Abstract
The selection of efficient and environmentally friendly extractants is crucial for extractive distillation (ED), and the microscopic mechanism of extractants in ED is still unclear. For the benefit of interpreting the microstructure distribution and phase behavior of the mixed system, this paper studied it by quantum chemical (QC) calculation and molecular dynamics (MD) simulation. Firstly, 1,3-dimethylimidazolium hexafluorophosphate [Mmim][PF6], 1-ethyl-3-methylimidazolium hexafluorophosphate [Emim][PF6] and organic solvent DMSO were screened based on COSMO-RS model and relative volatility. The bond length, bond energy, total electron density and deformation charge density of [Mmim][PF6], [Emim][PF6], DMSO extractant and ethyl acetate were analyzed by QC, the intrinsic properties of the chosen extractant and azeotropic system, as well as the interactions among the three extractants and ethyl acetate, were investigated. Then, the effect of extractant on the separation performance of cyclohexane ethyl acetate azeotrope in solvent environment was further studied by MD simulation. The two-dimensional mass density distributions (ANDDs) visualized the mixing behavior and structural distribution of the three extractants with the azeotropic system in the ternary system respectively, and the hydrogen bonding statistics indicated a high number of hydrogen bonds between [Mmim][PF6] and ethyl acetate. The radial distribution function (RDF) indicated that the extraction effect of [Mmim][PF6] was better and [PF6-] played a dominant role in the separation of azeotropic system. The strong interaction between [Mmim][PF6] extractant [PF6-] and ethyl acetate was further verified by the spatial distribution function (SDF). Ultimately, through Aspen Plus software simulation, it was found that the [Mmim][PF6] extractive distillation process was superior to the traditional solvent DMSO process, TAC was reduced by 8 %, and gas emissions were reduced by 5 %. Through the combination of QC, MD, and process simulation offer theoretical guidance for the efficient separation of the cyclohexane-ethyl acetate system and provide a specific reference value for the selection of the optimal extractant.
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