| Article ID | Journal | Published Year | Pages | File Type |
|---|---|---|---|---|
| 55067 | Catalysis Today | 2012 | 6 Pages |
High-purity oxygen was produced by dead-end Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) tube membranes which were sealed by a reaction-diffusion sintering process. First, phase stability of BSCF membrane in a pure oxygen atmosphere – as it is present on the permeate side of the membrane – was studied at 750 and 950 °C, respectively. After the identification of stable operation conditions of BSCF membranes, we studied the oxygen permeation at 950 °C using dead-end BSCF tubes (1 cm outer diameter, 1 mm wall thickness) in (i) a pressure-driven process, (ii) a vacuum process, and (iii) combining both techniques. In all cases, a high oxygen purity of almost 100 vol.% can be obtained at operation temperatures ≥ 850 °C. The oxygen permeation flux, the oxygen recovery, and the oxygen ionic conductivity were investigated. It was found that – for the same oxygen partial pressure difference – the oxygen permeation flux in the vacuum process is significantly higher than that in the pressure-driven process at all investigated temperatures. Moreover, in all cases, oxygen permeation and oxygen ionic conductivity can be described by the Wagner theory for bulk diffusion of oxygen ions as rate-limiting step with the logarithmic ratio of the oxygen partial pressures on feed and permeate sides as driving force.
Graphical abstractFigure optionsDownload full-size imageDownload high-quality image (184 K)Download as PowerPoint slideHighlights► At the low T of 750 °C BSCF is not stable, a new phase of a hexagonal perovskite Ba0.5±0.1Sr0.5±0.1CoO3−δ is formed from cubic BSCF. ► No phase transformation was found by treating of BSCF at 950 °C in a pure oxygen atmosphere. ► Stable oxygen permeation fluxes were found at T ≥ 850 °C and almost 100 vol.% oxygen is obtained. ► Space-time yield of oxygen production can be raised using oxygen-enriched air as feed at relatively low feed pressure of a few bar. ► Oxygen permeation for (i) vacuum and (ii) pressure-driven (up to 5 bar) operation can be described well by the Wagner theory.
