Ionic conducting ceramic and carbonate dual phase membranes for carbon dioxide separation

A dense membrane consisting of two-phases: molten carbonate for the conduction of carbonate ions and Bi _1.5Y _0.3Sm _0.2O ₃ (BYS) for the conduction of oxygen ions, was synthesized and used for selective permeation of CO ₂ at high temperatures. Since CO ₂ is transported by CO ₃ ^2-, these membranes provide infinite selectivity for CO ₂ over other species such as Ar, He or N ₂.The dual-phase membranes were synthesized by the direct infiltration molten carbonate into porous BYS supports with internal surface modified with γ-Al ₂O ₃ to improve the wettability. Permeation took a long time to reach a steady state at the initial stage of high temperature CO ₂ separation due to the reversible phase transform of the oxygen ions conduction phase between the rhombohedral structure and cubic fluorite structure. The CO ₂ permeation flux for the dual phase membrane increases with increasing temperature (500-650°C) with apparent activation energy for CO ₂ permeation of 113.4kJ/mol. The CO ₂ permeation flux increases with increasing sweep gas flow rate and reaches a value of 0.083mL/cm ²/min at 650°C and helium flow rate of 125mL (STP)/min. The BYS-carbonate membrane offers higher CO ₂ permeance than carbonate dual-phase membranes with lithium-cobaltite or yttrium stabilized zirconia as the oxygen ionic conducting phase.