Study On Optimization And Control For Separating Azeotropic Systems By Ionic Liquid-Based Extractive Distillation

Ethyl acetate,acetonitrile,2-butanone and ethanol are extremely important chemical raw materials,and often exist in industrial applications in the form of azeotropes which cannot be separated by conventional techniques.Special distillation techniques are usually used to separate these azeotropes.Extractive distillation as one of special distillation techniques has the advantages of low energy consumption and simple operation.Choosing high-performance entrainers is the key to improving extractive distillation processes.In recent years,ionic liquids as a new type of green entrainers have received extensive attention due to their high recovery rate and high designability.Therefore,the study of ionic liquids as entrainers has considerable scientific significance and economic value for extractive distillation processes.However,in the face of a large number of ionic liquids,computer-aided methods can improve the efficiency of screening entrainers.Firstly,the molecular simulation software Material Studio is used to optimize the structure of cations and anions respectively.Based on the optimized structure,the COSMO files are generated by the energy caculation,and then the effective surface shielding charge density(σ-profile)of each inoic are caculated through the program of the COSMO-SAC model.The linear combination method is established the σ-profile database of 326 ionic liquids and the COSMOSAC model is used to caculated the infinite dilution activity coefficients of ethyl acetate,acetonitrile,2-butanone and ethanol in 326 ionic liquids.Based on the infinite dilution activity coefficients,the solubility,selectivity and performance index of the ionic liquid are calculated as the evaluation indicators to seclect the appropriate entrainers,and the σ-profiles of them are analyzed.Then the two traditional organic solvent entraines are screened out using the Aspen Plus software.and the traditional organic solvent extraction agent for ethyl acetate/acetonitrile system and 2-butanone/ethanol system was carried out.The trational extractive distillation processes,two flashs recovery ionic liquid processes and flash-stripper recovery ionic liquid processes are designed.This thesis evaluates the economics and control properities of the design process by calculating the total annual cost(TAC)and the condition number(CN),and uses a multi-objective optimization strategy based on the second-generation genetic algorithm to optimize the free design variables of the process,and establishes the joint optimization platform of Aspen Plus and Matlab obtains the Pareto solution set diagram between the total annual cost(TAC)and the condition number(CN)of each process,which provides a decision space for the process design.According to the Pareto solution set diagram,the trade-off design PO of TAC and CN is selected to study the dynamic control performance under the temperature control structure.The results show that the processes have a certain anti-disturbance ability under ±10%flow disturbance and composition disturbance.For these two separation systems,compared with the trational entrainers,the use of ionic liquids can greatly reduce the TAC and energy consumption of the processes.Choosing the structure of the flash-stripper can alleviate the high vacuum requirement of the second flash in the extractant recovery part,and it has certain economic advantages when the purity of the ionic liquid in the liquid phase produced by the first flash is relatively high.