Kinetic studies on the formation of zeolite ZSM-5

Abstract

Zeolite ZSM-5 was synthesized from sodium tetrapropylammonium aluminosilicate gels and tetrapropylammonium silicate gel. Effects of varying the ratio SiO₂/Al₂O₃ and alkalinity in the starting gels and the reaction temperature were studied. The alkalinity was found to affect the rate of nucleation more than the rate of crystal growth. An optimum alkalinity exists in the synthesis of ZSM-5; the optimum value is closely related to the value of SiO₂/Al₂O₃ ratio in the batch composition. The apparent activation energies for nucleation and crystal growth are 38 and 46 kJ mol^–1, respectively, for the aluminium-free silicate system and 25 and 29 kJ mol^–1, respectively, for the aluminosilicate system with SiO₂/Al₂O₃= 70. The results are consistent with a complicated solution mechanism of crystallization.