High-pressure CO₂ permeation properties and stability of ceramic-carbonate dual-phase membranes

CO₂ permeation properties and stability of ceramic-carbonate dual-phase membranes at high pressures/temperatures are critical to their CO₂ separation and membrane reactor applications, but such data are not available in the literature. This work aims to study the effect of high transmembrane pressure on CO₂ permeation flux and the stability of molten carbonate in the dual-phase samarium-doped ceria (SDC) and molten-carbonate (MC) membranes. Dead-end porous SDC tubular supports were made by a cold isostatic press (CIP)/sintering method with a low porosity (below 7%), and gas-tight SDC-MC membranes were prepared by direct infiltration of molten lithium and sodium carbonate mixture into SDC pores, with a MC volume fraction less than 7%. CO₂ permeation/separation tests were performed on the SDC-MC membranes using feed gas of equal molar CO₂/N₂ mixture at feed pressures up to 15 atm and sweep gas of helium at 1 atm. CO₂ permeation flux for the SDC-MC membranes depends logarithmically on feed/permeate CO₂ pressure ratio in 660–810^oC. The temperature dependence of CO₂ permeation shows activation energy of 30 kJ/mol. Due to the small MC volume fraction and hence low effective carbonate conductivity, CO₂ permeation of the SDC-MC membranes is dominated by the carbonate ionic conduction in the MC phase. The SDC-MC membranes remain in the same structure, morphology, and gas-tightness after CO₂ separation tests at high feed pressures and temperatures, showing high stability of SDC-MC membranes for high-temperature, high-pressure separation and chemical reaction applications.