Crystallization and metastable phase transformations of zeolite ZSM-5 in the (TPA)2O$z.sbnd;Na2O$z.sbnd;K2O$z.sbnd;Al2O3$z.sbnd;SiO2$z.sbnd;H2O system

Abstract Zeolite ZSM-5 was synthesized as the only crystalline phase from Na-TPA, and for the first time from the K-TPA, and Na,K-TPA mixed cation systems. As the organic cation/ alkali metal cation ratio was decreased in the reaction mixture, metastable phases were found to coexist with ZSM-5. These were an “analcime-like” phase, and a “mordenite” phase in the Na-TPA system, and a “harmotome-like” phase in the K-TPA system. An isothermal metastable phase transformation diagram was developed for the Na-TPA system. A “gismondine-like” phase was added to the metastable phases coexisting with ZSM-5 and the crystallization sequence, mordenite, ZSM-5, analcime was found to change to gismondine, mordenite, ZSM-5, analcime with the addition of alkali metal salts to the reaction mixture. The “apparent activation energies” obtained for ZSM-5 were 25.57 and 19.41 kcal/gmole for nucleation and crystallization, respectively. The synthesis system could be modified as a result of the cation replacements and the exploratory runs with salt additions, to result in pronounced changes in the morphology, i.e., either to yield larger single crystals or crystal aggregates, desired for the commercial applications.