Hydrogen (H2) as zero CO2 emission energy resource is widely used in petrochemical, semiconductor and fuel cells. The coke oven gas (COG) contains 54-59 % H2, 21-28 % CH4 and a small amount of CO, CO2, N2, H2O, H2S, hydrocarbons. Over 50% COG is currently utilized as burning fuel. It is highly desired to recover H2 from COG as a green energy resource. Membrane gas separation has the advantages of low energy consumption and environmental friendliness compared to traditional cryogenic distillation and adsorption. Because of thermal and chemical stability, zeolite membranes are deemed as the ideal materials for H2 separation. Zeolite membranes with LTA and MFI topology were initially used to separate H2/CH4, but only Knudsen selectivity was obtained. All-silica STT zeolite possesses seven-membered ring (7MR) windows and 9MR windows (0.24 × 0.35 nm and 0.37 × 0.53 nm, respectively, Figure 1a-b), which is expected to achieve high H2/CH4 selectivity based on the view of size-exclusion. However, the synthesis of STT zeolite membranes was extremely challenging because of HF used and long-term synthesis. Herein all-silica STT zeolite membranes were prepared from the fluorine-free precursor and the crystallization period was shortened by 75% at the elevated temperature. The synthetic membrane showed H2 permeance up to 2.9 × 10-8 mol m-2 s-1 Pa-1 and H2/CH4 selectivity up to 53.8 at 298 K. The H2 permeance increased by 24% at 473 K (Figure 1c), indicating STT zeolite membranes are more suitable for high-temperature H2 separation. More importantly, the membrane was stable up to 336 h in the simulated COG containing CO, C2H6 and H2S (Figure 1d), which should be prevented from feeding to Pd and commercial polymeric membranes.

Fluorine-free synthesis of all-silica STT zeolite membranes for H2/CH4 separation

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