Synthesis And Characterization Of ZSM-5and Fe-ZSM-5Zeolite Membranes And Their Application For Desalination

MFI-type zeolite membranes have evoked much attention due to their uniquepore structure and easily modified Si/Al ratio. Fe-ZSM-5membranes pose greatadvantages for catalytic reactions owing to the incorporation of Fe. Up to present, thegreat attention has been paid to the MFI-type zeolite membranes due to theirapplications in catalysis, separation and microelectconics.In this work, firstly, the silicalite-1crystals sized at450nm was prepared. Then,dense and defect-free ZSM-5and Fe-ZSM-5membranes were obtained on α-Al2O3substrates by secondary growth under453K for10h. The pore size distributiondemonstrated that defects as large as3.5nm existed in ZSM-5membranes because ofthe template removal under high-temperature calcination at723K. The size of pore inFe-ZSM-5membranes calcined under low-temperature at623K was between0.4~0.6nm, indicating no obvious large defects.Secondly, the effect of alkali treatment on zeolite membranes was also studied,and the contact angle was measured to examine the change of in hydrophilicity. Theresults showed that the contact angle of ZSM-5membrane changes from55.1°to45.4°and the contact angle of Fe-ZSM-5membrane decreases from75.3°to65.2°after ZSM-5and Fe-ZSM-5membranes were treated with0.1mol/L NaOH solutionfor2h, indicating that the zeolite membrane surface hydrophilicity increased after thetreatment by NaOH solution. The pervaporation tests showed that the permeation fluxand the separation factor of the zeolite membrane were improved by conducting thealkali treatment. For Fe-ZSM-5membrane, the permeation flux was changed from0.61kg·m-2·h-1to2.01kg·m-2·h-1while the separation factor was varied from11.8to21.0.Finally, ZSM-5and Fe-ZSM-5zeolite membranes were tested with respect topervaporation and reverse osmosis processes. The results indicated that defects in thezeolite membrane, hydrophilicity and composition of the feeding solution made agreat difference in the desalination results. Compared to ZSM-5membranes,Fe-ZSM-5membranes showed more satisfactory separation results. When dealing with0.1mol/L NaCl solution, the ion rejection rate of Fe-ZSM-5membrane for thepervaporation and the reverse osmosis processes was98.61%and98.61%,respectively; The fluxes were0.76and1.90kg·m-2·h-1, respectively. When dealingwith multi-component solution (0.1mol/L NaCl-0.1mol/L KCl-0.1mol/L CaCl2), therejection of ZSM-5and Fe-ZSM-5membrane is increasing along with increasing ofthe hydrated ion diameter.