Hydrogen production from methane by using oxygen permeable ceramics

Oxygen permeable ceramics based on mixed conductors attracting much attention for use in partial oxidation of hydrocarbons as a novel technique for syngas and pure hydrogen production. This paper describes the preparation and oxygen permeation properties including the methane reforming property of a novel member of oxygen permeable ceramics. The materials used are solid solutions of (La_0.5Ba_0.3 Sr_0.2)(Fe_xIn_1-x)O_3-δ. The single phase of perovskite-type (La_0.5Ba_0.3 Sr_0.2)(Fe_xIn_1-x)O_3-δ is obtained in the range of x=0.4 to 0.9. The highest oxygen flux densities of 2.2 and 11 μmol/cm² s (membrane thickness, L=0.2 mm) are attained for (La_0.5Ba_0.3 Sr_0.2)(Fe_xIn_1-x)O_3-δ (x=0.6) at 1000°C under He/air and CH₄/air gradients, respectively. The electrical conductivity of (La_0.5 Ba_0.3Sr_0.2)(Fe_0.6In_0.4) O_3-δ is dominated by p-type conduction having a slope of 1/4 under the high P(O₂) region. The oxide-ion conductivity of the same sample is estimated to be 0.05 S/cm at 800°C. Even though the oxygen flux density slightly decreases with increasing time, high CO selectivity of 90% is kept for 100 h. The oxygen flux density of the solid solution is also discussed in the context of surface exchange kinetics.