Experimental Research And Process Simulation For Separation Of Ethanol And Water With Extractive Distillation

Ethanol is an important organic solvent, and it can be used as liquid fuel and chemical resource. But ethanol and water can form azeotropic. And high purity ethanol product cannot be obtained using traditional distillation technology. Extractive distillation can solve the problem well, because it combines the advantages of solvent extraction (high separation efficiency) and distillation (easy operation and high capacity).The selection of an efficient and suitable entrainer is the key technology to ensure an economic operation. Due to their unique advantages such as nonvolatility, salt effect, high separation ability, regeneration, liquid state around room temperature, and thermal and chemical stabilities, ILs have received considerable attention in the recent years for their use in extractive distillation for separation of olefins and alkanes, alcohols and aliphatics, alcohols and water, and many other systems. By far, all the IL entrainers used in extractive distillation of ethanol and water system have been limited to the single ILs, and the separation effect is poor. Now ethylene glycol is used as entrainer in the industry, but it has disadvantages of poor separation effect, big solvent ratio and solvent loss. As a result, this paper proposes two kinds of composite extracting agent, respectively is:ionic liquids plus solid inorganic salts, ethylene glycol and ionic liquids. From the amount of research results, it shows that [EMIM]+[Ac]-(breaking the ethanol and water azeotrope at xIL= 0.013) has a significant effect on increasing the relative volatility of ethanol to water. Meanwhile, considering the melting point and its relatively low viscosity,[EMIM]+[Ac]-might be a suitable candidate as entrainer for potential industrial application. Thus two kinds of new entrainers were proposed in this work:the mixture of ionic liquid (IL)[EMIM]+[Ac]-plus solid inorganic salt and the mixture of ethylene glycol (EG) plus IL [EMIM]+[Ac]-. The new entrainers proposed in this work can also be applied to the separation of other aqueous solutions due to their similar separation mechanism.The focus of this work is on1) finding out the optimum entrainer mixture of IL and solid inorganic salt by means of the combination of VLE experiments and COSMO-RS (Conductor-like Screening Model for Real Solvents) model and obtaining the Vapor-liquid equilibrium (VLE) data over a full concentration range;2) doing the VLE experiment for the system of ethanol+water+EG+IL;3) trying to seek for some theoretical insights at the molecular level by analyzing the binding energy, σ-profile, and the mixing enthalpy by means of Density Functional Theory (DFT) and COSMO-RS model;4) comparing the separation ability of various entrainers;5) determining how much heat duty could be saved in the extractive distillation process using the new entrainers in comparison with the benchmark entrainer ([EMIM]+[Ac]-) or EG. For this purpose, the mathematical model for extractive distillation process was established, into which the phase equilibrium model (i.e. the NRTL model) obtained in this work was incorporated; and Thus, this work ranges from the molecular level to industrial scale.The main results are:1) compared with the benchmark IL or EG, the two kinds of mixture entrainers all increase the separation ability of ethanol and water, and the separation ability increases along with the addition of the mixed entrainers.2) using the means of Density Functional Theory (DFT) and COSMO-RS model can get some theoretical insights at the molecular level by analyzing the binding energy, σ-profile, and the mixing enthalpy;3) obtaining the NRTL model parameters, and the average relative deviation (ARD) is within the reasonable range, which proving the model is suitable for the system researched;4) simulation process show that the new entrainers all decrease the energy, comparing with the benchmark entrainers, the mixture of [EMIM]+[Ac]-plus KAc decrease19.04%(without HI),19.75%(with HI), the mixture of EG plus [EMIM]+[Ac]-decrease15.02%(without HI),16.51%(with HI). It should be mentioned that the former mixture entrainer change the process but the later one doesn’t.