(399m) Fabrication of Dense ZSM-5 and Fe-ZSM-5 Membranes for High Throughput Desalination

Seawater desalination has been a hot topic worldwide due to the increasing need of fresh water. Zeolite membranes with uniform and molecular-sized pores have excellent thermal, mechanical and chemical stabilities. They keep stable when being applied in a long-term desalination process. The pore size of MFI-type zeolites is about 0.55 nm, continuous MFI-type zeolite membranes could be used for efficient desalination processes with a high rejection rate of ions.

The seed layers of silicalite-1 crystal grains sized at ca. 450 nm were prepared on porous alpha-alumina substrates using the spin-coating technique. Dense and defect-free ZSM-5 and Fe-ZSM-5 membranes were fabricated over porous alpha-alumina supported seed layers by secondary growth. The synthesized MFI membranes were characterized by using SEM, XRD, FT-IR, UV-Vis, TG, BET and contact angle measurements. According to the permporometry measurements, the defect size of ZSM-5 membranes could be as large as 3.5 nm after template removal at 450 °C. However, the defect size of Fe-ZSM-5 membranes was less than 0.6 nm when calcined under low-temperature.

The synthesized ZSM-5 and Fe-ZSM-5 membranes were tested with respect to pervaporation and reverse osmosis processes. The results indicated that defects inside zeolite membranes, the surface hydrophilicity of membranes, and the composition of feeding solutions were key factors in desalination processes. Compared with ZSM-5 membranes, Fe-ZSM-5 membranes possessed more satisfactory desalination performance. When dealing with 0.1 mol/L NaCl solution, the ion rejection rate of Fe-ZSM-5 membrane could be up to 98.6% for pervaporation and 93.9% for reverse osmosis, the corresponding fluxes were 0.76 and 1.90 kg/(m²·h), respectively. With respect to multi-component solutions such as 0.1 mol/L NaCl_0.1 mol/L KCl_0.1 mol/L CaCl₂, the rejection rate of ZSM-5 and Fe-ZSM-5 membranes would be closely related to their hydrated ion diameters.

Acknowledgements

This research was supported by the National Natural Science Foundation of China (Grant No. 21136008) and the State Oceanic Administration of China (Grant No. 201105026)