Study On Hydrothermal Synthesis Of Nano-ZSM-5with Low SiO₂/Al₂O₃Molar Ratio

ZSM-5zeolite is a aluminosilicate which has unique three-dimensional miropore structure. Because its well water thermostability and skeleton thermostability, relative strong acidity, ZSM-5is an ideal material of catalysis. It has been widely used in aromatic hydrocarbon alkylate, catalytic cracking, the light hydrocarbon aromatization, methyl alcohol system gasoline and such like industry. Since1972Mobil corporation firstly synthesized ZSM-5zeolite, researchers have been looking for the ideal synthesis condition to obtain zeolite that has better catalytic performance. SiO2/Al2O3molar ratio is one of important factors for zeolite acidity. Especially, ZSM-5with low SiO2/Al2O3molar ratio has great application prospect in catalytic cracking, due to more acidic positions.In this paper, in order to solve the problem of poor zeolite stability, narrow synthesized phase region, miscellaneous crystals, low crystallization in the synthesis of ZSM-5with low SiO2/Al2O3molar ratio, a series of ZSM-5with low SiO2/Al2O3molar ratio has been synthesized. Zeolite samples were characterized by X-ray diffraction(XRD), Scan electron moeroscope(SEM). The following information has been obtained:(1)In N-butylamine template system, N-butylamine as a big molecule, Too much could hinder the aluminum to enter the zeolite skeleton, too little will ease the effect as structure directing agent and is not conducive to the crystallization. The addition of seeds could accelerate the crystal rate, increase the crystallinity, but too many seeds will reduce the crystallinity. Alkali metal cation has small ionic radius, it will not only be conducive for the aluminum to enter the zeolite skeleton, accelerate the crystal rate, but also reduce the crystal size, which lead to low crystallization. OH-could increase the nucleation rates as strong mineralizer, while too high alkalinity may increase the solution of zeolite, so it is necessary to find a proper OH-/Si molar ratio when synthesize low SiO2/Al2O3ZSM-5.(2)In template-free system, seeds do little effect to synthesis when the amount between2g～4g. Alkali metal cation could accelerate the crystal rate. NaCl will not reduce the crystallinity, it is different from N-butylamine template system.(3)We can hardly obtain low SiO2/Al2O3ZSM-5in agitation. The product will crystallize entirely and quickly, and also has low crystallinity.