Synthesis and performance of STT zeolite membranes for He/N₂ and He/CH₄ separation

Helium (He) extraction from natural gas is energy extensive because of the extremely low He fraction and operating temperature. Membrane gas separation is highly desired because of the atmospheric temperature operation. Herein all-silica STT zeolite membranes were prepared on four-channel hollow fibers for He/N₂ and He/CH₄ separation. The effect of synthesis time (1–4 days) on the membrane texture and separation performance was investigated. Initially both 7MR and 9MR channels served as the transport pathway, however, 7MR channels became the dominated one once the synthesis period beyond 2 days at synthesis temperature of 453 K. The size-exclusion effect of He over N₂ and CH₄ was much stronger than the current 8MR zeolite membranes. Therefore, the He/N₂ selectivity was up to 25.4 and the He/CH₄ selectivity was 87.6. The He concentration could be enhanced by 15 ∼ 18 times towards the simulated stream containing 0.2 % He at 0.7 MPa. Most importantly, the membrane performance was stable in the practical feed containing 1 mol% ethane for up to 450 h.