Extractive Distillation For Azeotropic Mixture Of Methanol And Methyl Acetate With Ionic Liquids As Solvent

In the production of p-phthalic acid and polyvinyl alcohol,large amount of methyl acetate is produced as by-product,while the industrial use of methyl acetate is limited,so it is usually hydrolyzed to methanol and acetic acid and recycled.In order to improve the hydrolysis process,the separation of methanol-methyl acetate in the hydrolysis mixture was investigated in this thesis.The azeotropic mixture of methanol-methyl acetate was separated by extractive distillation using ionic liquid as solvent which can make methanol as volatile component.In this paper,the conductor-like screening segment activity coefficient（COSMO-SAC）model was utilized to screen ionic liquid solvents,and 1-octyl-3-methylimidazolium bistrifluoromethanesulfonamide（[OMIM][Tf₂N]）and 1-octyl-2,3-dimethylimidazolium bistrifluoromethanesulfonamide（[OMMIM][Tf₂N]）were selected as ionic liquid solvents to separate the methanol-methyl acetate azeotropic mixture via extractive distillation.Isobaric vapor-liquid equilibrium（VLE）data for the methanol-methyl acetate-[OMIM][Tf₂N]and methanol-methyl acetate-[OMMIM][Tf₂N]were measured at101.3 k Pa.The experimental data indicate that the ionic liquids can eliminate the azeotropic point of methanol-methyl acetate and make methanol as the volatile component.The experimental data were correlated by nonrandom two-liquid（NRTL）model and universal quasichemical functional-group activity coefficients（UNIFAC）model,the parameters of the two models were obtained,and the NRTL model is more accurate.The VLE data show that the selectivity of[OMMIM][Tf₂N]is a little larger that of[OMIM][Tf₂N].The Aspen Plus simulation software was employed to simulate the extractive distillation process of methanol-methyl acetate with[OMMIM][Tf₂N]as solvent.The influences of feed location,the number of stage,solvent ratio,feeding location of solvent,feeding temperature of solvent and reflux ratio on the purity of methanol and the heat duty of reboiler were investigated,and the appropriate operational and structural parameters were determined by the sensitivity analysis of the extractive distillation column.The dynamic simulation of the extractive distillation process was carried out by Aspen Dynamics.Three different control schemes were designed,and the control ability of the schemes was tested by feed disturbances,then the optimal control scheme was selected.