| Ceramic membranes are known to be superior to polymeric membranes due to there some special advantages, such as better chemical and thermal stability, high mechanical properties, better solvent resistance, better microbial erosion resistance, better aging resistance, longer service life and environmentally friendship. In the past twenty years, increasing attention has been paid to ceramic membranes. Nowadays, ceramic membrane are widely applied in various fields, including environmental engineering, energy engineering, chemical industry, food industry, pharmaceutical industry and so on. Therefore, ceramic membranes and related separation technologies could play an important role in promoting energy saving and emission reduction, and are very propitious to sustainable development of social economy. However, there are still many bottlenecks that restrict the further development of ceramic membranes. Most of all, the preparation of traditional ceramic membranes often needs multiple steps, and leads to a complicated production process and a high cost, limiting its scope of applications.In this thesis, we fabricated asymmetric porous planar membranes and hollow fiber membranes with high performance by a combined phase-inversion and sintering method. It is expected that such technology could give significantly affect to ceramic membranes that simplify the preparation process, reduce the production cost, improve the performance and expand their scope of applications. At the same time, we developed the characterization techniques of porous ceramic membranes. Especially, we introduced two novel Otsu threshold image segmentation method and SR-CT three-dimensional reconstruction method to analysis the pore structure of the porous ceramic membranes. Lastly, we focused on the research of surface modification of ceramic hollow fibers and applied in membrane distillation process.Chapter1is the literature review, it briefly describes the research status of porous ceramic membranes, including introduction of the classification, preparation technology and characterization techniques, etc. Lastly, it is focused on the introduction of the theories of membrane distillation, the research status of membrane materials for membrane distillation process and the existing shortcomings.In Chapter2, porous alumina planar membranes were prepared by a combined phase inversion tape-casting and sintering method, and the as-prepared membranes were characterized by several techniques. The planar membrane has a thickness of0.7 mm, and a porosity of58.6%. The membrane showes an excellent asymmetric structure consisting of two layers:a thick finger-like layer with the thickness of0.6mm and the porosity of59.6%, a thin sponge-like layer with the thickness of0.1mm and the porosity of35.1%. BSE-SEM images using Otsu threshold image segmentation method and SR-CT three-dimensional restructuon method were used for analyzing the pore parameter of the membrane. and the values of porosity calculated by the two methods fit well with the results determined by Archimedes method. What’s more, using the SR-CT method, the pores’connectivity of the porous membrane in three-dimensional could be obtained, which is very difficult for the other two-dimensional method. The planar membranes also have good N2permeance and pure water flux performance, which can give great potential in water treatment, desalination, pharmaceutical preparation and many other aspects.In Chapter3, porous alumina hollow fiber membranes were prepared by a combined phase inversion and sintering method, and the influence of internal coagulants on the micro structure and properties of the hollow fibers were investigated. When the internal coagulants were pure water or ethanol aqueous solution with low concentration, the as-prepared hollow fibers showed a classic sandwich-structure, which containing two finger-like layer near the inner and outer surface, and a thin sponge-like layer in the middle. When the concentration of ethanol increased in the internal coagulants, the gelling ability of the internal coagulants decreased and the as-prepared hollow fiber have a lager diameter, a thinner wall thickness, and the finger-like void originated from the outer side to the inner side. When the inner coagulant contains75vol%ethanol, its gelling ability was so weak that the instantaneous phase inversion was hardly to occur, and the inner side of the hollow fiber formed sponge-like voids instead of finger-like layer. At the same time, the porosity, average pore size, nitrogen permeability and pure water permeability of the hollow fiber increased when the concentration of ethanol increase in the internal coagulants, the maximum appeared when the internal coagulants contains50%ethanol. When the ethanol concentration was75%, all of the parameters began to decrease. It revealed that structural adjustment of the hollow fiber could be achieved by change the composition of the internal coagulants. Partly reduce the gelling ability of the internal coagulant is beneficial to the properties of the hollow fiber.In Chapter4, the hydrophobic porous alumina hollow fiber membrane was explored targeting water desalination application. The alumina hollow fiber was prepared by the phase inversion&sintering method. The surface of the hollow fiber was grafted with fluoroalkylsilane (FAS) by immersion in its ethanol solution. The FAS-grafted hollow fiber exhibited a much larger water contact angle (130°) than the un-grafted one (48°), revealing that the grafting had converted the fiber surface from hydrophilic to hydrophobic. The hydrophobic hollow fiber remained well permeable to nitrogen after FAS grafting, but completely blocked liquid water permeation at pressures less than～1.5bar. The water desalination performance of the hollow fiber was tested by exposing the shell side of the fiber to an aqueous solution of4wt%NaCl at80℃and vacuuming the lumen side of the fiber to a pressure of0.04bar. A water flux as large as42.9Lm-2h-1was attained with a salt rejection over99.5%, which is comparable to the best of the polymer membrane. Since the ceramic hollow fiber membrane exhibited much better durability than the polymer counterpart, it is promising for practical applications in water desalination.In Chapter5, the hydrophobic porous YSZ hollow fiber membrane was explored targeting water desalination application. YSZ ceramics have better chemical and mechanical stability than alumina ceramics. The YSZ hollow fiber was prepared by the phase inversion&sintering method. Compared with the alumina hollow fibers, the YSZ hollow fibers have thinner thickness of sponge-like layer, higher porosity (54%) and smaller average pore size (0.55μm). The FAS-grafted YSZ hollow fiber exhibited a much larger water contact angle (139°) than the un-grafted one (50°), revealing that the grafting had converted the fiber surface from hydrophilic to hydrophobic. The hydrophobic YSZ hollow fiber remained well permeable to nitrogen after FAS grafting, but completely blocked liquid water permeation at pressures less than～-2.9bar. The water desalination performance of the YSZ hollow fibers were tested by exposing the shell side of the fiber to an aqueous solution of4wt%NaCl at80℃and vacuuming the lumen side of the fiber to a pressure of0.04bar. A water flux as large as48.3Lm-2h-1was attained with a salt rejection over99.7%, which show better performance than the alumina hollow fibers. Such excellent performance is promising for practical applications in water desalination.In Chapter6, the researches presented in this dissertation are evaluated and future work concerning the development and challenge of ceramic membranes and membrane distillation are discussed. |
PDF Full Text Request