Study on the mechanism of extractive distillation separation of cyclohexane/ethanol azeotrope based on ionic liquid and molecular liquid mixed solvent as extractant

The development of high-performance new extractants is crucial for the separation of azeotropes by extractive distillation (ED). In this paper, an effective method for the separation of azeotropes by ED using IL mixed extractants ( ILMEs ) is proposed. Based on the COSMO-SAC thermodynamic model and relative volatility, the optimal extractants [Dmim][Ac] and DMSO were selected respectively. The structure–activity relationship between single extractant and ILMEs was analyzed by quantum chemistry ( QC ) calculations. Molecular simulation results showed that compared with single extractant, the addition of DMSO increased the interaction sites between ethanol and extractant, which made ILMEs ( [Dmim][Ac] + DMSO ) easier to combine with ethanol to form H-bond, thus facilitating the separation of cyclohexane/ethanol. H in DMSO mainly forms C2–H5…O3 hydrogen bonds with O in ethanol, and O in [Ac]− mainly forms C1–O4…H4 H-bond with H in ethanol. Through molecular dynamics ( MD ) simulation, the phase behavior and structural distribution of ILMEs and azeotropes under different mixed solvent ratios were explored from the microscopic mechanism, so as to determine the optimal mixing ratio. The MD results showed that the interaction between [Dmim][Ac] + DMSO and ethanol was enhanced with the addition of DMSO. When the amount of [Dmim][Ac] is reduced to DMSO:[Dmim][Ac] = 4:1, the interaction between ethanol and the mixed extractant in the quaternary system is the strongest, and the ethanol molecule is completely immersed in the mixed extractant, cyclohexane and ethanol are completely separated and the aggregation behavior is maximized, indicating that the mixed solvent ratio DMSO: [Dmim][Ac] = 4: 1, the separation effect is the best. Finally, the separation of ILMEs and DMSO cyclohexane/ethanol azeotrope was simulated by Aspen Plus V12, and the feasibility of ILMEs as extractant was verified. The results show that compared with the traditional organic extractant DMSO, ILMEs have potential environmental and economic advantages. The total annual cost (TAC) is reduced by 13.65 % and the gas emission is reduced by 23.04 %. This study provides theoretical guidance for the study of ED mechanism and the determination of solvent ratio of mixed extractants.