New high temperature sealing technique and permeability data for hollow fiber BSCF perovskite membranes

Oxygen permeation through BSCF perovskite hollow fiber membranes has been investigated in a laboratory scale reactor in a temperature range of 850-1000 °C at atmospheric pressure. An experimental study was conducted with particular focus on a new sealing technique which was found to provide fully gas-tight conditions with a 100% success rate for the 6 membranes reported in this work (and for 15 membranes in total). An overview of experimental tests on other sealants proposed in the literature is given. A new method for checking the sealing is suggested that allows detecting the possible leakages in all the parts of the membrane module. A loose-end reactor with a shell-and-tube layout is presented which allows accurate measurements of both gas leakages (if any) and product gas composition in a wide range of operating conditions (flow rates on both the permeate and feed side, O2 feed partial pressure, temperature). Permeation fluxes were studied for BSCF membranes with different thicknesses (0.2 and 0.5 mm) using He as sweep gas. The O2 flux increased with both increasing the O2 driving force (i.e., the O2 partial pressure difference through the dense ceramic layer) and the reactor temperature. Long term tests (600 h) have been carried out proving the high stability of both the membranes used and the newly proposed sealing technique. The presence of both O2 bulk diffusion and surface exchange resistance is suggested to limit the permeation rate of the ceramic hollow fibers for the range of wall thicknesses investigated. Finally, LSCF capillaries have also been successfully sealed allowing to extend the use of the proposed gas tight sealing system to different compositions of hollow fibers perovskite membranes.