Molecular Design Of Double Salt Ionic Liquid Solvent For Extractive Distillation

Extractive distillation is an effective method to separate azeotropic mixtures,and the selection of solvents is the key problem.Ionic liquids are effective green solvents in extractive distillation.Double salt ionic liquid（DSIL）has better physical-chemical properties than single ionic liquid,so it has great appilication potential in extractive distillation.The molecular design of DSIL solvent is a key problem in the research of extractive distillation using DSIL as solvent.The infinite dilution activity coefficient data of organic solutes in various ionic liquids in the literature were collected,and the infinite dilution activity coefficient data calculated by COSMO-SAC were utilized as supplement.The group interaction parameters for the mod.UNIFAC model that are related to ionic liquids groups,are correlated by the infinite dilution activity coefficient data.Based on genetic algorithm and the mod.UNIFAC model,a computer-aided molecular design method was proposed for the selection of DSIL solvents in extractive distillation.Firstly,the separated system was determined,and the pre-selected groups were coded;Secondly,the molecules were synthesized according to the combination rules of DSIL,and the evaluation function was based on selectivity and solubility calculated by mod.UNIFAC,and S-type function was used for comprehensive evaluation,then the optimization of DSIL solvents were carried out by the selection,crossover and mutation operators in genetic algorithm.A feasible molecular judgment rule and an infeasible molecular repair method were proposed for the infeasible molecules produced in the molecular design process.For the tert-Butyl alcohol+water system and methanol+methyl acetate system,the DSIL solvents were selected by the above molecular design method,which were[C₂mim]-[DCA]_0.5[OAc]_0.5 and[C₈mim]-[Br]_0.5[Tf₂N]_0.5.The effectiveness of[C₂mim]-[DCA]_0.5[OAc]_0.5 to separate tert-Butyl alcohol and water was validated by the literature data published by our research group.The vapor-liquid equilibrium of methanol-methyl acetate-[C₈mim]-[Br]_0.5[Tf₂N]_0.5 was measured experimentally,and the effectiveness of[C₈mim]-[Br]_0.5[Tf₂N]_0.5 was verified by the experiments.The results of the experiments and the literature data indicate that the molecar design method is reliable.