Permeation and Stability Properties of Asymmetric and Disk Shaped Oxygen Permeable Membranes Intended for Syn-Gas Production

Abstract

In this study, the oxygen permeation and stability properties of disk shaped and asymmetric membranes, both of the composition La0.2Sr0.8Fe0.8Al0.2O3-δ were investigated. Strontium doped Lanthanum ferrite is an oxygen deficient mixed ionic electronic conducting perovskite related material. Co-doping with Aluminum enhances the stability of the system. Received precursor was ball milled and sieved to 250 µm. Phase purity was determined by means of X-ray diffraction. Further on particle size distribution and surface area data were collected by dynamic light scattering and nitrogen absorption (BET).Ceramic disks were fabricated by dry uniaxial dye pressing and sintered at different temperatures. Densities of green bodies were measured by geometric means to be approximately 40% of theor. and final densities were measured using Archimedes method. to be approximately 96% of theor. at a sintering temperature of 1230 °C for 2 h in air.Asymmetric membranes consist of a porous support and a dense functional layer. For preparation of porous supports the powder precursor was mixed with 30 wt-% carbon black and 3 wt-% ethyl cellulose. Supports were calcined at 950 °C and then dip coated with a stabilized suspension of La0.2Sr0.8Fe0.8Al0.2O3-δ in ethanol. After dip coating, membranes were pre sintered at 1100 °C, dip coated again and finally sintered at different temperatures. Visual densities were investigated by scanning electron microscopy. Final sintering parameters were 1230 °C for 2 h respectively. Furthermore, investigations on surface modification were carried out by wet chemical etching using 6M hydrochloric acid, resulting in a partly or complete dissolved functional layer.Oxygen flux of membranes was finally measured in a flux furnace with coupled gas chromatograph.Disk shaped membranes reached oxygen flux values up to 1.77 ml*min-1*cm-2 and asymmetric membranes up to 15.33 ml*min-1*cm-2. After flux measurements were completed, the membranes were checked for degradation by means of XRD and SEM/EDS. Both, disk shaped and asymmetric membranes were overall single phase but showed some morphological degradation.