α-Al2O3 Supported Silicalite-1 Membranes: Surface Modification and Performance on Selective Permeation of Ethanol

The silicalite-1 membrane on the alpha-Al2O3 substrate synthesized by the secondary growth method was modified to improve its surface hydrophobicity with dodecyltrimethoxysilane (DMS) and stearic acid (STA). The FTIR spectroscopy and contact angle measurements revealed that modifying agents were presented at the silicalite-1 membrane surface by chemical bonding and the surface wetting property was varied from hydrophilic to hydrophobic. The optimum pretreatment temperature was 150 degrees C, and the optimum mass fraction of the modifying agents was ca. 10%. Moreover, the relationship between wetting property and thermal stability was also investigated, the results showed that the modified membrane with DMS possessed good hydrophobicity below 250 degrees C in air. For the recovery of ethanol from its aqueous solution, although the defect size of the silicalite-1 membrane was ranged from 1 nm to 5 nm, the separation factor of the modified membrane was up to 21.6 which is five times higher that without surface modification.