Reactive Distillation Process Of Ethyl Acetate Catalyzed By Tungstophosphoric Acid

Ethyl acetate(EA) is an important chemical material and green solvent with low toxicity,which has been used in a wide range of industrial application such as painting,coating and perfume.The most important synthesis process of EA is the esterification of acetic acid(HAC) with ethanol(EtOH),which can make use of biological resources indirectly.Thus,with the exhaustion of petrochemical resources, the direct esterification has very good prospects for developments.The esterification reaction is reversible;so many research workers took advantage of reaction distillation technology to improve the synthesis process of EA which has been industrialized through the integration of reaction with distillation in recent years.In consideration of the strong corrosion of equipments brought by the traditional esterification catalyst sulfuric acid,this paper will choose tungstophosphoric acid that is a strong heteropoly acid as the catalyst of esterification,so that the problems of catalytic activity and equipment corrosion is solved.However,information related to the quantity study on the kinetics of esterification of acetic acid with ethanol catalyzed by tungstophosphoric acid is scarce in the literature,which results in the difficulty in evaluating the value of process industrialization.In a series of experiments,the reaction rate constants of esterification catalyzed by tungstophosphoric acid were measured under atmospheric pressure and at the temperatures ranging from 333.15K to 378.15K.Then the quantitative expression of kinetic equation and kinetic parameters were obtained.This work provides a basis for quantitative calculation of reaction rate in the reactive distillation in industrial production of ethyl acetate.This study shows that the esterification of acetic acid with ethanol catalyzed by tungstophosphoric acid is a second-order reaction.The reaction rate constants can be described by Arrhenius equation,and changed with temperature and also the concentration of tungstophosphoric acid.Within the range of studied temperatures and catalyst concentration,the activation energy and pre-exponential factor increased when the concentration of tungstophosphoric acid increased.The pre-exponential factor k₀=exp(-4.23247+3.27731^*X_HPWu),while the reaction activation energy(E_a)/R=53.56093^* exp(X_HPWu/0.39354)+5160.65301.As the activation energy changes slightly with the concentration of tungstophosphoric acid catalyst,the mean value was adapted to simplify the kinetic equation.The activation energy E_a is equal to 45.52KJ mol^-1,and the pre-exponential factor k₀=(0.03244+0.13889^* X_HPWu),which demonstrates that the pre-exponential factor increases linearly with catalyst concentration.The two kinetic equations were used to calculate the ethanol concentration under experimental conditions,and the obtained results show that both of the equations can calculate the esterification reaction rate under other conditions accurately.In the reactive distillation process of ethyl acetate synthesis,this work takes excessive acetic acid extraction to maximize the conversion of ethanol and to reduce the azeotrope of ethanol,water and ethyl acetate in the upper section of column. Tungstophosphoric acid acts as homogeneous catalyst of this esterification,therefore, how to recovery catalyst and the excess acid from the bottom stream of esterification column is a key problem to industrialize this esterification process.Based on the four-column reactive distillation process put forward by Ye Kongmeng,in this paper,the distillate rate and side rate of esterification column were increased to reduce the amount of ethanol and ethyl acetate in the bottom stream.As a result,the acetic acid and water can be separated through a separation column,after the separation,the H₂O stream containing 99.5%water was discharged from this process,while all the catalysts and 99.7%acetic acid was recycled into the esterification column by CH₃COOH stream.In this paper,based on the recycle of catalyst and acetic acid,the number of acetic acid-water separation is reduced to one in the improved process,without affecting the acetic acid-water separation.Compared with the former reactive distillation process,cooling duty of condenser has been reduced by 24.69%, decreasing from 943.61KW to 710.66KW;heat duty of reboiler has been reduced by 24.72%.These improvements have saved equipment investments,reduced the energy consumption of this separation and heightened economic performance of this process.