| Summary: | 碩士 === 嘉南藥理科技大學 === 環境工程與科學系暨研究所 === 99 === Abstract
The purpose of this investigation is to develop new wet phase inversion technologies for hollow fiber membrane preparation and applied those membranes for dehydration of water/ethanol mixtures by pervaporation. The new technologies include outer skin layer control and inner skin layer control method of the asymmetric hollow fiber membranes. In the case of outer skin layer control system, the delay demixing technology was used to dominate the outer skin layer thickness of hollow fiber membranes by addition of co-solvent in casting solution and air gap control in the membrane preparation. The control of coagulation polarity is another method to dominate the outer skin layer structure of hollow fiber membrane. Light transmittance measurements were made to explore the influence on the delay demixing behavior of casting solution in the membrane formation. The effects of membrane formation pathways on the cross section structure and separation performance of hollow fiber membranes were also investigated in this study. In the case of inner skin layer control system, the bore liquid control and considering on the polarity of bore liquid were investigated for the delayer demixing behavior in the membrane formation. Polarity of bore liquids is one of the importance factors to dominate the delay demixing behavior of inner skin layer in membrane formation. Increase the delay demixing time of the casting solution enhanced the skin layer thickness of hollow fiber membranes and altered the membrane cross section structures. The polarity of polymer was also considered in this case and the separation performances for dehydration of ethanol/water mixture were also discussed.
In the first part, the macro pore development was inhibited by the delay demixing of casting solution with adding chloroform and H2O as the coagulant in membrane formation. It was found that defects formed on the outer skin layer and induced the low separation factor of hollow fiber membranes. By considering the air gap to improve skin layer formation, the chloroform vaporized in the air and then enriched the polymer concentration of outer layer casting membrane with chloroform addition in casting solution. The rich polymer concentration effectively increased the skin layer thickness and decreased defects on the surface of hollow fiber. The observation of fiber cross section indicated that the dense skin layer and sponge sublayer were formed by using this method. while the increase the air gap distance, orientation of polymer chain in casting solution were found and affected the skin formation. By using the above technologies, the optimum outer skin layer structure can be prepared by inducing the influent factors in the wet phase inversion system.
In the second part, this study focuses on the effect of polarity of coagulant on the inner skin layer formation and the influential factors on the final structure of hollow fiber membrane. It was found that the n-butanol was the best bore liquids and owns the well delay demixing behavior in membrane formation. The hollow fiber membrane with butanol as bore liquid effectively enhanced the inner skin layer thickness and also showed the good separation performance in dehydration of ethanol mixtures. On the other hand, the sulfonated polysulfone was used as the membrane material and utilized wet phase inversion method to prepare hollow fiber membrane with butanol as bore liquid. It was found that the polar polymer reduced the delay demixing behavior and limited the skin layer thickness. The decrease in separation performance with increasing the degree of sulfonation of polysulfone membranes was found in this case. The mixture bore liquid was considered for improving the delay demixing behavior of suffocated polysulfone membrane. Equal n-hexane and butanol were used as the mixed bore liquid in sulfonated polysulfone membrane preparation. It was found the delay demixing behavior significantly improved and formed a good skin layer structure. It is suggested that the mix solvents can be used as optimum polarity bore liquid in membrane formation and significantly improved the pervaporation performance.
It was concluded that the outer skin layer structure of hollow fiber membrane can be prepared by co solvent addition method and suitable polarity medium as the coagulant in membrane formation. It is indicated that the suitable bore liquid to form inner skin layer structure is superior to the outer skin layer formation method by considering the economic factors. This study had successful prepared the well inner and outer skin layer hollow fiber membranes by considering the membrane formation conditions and membrane formation methods.
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