Synthesis Of Microsized And Nanosized NaY Zeolite With High Molar Ratio Of Silica To Alumina

Nanoparticle NaY zeolite can noticeably improve the catalytic cracking selectivity with reduced coking, and increase both diesel yield and the gasoline qulity due to the fact that nanosized Y have high surface areas, fast diffusion characteristics. However, the thermal stability, hydrothermal stability and catalytic activity of NaY zeolite decreased obviously with decreasing the particle size. If the particle size varies within a certain range, the higher the framework SiO2/AI2O3 radio of zeolite, the higher the thermal stability and hydrothermal stability. Therefore, superior properties NaY zeolite can be obtained by increasing the framework SiO2/Al2O3 radio when the particle size is controlled unchanged.Nanosized NaY molecular sieves with high crystallinity were synthesized using commercial raw materials without the presence of additive via hydrothermal method. The influences of aging period of the seed-gel, the temperature and route of gelation, and the alkalinity of the initial gel on the formation of NaY nanoparticles were investigated by XRD, SEM and TEM. The results show that the grain size can be effectively controlled by adding seed-gel of aging 4 days, and the framework SiO2/Al2O3 ratio can be increased by suitable gelation temperature and route. The grain size and framework SiO2/Al2O3 ratio can be decreased by reducing the alkalinity of synthetic system. The nano-NaY products with the average grain size at a range of 82-105 nm and the framework SiO2/Al2O3 ratio at 3.9-4.0 can be synthesized by optimizing the synthesis conditions.The effect of different dispersions on dispersal state of microsized NaY zeolite was investigated. Microsized NaY zeolite undergo aggregation when the sample is dispersed in the solution of electrolyte or surfactant Tween 20. The dispersant of PEG-2000 can prevent nanoparticle from aggregating due to its steric exlution. The result show that high dispersing microsized NaY zeolite can be obtained as combining different kinds of dispersion method.Based on the previous formula, microsized NaY zeolite with high molar ratio of Silica to Alumina was synthesized via secondary synthesis and direct-synthesis separataly, and the effect of synthesis congdition was investigate. Microsized NaY zeolite with 99.0%relative crystallinity and nSiO2/Al2O3=6.5 can be obtained by dealing the sample with (NH4)2SiF6 solution, when dealuminate degree R=40%. The nSiO2/AI2O3 of the sample can raise up to 6.7, when S-2 was selected as Silicon resourse to increase molar ratio of Silica to Alumina of initial gel, and the silicon addition is 30%. Microsized NaY zeolite with Framework SiO2/Al2O3=6.7 and relative crystallinity= 112.8%was obtained by optimizing the synthesis conditions via rational synthetic procedures.