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| Home > Publications database > Manufacturing of oxygen separation membranes in application relevant size |
| Conference Presentation (After Call) | FZJ-2015-04608 |
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2015
Abstract: Oxygen transport membranes (OTM) are a promising option to supply oxygen for industrial processes such as syngas production or for high-efficinent carbon capture processes based on oxyfuel combustion. OTM´s consist of a gastight Mixed Ionic Electronic Conductor (MIEC), which possesses infinitive oxygen selectivity, implying a defect-free membrane. At the same time, the oxygen flux in such MIEC membranes increases with decreasing thickness. Typical state of the art membranes consist therefore of a thin membrane layer with a thickness less than 100µm and a porous support for mechanical stability (asymmetric membrane). The support must show a low resistance against gas diffusion, requiring a sufficient high porosity in order not to limit the oxygen permeation.In the present study sequential tape casting is used for manufacturing thin, defect free, supported membranes. To achieve sufficient support porosity and low deflection after co-firing, different pore- forming agents were investigated. With regard to ensure chemical compatibility and to avoid thermal expansion mismatch between support and membrane, both were made from the same material. High performance perovskitic membrane materials were used, i.e. Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) and La0.6-xSr0.4Co0.2Fe0.8O3-δ (LSCF).The oxygen flux trough the membrane can be further increased by pressurizing the outer feed gas, thus also increasing the driving force. The membrane must be able to withstand such pressure, which can be ensured by the usage of tube shaped membranes or flat sandwich membranes consisting of an inner supporting structure covered completely by a dense membrane layer. A cavity is implemented for efficient removal of the permeated oxygen. Such flat components were manufactured from asymmetric membranes in application relevant sizes of approx. 100cm2 by lamination. The laminates can be designed for 4-End Mode, where the permeated oxygen is removed or reacts with a sweep gas. Also a 3-End mode is possible, where permeated pure oxygen is removed by a partial vacuum. Both concepts require a sealing of the open support surface at the components’ edges. In this work, ceramic pastes with a high green density were developed to provide a sufficient densification and gas tightness of the sealed areas after sintering. For a reliable operation of the membrane components, concepts for the formation of ceramic to ceramic and ceramic to steel joints are needed. By using brazes and solders which can withstand oxidizing and reducing atmospheres at the same time, a broad range of applications can be covered. According to this requirement, a full ceramic joining, the connection by reactive air brazing with silver/copper oxide-braze, and the soldering with pure silver was investigated. All these techniques were applied in order to build a first short stack for 3-End operation. Performance of the oxygen flux will be shown and bottlenecks for oxygen transport will be addressed. An outlook for improved membrane components will also be given.
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