A Study On The Modification Of Zeolite Y

Zeolite Y is the mainly active component of fluid catalytic cracking (FCC) and hydrocracking catalysts and its framework SiO2/Al2O3 molar ratio, extra-framework Na+ cations content and textural properties are critical factors which may strong affect the catalytic activity of Y zeolites. On the basis of the previous investigations towards these three aspects, the present paper concentrated mainly on the following two parts. On one hand, improving a method which can raise the SiO2/Al2O3 molar ratio of the zeolite framework and decrease the Na+ cations content through a greener and lower-energy process; on the other hand, optimization of the textural properties of Y zeolite by means of introducing mesopores into zeolite Y on the premise that the microporous structures of zeolites keep integrity. The details of the dissertation include:Part 1, a new method was developed to increase the framework SiO2/Al2O3 molar ratio of zeolite Y. Organic carboxylic acids with low boiling point, such as formic acid and acetic acid were used as chelating agent which can coordinate with the aluminum species in zeolites in their steam phase at high temperature. For NaY and HY zeolite with low framework SiO2/Al2O3 molar ratios, the steam of carboxylic acids can easily remove the framework aluminum ions, resulting in increase of both the framework SiO2/Al2O3 molar ratios and the mesopore surface areas. While as for USY-3 with high framework SiO2/Al2O3 molar ratio, the steam of organic carboxylic acids can only react with the extra-framework aluminum species (EFAls) occluded in the pores therefore improve the micropore accessibility. Besides, for NaY zeolite, after steam treatment, the dealuminated sample can be ion-exchanged directly with inorganic acid solution, aiming to remove the sodium ions. By combining the two procedures, the framework SiO2/Al2O3 of the zeolite Y can be increased to 14.5 and the content of sodium ions can be reduced to 0.8%, with 64% of relative crystalinity preserved. The whole process is green and environment friendly because firstly the unused organic acids can be recycled after steam treatment, and secondly the emission of ammonium-containing waste water can be avoided in the ion-exchange process.Part 2, mesopores are introduced into USY-3/USY-6 and HY zeolites with high and low silica to alumina molar ratio, respectively in the presence of surfactant CTAB in the alkaline solutions. For USY-3 and USY-6 zeolite, the zeolite microporous structures were seriously damaged after the formation of mesopores. While for the HY zeolite treated in deep-bed method combining with HNO3 acid leaching, the zeolitic structure was well preserved with obvious increase of external surface areas after alkaline treatment in the presence of CTAB. The resultant miro-mesoporous composites also have positive effect on FCC process when used as catalyst.