Synthesis and permeation properties of ion-exchanged ETS-4 tubular membranes

Zeolite membranes, which were composed of ETS-4 with Na cations, were prepared on porous -alumina tubes by hydrothermal synthesis. The membranes, which were formed under optimized conditions, sharply rejected molecules with sizes larger than 0.4 nm. For mixtures of N₂–CO₂, N₂–O₂, N₂–Ar and N₂–CH₄ systems, N₂ permeated faster than the coexisting gas. The N₂/O₂ separation factor for an equimolar mixture was in the range of 2.3–3.5, and the N₂ permeance was in the range of (0.55–2.8)×10⁻⁸ mol m⁻² s⁻¹ Pa⁻¹ at permeation temperatures of 283–333 K. Moisture had some effect on the permeation properties for N₂–O₂ mixtures. The separation factor for the N₂/CH₄ system was larger than that of the N₂/O₂ system. When the membrane was ion exchanged with either Li⁺ or Sr²⁺, the separation factors for N₂/O₂ and N₂/CH₄ systems increased, while the permeances decreased.