Mixed ionic-electronic conducting composite-based ceramic-carbonate dense membranes for CO2/O2 counter-permeation and CO oxidation

Abstract

Dense inorganic membranes made of the ionic conductor Ce0.80Sm0.15Sr0.05O2-δ and the electronic-ionic conductor Sm0.6Sr0.4Al0.3Fe0.7O3-γ were infiltrated with molten carbonates. One side of the membrane is supplied with CO, and the opposite side is fed with O2. The CO oxidation and CO2/O2 counter-permeation fluxes are studied as functions of temperature and weight percent of the mixed ionic-electronic conductor phase. The O2 counter-permeation was correlated to the oxygen ionic flux counter-permeation consumed for CO oxidation and CO32− formation for CO2 permeation. The Ce0.80Sm0.15Sr0.05O2-δ/Sm0.6Sr0.4Al0.3Fe0.7O3-molten carbonates system exhibits higher oxygen ionic flux counter-permeation than Ce0.80Sm0.15Sr0.05O2-δ-molten carbonates system, producing a larger amount of CO conversion in the first case. The limiting factor for the O2 counter-permeation and CO2 permeation in triple-phase membranes is the oxygen ionic conductivity. In dual-phase membranes, the redox reaction for oxygen dissociation becomes vital for oxygen ionic flux. However, the limiting factor for the O2 permeation flux is the oxygen ionic transport in the ceramic phase. On other hand, the limiting factor for the CO2 permeation is attributed to both the ionic transport in the molten carbonates and the ceramic phase. The weight percent of the perovskite Sm0.6Sr0.4Al0.3Fe0.7O3 was varied to study the effect of its electronic property on the CO2/O2 counter-permeation flux and CO oxidation, establishing that the electronic nature of Sm0.6Sr0.4Al0.3Fe0.7O3 enhances the formation of oxygen ions. This increases the carbonate ions concentration on the surface of the CO-supply membrane side, which raises the driving force for CO2 permeation. Also, the CO2 formation rate on the oxygen supply side is faster than on the CO-supply membrane side. The formation rate of molecular oxygen is lower than the CO2 formation rate.