Abstract

Oxygen transport membranes made of Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ (BSCF) were manufactured by tape casting and co-firing. The disk-shaped membranes consisted of a top gastight layer (70 μm thick) and a porous substrate (830 μm thick) with 34% open porosity. The variation of the permeation operation conditions allowed (i) the identification of the different limitations steps in the permeation process, i.e., bulk oxygen ion diffusion, catalytic surface exchange and gas phase diffusion in the membrane compartments and porous substrate, and (ii) the ultimate optimization of the oxygen flux. The variables considered in the systematic permeation study included the inlet gas flow rate of the sweep and air feed, the temperature and the nature of the oxygen feed gas (air or pure oxygen). Moreover, the influence of the deposition of a catalytic activation layer (17 μm thick) made of BSCF on top of the thin gastight layer was investigated. As a result of this parametric study, unpreceded oxygen flux values were achieved, i.e., a maximum flux of 67.7 ml(STP) min⁻¹ cm⁻² was obtained at 1000 °C using pure oxygen as the feed and argon as the sweep, while a flux of 12.2 ml(STP) min⁻¹ cm⁻² at 1000 °C was obtained when air was used as the feed.