Using Silicalite-1 Zeolite As Seeds For Preparation And Controlling Structure Of Ge-ZSM-5 Membrane And Study On Its Pervaporation

Zeolite membranes as a new kind of inorganic membrane materials, are becoming the ideal separation and catalytic materials, for they not only have high thermal resistance, chemical resistance and good mechanical strength of inorganic membrane, but also have well-defined pore structure of zeolites. Simultaneous introducing Al and Ge into the frameworks of zeolite give rise to the Ge-ZSM-5 membrane hydrophilicity and acid resistance. The high concentration acetic acid solution can be dehydrated and obtain pure acetic acid through this membrane by pervaporation techenology, and this process is effective and energy-efficient. Therefore, the synthesis and applications of Ge-ZSM-5 zeolite membrane have a wide application prospect in the field of membrane separation.Using secondary growth to prepare zeolite membrane can improve the reproducibility and the controllability. Pervaporation performance of the membrane is closely related to its microstructure such as orientation and thickness. In this peper, Ge-ZSM-5 membranes were synthesized by secondary growth and microstructure of membranes was adjusted, then discussed the relationship among pervaporation performance, microstructure and ingredient of the membrane. The Silicalite-1 seeds, seed layers and membranes were investigated by means of X-ray diffraction(XRD), scanning electron microscope(SEM). Then, we studied the pervaporation performance of membrane for separation of acetic acid/water mixture. The results are as follows:1. Using hydrothermal synthesis method can obtain Silicalite-1 zeolite seeds with mean size of 500nm, plat shape and almost no twins. It shows that the twin crystals will reduce when the template content is lower in synthesis solution, the crystallization tempreature is higher, and use the oli bath to heat.2. The b-oriented seed layers were prepared on α-Al2O3 substrates by our ultrasonication-electrostatic adsorption method. This method is easy to operate, and the flat seeds prefer to deposit on the substrates with b-axis perpendicular to the substrate, especially, on the smooth substrate.3. The microstructure of Ge-ZSM-5 membranes (orientation, thickenss) is affected by crystallization temperature, the alkalinity and concentration of nutriment in the synthesis solution, and calcination of seed layers. A higher crystallization temperature is beneficial to the intergrowth of seeds, and membrane is more thicker. With increase of the concentration of template (TPAOH) in synthesis solution, the thickness of membrane will reduce. When the concentration of template is moderate, the preferentially b-oriented membrane will be obtained. Decrease the concentration of nutriment by pretreating the synthesis solution will suppress the new nucleation in some degree during secondary growth and high quality membrane is prepared.b-oriented membranes will be obtained more easily by secondary growth from the calcined seed layers.4. Low crystallization temperature is disadvantage of incorporation of heteroatoms. When the alkalinity of synthesis solution is too high, the amount of Ge and Al in membrane will both reduce. Calcination of seed layers can increase the concentration of Al.5, The microstructure and ingredient of membrane effect the pervaporation performance. Only when the amount of Ge and Al in membrane is right, can the mixture be separated. The pervaporation flux of b-oriented membrane is higher, and the randomly oriented membrane which is made by decreasing concentration of nutriment in synthesis solution shows higher separation selectivity.