DENSE CERAMIC MEMBRANES FOR PARTIAL OXIDATION OF METHANE TO SYNGAS

Several perovskite-type oxides (ABO(3)) containing transition metals o n the B-site show mixed (electronic/ionic) conductivity, These mixed-c onductivity oxides are promising materials for oxygen-permeating membr anes that can operate without electrodes or external electrical circui try. Oxides in the system La-Sr-Fe-Co-O permeate large amounts of oxyg en, and extruded tubes of these materials have been evaluated in a rea ctor operating at ca, 850 degrees C for direct conversion of methane i nto syngas (CO+H-2) in the presence of a reforming catalyst. Methane c onversion efficiencies of > 99% were observed, and some of the reactor tubes have been operated for over 1000 h. Membrane tubes were fabrica ted from calcined powders by a plastic extrusion technique. Ceramic po wders in the La-Sr-Fe-Co-O system were made by solid-state reaction of the constituent carbonates, oxides, and/or nitrates. The chemical-pha se behavior of the ceramic powders with varying stoichiometries were s tudied by high-temperature in-situ X-ray diffraction (XRD) as a functi on of oxygen partial pressure. The sintered extruded tubes were also c haracterized by XRD and scanning electron microscopy.