The Design And Optimization Of Pyridine-acetonitrile-water System

Pyridine and acetonitrile are important raw materials in chemical process and widely used in pharmaceutical,chemical sector.Nowadays the awareness of energy conservation and emissions reduction and resource recycling improves gradually.In order to reduce environmental pollution and waste of resources,the resource recycling of pharmaceutical industry which produces a large number of useful substances in waste water becomes an important industrial process.The large amount of waste liquid which containing pyridine and acetonitrile is produced in the synthesis process of hepatitis C drugs.The separation of this mixture system is designed and optimized in this paper.The mixture of pyridine,acetonitrile and water can form two kinds of binary azeotrope,so the mixture cannot be separated completely through conventional distillation.By analyzing the residue curve map of this ternary mixture,acetonitrile is selected as an entrainer.The pyridine purity in the bottom column can exceed 99.5% while the acetonitrile-water mixture is the overhead product.It is known that the system of acetonitrile and water is sensitive to pressure and thus can be separated by extractive distillation,so in this study,pressure-swing distillation and extractive distillation are used to separate the acetonitrile-water mixture.Based on the above analysis,two separation processes are designed and the purity of the acetonitrile product and pyridine product can exceed 99.5%,respectively.In this paper,Aspen Plus software is used to simulate the separation of this ternary mixture.The purity of acetonitrile and water together with the total energy consumption of column bottoms are chosen as objective functions.The operating parameters of distillation columns are preliminarily optimized by single-factor analysis,thus the ranges of operating parameters are reduced.In order to search the optimal parameters combinations,the central composite design and response surface methodology are used to optimize the whole process.Comparing the results of response surface methodology and single-factor optimization,it was found that reboiler duty can be saved 37.27% by azeotropic-extraction distillation system and reboiler duty can be saved 27.36% by azeotropic-pressure swing distillation system.Based on the optimization parameters,the heat integration of the process is reformed and the azeotropic-extraction distillation system can provide 12.3% energy saving and azeotropic-pressure swing distillation can provide 33.0% energy saving.By comparing the results of different processes,the azeotropic distillation combined with pressure-swing distillation process is the more economical for separating this ternary mixture.