Study And Simulation Of Separation Behavior Of Imidazoles Ionic Liquids For Methanol-ethyl Formate Azeotrope System

Methanol and ethyl formate are widely used chemical raw materials.In the industrial production of methanol,an important synthesis method is the catalytic hydrogenation of carbon monoxide,which is limited by thermodynamic equilibrium,and the by-product ethyl formate will be produced in the synthesis process.However,methanol and ethyl formate can form azeotrope at room temperature and pressure.Extractive distillation is usually used to realize azeotropic separation,while conventional extractants have some disadvantages such as high volatility and high toxicity.Ionic liquids have the characteristics of low toxicity,low corrosiveness and almost no volatility at room temperature and pressure,so they have broad application prospects in the field of separation.Therefore,ionic liquid was selected as extractant to carry out extractive distillation of methanol-ethyl formate azeotrope system.First of all,the COSMOTherm X software based on COSMO-RS theory was used to screen 625 ionic liquids with 25 common cations and 25 anions.Combined with the solubility and selectivity parameters of ionic liquids for methanol and ethyl formate,as well as the availability and preparation feasibility of ionic liquids.Four extractants were selected:(1-Ethyl-3-methylimidazolium diethylphosphate [EMIM] [DEP]),1-butyl-3-methylimidazolium diethylphosphate [BMIM] [DEP],1-ethyl-3-methylimidazolium acetate([EMIM] [OAC]),1-butyl-3-methylimidazolium acetate([BMIM] [OAC])as extractants for separating methanol-ethyl formate azeotrope system.Three kinds of ionic liquids: [EMIM][DEP],[EMIM][OAC] and [BMIM][OAC]were prepared by fractional synthesis respectively.Abbe refractive index and elemental analysis of C,N,H and S show that the purity of the prepared and purchased ionic liquids meets the requirements of gas-liquid equilibrium experiments.Under the condition of 101.33 k Pa,the gas-liquid equilibrium data of methanolethyl formate binary system were measured,and the thermodynamic consistency was tested by area integration method.It is found that the gas-liquid equilibrium device accords with the experimental conditions.The vapor-liquid equilibrium data of the ternary system of methanol-ethyl formate-ionic liquid([EMIM] [DEP],[BMIM] [DEP],[EMIM] [OAC],[BMIM] [OAC])were measured at standard atmospheric pressure.The experimental results show that the addition of four kinds of ionic liquids can move the gas-liquid equilibrium curve away from the diagonal,and the higher the concentration of ionic liquids is,the greater the offset is.After the addition of ionic liquids,due to the increase of the equilibrium temperature of the dependence system of the solution,it is positively correlated with the concentration of ionic liquids,and the relative volatility of ethyl formate is improved by the addition of ionic liquids.The addition of four kinds of ionic liquids makes ethyl formate accumulate more in the gas phase,resulting in salting-out effect,the higher the concentration,the more obvious the salting-out.By comparing the vapor-liquid equilibrium data,it is found that all the four ionic liquids have the ability to break the azeotropic system and separate the azeotropic system,and the separation effect of [EMIM] [OAC] is the best.The mechanism of separation of methanol and ethyl formate by ionic liquids was analyzed from the point of view of quantum chemistry.σ-profiles,structure optimization frequency calculation,RDG visualization analysis and interaction energy were obtained by COSMO-RS theory and Gaussian09.The analysis shows that the interaction force between methanol and ethyl formate is much smaller than that of four ionic liquids on methanol and ethyl formate,and the interaction force of ionic liquids on any component is satisfied: [BMIM] [DEP] < [EMIM] [DEP] < [BMIM] [OAC] <[EMIM] [OAC].Ionic liquids have a stronger hydrogen bond with methanol,which reduces the volatility of methanol and makes ethyl formate more volatile,which shows that the volatility of ethyl formate is higher than that of methanol,thus breaking the azeotrope to realize the separation of components.