Sodalite (SOD) [1-3] and Deca-dodecasil 3R (DDR) [4-6] are promising membrane materials for hydrogen separation from larger gas molecules due to their 6-membered ring (0.28 nm) and 8-membered ring pore (0.36×0.44 nm), respectively. The SOD and DDR membranes were hydrothermally synthesized on porous alpha-alumina supports by in-situ crystallization and seeded secondary growth methods. The X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques were applied to investigate the phase composition and microstructure of the membranes and corresponding bulk zeolite phases. Defective sodalite membranes were successfully modified by chemical vapor deposition (CVD) technique using tetraethylorthosilicate (TEOS) as the silica source. The CVD-modified sodalite membranes exhibited significantly enhanced H2/CO2 permselectivity of 41 and 45 at 550 oC for low- and high-silica sodalite membranes, respectively. H2/CO2 permselectivity of defective DDR membranes obtained by in-situ crystallization increased from 2.6 to ~33 at 550 oC after CVD modification. For largely defect-free DDR membranes obtained by seeded secondary growth, H2/N2 permselectivity increased from ~10 to 14 by the atomic layer deposition (ALD) of thin Al2O3 layer on the surface of the DDR membrane at 25 oC. These results indicated that ultramicroporous SOD and DDR membranes are highly promising for H2 separation from various H2-containing process streams, such as syngas from the water-gas-shift reaction.

Acknowledgements

The financial support from Ohio Coal Development Office (OCDO) is gratefully acknowledged.

References

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