SYNTHESIS OF HIGH SILICA ZEOLITE-Y

Zeolite Y with SiO2/Al2O3 molar ratios = 5.5 approximately 6.0, were synthesized from the reaction mixtures whose molar ratio were (2.541-2.943)Na2O-Al2O3-(9.81-13)SiO2-(104.2-120.4)H2O, using colloidal silica, silica sol and sodium aluminate solution. The changes in chemical composition of solid and liquid phases on the course of zeolitization were analyzed by XRD, MASNMR, SEM observation, and chemical analyses. After the ageing at 25-degrees-C for 24 h, only a small amount of silica reacted with sodium aluminate solution, and the concentration of silica in liquid phase was very low. After the heating at 99.5-degrees-C for 1 h, Si-29-MASNMR signals shifted to lower fields, and the concentration of silica species increased up to 1.2 approximately 1.6 mol/dm3, though the concentration of aluminate ions decreased to 0.01 approximately 0.02 mol/dm3. During the induction period, the concentrations in liquid compositions were kept at nearly constant. With decreasing Na2O/SiO2 molar ratio of reaction mixture, Na+/SiO2 ratio in liquid phase decreased. When the value of Na+/SiO2 in liquid phase decreased to 0.84 or less during the crystallization, spherulites of chabazite and gmelinite appeared. The changes of Si-29-MASNMR signals seemingly showed the solid-solid transformation mechanism on the formation of zeolite Y. However, the XRD and chemical analyses of solid phases proved the formation of zeolite Y with SiO2/Al2O3 = 5.985, from amorphous solid with SiO2/Al2O3 = 7.0-7.2. These results show the liquid-solid transformation mechanism on the formation of zeolite Y.