doi:10.1016/j.memsci.2008.07.008 
Copyright © 2008 Elsevier B.V. All rights reserved.
Enhancement of oxygen permeation through La0.6Sr0.4Co0.2Fe0.8O3−δ hollow fibre membranes by surface modifications
Received 22 May 2008;
Abstract
La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) mixed conducting hollow fibre membranes were prepared via the combined phase inversion and sintering technique. A porous layer of silver or LSCF perovskite was coated on the outside surface of the hollow fibres to improve the surface exchange kinetics. Oxygen permeation fluxes through both the modified and the unmodified LSCF hollow fibre membranes were measured under air/He gradients at different temperatures. The oxygen permeation process through the unmodified LSCF hollow fibre membranes is mainly controlled by the oxygen dissociation on the membrane surface exposed to feed gas of air. After surface modifications, the oxygen permeation fluxes can be improved from the original values of 0.01–0.81 mL standard temperature and pressure (STP) cm−2 min−1 in the unmodified hollow fibre membrane to 0.08–1.85 mL cm−2 min−1 in the Ag-coated membrane and to 0.05–1.48 mL cm−2 min−1 in the porous LSCF-modified membrane, respectively, in the temperature range of 700–1000 °C. The maximum enhancements for the Ag-coated and the porous LSCF-modified membranes are achieved at 800 °C to be 17.8 and 9.3 times the original flux, respectively. Due to the surface modifications, the operating temperature to achieve anticipated oxygen permeation fluxes of commercial interest can be reduced noticeably.
Keywords: Hollow fibre membrane; Mixed conductor; Oxygen permeation; Surface modification
Article Outline
Fig. 1. (A) LSCF hollow fibre membranes and (B) schematic graph of the hollow fibre permeation cell.
Fig. 2. SEM micrographs of the unmodified LSCF hollow fibre membrane (a) cross-section, (b) fibre wall, (c) outside surface, (d) inside surface and (e) central dense layer.
Fig. 3. Plots of (a) oxygen permeate concentration and (b) oxygen permeation flux against the sweep gas flow rate at different temperatures for the unmodified LSCF hollow fibre membrane.
Fig. 4. SEM images of the outside surface of the Ag-modified hollow fibre membrane sintered at (a) 750 °C, (b) 850 °C, (c) 950 °C and (d) 1050 °C.
Fig. 5. SEM images of the outside surface of the hollow fibre membrane coated with LSCF perovskite layer (a) cross-section and (b) interface between the LSCF coating and the fibre membrane bulk.
Fig. 6. Comparison of the modified and the unmodified hollow fibre membranes in oxygen permeation () unmodified membrane, (●) Ag-modified membrane, (
) LSCF coated membrane, (A) oxygen permeation flux and (B) oxygen concentration in the effluent stream.
Fig. 7. Average enhancement factors of the Ag modified and the LSCF perovskite coated hollow fibre (HF) membranes as a function of operating temperature.
