Primary Hydrothermal Synthesis And Technological Conditions Optimization Of ZSM-5 Membrane

Zeolite membranes have many excellent features compared to organic membranes, such as high thermal stability, anti-acidity and hydrothermal stability, as well as good catalytic properties. As its great varieties and different properties, zeolites supply wide spaces for development of inorganic membranes. ZSM-5 zeolite membrane has been extensively studied and reported, which has a high potential in research and development. ZSM-5 zeolite membrane was first synthesized by Mobil Company in the middle of 1960s; afterwards a research fever on its preparation and application was aroused.Based on literatures home and abroad on synthesis and applications of ZSM-5 zeolite membranes, an in-situ hydrothermal synthesis method was introduced to prepare ZSM-5 membrane without cracks, of which the crystal grains and the orientation are uniform, the crystal size is ca. 100μm. Many factors on affecting the quality of ZSM-5 membrane have been discussed and the thermal stability of products has also been explored systematically. The detailed descriptions are as follows.ZSM-5 zeolite membranes were successfully primary-synthesized by in-situ hydrothermal method on the self-made ceramic support with the Tetrapropylammonium hydroxide (TPAOH) as the templating agent. Many key factors during the growing process of zeolite membranes were discussed, such as the dosage of alkali (pH), crystallizing time and the dosage of the template. The best molar composition and crystallizing time were optimized: 61.73 TPAOH:1201.23 SiO2:1.0 Al2O3:27037 H2O,48 h. This method is relative easy, inexpensive and free of special unit, in addition, the raw material is abundance. Furthermore, ZSM-5 zeolite membranes are also received with tetrapropylammonium bromide (TPABr) as template. A comparison on morphology and structure has been made between the products synthesized with TPAOH and TPABr.The technique for template removing has also been investigated, which plays an important role in membrane preparation and affects the quality of membrane greatly. The optimized template removing condition:calcined from room temperature to 350℃with a heating rate of 1℃/min, then raising the temperature to 550℃with a heating rate of 0.5℃/min and maintained for 5 h. Moreover, the thermal stability of as-synthesized membranes has been studied. The nitrogen permeability of as-obtained membrane remains after roasted for 5 h at a series of temperatures, which gives a conclusion that the as-obtained membranes have a high temperature resistance during the selected temperature region.