Study On Synthesis Of High Purity Propionate By Catalytic Distillation

As electrolyte additives with low freezing point and viscosity,n-propyl propionate and ethyl propionate can effectively improve the performance of lithium batteries.With the development of new energy automobile industry,the demand of high purity n-propyl propionate and ethyl propionate are increasing sharply.At present,the batch process is used to produce n-propyl propionate and ethyl propionate,which has the disadvantages of low conversion,high energy consumption,more industrial waste and low output.In this work,npropyl propionate and ethyl propionate were synthesized by continuous catalytic distillation with heterogeneous catalyst.The design of reactive distillation is a complicated problem.Firstly,it is necessary to determine whether reaction and distillation can be coupled.Secondly,it is necessary to provide theoretical basis for the process construction of reactive distillation.Finally,it is necessary to determine the optimal process through process simulation and optimization.Taking propionate system as an example,the design strategy of reactive distillation process is divided into three steps:(1)determining accurate reaction kinetics and thermodynamics model,(2)feasibility analysis and conceptual design,(3)process construction,simulation and optimization.Based on it,thermodynamics,conceptual design and process design and optimization for synthesis of n-propyl propionate and ethyl propionate by reactive distillation were investigated in this project.This thesis mainly includes the following parts:(1)For n-propyl propionate and ethyl propionate quaternary systems,the accurate thermodynamic model was determined.Accurate thermodynamic model is the basis for subsequent conceptual design and process simulation.The isobaric vapor-liquid equilibrium data of the binary systems contained in n-propyl propionate and ethyl propionate quaternary systems were measured.The Wilson,NRTL and UNIQUAC models were used to fit the binary vapor-liquid equilibrium data,and the binary interaction parameters were obtained for these three activity coefficient models.The accuracy of the fitting experimental data for the three models was compared,so as to determine the most suitable activity coefficient model.By calculating the deviations between the experimental values and the estimated values of the three models,the following conclusions can be obtained: for the ethyl propionate system,the data estimated by using Wilson,NRTL or UNIQUAC model are in good agreement with the experimental data for the three measured binary systems.The Wilson,NRTL and UNIQUAC binary interaction parameters obtained by the regression of the experimental data can be used to describe the phase behavior of corresponding binary systems effectively.For the n-propyl propionate system,UNIQUAC model is the most suitable for describing the phase behavior of this quaternary system because of the best agreement between its estimated data and the experimental data.(2)Residue curve method was used for conceptual design of n-propyl propionate and ethyl propionate synthesized by reactive distillation.The preliminary configuration and initial operating parameters of reactive distillation column were obtained by conceptual design,which simplified the design process of reactive distillation.A reactive residue curve model suitable for complex systems involving multiple chemical reactions and liquid-liquid phase splitting was derived.The residue curve calculation program was written by Matlab.The non-reactive residue curve maps,reactive residue curve maps and bifurcation analysis diagrams of n-propyl propionate and ethyl propionate systems were obtained by calculation.The non-reactive residue curve maps include residue curve maps for ternary systems and non-reactive residue curve maps for quaternary systems.The information of singular points,liquid-liquid phase splitting regions,distillation regions and distillation boundaries were obtained by non-reactive residue curve maps analysis.The reactive residue curve maps show the variation of reactive residue curves,distillation regions and singular points with the reaction extent.The bifurcation diagrams show the variation of singular points with the reaction extent.The conceptual design methods used in this work include non-reactive residue curve maps analysis,reactive residue curve maps analysis,bifurcation analysis and thermodynamic method.The information such as the number of feed streams,the feed location,the feed molar ratio of reactants,whether the rectifying and stripping sections are needed,the value of Damk?hler number,the composition of top and bottom streams and the preliminary configuration of the reactive distillation column can be obtained by conceptual design.(3)The process construction,simulation and optimization of n-propyl propionate and ethyl propionate synthesis via reactive distillation were carried out.The model accuracy was verified before the process construction.For the n-propyl propionate system,the reactive distillation-extractive distillation hybrid process,the reactive distillation-pervaporation hybrid process and the reactive distillation coupled with a decanter-pervaporation hybrid process were constructed to produce n-propyl propionate.For the reactive distillation column,the bottom product is pure n-propyl propionate,and the distillate is a ternary mixture of 1-propanol(1)+ n-propyl propionate(2)+ water(3).This ternary mixture was separated by extractive distillation and pervaporation membrane respectively to achieve the withdrawing water,as well as the recovery of unreacted reactants.The pervaporation module was written by Aspen Custom Modeler to realize strict simulation of pervaporation membrane.Sensitivity analysis and economic comparison of the three hybrid processes were carried out,and the reactive distillation-pervaporation hybrid process was determined to be the optimal process.Finally,genetic algorithm was used to optimize this process globally,and the optimal operating conditions of reactive distillation-pervaporation hybrid process were obtained.Compared with the result of sensitivity analysis,the total annual cost obtained by genetic algorithm is reduced by 22.4 %.For the ethyl propionate system,the reactive distillationpervaporation hybrid process was constructed to produce ethyl propionate.Genetic algorithm was used to optimize this process globally,and the optimal operating conditions of reactive distillation-pervaporation hybrid process were obtained.Compared with the result of sensitivity analysis,the total annual cost obtained by genetic algorithm is reduced by 10 %.