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Preparation of ZSM-5 molecular sieve by diatomaceous earth in-situ crystallization

ABSTRACT With diatomaceous earth as raw material and sodium aluminate as aluminum source by adopting TBAB template, ZSM-5 molecular sieve was synthesized by hydrothermal method of in-situ crystallization which shall be reacted in alkali liquor. The influence of silicon-aluminum ratio, pH value, hydro-thermal crystallization temperature, crystallization time and other factors during the synthesis process on crystallized product were systematically observed by combining XRD, SEM and BET. In addition, it was determined that optimized process parameters of hydro-thermal synthesis of molecular sieve were: the usage amount of sodium aluminate was 6% of purified diatomaceous earth; the system pH value was 13.50; crystallization temperature was 170°C and crystallization time was 48 h. Compared with raw material of diatomaceous earth, the shape of ZSM-5 molecular sieve was changed from disk into clustered crystal; the specific surface area was increased from 7.247 m2/g to 199.280 m2/g; and pore volume was increased by nearly twice. The process of composing ZSM-5 molecular sieve with cheap diatomaceous earth as silicon source has great value in application.