Mixed-conducting ceramic-carbonate dual-phase membranes: Gas permeation and counter-permeation

CO₂ and O₂ permeable ceramic-carbonate dual-phase membranes can be used in membrane reactors for applications such as selective oxidation of hydrocarbons. Two ceramic-carbonate dual-phase membranes consisting of mixed electronic-ionic conducting perovskite-type ceramics of Pr_0.6Sr_0.4Co_0.2Fe_0.8 and SrFe_0.9Ta_0.1O_3-δ are studied for CO₂ and O₂ permeation and counter-permeation. The geometric factors for the carbonate phase and ceramic phase, obtained from the data of helium permeation and electrical conductivity, are used to calculate the effective carbonate and oxygen ionic conductivity in the carbonate and ceramic phase. Without counter-permeation, O₂ permeation through the dual-phase membrane is controlled by oxygen ionic conduction in the ceramic phase and CO₂ permeation is determined by the total conductance including effective carbonate and oxygen ionic conductivities in both phases. When the dual-phase membrane is exposed to CO₂ on one side and O₂ on the other side, counter-permeation of CO₂ and O₂ occurs in the opposite directions across the membrane. With CO₂ counter-permeation, the oxygen ionic flux is higher than that without counter-permeation due to an increase in the driving force for oxygen transport. CO₂ permeation consumes oxygen ions transporting through the membrane, resulting in a lower O₂ permeation flux compared with the O₂-only permeation case. However, O₂ counter-permeation has negligible effect on CO₂ permeation flux for the dual-phase membranes.