Hydrogen Production from Methane by Using Composite-Type Oxygen Permeable Membranes
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Hydrogen Production from Methane by Using Composite-Type Oxygen Permeable Membranes Hitoshi Takamura1,2, Masayuki Ogawa1,2, Yusuke Aizumi1,2, Atsunori Kamegawa1,2 and Masuo Okada1,2 1 Department of Materials Science, Graduate School of Engineering, Tohoku University, 6-6-02 Aramaki Aza Aoba, Sendai 980-8579, Japan 2 CREST, Japan Science and Technology Agency, Kawaguchi, Japan ABSTRACT This paper describes preparation and methane reforming characteristics of a proto-type reformer based on a composite-type oxygen permeable membrane. The tape-cast membrane of Sm-doped CeO2 - 15 vol% MnFe2O4 composite was combined with a ferric stainless steel separator with a same thermal expansion coefficient. For the reformer module, high CH4 conversion, CO and H2 selectivity of 96%, 84%, and 89% were achieved, respectively. Based on C, H, and O balances, oxygen permeation flux was found to be 5.7 μmol/cm2 s. Joule heat caused by oxygen permeation was estimated to be approximately 17.5 W, and this covered most part of heat required for reforming reactions. INTRODUCTION Oxygen permeable membranes based on mixed oxide-ion and electronic conductors have been widely studied for use in partial oxidation of methane to produce syngas and hydrogen. To realize a reformer of partial oxidation of methane by using the membranes (MPOX reformer), to date, a number of oxygen permeable membranes have been developed [1, 2]. In addition to perovskite-type oxides such as (Ba, Sr)(Co, Fe)O3- and (La, Sr)(Ga, Fe)O3- [3, 4], composite-type membranes consisting of acceptor-doped CeO2 as an oxide-ion conductor and MnFe2O4 as an electronic conductor also exhibit a high oxygen flux density of 10 μmol/cm2 s at 1000 °C [5, 6]. Compared to perovskite-type oxides, the advantages of composite-type membranes are higher mechanical strength and low thermal expansion coefficients. For example, a thermal expansion coefficient of the composite of Sm-doped CeO2 - 15 vol% MnFe2O4 (CSO-15MFO) is approximately 11x10 -6 / °C between room temperature and 1000 °C. This value is almost same as that of yttria-stabilized zirconia, suggesting that component materials such as ferric stainless steel and sealing glass developed for solid oxide fuel cells can be used for the MPOX reformer. In this study, oxygen permeable membranes of CSO-15MFO with dimensions of 3.6 cm x 3.6 cm x 135 μm have been prepared by using a tape-casting technique, and combined with a ferric stainless steel separator to form a proto-type of MPOX reformer. The methane reforming properties of the MPOX reformer have been evaluated in the context of efficient usage of exergy. EXPERIMENTAL DETAILS Samples of (Ce0.85Sm0.15)O2 - 15 vol% MnFe2O4 (CSO-15MFO) were prepared by a conventional solid-state reaction. A tape-casting technique was used for the fabrication of membranes with dimensions of 3.6 cm x 3.6 cm; Additives and process parameters have been
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described elsewhere[7]. In this study, the membrane sintered had a thickness of 135 μm. The membrane was then attached to a ferric s
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