Morphology, performance and stability of multi-bore capillary La0.6Sr0.4Co0.2Fe0.8O3-δ oxygen transport membranes

Abstract

Mixed ionic-electronic conducting 3, 4, 7-bore capillary membranes made of La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) were successfully prepared by the combined phase inversion/sintering technique. The membranes fabricated have asymmetric wall structures with micro-channels formed in between surfaces, and dense layers sandwiched in between the micro-channels. By changing the solvent from DMSO to NMP, changes in the morphology of the 7-bore membrane were observed, where the separation layer has reduced its effective thickness. The multi-bore membranes exhibited 3-point bending fracture loads of 10.4, 13.5, 15.4 and 11.7 N with a 3 cm testing span for the 3-bore, 4-bore, 7-bore-DMSO and 7-bore-NMP samples, respectively, which are much stronger than single-bore hollow fibre membranes. Oxygen permeation of the multi-bore membranes was measured with a sweep gas flow through lumen and the effect of operating temperature has on the performance was studied between 750 °C to 1000 °C. Oxygen fluxes measured are comparable to typical sandwich-like structured single-bore hollow fibres at temperatures below 900 °C, but are notably higher at higher temperatures owe to their thinner membrane walls. The 200-h long-term permeation test conducted on the 7-bore membrane showed a slight increase in permeation flux, but the sign of kinetic demixing/decomposition appeared on the outer surface, where the surface of the thinnest membrane walls underwent faster demixing/decomposition than the thickest walls. In summary, the results demonstrated that multi-bore configurations can achieve optimised material distribution during the fabrication, and can obtain strong mechanical property, high permeation flux for the final products whilst maintaining high membrane area to volume ratios.