| Dimethyl carbonate(DMC)and ethanol are important raw materials for the synthesis of diethyl carbonate and ethyl methyl carbonate by transesterification.It is impossible to separate ethanol and DMC by normal distillation because the mixture of ethanol and dimethyl carbonate can form an azeotrope at normal pressure with a minimum azeotropic point.Ionic liquids provide a new scheme for extractive distillation separation of ethanol-DMC because of their unique properties,such as salt and solvent effect,stable thermodynamic and chemical properties and designability.In this work,three imidazolium ionic liquids(ILs)with the same anion,including 1-hexyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide([HMIM][NTf2]),1-butyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide([BMIM][NTf2]),1-ethyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide([EMIM][NTf2]),were selected as extractants for the azeotrope system of ethanol-DMC.The vapor-liquid equilibrium(VLE)data of ethanol-DMC binary system and ethanol-DMC-ILs ternary system were researched,and the effect of ILs on the VLE of the azeotropic system was analyzed.The applicability of four thermodynamic models to the studied system was investigated,and the process simulation of ILs[BMIM][NTf2]extractive distillation was carried out.(1)The VLE data of ethanol-DMC binary system was determined using the modified Othmer still at normal pressure(101.3 kPa),and the reliability of the experimental apparatus and equipment was verified.The VLE data of ethanol-DMC-[HMIM][NTf2],ethanol-DMC-[BMIM][NTf2],ethanol-DMC-[EMIM][NTf2]ternary systems were also obtained.(2)The experimental results indicated that the three ILs[HMIM][NTf2],[BMIM][NTf2],[EMIM][NTf2]all had a salt effect on the ethanol-DMC system,which reduced the activity coefficient of DMC.The higher the molar fraction of ionic liquids added,the stronger the salt effect.Comparing the separation efficiency of three ILs,[HMIM][NTf2]is the best,[BMIM][NTf2]is the second,and[EMIM][NTf2]is worse.It shows that the longer the cationic carbon chain was,the stronger the salt effect produced by ionic liquids was.(3)Three activity coefficient models,Wilson,NRTL and UNIQUAC,were used to correlate the VLE data of ethanol-DMC.The three models had good correlation effects for binary systems,with the average relative deviation(ARD)of 1.15%,1.09%and 1.26%,respectively.Wilson,NRTL,UNIQUAC and eNRTL four activity coefficient models were used to correlate VLE data of ethanol-DMC-ILs.The correlation effect of the Wilson,NRTL,UNIQUAC models was good and the ARD is not more than 2%.The ARD of eNRTL model is too large to be suitable for this studied system.(4)The virtual components of ionic liquids were established Using Aspen Plus.The feasibility of separating ethanol-dimethyl carbonate by extractive distillation of ionic liquids[BMIM][NTf2]was explored and the process simulation was carried out based on NRTL model.The process optimization was carried out to determine the optimum operating parameters with the goal of minimizing the total annual cost(TAC).Comparing the simulation results of extractive distillation of ionic liquids[BMIM][NTf2]and furfural,the results showed that[BMIM][NTf2]had less extractant dosage and higher recovery rate,and the TAC was small.[BMIM][NTf2]has a good prospect of popularization and application.In summary,the first use of ionic liquids as extractant was carried out for extractive distillation separation of the ethanol-DMC azeotrope system.And The VLE data of ethanol-DMC-[HMIM][NTf2],ethanol-DMC-[BMIM][NTf2]and ethanol-DMC-[EMIM][NTf2]were researched,which provided data support and theoretical basis for ionic liquid extractive distillation separation of ethanol-DMC azeotrope.The interaction parameters of ethanol,DMC with[BMIM][NTf2]in the activity coefficient model were applied to the process simulation software to complete the simulation and optimization,which verified the feasibility of ionic liquid extractive distillation process. |
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