Hydrothermal crystallization of zeolite beta using tetraethylammonium bromide

The synthesis of zeolite beta was systematically studied with tetraethylammonium bromide (TEA-Br) as an organic template and silica sol as the source of silica under the static and the stirred conditions in the temperature range of 373–443 K. The effect of the SiO2Al2O3 ratio, alkalinity, gel dilution, amount of the seed crystals and alkali metal, nature of the organic template, and time and temperature of the synthesis was investigated. The influence of these parameters on crystallization kinetics and crystal morphology of zeolite beta was characterized using XRD, SEM, d.t.a./t.g., framework i.r. techniques, and sorption of different probe molecules. The optimized gel composition was found to be within the range SiO2Al2O3 = 15–58, H2OSiO2 = 18–25, TEA+SiO2 = 0.25–0.50, Na2OSiO2 = 0.08–0.12, and OH−SiO2 = 0.7–1.05. In some cases, seed crystals of zeolite beta were used up to 0.3 wt% of the estimated yield of the solid product. The crystallization time varied from 2 to 13 d. The apparent activation energies for the process of the crystallization and nucleation were evaluated to be Ec = 45.54 kJ/mol and En = 54.25 kJ/mol. Almost 100% synthesis efficiency (based on the input moles of SiO2 and Al2O3 in the gel) was achieved during synthesis. The unreacted template in the mother liquor was used further by recycling. The cylindrical crystallites varied in size from 0.4 to 1.0 μm with variation in the synthesis parameters. The decrease in the product SiO2Al2O3 ratio from 57 to 19 and a corresponding decrease in the crystallite size was found to be consistent with the increase in the water-sorption capacity. These results suggest the use of TEA-Br as an organic template for the manufacture of zeolite beta to be commercially economical. The increase in the gel SiO2Al2O3 ratio and synthesis temperature led to the cocrystallization or the crystallization of pure ZSM-12.