Sifting Of Solvent And Process Simulation Of Water+Tert-butanol Azeotropic System

Tert-butanol is an important organic chemical raw material.Tert-butanol dehydration is an important challenge in the process of tert-butanol purification.Combining the advantages of low eutectic solvent,low vapor pressure,strong separation ability,good stability,low viscosity and easy availability of raw materials,westudiedtheternary/quaternaryvapor-liquidequilibriumdataof water+tert-butanol+solvents,and correlated the experimental data with the NRTL equation.The extractive distillation process was simulated using the obtained binary parameters.The separation performance of different solvents for water+tert-butanol system was comprehensively compared.At 101.3 kPa,the isobaric vapor-liquid equilibrium data of water（1）+tert-butanol（2）+ethylene glycol（EG）,glycerol（G）,diethylene glycol（DEG）,triethylene glycol（TEG）,tetraethylene glycol TEEG and diethylene glycol（DPG）（3）ternary system were measured.We obtained the activity coefficient and relative volatility of the volatile components.The NRTL equation was used to correlate the vapor-liquid equilibrium data and the experimental results agree well with the calculated results.For the water（1）+tert-butanol（2）+ethylene glycol（3）system,the average absolute deviations of the equilibrium temperature and the vapor phase molar composition of tert-butanol areδT=0.22 K andδy=0.0011,respectively.The results showed that glycerol and ethylene glycol are two kinds of effective solvents.The solvent mass fractions of ethylene glycol and glycerol are w₃=0.265,0.215,respectively,to break water+tert-butanol azeotropic system.For the quaternary system,at 101.3 kPa,we measured water（1）+tert-butyl alcohol（2）+ethylene glycol（EG）（3）+choline chloride（4）and water（1）+tert-butanol（2）+glycerol（EG）（3）+choline chloride（4）quaternary isobaric vapor-liquid equilibrium data.The thermodynamic model of the quaternary system was established using the NRTL equation,and the vapor-liquid equilibrium data was calculated using the obtained parameters.The results show that the experimental results are perfectly reproduced.We also calculated the isobaric vapor-liquid equilibrium data for x?₂=1（x?₂=x₂/（x₁+x₂））,and studied the minimum amount of solvent needed to break the azeotrope of water+tert-butanol.The amount of solvent needed to break the azeotrope of each solvent are:EG:ChCl（2:1）,w_s=0.135,x_s=0.116;EG:ChCl（4:1）,w_s=0.165,x_s=0.159;EG:ChCl（8:1）,w_s=0.195,x_s=0.203;G:ChCl（8:1）,w_s=0.205,x_s=0.164.For the eutectic mixture with an EG+ChCl molar ratio of2:1,its performance is equal to[emim][OAc]（ws=0.115）,[bmim][OAc]（w_s=0.145）,[emim][Cl]（w_s=0.105）.However,compared to ionic liquids,the eutectic solvent has a lower viscosity and is cheaper.We believe that the eutectic solvent with a 2:1 molar ratio of ethylene glycol and choline chloride is a potential extractant.Based on the NRTL activity coefficient model,four kinds of extractants,namely ethylene glycol,glycerol,ethylene glycol and choline chloride（2:1）,and glycerol plus choline chloride（8:1）,were selected and perform extractive distillation simulations for water+tert-butanol azeotropic system by Aspen plus.The influences of number of stages,feed stage of azeotrope,reflux ratio,feed stage of extractant,solvent ratio（S/F）on extractive distillation were studied.The results show that ethylene glycol+choline chloride（2:1）is a potentially efficient and inexpensive green solvent for achieving the same separation task in terms of separation efficiency and energy consumption.This paper provides reliable experimental data and theoretical basis for the application of eutectic solvent in the separation of water+t-butanol azeotrope.