Oxygen permeation and stability investigations on MIEC membrane materials under operating conditions for power plant processes

MIEC membranes (mixed ion-electron conducting membranes) are attracting increasing interest for industrial applications in which oxygen-enriched air or pure oxygen is used. One of these applications is the oxyfuel power plant process. High oxygen permeability and adequate chemical stability under operating conditions, especially with respect to CO2 and SO2, are therefore essential. In the work described here, permeation and chemical stability tests were performed with tubular membranes made of Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF), Sr0.5Ca0.5Mn0.8Fe0.2O3−δ (SCMF) and La2NiO4+δ. To investigate the effects on the materials, microstructure analysis were performed before and after each experimental run by means of energy-dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results show that the highest permeability can be reached with BSCF membranes, but BSCF displays instability with respect to CO2. The other materials show higher chemical stability without any significant degradation effects caused by CO2, but they do display instability if the sweep gas contains 360 ppm SO2. Furthermore, poisoning of the membrane materials by chromium evaporated from the steel was detected in the case of BSCF and SCMF membranes.