Preparation of the silicalite membranes using a seeding technique under various hydrothermal conditions

Preparation of the silicalite membrane with a seed technique on the porous sintered stainless steel support disk with an average pore diameter of 2 µm was examined under various hydrothermal synthesis conditions. Effects of the chemical composition of the starting hydrogel and the seed crystal size on the silicalite membrane formation were studied systematically. The reproducibility of the seed technique was high as compared with a conventional method without seeds. The silicalite membrane was obtained when the TPABr concentration in the hydrogel was very low (0.003 #TPABr/SiO2#0.005). It was also found that the pervaporation performance of the silicalite membrane obtained was greatly dependent on the crystal size of the silicalite seed. The highest separation factor was obtained when seed crystals with 12 µm in size were used.

Fig. 4. Effect of reaction time on pervaporation performance of the silicalite membranes. Feed temperature: 30°C, feed ethanol concentration: 5 vol%. ", flux; !, separation factor ". Table 4 Effect of amount of seed crystals on the pervaporation performance of silicalite membranes Silicalite Condition of quantity, mg the membrane Flux, kg/m2%h Separation factor " 0.31 0.26 0.22 — 23.4 29.5 35.1 — Membrane Membrane Membrane Detached as shown in Fig. 3. These results indicate that the most suitable reaction time on the silicalite membrane preparation using a seeding technique is 48 h. Next, to elucidate the influence of the amount of seed crystal on the pervaporation performance, the silicalite membrane was prepared changing the amount of seed crystal. The results were shown in Table 4. The improvement of the pervaporation performance of the silicalite membrane was observed with the amount of seed crystal. However, the silicalite membrane obtained using the seed crystal over 0.1 g was detached from the support disk.