Oxygen permeation, thermal and chemical expansion of (La, Sr)(Fe, Ga)O 3− δ perovskite membranes

Abstract

Dense ceramic membranes made from mixed conductors are interesting because of their potential applications for methane conversion into syngas (H 2 and CO mixture). Such membranes need to present a low differential dimensional variation between the opposite faces submitted to a large gradient of oxygen partial pressure, in order to minimize mechanical stresses generated through the membrane thickness. Besides, high oxygen permeability is required for high methane reforming rate. La (1− x) Sr x Fe (1− y) Ga y O 3− δ materials fulfil these two main requirements and were retained as membranes in catalytic membrane reactors (CMR). The variations of expansion and oxygen permeation of La (1− x) Sr x Fe (1− y) Ga y O 3− δ perovskite materials with the partial substitution of lanthanum and iron cations, temperature and oxygen partial pressure, were studied. For low temperatures (<800 °C), the thermal expansion coefficient (TEC) value of La (1− x) Sr x Fe (1− y) Ga y O 3− δ materials is independent of cation substitution and of oxygen partial pressure in the range tested (10 −5 to 0.21 atm). For higher temperatures (>800 °C), TEC, then dimensional stability of the membrane, and oxygen permeation of La (1− x) Sr x Fe (1− y) Ga y O 3− δ materials, are significantly affected by Sr content and oxygen partial pressure. Ga has a stabilisation effect on the TEC and has no influence on oxygen permeation flux. A good compromise between dimensional stability and oxygen permeation of materials was found to be La 0.7Sr 0.3Fe 0.7Ga 0.3O 3− δ composition.