Screening Of Ionic Liquid,Experimental Verification And Process Simulation For Methanol-Methyl Propionate Separation

Methyl propionate is an important industrial raw material,which is often used as intermediate in the synthesis of methyl methacrylate and spice additive.Methyl propionate is obtained by esterification of methanol and propionic acid.The azeotropic system formed by methyl propionate and methanol is one of the major challenges in the production and refining of methyl propionate.Due to the high boiling point and high stability of ionic liquids,which are different from conventional solvents,more and more attention has been paid to the research on the extraction and separation of azeotropic systems by ionic liquids.In this paper,the potential ionic liquid additive for the extractive distillation of methanol-methyl propionate azeotropic system was selected through the way of theory research and experiment validation.The vapor-liquid equilibrium data of methanol(1)+methyl propionate(2)+ionic liqui(3)were determined and then correlated using NRTL equation.The process of extractive distillation was designed and simulated by Aspen Plus,which provided theoretical reference for its industrial application.The COSMO-SAC model was used to predict the vapor-liquid equilibrium of methanol-methyl propionate mixture with 196 kinds of ionic liquids consisting of 14 kinds of cations,such as imidazole cations and pyrrole cations,and 14 kinds of anions like halide anions and sulfate anions.Three ionic liquid additives 1-butyl-3-methylimidazolium bis(trifluoromethyl-sulfonyl)imide([BMIM][NTf2]),1-butyl-2,3-methylimidazolium bis(trifluoromethyl-sulfonyl)imide([BMMIM][NTf2])and 1-hexyl-3-methylimidazolium bis(trifluoromethyl-sulfonyl)imide([HMIM][NTf2])were selected as potential additives.The interaction energy between ionic liquid and methanol or methyl propionate was calculated as well as the charge density profiles.The mechanism of ionic liquid promoting the separation of methanol-methyl propionate azeotropic system was analyzed from the molecular level,and it was found that the interaction energy between ionic liquid and methyl propionate was greater than that between methanol and methyl propionate,thus increasing the relative volatility of methanol.The vapor-liquid equilibrium data of methanol(1)+ methyl propionate(2)?[BMIM][NTf2](3),methanol(1)+ methyl propionate(2)+[BMMIM][NTf2](3)and methanol(1)+methyl propionate(2)+[HMIM][NTf2](3)ternary systems at different ionic liquid concentrations were determined in the Ellis still.The results indicated that all the three ionic liquids could promote the separation of methanol-methyl propionate azeotropic system,and the separation effect was improved with the increasing concentration of ionic liquid in the system.The azeotropic point was eliminated when the ionic liquid concentration reached up to 0.2 in mole fraction,and the separation effect of[HMIM][NTf2]is significantly better than the other two additives.The NRTL model was used to correlate the experimental data,and the binary interaction parameters were obtained.The methanol-methyl propionate extractive distillation process with[HMIM][NTf2]as additive was established by Aspen Plus software.The application effect of ionic liquid in extractive distillation was simulated,and the effects of stage number,reflux ratio and feed position on the product and energy consumption of extractive distillation were studied.The process conditions were optimized and the process parameters were determined,which provided basic data and theoretical reference for the practical application of ionic liquid in the extraction distillation of azeotropic system.