Effects of separation layer thickness on oxygen permeation and mechanical strength of DL-HFMR-ScSZ

Abstract

It has been demonstrated in our previous studies that in order for greater methane conversion and less coke-formation, a higher oxygen permeation rate through the outer oxygen separation layer of a functional dual-layer ceramic hollow fibre membrane is needed. Besides new membrane materials with higher oxygen permeability, another way of improving oxygen permeation is to reduce the separation layer thickness, although this strategy is limited by the characteristic thickness, Lc, where bulk diffusion and surface oxygen exchange are both important. As a result, a series of La0.80Sr0.20MnO3−δ (LSM)-Scandia(10%)-Stabilized-Zirconia (ScSZ)/ScSZ-NiO functional dual-layer hollow fibres (DL-HF) with an outer oxygen separation layer thickness between approximately 8.0 and 72.4 μm were fabricated in this study, by using the single-step co-extrusion and co-sintering process. The effects of separation layer thickness on oxygen permeation and mechanical strength were investigated. The oxygen permeation of the LSM-ScSZ separation layer is more likely to be controlled by surface exchange at higher temperatures, and changes to mixed control by both bulk diffusion and surface exchange at lower temperatures. A thicker separation layer also results in a thinner catalytic substrate layer, and subsequently decreases the mechanical strength of the dual-layer hollow fibre membrane.