Process Intensification On The Separation Of Methanol-ethanol-water By Extractive Distillation

Methanol and ethanol can not only be used as fuel and oil additives in the field of energy,but alao as raw materials for high value-added products in pharmaceutical,textile and chemical industries.As the by-product during the preparation of making methanol and ethanol from syngas,water will influence the purity of target products and generate negative impacts on subsequent industrial processes.For this reason,it is necessary to separate alcohols from water.However,the existence of the co-boiling point increases the difficulty of separation.Thus,special solvents and equipments need to be applied to strengthen the separation effects.This work explores the separation process from multiple scales.At the experimental level,it is proved that the ionic liquid[EMIM][DCA]screened out based on COSMO-RS model can be used as entrainers to separate alcohols-water,and the prediction accuracy of thermodynamic model is verified;On the molecular level,the separation mechanism of the ionic liquid entrainer was explored by means of quantitative calculation;On the system level,the process flow is designed and optimized to achieve the separation purpose while further improving the effects of energy saving and emission reduction.Firstly,the relative volatility(α12)was used as the screening index,and the organic solvent ethylene glycol(EG)was selected as the reference entrainer.Based on COSMO-RS theory,the[EMIM][DCA]was selected as the ionic liquid entrainers with high selectivity((?))and solubility(SP),low density,viscosity and melting point as well as good thermal stability.Secondly,the influences of temperature and composition on the saturated vapor pressure of three binary systems[EMIM][DCA]-methanol/ethanol/water and the influence of different concentrations of[EMIM][DCA]on the isobaric vapor-liquid equilibrium(VLE)of methanol/ethanol-water were investigated experimentally,and the accuracy of the model was verified by comparing the predicted values of UNIFAC model and experimental values.Then,COSMOthermX,Gaussian09,and Multiwfn software were used to explore the separation mechanism from the aspects of excess enthalpy(HE),binding energy and electrostatic potential(ESP)at the molecular level based on COSMO-RS theory,DFT theory,and RDG method.It was confirmed that not only the type but also the intensity of interaction between[EMIM][DCA]and components to be separated were beneficial to separation process.Finally,the conventional ternary extractive distillation(CTED)process with single entrainers EG/[EMIM][DCA],compound entrainers[EMIM][DCA]+EG,and the extractive dividing wall column(EDWC)separation process with compound entrainers were designed and optimized respectively.The annual total cost(TAC),carbon dioxide(CO2)emission,thermodynamic efficiency(η),and energy consumption were used as evaluation indexes to evaluate the separation process and provide guidance for industrial application.