Separation Of Alcohol-ester Azeotropic System By Extractive Distillation With Imidazolium-based Ionic Liquid As Solvent

The production of ampicillin sodium generates a large amount of industrial wastewater containing ethyl acetate and isopropanol,and similarly,the production of n-propyl acetate generates a waste stream containing methyl acetate and methanol.Ethyl acetate,methyl acetate,isopropanol and methanol are important chemical products and industrial raw materials,which are widely used in pharmaceuticals,paints and other fields.In order to avoid environmental pollution and resource waste,it is necessary to recycle this type of waste liquid containing ester-alcohol.However,methyl acetate-methanol belongs to binary azeotropic mixture,while ethyl acetate-isopropanol-water belongs to ternary multi azeotropic mixture,and it is difficult to separate this kind of mixture by traditional distillation methods.Usually,special distillation methods are mostly used in industry to separate azeotropic mixtures,including extractive distillation,variable pressure distillation,azeotropic distillation,etc.Among them,the extractive distillation method is widely used for the separation of azeotropic mixtures with the advantages of simple operation,large processing capacity and mature technology.And the selection of extractant is the key link in extractive distillation.As a new generation extractant,ionic liquids（ILs）are widely studied for their designability,easy recovery,difficult volatility,high thermal stability and other advantages.Although extractive distillation is an effective method for separating azeotropic mixtures,there is still the problem of high energy consumption.Therefore,it is necessary to design energy-efficient and environmentally friendly process intensification techniques.In view of the above problems,it was decided in this study to use ILs-based entraining agents,as well as process intensification techniques to achieve efficient separation of the above azeotropic mixtures.Firstly,the optimal entrainment agent was screened using the model screening method;secondly,the separation mechanism was investigated at the molecular level using various quantitative calculation methods;finally,the separation process was simulated and optimized at the system level,aiming to achieve effective separation while achieving energy saving and emission reduction.The specific work is as follows.（1）Using Aspen software,we performed a screening of the vapor-liquid equilibrium for various solvents in the ethyl acetate/water,ethyl acetate/isopropanol,and isopropanol/water systems,and the best results were obtained with dimethyl sulfoxide as entrainer.In addition,Solvents[EMIM][AC]with higher solubility and selectivity than DMSO and lower melting point,lower density and better thermal stability were screened from 225 ILs based on COSMO-RS theory using COSMOtherm X software as ILs entrainment agents for the separation of ethyl acetate-isopropanol-water and methyl acetate-methanol systems.（2）Using quantitative computational software,such as COSMOtherm X,Gaussian09,Multiwfn,and Visual Molecular Dynamics,based on the COSMO-RS theory,density general function theory,and visual analysis methods,we explored the separation mechanism of the ethyl acetate-isopropanol-water system（or methyl acetate-methanol system）in depth at the molecular level.Specifically,we investigated the surface charge density distribution（σ-Profile）,electrostatic potential（ESP）,independent gradient model（IGM）,and atoms in molecules（AIM）.Our analysis demonstrated that the interaction type and strength between the extractant and the separated substance are favorable for the separation of ester alcohols.（3）We designed and optimized the conventional separation process for the single DMSO entrainer,single ionic liquid[EMIM][AC]entrainer,mixed ionic liquid[EMIM][AC]+organic solvent DMSO entrainer,and mixed entrainer next-door distillation column,as well as the ester exchange reaction extractive distillation（RED）process with ionic liquid[EMIM][AC]as an entrainer.In addition,we evaluated the separation process using carbon dioxide（CO₂）emissions,thermodynamic efficiency（η）,energy consumption,and total annual cost（TAC）as criteria to provide theoretical guidance for industrial applications.