Abstract
Silicalite membranes were prepared by a single hydrothermal synthesis on seeded porous tubular supports. The support tubes were simply seeded by a water slurry of silicalite particles or by repeated dip coating in a suspension of colloidal silicalite particles. It was found that a crystal growth behavior was strongly dependent on seeds. Silicalite crystals slowly grew onto the unseeded and nanoscale-silicalite-seeded supports under the present synthesis conditions, leading to the formation of an incompact crystal layer, especially on the unseeded support. On the other hand, silicalite crystals preferentially grew onto the support tubes seeded with silicalite powders (particle size up to 4 μm) under the same synthesis condition. The silicalite seed particles mainly provided nucleation sites and enhanced silicalite crystal growth in all directions onto the support, resulting in the formation of a thin and dense crystal layer. The higher crystallization temperature, faster crystal growth rate is the favorable condition for preparation of the silicalite membranes with high pervaporation performance. For example, the high ethanol/water separation factor of 89 with a high flux of 1.8 kg/m2·h for a feed concentration of 5 wt % ethanol at 60 °C was obtained through the silicalite membranes prepared on silicalite-seeded α-Al2O3 tubes at 185 °C for 5.5 h of hydrothermal treatment. The silicalite membranes prepared by the same method also showed good separation for n-butane and isobutane (an ideal separation factor larger than 10 at 200 °C).
Published Version
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