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 alpha-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-CO2, N-2-O-2, N-2-Ar and N-2-CH4 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 N2 permeance was in the range of (0.55-2.8) x 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/CH4 system was larger than that of the N-2/O-2 system. When the membrane was ion exchanged with either Li+ or Sr2+, the separation factors for N-2/O-2 and N-2/CH4 systems increased, while the permeances decreased. (C) 2001 Elsevier Science B.V. All rights reserved.