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 α-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 N 2 –CO 2 , N 2 –O 2 , N 2 –Ar and N 2 –CH 4 systems, N 2 permeated faster than the coexisting gas. The N 2 /O 2 separation factor for an equimolar mixture was in the range of 2.3–3.5, and the N 2 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 N 2 –O 2 mixtures. The separation factor for the N 2 /CH 4 system was larger than that of the N 2 /O 2 system. When the membrane was ion exchanged with either Li + or Sr 2+ , the separation factors for N 2 /O 2 and N 2 /CH 4 systems increased, while the permeances decreased.