Seeded synthesis of small polycrystalline NaY zeolite membrane using zeolite structure-directing agent and its pervaporation performance

Continuous and polycrystalline NaY zeolite membranes were synthesized successfully on porous α-Al₂O₃ tubes by zeolite structure-directing agent (ZSDA) method. This ZSDA method consists of two steps: preparation of NaY ZSDA and growth of NaY zeolite membranes with ZSDA by the secondary hydrothermal treatment. The synthesis parameters, such as aging time, aging temperature and the amount of ZSDA added, etc. were investigated. Scanning electron microscopy and X-ray diffraction technology were used to characterize the morphology and the crystal structure of the as-synthesized zeolite membranes, respectively. The results indicated that the growth of NaY zeolite membranes on the supports depended strongly on ZSDA, which could not only accelerate the formation of NaY zeolite membranes but also inhibit the transformation of NaY zeolite phase. It was also found that the prolonged aging time, the lower aging temperature and the increasing amount of ZSDA resulted in a crystal size diminution of the product, thus linking the aging process directly to the increasing number of formed nuclei. Compared with the larger crystal NaY zeolite membrane, the small crystal NaY zeolite membrane exhibited much higher separation selectivity. At 308 K, the highest separation selectivities achieved towards 1,3-propanediol/glycerol and 1,3-propanediol/glucose were 80 and 2,400, respectively.