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 (σ_{h {radical dot}}) of the MCOC phase. The CO₂ permeation flux increases with increasing ionic conductivity (σ_{V {radical dot} {radical dot}}) of the MCOC phase at a low electronic conductivity, i.e., σ_{h {radical dot}} ≤ 0.1 S / cm, while decreases with an increase of σ_{V {radical dot} {radical dot}} at a high electronic conductivity, i.e., σ_{h {radical dot}} > 1 S / cm. For pure CO₂ permeation, the CO₂ permeation flux increases with the increase of σ_{V {radical dot} {radical dot}} 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.