Microstructure Tuning Of Oxides And Their Applications In Oxygen Production And Hydrodesulfurization

The changing of microstructure will make oxides have unique physical and chemicalproperties, which shows its great value not only in basic theoretical research but alsoindustrial application. This dissertation is intended for the development of mixedconducting ceramic hollow fibre membranes and alumina with novel microstructure. Theas-synthesized samples were characterized by means of techniques such as X-ray diffraction(XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) andN2adsorption-desorption analysis. More detailed work in this dissertation is discussed asfollows:Honeycomb-structured La0.6Sr0.4Co0.2Fe0.8O3-(LSCF) hollow fibre membranes havebeen developed by changing the internal coagulant using phase inversion/sinteringtechnique. The sintered fiber exhibits only one dense layer near the outer cross section layerfollowed by a porous finger-like layer in the middle, which extends to the innercross-section layer. And the hollow fiber’s inner surface shows honeycomb structureformation containing a large amount of uniform circular pores with diameters between20to25μm. This unique structure will dramatically decrease the resistance of bulk diffusion andincrease the rate of the surface reaction, thus the oxygen permeation fluxes. The oxygenpermeation flux of the honeycomb-structured LSCF hollow fibre membrane was up to1.58mL·cm-2·min-1at950°C.Significant improvement of the oxygen permeation flux of hollow fibre membrane wasachieved by microstructure modification using noble metal. The beneficial effect ofdepositing Ag and Pt is confirmed after the modification, and Pt is more effective than Ag.The honeycomb-structured LSCF hollow fibre membrane modified by Pt reached3.99mL·cm-2·min-1at950°C. This is the best value among the reported LSCF membranes underthe gradient of air/helium (or other inert gases). Furthermore, an oxygen spillovermechanism has been put forward to explain the effect of noble metal on the improvement ofoxygen permeation fluxes.Ba0.5Sr0.5Co0.9Nb0.1O3-(BSCN) powders were used to modify the surfaces of the conventional LSCF hollow fibre membranes. It was found that all the BSCN-coated fibresexhibit noticeably higher oxygen fluxes than the unmodified membrane. Coating bothsurfaces of the LSCF membrane with BSCN porous layer make the membrane have bestoxygen permeation performance. And the anticipated oxygen permeation flux of1.66mL·cm-2·min-1can be achieved at950°C. A long-term operation test of120h implies thatthe BSCN-coated LSCF membrane shows high stability at least under the investigatedoperational conditions.Perovskite Ba0.5Sr0.5Co0.8Fe0.2O3-(BSCF) hollow fibre membranes with high oxygenpermeation performance were fabricated. The membrane possesses a novel morphologyconsisting of one dense layer and one porous layer after calcination at1050°C. The resultof oxygen permeation test indicated the oxygen permeation flux through the BSCF hollowfibre membrane sintered at1050°C was approximately11.46mL·cm-2·min-1at950°Cwhen the helium sweep rate was kept at200mL·min-1. Among the tested MIEC membraneswithout additional catalyst, so far this is the highest oxygen flux being observed. The BSCFhollow fibre membrane showed a stable oxygen permeation flux of8.60mL·cm-2·min-1overthe investigated period of120h at900°C. Moreover, a mechanism has been put forward toexplain the effect of sweep gas rate on the high oxygen permeation fluxes in BSCFmembrane.PMMA colloidal crystal template was obtained by centrifugation from monodispersePMMA microspheres which were synthesized using a modified emulsifier-free emulsionpolymerization technique. It was found that the particle size distribution of the microspheresis narrow. And the colloidal crystal template is uniform and ordered. The synthesis strategyof three-dimensionally ordered macroporous (3DOM) alumina is based on a sol-gel processusing a colloidal crystal template method in which a triblock copolymer F127is employedas the mesoporous structure-directing agent. The results showed that all the synthesizedalumina samples possess a highly ordered macroporous structure. The sample calcined at800°C with a surface area of79m2·g-1exhibited the ordered mesopores within the walls ofthe macroporous cages. The co-existence of the interconnected macroporous and mesoporous structure of the prepared γ-alumina enables it to be an effective catalyst supportwith favorable accessibility of the reactants to the active sites. HDS of DBT was chosen totest the catalytic performance of the3DOM γ-alumina supported CoMo-based catalystwhich displayed a high desulfurization ratio of98.23%under the reaction temperature of300°C.