Modeling and analysis of carbon dioxide permeation through ceramic-carbonate dual-phase membranes

A theoretical model has been developed for CO2/O2 permeation through a dual-phase membrane consisting of mixed-conducting oxide ceramic (MCOC) and molten carbonate (MC) phases. Somewhat simpler theoretical CO2 permeation equation is obtained for the special case or pure CO2 permeation case, i.e., oxygen partial pressure in the feeding gases is zero or electronic transference number of the MCOC phase is zero. The results show that CO2 permeation flux is much improved by involving oxygen permeation, which is more than one order of magnitude higher than the corresponding CO2 permeation flux for a pure CO2 permeation case. The fluxes of CO2 and O2 increase with increasing O2 partial pressure in the feeding gases. Both the CO2 and O2 permeation fluxes increase with increasing electronic conductivity (σhσh) of the MCOC phase. The CO2 permeation flux increases with increasing ionic conductivity (σVσV) of the MCOC phase at a low electronic conductivity, i.e., σh≤0.1 S/cmσh≤0.1 S/cm, while decreases with an increase of σVσV at a high electronic conductivity, i.e., σh>1 S/cmσh>1 S/cm. For pure CO2 permeation, the CO2 permeation flux increases with the increase of σVσV and decreases with increasing molten carbonate volume fraction. An ordered ceramic pore structure benefits CO2 and O2 permeation. The modeling results are compared with experimental data, and a reasonable agreement is obtained between modeling and experimental data.