Process Design And Optimal Control Of Separating Propylene Glycol Methyl Ether-water With Mixed Solvent

Based on the heterogeneous azeotrope of propylene glycol methyl ether and water,the effects of different proportion of solvent on the separation performance,the economy,environmental impact and thermodynamic efficiency of feed preheating process and partial heat integration process are studied with the help of Aspen Plus and Aspen Plus dynamics software.At the same time,the dynamic control performance of liquid-liquid extraction azeotropic distillation process with mixed solvent is investigated and compared with that of single solvent process.Based on the principle of selectivity,chloroform and 2-EA are selected as the mixed solvent.Aiming at the minimum annual total cost,the sequential iterative optimization algorithm is used to optimize the mixing process of chloroform and 2-EA as the mixed solvent,and the optimal solvent ratio,process operating parameters and TAC are obtained.The TAC of the mixed solvent(70 mol% chloroform and 30 mol% 2-EA)is reduced by 34.41% and 26.7%,respectively,which is compared with that of chloroform and 2-EA.By analyzing the influence of different components of mixed solvent and single solvent on the heat duty of distillation column,it is proved that the mixed solvent takes a lot of water,which leads to a smaller heat duty for subsequent separation and then reduces the TAC of the process.Based on the process of optimum proportion of solvent,the energy-saving process is studied.The results show that the TAC of feed preheating process is reduced by 17.73% and the carbon dioxide emission is reduced by 12.32%.The exergy loss inside the distillation column is reduced and the thermodynamic efficiency of the process is improved by increasing the feed temperature.The TAC of partial heat integration process is reduced by 22.55%,the carbon dioxide emission is reduced by 16.40%,and the thermodynamic efficiency is increased by 15.6%.Based on the liquid-liquid extraction azeotropic distillation process with 70 mol% chloroform and 30 mol% 2-EA as mixed solvent,the dynamic performance of the process is investigated.By introducing the disturbance of ± 20% feed flow and feed composition to analyze the process,the proposed cascade control structure of composition and reflux ratio has very good anti disturbance performance for the mixed process,and realizes the effective control of liquid-liquid extraction azeotropic distillation.By comparing the dynamic performance of single solvent process,it is found that the dynamic performance of single solvent process is better than that of mixed solvent process.In order to further compare the dynamic performance of the two processes,the corresponding control structures of the mixed solvent process are applied to the single solvent process.By comparing the ISE of the mixed solvent process,it is found that the ISE of the mixed solvent process is greater than that of the single solvent process.Through the analysis of the results,it shows that the mixed solvent process has a great advantage of energy saving,but the dynamic control performance is inferior to the single solvent process.