Performance of membranes based on novel Ce_0.8Sm_0.2O_2-δ /Ag cermet and molten carbonates for CO₂ and O₂ separation

This work proposes a cermet infiltrated with a mixture of Li₂CO₃/Na₂CO₃/K₂CO₃ as a dense membrane to selectively separate CO₂ and O₂ at high temperatures. The cermet consisted of a mixture of the Ce_0.8Sm_0.2O_2-δ (SDC) ceramic and silver as the metallic phase. This type of membrane is a novel design of the ceramic/carbonates type and represents an improvement of state-of-art designs by avoiding microstructural changes in the metallic phase and improving chemical inertness and wettability with the carbonate phase. First, an SDC nanostructured powder was chemically synthesized by direct combustion of urea: lanthanide nitrates-based deep eutectic solvent; then, SDC and silver powders were mixed in a 50:50 vol% ratio by using high energy ball milling. The mixture was uniaxially pressed and sintered to form a support. This cermet exhibited excellent wettability properties against the ternary molten carbonate phase; therefore, it readily allowed infiltration of the molten salts to form a dense membrane. Hence, the cermet showed excellent electronic conductivity as well as corrosion resistance in contact with carbonates for 200 h of continuous immersion. The cermet-carbonate membrane showed permselectivity by separating CO₂ and O₂ at high temperatures. It reaches simultaneous permeation values of 0.49 and 0.26 ml·min⁻¹·cm⁻², for CO₂ and O₂, respectively, at 850 °C. Finally, continuous permeation tests at 825 °C for 85 h proved the excellent chemical stability of the cermet-carbonate membrane. Any chemical reactivity was not observed between the cermet and the carbonates.