Study And Application Of Thermodynamic Insight On The Pressure Swing Distillation And Extractive Distillation Process

Pressure swing distillation and extractive distillation are the widely applied separation techniques for separating azeotropes.However,they still face the problems such as high energy cost,high capital cost and less knowledge of thermodynamic insight,especially when the mixture is ternary azeotrope.Thus,in this work,thermodynamic insight on the binary and ternary azeotropes related to tetrahydrfuran which involves the temperature and composition?T-xy?map,the ternary map,the residue curve maps,the univolatility curves and the distillation boundaries is investigated to find the energy conserving method for the pressure swing distillation and extractive distillation process to effectively guide their design.The main investigation content and results are as follows.?1?Pressure swing distillation for separating binary azotrope is investigated.THF/water and methanol/THF are taken as the investigation case.First,the feasibility of pressure swing distillation is investigated by analyzing the changing tendency of azeotropic composition and temperature with the variation of pressure.According to the feed composition and the top distillate composition under high and low pressure as well as the T-xy map,the feasible separation sequences are determined.To solve the problem of how to determine the amount of recycling flowrate and its composition,we propose employing the genetic algorithm?GA?to optimize all the varaibles for the determination.The results showed that the total annual cost?TAC?and CO₂ emissions of the obtained pressure swing distillation process is 10.5%and 17.3%lower than that in the literature.This demonstrated the effectiveness of GA optimization as well as the nessecity of the global optimization.?2?The pressure swing distillation process of ternary azeotropes belonging to class2.0-2b is investigated.Methanol/THF/water is taken as the investigation case.Extremum estimation method is employed for the evaluation of feasible separation sequences for the first time.Based on the analysis of ternary map,residue curve map,distillation boundary and the component balance line,three basical rules are found and the feasible separation sequences over all the feed composition are determined.Taken the feed compositon of methanol:THF:water=0.375:0.25:0.375 as an example,two pressure swing distillation processes with different separation sequences are designed and optimized by GA.The influence of separation sequences on the TAC and CO₂ emissions are analyzed.?3?The extractive distillation process for the separation of minimum binary azeotrope belonging to calss 1.0-1a is investigated.THF/water and methanol/THF are taken as the case study.Based on the analysis of thermodynamic insight,the feasibility of the extractive distillation is analyzed and the entrainer is selected.The new concept of ROE is proposed for the first time to simply evaluate the operating pressure.Reduced pressure extractive distillation is designed and optimized.The results showed that reduced pressure is not only benefit for the conventional extractive distillation process but also in favor of the heat integrated extractive distillation process,which also validated the effectiveness of the proposed concept ROE.?4?A systematic method is proposed for the extractive distillation of ternary azeotrope belonging to class 2.0-2b.This method involes thermodynamic insight related to the ternary map,residue curve map and univolatility curves to determine the feasible separation sequeces and the best entrainer,process design,optimization and intensification.First,we propose an extractive distillation process?S3?which could break one of the azeotropes without entrainer based on the thermodynamic insight and bifurcation theory.The separation of methanol/THF/water is taken as the study case.Based on the thermodynamic insight,three feasible separation sequences are found and the corresponding extractive distillation processes are designed and optimized by GA.Heat integration and heat pump technique are introduced to further reduce the energy cost and TAC.Tweleve heat integrated extractive distillation processes are optimized simutaneouly by GA to save the repetitive optimization time.Four VRC processes are designed and compared.?5?The pressure swing distillation processes and extractive distillation processes for the separation of THF/water,methanol/THF and methanol/THF/water are compared,respectively.The results showed that the extractive distillation process performs better than pressure swing distillation process in both economic and environmental aspects.This result could offer reference for the industrial production.