Preparation And Modification Of Hollow Fiber YSZ And BSCF Ceramic Membranes For Oxygen Permeation

Because of the 100% oxygen selective permeability, ceramic oxygen permeable membranes show broad application prospects in air/oxygen separation and various hydrocarbon reforming membrane reactors. For practical application, the shape of oxygen permeable membranes have great influence on the performance and manufacturing of oxygen generating plant. Traditional round flat oxygen permeable membranes have small membrane areas and the thickness are difficult to reduce. Thus the oxygen permeability is relatively low. Compared with the flat membranes, hollow fiber ceramic membranes have high packing densities and specific surface areas. The oxygen permeation membranes with hollow fiber shapes not only increase the oxygen permeability, but also promote the applications of oxygen permeable membranes. In order to obtain higher oxygen permeability, surface coating can be used to modify hollow fiber membranes. In this dissertation, key process parameters of dry-wet spinning for preparing the hollow fiber membranes are determined. Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) powders were synthesized by solid-state reaction, and used to prepare BSCF hollow fiber membranes. Hollow fiber membranes were modified by surface coating with a BSCF porous layer and their properties were studies after surface modification. In addition, based on hollow fiber membranes, a novel type of ceramic oxygen permeation membranes device was designed and the structural characteristics and operation methods of the device were detailed descripted.By investigating the microstructure of YSZ hollow fiber membranes, dry-wet spinning process parameters such as the polymer content, injection flow rate, sintering time and sintering temperature were determined. The mass ratio of YSZ and polymer is 5:1, giving rise to a moderate viscosity of the casting slurry. The injection flow rate of molding process will have a direct influence on the thickness of the hollow fiber membranes. When the injection flow rate is 4-6ml/min, the hollow fiber membrane shows the best performance. The sintering process plays an important role on the densification of hollow fiber membranes. By sintering at 1500℃ for 5 hours, the hollow fiber membrane have uniform grains and dense surface.The single perovskite phase BSCF powders were synthesized by solid-state reaction method. One end-closed BSCF hollow fiber membranes was prepared by the dry-wet spinning process. The closed end, surface, cross section and the coating layer of the hollow fiber membranes were observed by scanning electron microscope. The results showed that the closed end and surface of hollow fiber membranes are dense with an asymmetric structure cross section and the modified coating layer is a porous structure. The oxygen permeability of hollow fiber membranes before and after modification were tested. The results show that the oxygen permeation rate of modified hollow fiber membranes increases from 1.495 to 2.837ml/(cm2 min) at 900℃. And at 700℃, the oxygen permeation rate of modified hollow fiber membranes increases from 0.413 to 1.371ml/(cm2 min). By calculated, the activation energy of oxygen permeation decreases form 58.52 to 34.07kJ/mol with a decrease range about 40%.Although the hollow fiber oxygen permeable ceramic membranes have been more common, the application is rarely reported. Therefore, a novel design of the hollow fiber membrane device for the preparation of pure oxygen were proposed with detailed description of the components, assembly methods, operation process and replace method. Moreover, the characteristics and advantages of the device were introduced.