Study on the Development of Membrane Reactor Utilizing Thermal Diffusion of Oxide Ion

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Methane conversion technologies have been studied by many investigators with the aim of developing a novel use of natural gas. We found that lattice oxygen of lead oxide on MgO converted methane to C2 with high activity and selectivity by oxidative coupling of methane. Therefore, we developed membrane reactors where lead oxide works as the oxygen carrier. The membrane reactors are classified into three categories : Catalyst oxide film on a porous tube ( Type A ) ; Liquid film containing catalyst oxide on porous tube ( Type B ) ; Oxide membrane with catalysis (Type C ) . In this research the type A and C were mainly studied.The leak-free oxide film on porous tube is essential for type A membrane. Lead oxide mixed with silica powder melts at 750-800ﾟC,though the melting point of PbO is 900ﾟC and that of SiO_2is 1500ﾟC.Therefore, a glassy and non-porous membrane was established by firing PbO-methanol slurry coated on SiO_2-Al_2O_3 tube. The activity was promoted by the surface modification. The reaction rate was accelerated by alkali oxide addition in the PbO film according to the basicity of the additive. With K_2O addition the C2 formation rate was doubled.Perovskite oxide with high oxygen-mobility were tested as tube material of type C membrane by stoichiometric reaction between the oxide and methane. Theactivity of modified ( La-Sr ) CoO_3 system was higher than that of Pb_<0.02>Mg_<0.98> O oxide which is a model of active site of the type A and B membrane reactor. Therefore, type C membrane reactor was made using SrCoO_3 for comparison with membrane reactors of other types. The specific activity per surface area of type C was two orders of magnitude higher than that of others in the wide range of reaction temperature.