Synthesis of mixed-conducting membranes with improved properties for membrane reactor applications

Dense ceramic membranes with mixed ionic electronic conducting characteristics that can selectively transport oxygen or hydrogen continue to attract significant interest. These materials transport oxygen ions or protons as well as electrons and electronic-holes while maintaining electroneutrality. As electrons can transport through the materials, external electrodes and circuits are not needed. The driving force for ionic transport through the membranes is an oxygen or hydrogen partial pressure difference on either side of the membrane that introduces a chemical potential gradient across the membrane. As these materials transport oxygen or hydrogen in ionic form, the theoretical selectivity is 100%. Utilizing these materials in membrane reactors can enhance the yield of a thermodynamically limited reaction by selective removal of a product.;The purpose of this dissertation is to improve the mechanical strength and chemical stability of mixed-conducting membranes for use in membrane reactors. The three main objectives covered are: (1) determine the electrical conductivity and oxygen permeation of SrCoFeOx membranes in inert and reducing environments, (2) the effect that zirconium doping has on the hydrogen permeation and chemical stability of SrCe0.95Tm0.05O3-delta membranes, and (3) the performance and stability of SrCoFeOx or SrCe0.75Zr0.20Tm0.05O3-delta membranes in catalyzed membrane reactors.;SrCoFeOx membranes have significantly higher oxygen flux values when a reducing gas is present on the sweep side of the membrane due to a large oxygen partial pressure differential across the membrane and more favorable surface reaction kinetics that preserve a low oxygen partial pressure. SrCoFeO x membranes are mechanical stable in a membrane reactor for the partial oxidation of methane and the use of different catalysts emphasizes the effect that the methane oxidation rate on the reducing side of the membrane has on the oxygen flux. SrCe0.75Zr0.20Tm0.05O 3-delta membranes have a larger hydrogen flux and superior chemical stability over SrCe0.95Tm0.05O3-delta in carbon dioxide containing environments. SrCe0.75Zr0.20Tm 0.05O3-delta membranes exhibit good chemical stability after use in a catalyzed steam reforming of methane membrane reactor for over 400 hours.