【作者】 方宏；

【导师】 陈初升；

【作者基本信息】 中国科学技术大学 ， 材料学， 2013， 博士

【摘要】 陶瓷膜相比于高分子膜,具有化学稳定性好、热稳定性好、机械强度高、耐有机溶剂、耐微生物侵蚀、耐老化、使用寿命长、对环境友好等诸多优点,受到越来越多的关注,在环境工程、能源工程、化学工程、食品工业、医药工业等多个领域有广泛的应用前景。陶瓷膜技术的应用对于实现节能减排,促进社会经济的可持续发展具有重要的意义。然而陶瓷膜的发展仍然存在许多制约的瓶颈,尤其是传统的陶瓷膜制备过程繁琐,工艺复杂,成本居高不下,极大的限制了其应用范围。本课题基于相转换法一次成型技术结合一次高温烧结制备高性能的非对称多孔陶瓷平板膜和中空纤维膜,有望大幅度简化陶瓷膜的制备工艺,降低陶瓷膜的制备成本,提高陶瓷膜的性能并拓展其应用范围。同时,本课题中发展了多孔陶瓷膜的性能表征技术,尤其是结合Otsu图像分析技术和SR-CT三维重构技术来表征多孔材料的孔隙结构。最后,本课题着重研究了多孔陶瓷纤维膜表面修饰在膜蒸馏过程中的应用。第一章主要系统的介绍了多孔陶瓷膜的研究现状,包括多孔陶瓷膜的分类、制备工艺介绍、表征方法介绍等。最后着重介绍了膜蒸馏技术的原理、膜蒸馏材料的研究现状及存在的不足。第二章主要研究了利用相换转流延法结合高温烧结制备氧化铝多孔平板膜,并发展了多种表征手段对制备的平板膜进行表征。所制备的氧化铝多孔平板膜厚度约为0.7mm,孔隙率高达58.6%,具有典型的非对称结构,包含一个厚的指状孔层,厚度约0.6mm,孔隙率约为59.6%,以及一个很薄的海绵状孔层,厚度约0.1mm,孔隙率约为35.1%。采用基于Otsu图像分析技术的二维BSE-SEM方法和基于SR-CT技术的三维重构法分析多孔平板膜的孔结构,两种方法计算得到的孔隙率都和阿基米德法吻合得较好。同时利用SR-CT方法可以获得多孔平板膜孔隙的三维连通情况,这是其他二维方法很难做到的。制备的氧化铝多孔平板膜具有优异的渗透性能,在水处理、海水脱盐、医药生产等诸多领域有巨大的应用潜力。第三章主要研究了利用相换转纺丝法结合高温烧结制备氧化铝多孔中空纤维膜,同时考察了内凝聚剂对中空纤维膜结构的影响。当内凝聚剂为纯水或者低浓度的乙醇水溶液时,.制备的中空纤维膜呈现典型的三明治结构,膜的内侧和外侧各有一个厚的指状孔层,以及中间包含一个薄的海绵状孔层。随着内凝聚剂中乙醇含量的增加,胶凝能力下降,制备的中空纤维膜外径变大,膜壁变薄,外层的指状孔不断向内侧扩展。当内凝聚剂中乙醇的含量达到75vol%时,胶凝能力太弱以至于湿膜的内侧难以发生瞬时分相,而指状孔层几乎消失,形成海绵状孔层。同时,制备的中空纤维膜的孔隙率、平均孔径、氮气渗透通量、纯水渗透通量随着内凝聚剂组成中乙醇含量的增加先增大,在乙醇含量为50%时达到最大值,当乙醇含量为75%时又出现下降趋势。研究表明,通过改变内凝聚剂的组成可以实现对陶瓷中空纤维膜微观结构的调控优化,适当降低内凝聚的胶凝能力对优化膜的结构性能是有利的.第四章主要研究了氧化铝多孔中空纤维膜表面修饰变为疏水性并应用于真空式膜蒸馏过程。采用相转换法＆烧结制备的氧化铝多孔中空纤维膜通过氟硅烷(FAS)表面修饰由原来的亲水性变为疏水性,接触角由修饰前的480变为了130°,并且FAS修饰后的中空纤维膜与修饰之前相比透气性能几乎没有变化,但是纯水渗透性能改变显著,在压差大于1.5bar时,才观测有水透过。FAS表面修饰的中空纤维膜应用于真空式膜蒸馏过程,并表现出优异的性能。在热侧为80°C,4wt%的NaCl水溶液,透过侧通过抽真空使压力维持在0.04bar时,获得了非常高的水通量42.9Lm-2h-1,并且NaCl离子的截留率大于99.5%,性能可以与目前研究的性能最好的高分子膜相媲美。本论文所研究的表面修饰的氧化铝中空纤维膜在海水淡化等领域有非常好的应用潜力。第五章主要研究了8%氧化钇稳定的氧化锆(YSZ)多孔中空纤维膜表面修饰变为疏水性并应用于真空式膜蒸馏过程。YSZ陶瓷相比于氧化铝陶瓷具有更优异的化学稳定性和机械强度,在本论文中采用相转换法与高温烧结相结合制备了非对称结构的多孔YSZ中空纤维膜,与之前研究的氧化铝中空纤维膜相比,海绵状孔层更薄,同时具有更高的孔隙率(54%)和更小的孔径(0.55μm)。通过FAS表面修饰由原来的亲水性变为疏水性,接触角由修饰前的50°变为了1390.FAS修饰后的中空纤维膜与修饰之前相比透气性能几乎没有变化,但是纯水渗透性能改变显著,在压差大于2.9bar时,才有水透过。FAS表面修饰的中空纤维膜应用于真空式膜蒸馏过程,并表现相比于之前研究的氧化铝中空纤维膜具有更优异的性能。在热侧为80°C,4wt%的NaCl水溶液,透过侧通过抽真空使压力维持在0.04bar时,获得了非常高的水通量48.3Lm-2h-1,并且NaCl离子的截留率大于99.7%.本课题中所研究的表面修饰的YSZ中空纤维膜由于其优异的性能,在海水淡化等领域有非常好的应用潜力。第六章对本论文的工作进行了总结,并对多孔陶瓷膜及膜蒸馏技术的应用前景和面临的挑战进行了展望。更多还原

【Abstract】 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.更多还原