Mixed oxygen-ion and electron conducting dense ceramic membranes are now on their way to integrated chemical and power plant applications that require a continuous feed of pure oxygen or oxygen-enriched gases. However, the variety of potential membrane applications represent a large span of process conditions a membrane has to meet. In an Oxy-Fuel power plant process, the membrane would be subjected to a rather small gradient of oxygen partial pressure, whereas in a chemical process such as membrane-assisted syn-gas production the membrane would be exposed to an extremely large partial pressure difference. However, there are a few requirements that are valid for all these applications. Among the most important requirements is that the membrane must be optimized towards a maximum permeation flux. This may be achieved by improving the transport properties of the membrane material and/or by optimizing the membrane geometry. In this paper, a case study of the perovskite-based membrane material Ba(Co,Fe,Zr)O3 [1] will be presented. We have determined the transport properties of this material for a wide range of parameters (oxygen partial pressure, temperature, membrane thickness and membrane geometry). A defect chemical and transport model was applied to this experimental data set, which provides us with an excellent description of the permeation properties of Ba(Co,Fe,Zr)O3 membranes with planar and tubular geometries. The modelling results highlight the important role of oxygen exchange at the membrane surfaces where oxygen is transferred from the gas to the solid phase and vice versa. Furthermore, under certain conditions, the oxygen permeation flux is strongly affected by the membrane microstructure.

[1] C. Tablet, G. Grubert, H. Wang, Th. Schiestel, M. Schroeder, B. Langanke, J. Caro, J.,
      Catal. Today, 104 (2005) 126.

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1. Stability and oxygen transport properties of BaCo_0.8-xFe_xNb_0.2O_3-δ perovskite membranes in CO₂-containing atmosphere