(76d) A Membrane Reactor Concept for Simultaneous Production of Pure Hydrogen and Synthesis Gas Over Ceramic Materials

The thermochemical water splitting, in particular when combined to solar energy supply, is one of the most promising routes for long-term sustainable hydrogen production. The technology however has major drawbacks such as the batchwise character of the process, the high temperatures required for material reduction (regeneration) and the low hydrogen yields. In this paper experimental demonstration is provided of a novel concept for hydrogen production by a two-step thermochemical water splitting process simultaneously with synthesis gas production by a stepwise redox methane oxidation reaction. It is based on a LaxSr1-xMO3-d (M=Mn, Fe) dense membrane reactor which ensures isothermal and continuous production of high purity hydrogen. The membrane reactor consists of 2 compartments, separated by a dense perovskitic oxygen conducting membrane, with controlled number of anion vacancies. Water vapor is fed to compartment 1 of the reactor where it is decomposed producing hydrogen and lattice oxygen that fills the membrane vacancies. Due to chemical potential difference, oxygen is transported through the membrane to the opposite side where either it is desorbed as molecular O2, when inert gas flows in compartment 2 or removed by an oxidizable species such as CH4. It appears that although operation is possible with water as the only reactant and unforced oxygen desorption due to partial pressure difference, the hydrogen yield increases by a factor of 3 when forced oxygen removal takes place by methane oxidation. In that case the product in compartment 2 is synthesis gas. The preparation of the membranes involves material synthesis, roll-granulation, uniaxial compaction and sintering [1-2]. The final membranes are disc shaped pellets with a diameter of 10mm and thickness 1-5 mm. The redox catalytic properties of materials used for the membrane preparation, LaxSr1-xMeO3, are investigated as a function of the composition, the oxygen deficiency, the temperature and some synthesis process parameters. Stable and reversible catalyst performance was observed at least after eight complete oxidation / regeneration cycles. REFERENCES [1] A. Evdou, V. Zaspalis, L. Nalbandian, La(1-x)SrxMnO3-ä perovskites as redox materials for the production of high purity hydrogen, International Journal of Hydrogen Energy 33 2008, 5554?5562 [2] A. Evdou, L. Nalbandian, V.T. Zaspalis, Perovskite membrane reactor for continuous and isothermal redox hydrogen production from the dissociation of water, Journal of Membrane Science 325 (2008) 704?711