MFI ZEOLITE CRYSTALLIZATION UNDER CONTROLLED DOSAGE OF TPA TEMPLATE

Synthetic conditions of MFI zeolite with SiO2/Al2O3 = 25 have been inv estigated with the intention of obtaining pure crystals with high cata lytic activity and stability for the vapor-phase isomerization of dime thylnaphthalenes (DMN). The dose ratio of the template tetra-n-propyla mmonium cation, TPA, to alumina, TPA/Al2O3, was varied from nil to the conventional dosage level for the manufacture of MFI zeolite. The sur prisingly low dose ratio of TPA/Al2O3 = 0.2 was found sufficient for t he primary object and was named ''TPA-Type'' MFI. This MFI had crystal lite size of 0.05-0.2 mu m that formed cauliflower-like coagulated bal ls (1-5 mu m) that were connected by the second-order assembly. As com pared with the conventional ''TPA-MFI'' and ''TPA-free'' MFI zeolites, ''TPA-Type'' MFI had several merits. It showed superior activity in t he DMN isomerization, presumably due to the lower SiO2/Al2O3 ratio at which the present method showed a distinctive effect. Other merits of this ''TPA-Type'' MFI were easy filtration, less laborious waste-water treatment, and reduced exotherm in the calcination process of organic template for ion-exchange operation.