The Study On Extraction And Distillation Of Dimethyl Carbonate + Methanol Azeotropic System By Ionic Liquid Composite Solvent

As a green chemical product,dimethyl carbonate has functional groups,such as carbonyl,methoxy,etc.It can participate in many chemical reactions and has a wide range of applications.At present,excess methanol is usually used as raw material in the production process of dimethyl carbonate.Under normal pressure,methanol and dimethyl carbonate form azeotrope,which cannot be separated and purified by distillation process,which causes trouble for further development and large-scale application of dimethyl carbonate.At present,the industrial separation methods of dimethyl carbonate+methanol azeotropic system include low temperature crystallization,pressure swing distillation,azeotropic distillation and extractive distillation.Extractive distillation is one of the most commonly used methods for the separation of azeotropes because of its wide application and less stringent requirements.The extractant is a decisive factor for the success of extractive distillation.So far,the extractants which can effectively extract and distill the binary azeotropic system of dimethyl carbonate and methanol include:organic solvent,ionic liquids and compound solvents composed of ionic liquids and organic solvents.The selection methods of extractant are mainly through model prediction and experiment.The prediction method has high efficiency,low screening cost,but low accuracy;the experimental method is time-consuming and labor-consuming,but the results are accurate.In this paper,the separation effect of the azeotropic system of dimethyl carbonate and methanol is studied by the method of prediction and experiment.The main work of this paper is as follows:UNIFAC method was used to predict the suitable organic solvents as extractant to separate dimethyl carbonate and methanol binary azeotrope.The order of extractive efficiency of organic solvents was carbon disulfide>glycol>chlorobenzene>furfural.Carbon disulfide is toxic,so glycol is choosed.At 101.3 kPa,the isobaric vapor-liquid equilibrium data of methanol+dimethyl carbonate+glycol were measured.The results showed that the azeotropic point could be eliminated when the mole fraction of glycol reached 0.3.The higher the extractant content,the better the extraction effect and the higher the equilibrium temperature.The feasibility of traditional and functional ionic liquids as extractants was verified to separate dimethyl carbonate and methanol mixture by extractive distillation.The traditional imidazole ionic liquids includs 1-butyl-3-methylimidazolium hexafluorophosphate([BMIM][PF6])and 1-octyl-3-methylimidazolium hexafluorophosphate([OMIM][PF6]).The functional ionic liquid means diethanolamine formate.At 101.3 kPa,the vapor-liquid equilibria of {methanol+dimethyl carbonate+|bmim][PF6]}and {methanol+dimethyl carbonate+[OMIM][PF6]} were measured.The molar fractions of imidazole ionic liquids were 0.05,0.1,0.15 and 0.2.The mole fractions of diethanolaminates are 0.1 and 0.3.The results show that the two imidazole ionic liquids can produce salting out effect on the methanol and increase the relative volatility of methanol to dimethyl carbonate.When the mole fraction reaches 0.15,[BMIM][PF6]and[OMIM][PF6]can completely break the azeotropic system.The equilibrium temperature is 347.5 K and 356.7 K,respectively.The order of extractive efficiency is[BMIM][PF6]>[OMIM][PF6].When the mole fraction of diethanolaminate reaches 0.3,the azeotropic mixture can be effectively separated.