Hydrogen Production From Methane by Using Oxygen Permeable Ceramics

Oxygen permeable ceramics based on mixed conductors are 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 methane reforming property of a novel member of oxygen permeable ceramics. The materials used are solid solutions of (La_0.5Ba_0.3Sr_0.2)(Fe_xIn_1−x)O_3−δ. The single phase of perovskite-type (La_0.5Ba_0.3Sr_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/cm ² s are attained for (La_0.5Ba_0.3Sr_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_0.5Ba_0.3Sr_0.2)(Fe_0.6 In_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.