The Novel Equipment And Process Study Of Microwave-induced Falling Film Evaporation Separation

Microwave-induced film evaporation separation process has been reported recently to separate the polar/nonpolar mixture.However,the efficiency of the separation is still too low for practical applications,which requires further enhancement via different strategies such as optimization design of evaporator structure.In addition the depth understanding of the separation mechanisms is great importance for better utilization of the microwave-induced separation process.To carry out these investigations,a novel microwave-induced falling film evaporation instrument was developed in this paper,which aimed to solve the problems of previous evaporators,such as low separation efficiency through structural optimization.Then,based on the improved falling film evaporator,several binary systems with different characteristics were selected to further explore the application of microwave-induced evaporation separation technology in different binary systems to achieve the separation of binary mixtures,and explore the mechanism of microwave-induced separation.In this paper,the influence of microwave irradiation on vapor–liquid equilibrium（VLE）of two binary polar/nonpolar mixture with obvious polarity difference was first explored and the relationship between the influence degree and the polarity differences of components was also explored using the dual circulation vapor–liquid equilibrium device developed by our research group.The results demonstrated microwave irradiation has a certain effect on the VLE of ethanol-ethyl acetate system,but the effect on the VLE of H₂O-iso-octanol system was more significant than that of ethanol-ethyl acetate system.This indicated the greater the difference in polarity（or dielectric properties）between the two components of the binary system,the more obvious the effect of microwave radiation on the VLE.If the influence of microwave field on the vapor-liquid equilibrium of polar/weak polar and strong polar/non-polar systems is very different,the influence of microwave-induced process on the non-equilibrium steady-state evaporation separation of two systems is also necessarily different,which is of great significance for the study of the influence of microwave-induced on the non-equilibrium steady-state evaporation separation process.On the basis of the scraped-thin film evaporator previously by our research group and combined with theoretical analysis,a novel microwave-induced falling film evaporation instrument was developed and built.The experiment results demonstrated the separation performance of the new evaporation separation device has been improved remarkably.Using the scraped-thin film evaporator previously by our research group the microwave-induced increment of the isopropanol content in the vapor phase increased from 0.92%at 25 W·min·m L^-1 to 1.57%at 100 W·min·m L^-1when the initial content of isopropanol was 75.43%.Nevertheless,based on the novel falling film evaporation separation device,the microwave-induced increment of the isopropanol content in the vapor phase increased from 3.24%at 20 W·min·m L^-1 to 9.66%at 65 W·min·m L^-1 when the initial content of isopropanol was 72.51%Finally,microwave-induced evaporation separation process was applied to the separation of three binary systems with different polarity difference using the falling film evaporator developed in this work.The polar/weak polar system（ethanol-ethyl acetate and ethanol-methyl acetate）and the strong polar/nonpolar system（H₂O-DMC）were selected as the research object.For the polar/weak polar system,polar substances with high boiling point concentrate in the vapor phase,while weak polar substances with low boiling point concentrate in the liquid phase.For the strong polar/nonpolar system,the effect of microwave-induced separation was more obvious due to the significant polarity difference between DMC and H₂O.The results showed that microwave-induced evaporation technology broke through the azeotropic point of DMC-H₂O system and broke the equilibrium limit.This apparent induced effect was mainly related to the selective heating of microwave,the diffusion kinetics of polar molecules under microwave field and the destruction of hydrogen bonds between polar molecules.