Synthesis Of NaY Zeolite Using Mixed Clay Minerals By In-situ Crystallization And Its Dynamics Research

Diatomite was treated with alkali and structural transformation of the raw diatomite and modified diatomite was studied after heat-treatment at different temperatures. The microporous NaY zeolite has been synthesized via in-situ crystallization using kaolin and diatomite in different proportion. The synthesized samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and N2adsorption-desorption. The effects of feeding ratios on the relative cry stall ization of the products were particularly investigated. The formation mechanism of zeolite NaY was studied by a kinetic model of the system with the mass ratio of kaolin to diatomite6:4. The details are presented as follows.(1) Diatomite was treated with alkali and calcined at different temperatures. The raw diatomite and alkali-modified diatomite were characterized by XRD, Fourier transform infrared spectroscopy (FT-IR) and SEM. The results show that the raw diatomite from changbai area is transformed to cristobalite at1100℃and the alkali-modified diatomite is at950℃. The150℃difference of phase transformation between the raw diatomite and alkali-modified diatomite is possibly related to the presence of impure element such as Na in diatomite.(2) The microporous NaY zeolite has been hydrothermally synthesized by in-situ crystallization using kaolin and diatomite as silica source and metakaolin as aluminum source. The synthesized samples were characterized by XRD, SEM and N2adsorption-desorption. With different m(kaolin):m(diatomite) of6:4and2:8, the effects of different molar ratios of n(SiO2):n(Al2O3), n(Na2O):n(SiO2) and n(H2O):n(Na2O) on relative crystallinity of the NaY zeolite were investigated. The results show that under the condition of m(kaolin):m(diatomite) of6:4the relative crystallinity of NaY zeolite increases at first and then decreases with the molar ratio of n(SiO2):n(Al2O3) and n(Na2O):n(SiO2) increasing. The decline of the molar ratio of n(H2O):n(Na2O) in reaction system are favorable to the formation of NaY zeolite. Under the condition of m(kaolin):m(diatomite) of2:8, the situation for the relative crystallinity of NaY zeolite with increasing the molar ratio of n(SiO2):n(Al2O3) is similar to that under the condition of m(kaolin):m(diatomite) of6:4, and the relative crystallinity of NaY zeolite decreases with increasing the n(Na2O):n(SiO2) and declining the n(H2O):n(Na2O).(3) The optimizing crystallization conditions were obtained by studying the effects of different feeding ratios on the relative crystallization of NaY zeolite products. Under the condition of m(kaolin):m(diatomite) of6:4, the optimizing feeding ratios are n(SiO2):n(Al2O3) of7.0,n(Na2O):n(SiO2) of0.45and n(H2O):n(Na2O) of30, under which the relative crystallinity of the as-synthesized product is54.7%. Under the condition of m(kaolin):m(diatomite) of2:8, the optimizing feeding ratios are n(SiO2):n(Al2O3) of6.5, n(Na2O):n(SiO2) of0.5and n(H2O):n(Na2O) of55, under which the relative crystallinity of the as-synthesized product is56.3%.(4) The changes of solid phase or liquid phase components and the corresponding formation mechanism were investigated at different crystallization times with m(kaolin):m(diatomite) of6:4. In the solid phase, the changes of components were more obvious at the initial stage of crystallization. The SiO2content increases quickly between2and6hours and tends to stop. The content of Al2O3increases in5hours and then becomes stable, while the content of Na2O increases with prolonging the crystallization time. The content of SiO2increases firstly and then decreases, and then becomes stable after10hours in the liquid. The content of Al2O3decreases rapidly at the beginning of the reaction and becomes stable after10hours, which is realated to reaching an equilibrium between the dissolution rate of metakaolin and the formation rate of gel. The content of Na2O increases with prolonging the crystallization time. The changes of solid phase or liquid phase components were more obvious in the initial8hours during the crystallization. This shows that the induction period and nucleation period are the key periods in the initial hours during the whole crystallization. The system of NaY zeolite synthesized by in-situ crystallization using kaolin and diatomite belongs to a spontaneous nucleation system, and the activation energies of nucleation and crystal growth are49.39KJ/mol and33.59KJ/mol, respectively.