Process Optimization And Control Of Extractive Distillation For Separation Of Ternary System With Three Binary Azeotropes Containing Low Carbon Alcohol

In the process of fine chemical and pharmaceutical production,complex multi-component mixtures containing low carbon alcohols,esters and nitriles are produced.Because of the azeotropic phenomenon among components,the separation process is quite challenging.In this study,the separation process design of ternary systems containing isopropyl alcohol and water was studied with the systems of isopropyl alcohol/n-propyl acetate/water,isopropyl alcohol/acetonitrile/water and isopropyl alcohol/ethyl acetate/water as examples.The energy saving and dynamic control of the processes were studied.Steam recompression technology,coupled pervaporation and mixed solvent were used to simulate and optimize the separation process of the three systems to achieve energy saving.（1）Steam recompression technology was used for energy integration of extractive distillation column with COPs value of 11.41 in isopropanol/n-propyl acetate/water separation process.The energy recovery was 370.87 k W,the process energy consumption was reduced by 10.09%,and the total annual cost（TAC）was reduced by 7.95%.Global warming potential（GWP）and acidification potential（AP）decreased from 16.50 kg CO_2-Eq and 0.0295 kg SO_2-Eq to 8.92 kg CO_2-Eq and 0.0160 kg SO_2-Eq per 1 kmol of mixture treatment,respectively.（2）For isopropanol/acetonitrile/water system,The toxicity of dimethyl sulfoxide,N,N-dimethylformamide,glycerol and ethylene glycol and their effects on the vapor-liquid equilibrium of the system were investigated.In order to further reduce the energy consumption of the process,for the mixture of ethylene glycol and water,a mixed matrix membrane with polydopamine coated metal organic framework was used to separate water and ethylene glycol with the flux of 1.77 g·m^-2·h^-1 and 567g·m^-2·h^-1,the permeability of 4.44 g·m^-1·h^-1·k Pa^-1 and 74.41 g·m^-1·h^-1·k Pa^-1,respectively.Compared with extractive distillation,the energy consumption and TAC of pervaporation-distillation hybrid process are reduced by 45.91%and 21.11%.GWP and AP decreased from 12.62 kg CO_2-Eq and 0.0226 SO_2-Eq to 8.11 kg CO_2-Eqand 0.0145 kg SO_2-Eq per 1 kmol of mixture treatment.（3）For isopropanol/ethyl acetate/water system,the effects of dimethyl sulfoxide,N,N-dimethylformamide,N,N-Dimethylacetamide and ethylene glycol on the vapor-liquid equilibrium of the system were investigated,It was found that ethylene glycol had the greatest influence on the relative volatility of ethyl acetate-isopropanol,and dimethyl sulfoxide had the greatest influence on the relative volatility of isopropanol-water,so the mixed extractant had more advantages for the separation of the system.The optimal mixing ratio of solvent was 30%dimethyl sulfoxide+70%ethylene glycol.The TAC of mixed solvent process was 5.05%and 6.09%lower than that of using ethylene glycol and dimethyl sulfoxide as solvent,respectively.The heat duty of reboiler decreased by 6.64%and 6.43%..The dynamic control of separation of isopropanol/n-Propyl Acetate/water by extractive distillation was studied.The fixed reflux ratio and temperature/composition cascade control structure were proposed.The results show that the product purity of the three distillation columns can return to the set value in16 h when the feed flow disturbance of±10%is handled by the temperature/composition cascade control structure,and the product purity of the three distillation columns can return to the set value in 12 h when the feed flow disturbance of±10%is handled.For the heat pump distillation process,the product purity of the three distillation columns can return to the set value in 10 h in the face of±10%feed flow and composition disturbance by using the basic control strategy,so as to realize the robust control of heat pump distillation.