Abstract:

Zeolite A nano-crystals were readily self-assembled into uniform zeolite layers with high degrees of coverage on the surfaces of different substrates such as porous stainless steel(SS), ceramic and silicon wafer by a simple method mploying 3-aminopropyltriethoxysilane(AP-TMS) as linker reagent. The fabrication process involves two steps: (1) surface functionalization by immersion of the substrate into the ethanol solution with linker reagent in an autoclave at 373 K for 3 h; (2) zeolite deposition assembly by immersion of the functionalized substrate into the nano-zeolite suspension in ethanol under the same condition as above step. A continuous, intergrown, uniform zeolite membrane was obtained on the ssembled substrate by the secondary growth. The membrane pervaporation was carried out to evaluate the performance of NaA membrane for the separation of water-benzaldehyde mixture in the microreactor assembly at room temperature and 16.7 kPa vacuum pressure. It is shown that the membrane has an excellent selectivity for water. The separation factors for H₂O/benzaldehyde as high as 31 033 and 11 018 were obtained for benzaldehyde feed mass fraction of 99.5% and 97.0%, respectively. Influence of three linkers including AP-TMS, 3-chloropropyltriethoxysilane(CP-TMS), and 3-mercaptopropyltriethoxysilane(SP-TMS) for the zeolite crystals assembly on the substrates was investigated. It is found that using CP-TMS as linker, only a closely packed zeolite layer can be formed on the SS, while SP-TMS as linker, a zeolite layer can not be formed on any of these substrates. The reaction mechanism of the self-assembly and role of the linker were discussed.

Key words: Self-assembly, Zeolite membrane, Inorganic membrane, Microreactor