Molecular Design Of Ionic Liquid Entrainers For Extractive Distillation

Extractive distillation with ionic liquid as solvent, is an effective separationmethod for azeotopes and close-boiling mixtures. The key problem for such a processis the selection of ionic liquid solvent. A computer-aid molecular design (CAMD)method based on UNIFAC and genetic algorithm was proposed for the selection ofionic liquid solvent. The solvent for separation of ethyl acetate-ethanol was selectedby the CAMD method, and it was verified by the phase equilibrium experiments.Two methods based on COSMO-SAC model for the calculation of infiniteactivity coefficients of organic compounds in ionic liquids were evaluated, and themean logarithm absolute average deviations were0.64and0.59, respectively. TheUNIFAC group parameters for ionic liquid groups were correlated by the infiniteactivity coefficients data of organic solutes in ionic liquids calculated viaCOSMO-SAC.A computer-aid molecular design (CAMD) method was proposed for theselection of ionic liquid solvents. The UNIFAC groups were pre-selected according tothe mixture to be separated, then genetic algorithm was utilized for the design of ionicliquid solvent. S function was adopted for the evaluation of solvent selectivity andsolubility in CAMD method. The genetic algorithm with symbol coding was adoptedfor optimization of the ionic liquid moleculars, using selection operator, crossoveroperator and mutation operator. Feasible rules for ionic liquids were proposedaccording to the structure of ionic liquids, and the unfeasible molecular modificationmethods were also set up.The ionic liquid solvent for separation of ethyl acetate-ethanol was selected bythe CAMD method, and the ionic liquid1-ethyl-3-methylimidazolium acetate wasselected as the solvent. Vapor-liquid equilibrium and liquid-liquid equilibrium of ethylacetate-ethanol-1-ethyl-3-methylimidazolium acetate were measured, and theparameters of NRTL equation were correlated. The experimental results shown thatthe ionic liquid1-ethyl-3-methylimidazolium acetate is an effective solvent for theseparation of ethyl acetate-ethanol. It indicates that the CAMD method proposedabove is effective in ionic liquid solvent selection for extractive distillation.