 1-ethyl-3- methyl-imidazolium hydrogen sulfate ([EMIm][HSO4]), and 1-butyl-3-methyl- imidazolium hydrogen sulfate ([BMIm][HSO4]) as the extractants based on the mechanism analysis. The Liquid-liquid equilibrium(LLE) data of EAC-EA-ILs were measured at 298.15 K under atmospheric pressure; the effects of ILs with different alkyl chain lengths of cations on the extraction efficiency were investigated, and the influence of ILs with different anions was also verified through experiments. Meanwhile, we adopted the NRTL activity coefficient equation to regress the experiment data, and the interaction parameters were optimized by the least square method using Matlab 2014.