Processing, stability and oxygen permeability of Sr(Fe, Al)O3-based ceramic membranes

Abstract Minor additions of alumina into perovskite-type SrFe 0.7 Al 0.3 O 3− δ , a composition close to the solid solution formation limits in SrFe 1− x Al x O 3− δ system, result in decreasing thermal expansion and increasing oxygen permeability. The improved sinterability of SrFe 0.7 Al 0.3 O 3 -based composite with 3 wt.% Al 2 O 3 addition enables to fabricate high-quality tubular membranes for the methane conversion reactors. No essential degradation in the performance of SrFe 0.7 Al 0.3 O 3− δ membranes under air/CH 4 or air/H 2 H 2 O gradients at 973–1223 K was observed during 200–700 h. The stable operation under high oxygen chemical potential gradients is possible due to surface-limited oxygen transport, indicated by the dependencies of oxygen permeability on the membrane thickness. Applying porous layers of the same composition, synthesized via cellulose-precursor technique, onto the permeate-side surface leads to substantially higher oxygen fluxes. For a model reactor with the surface-modified SrFe 0.7 Al 0.3 O 3− δ membrane and commercial Ni/Al 2 O 3 catalyst, the CH 4 conversion rate achieved 90–97% at 1073–1123 K, when the CO selectivity was almost 100%.