Synthesis Of Ge-ZSM-5 Membranes By In Situ Hydrothermal Method And The Study Of Their Pervaporation Performance

Zeolite membranes as a kind of inorganic membrane materials, have regular pore, alterable pore diameter and potential application in the fields of catalysis, separation and photoelectricity. The super-hydrophilic Ge-ZSM-5 membrane has been prepared by our team on α-Al2O3 substrate by in situ hydrothermal method, and the membrane shows excellent pervaporation performance in the separation of ethanol/water mixtures.In this paper, we investigated the synthesis conditions of the hydrophilic Ge-ZSM-5 membrane and modified α-Al2O3 substrate by γ-Al2O3 film to made the surface of the substrate more smooth. With the modified substrate, the reproducibility of the membranes will be enhanced. The membranes were characterized by X-ray diffraction, SEM and EDX.When the dosage of template agent is low, Ge-ZSM-5 membrane synthesized on α-Al2O3 substrate is not dense, but the membrane becomes dense and the degree of coverage increases when the template agent increased; when crystallization temperature is lower, Ge-ZSM-5 membrane is not continuous, while higher crystallization temperature can make the membrane become more dense and continuous. When the gel composition was 0.195 Ge(C2H5O)4:19.5 SiO2:0.975 TPAOH:438 H2O, the crystallization time 24 h, the dosage of synthetic liquid 19mL, the crystallization temperature 180℃, a dense and continuous Ge-ZSM-5 zeolite membrane with thickness 43 μm was synthesized. At 70℃, the flux and separation factor of pervaporation for water/ethanol (5/95 wt%) are 0.473 kg/m2·h and 230 respectively by this Ge-ZSM-5 membranes.When TPAOH/SiO2 ratio increases, the alkalinity of synthetic solution increases, the germanium content in the membrane reduces correspondingly, aluminum content increases, because of the dissolution of aluminum owing high alkalinity increasing. At the same time, the germanium content in the membrane decreases and the content of aluminum increases correspondingly as the crystallization temperature increases. The results suggest that the increased crystallization temperature can improve the dissolution of aluminum.When the dosage of template agent is low, the Ge-ZSM-5 membrane synthesized on α-Al2O3 substrate coated with γ-Al2O3 membrane is not continuous, while membrane become dense with the template agent increased; when crystallization temperature is low, the Ge-ZSM-5 film contains a lot of pinhole defects, and higher crystallization temperature can make the membrane become more dense and continuous. When the synthetic liquid ratio was 0.195 Ge(C2H5O)4:19.5 SiO2:0.78 TPAOH:438 H2O, the crystallization time 24h, the dosage of synthetic liquid 19mL, the crystallization temperature 180℃, a dense and continuous Ge-ZSM-5 zeolite membrane was synthesized on α-Al2O3 support coated with γ-Al2O3 film, the membrane thickness is 34 μm. At 70℃, the flux and separation factor of pervaporation for water/ethanol (5/95 wt%) are 0.976 kg/m2·h and 64.7 respectively by this Ge-ZSM-5 membranes.