| Ceramic membranes show advantages over polymeric membranes in thermal and chemical stability, mechanical strength, and tunability of porous structure, and thus have found applications in chemical, biological, food, pharmaceutical industries and environmental engineering. Ceramic membranes in form of hollow fiber possess high surface-to-volume ratio, promising for applications that require compact modules. This thesis is thus devoted to the preparation and characterization of hollow fiber ceramic membranes.Chapter 1 gives a review of research on porous ceramic membranes in terms of properties, classification, preparation and applications.In Chapter 2, alumina hollow fibers were prepared by phase-inversion spinning followed by sintering. The relation between the preparation parameters and the structure of the resulting membranes was investigated. It was found that that the longer air gap led to the thinner wall of the hollow fibers. The composition and viscosity of the precursor slurry also affected the membrane structure greatly. The membranes formed under the optimal conditions were sintered at temperature of 1480 ℃. The as-prepared membrane exhibited a three point bending strength of 130.5MPa. The average pore radius was 1.12 μm, and the porosity 38.5%. The nitrogen permeation and pure water permeation were measured to be 1.28×10-6L/m2hbar and 1.31×10-4L/m2 hbar, respectively.In Chapter 3, a new variant of phase inversion spinning method was adopted for preparation of hollow fiber membrane with improved pore structures and permeation properties. An alumina slurry and a graphite slurry were extruded co-axially into a water bath, with the graphite located in the center and the alumina at the shell. Upon immersion in the water bath, the slurries were solidified starting from the shell side inward via the phase inversion mechanism. The as-formed green fiber consisted of alumina as shell and graphite as core. After firing at elevated temperatures, the graphite core was burned off, and the alumina shell was sintered into a hollow fiber. The as-prepared hollow fiber possessed a thin relatively dense outer layer supported by a thick finger-like porous layer. The nitrogen permeation and pure water permeation were measured to be 11.69×105Lm-2h-1 bar-1 and 8.01×103Lm-2h-1baf-1, respectively. The hollow fiber prepared with graphite as sacrificing agent showed much improved water and gas permeability over the membrane derived without the use of the graphite, which is attributed to the formation the straight open pores in the support.In Chapter 4, the SiC reinforced alumina hollow fiber membranes were prepared by the phase inversion/sintering method. The effects of the amounts of SiC nano fibers (2.5-10.0 wt%) on the mechanical strength, microstructure and water flux of the hollow fiber membranes were investigated. The results showed that without addition of SiC nanofibers, the maximum bending strength was about 154 MPa for the porous alumina hollow fiber sintered at 1510℃. However, the maximum bending strength of the reinforced membrane reached 218 MPa, in which 5 wt% SiC was incorporated and sintered at 1450℃; in other words, a 40% improvement in bending strength was achieved. After sintering at 1450℃, the 5% SiC reinforced membrane exhibited a porosity of 41.7% and a peak pore size of 1.35μm whereas the pure alumina membrane had a porosity of 37.5% and a peak pore size of 1.25 μm; the former showed a water permeability of 7.99 L m-2 h-1 kPa-1, which was 3.3 times higher than that of the latter. Therefore, the ceramic nanofiber reinforcement is promising for the development of high-performance ceramic hollow fiber membranes for practical applications.In Chapter 5, zeolitic imidazolate framework (ZIF)-8 membranes was synthesized on the outer surface of alumina hollow fibers using a concentrated synthesis gel. The resulting membranes were characterized by X-ray diffraction, scanning electron microscopy, focused ion beam/scanning electron microscopy and high-resolution transmission electron microscopy. The results showed that the crystalline ZIF-8 membranes were compact and continuous, and contained micro-cavities. Single gas permeances of H2, N2, CH4 and CO2 were determined as a function of permeation time at 25 ℃. H2, N2 and CH4 permeances almost did not change with the permeation time. However, CO2 permeance decreased from 9.8 × 10-8 to 1.7 × 10-8 mol/s m2 Pa within 12 h, and CO2 permeation led to an unrecoverable reduction in gas permeation rates in the further permeation experiments. After the first round tests, H2, N2, CH4 and CO2 permeances in the second round permeation tests dropped by 40%,24%,11%, and 6%, and remained constant in the further repeated measurements; the equilibrium ideal selectivities of H2/CO2, N2/CO2 and CH4/CO2 were 32.2,12.9, and 11.9, respectively; the H2/CO2 separation factor was 7.1 for a H2/CO2 binary mixture (45% H2). The small CO2 permeance should arise from the strong CO2 adsorption in ZIF-8 membranes with micro-cavities, and the adsorbed CO2 partially blocked the gas permeation.In chapter 6, the researches presented in this thesis are summarized, and recommendations for further research are presented. |
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