Multi-layer membrane composites and their use in hydrocarbon partical oxidation

#The present invention relates to multilayer composites having a multicomponent metallic oxide membrane. In another embodiment, the present invention also relates to the use of the composite in a hydrocarbon partial oxidation process.

#The use of multicomponent metallic oxide membranes that are selectively permeable to oxygen has been proposed for a variety of applications. Among these applications are oxygen separation and utilization, including the separation of oxygen from air, partial oxidation of hydrocarbons to produce chemicals in high temperature or electrocatalytic reactors, and complete oxidation of hydrogen or hydrocarbons in high temperature solid-oxide fuel cells.

#One type of multicomponent metallic oxide membrane is a non-porous mixed ionic conductor (MIEC) membrane. An MIEC membrane is illustrated schematically in FIG. 1. This type of membrane is useful in a process for partially oxidizing methane. In this process the MIEC membrane is used as a component of a membrane reactor. The membrane forms a barrier between two regions. One region contains a gas having oxygen molecules. A second region contains both the methane reactant and CO and hydrogen produced during the partial oxidation reaction. The CO and hydrogen produced during this reaction are frequently referred to as syngas.

#FIG. 1. A schematic of a mixed ionic electronic conductor (MIEC) dense membrane.

#FIG. 2. A schematic diagram of a membrane reactor with porous electrodes: (a) basic membrane geometry, (b) schematic of pore structure.

#FIG. 3. The calculated dependence of normalized oxygen flux in a dense membrane on membrane thickness and on the inlet and outlet pressures p' and p".

#Increasing oxygen transport flux in the membrane can lead to a reduction in the surface area and hence a reduction in the price of membrane reactors used in methane partial oxidation processes. Oxygen transport flux in the non-porous membrane is directly related to the coefficient of bulk ambipolar diffusion of oxygen and electron holes through the membrane, D.sub.a, and the coefficient for surface activation of the oxygen gas, K.sub.i. The flux can be increased by reducing the thickness, L, of the dense membrane until, L.about.L.sub.d, where

#L.sub.d =D.sub.a /K.sub.i (1)

#The length scale L.sub.d determines the transition from diffusion limited (L>>L.sub.d) to surface reaction rate limited (L<<L.sub.d) oxygen transport.