Predictive Thermodynamic Model And Its Application In Vapor-liquid Equilibrium Of Ethanol / Water-Ionic Liquid Systems

Ethanol is a common chemical product.It is volatile,colorless and transparent under normal pressure and temperature.Ethanol is a good solvent,It is not only widely used in the field of chemical industry,but also widely used in the fields of national defense,medical and health,food,transportation and so on.Some countries have used gasoline alcohol mixed with absolute ethanol and gasoline as power fuel.In response to the energy crisis,China has basically achieved full coverage of vehicle ethanol gasoline since 2020.In industrial applications,the common commercial ethanol is an azeotropic mixture containing 95.6wt%ethanol and 4.4wt%water.For the separation of ethanol and water,the traditional distillation process can not obtain high-purity ethanol.In this work,ionic liquids(ILs)were used as extractant to separate the mixtures of ethanol and water.The separation mechanism was analyzed at the molecular level,and the separation process of ethanol and water was simulated by the combination of conventional extractive distillation and heat pump.In this work,UNIFAC model,the most widely used predictive thermodynamic model in the field of chemistry and chemical engineering,is selected to correlate a large number of literature data,and the group interaction parameters of UNIFAC model of ethanol/water-ionic liquid systems are modified and supplemented.In terms of selecting ionic liquids as extractants to separate the system of ethanol and water,hydrophilic ionic liquids are usually used for dehydration.The commonly used anions are[Me SO₃]^-?[Et SO₄]^-?[DMPO₄]^-?[Ac]^-?[Cl]^-.Due to the relatively low price of chloride based ionic liquids(see Aladdin and Macklin websites),the liquid near room temperature and the strong hydrophilicity of chlorinated ionic liquids,we choose[BMIM][Cl][HMIM][Cl][OMIM][Cl]are candidate extractants.The microcosmic interaction of the mixed system was studied by COSMO-RS model.The surface charge density analysis showed that the anion[Cl]^-could form a strong hydrogen bond with water and easily bring water out of ethanol solution.The results of excess enthalpy analysis show that the mixing process of water+[BMIM][Cl]releases more heat than that of ethanol+[BMIM][Cl],which determines the improvement of the relative volatility of the azeotropic system.In this study,the vapor-liquid equilibrium experiments of water+[XMIM][Cl](X=B,H,O)and ethanol+[XMIM][Cl]were carried out.In addition,the UNIFAC model was used to predict the vapor-liquid equilibrium of the ternary system of ethanol-water-IL.The results showed that the existence of IL could effectively breake the azeotropic phenomenon of the binary system of ethanol-water.The microscopic mechanism of the separation behavior of the ethanol-water azeotrope mixture with[BMIM][Cl]as extractant was determined by the molecular dynamics(MD)simulation at the molecular level.The results showed that the strong HB interaction of ethanol/water-BMIM][Cl]disrupts the relatively weak HB interaction networks of ethanol-water,ethanol-Et OH and water-water,so as to enhance the free movement of IL in the mixed system.By weakening the hydrogen bond between ethanol and water,the azeotropic phenomenon of binary Et OH-H₂O systems can be effectively broken.Finally,using[BMIM][Cl]as extractant and embedding the binary group interaction parameters of UNIFAC model,the equilibrium stage model of the separation process of the ethanol-water binary system was established.The process simulation and optimized were performed at the industrial scale.The extractive distillation process intensified with the heat pump technology has the better economic and environmental efficiencies when compared with the conventional one.The energy consumption of the extraction distillation process intensified by the heat pump can be saved by 59.72%compared with that of the conventional extractive distillation process.The total annual cost and CO₂ emission of the former are reduced by 27.01%and 80.46%,respectively,compared with those of the latter.