Combining solid state grinding and steam-assisted crystallization for green organotemplate-free synthesis of ZSM-5

Abstract

Green synthesis of zeolite has been made much progress due to solvent-free grinding methods. Although solid-state synthesis is a simple green process with a high yield, its kinetics of the solid-phase crystallization process is still slow and the precursor materials are not uniformly heated throughout the reactor resulting into the poor uniformity of the particles. Herein, we report a high-efficiency organotemplate-free synthesis of ZSM-5 combining solid state grinding and steam-assisted crystallization. Solid state grinding (SSG) of aluminosilicate precursor avoids usage of solvent and steam-assisted conversion (SAC) in an organic-template-free condition grants a fast crystallization rate of ZSM-5. More importantly, the vapor fulfilled in the reactor ensures uniform heating of solid feedstock for crystallization of ZSM-5, leading the high crystallinity and the uniform particle size distribution. This combination can guarantee 100% relative crystallinity of ZSM-5 in 12 h, compared to that of 80% crystallinity from sole solid state at the same crystallization temperature (180 °C). Furthermore, this combination can achieve 83% relative crystallinity of ZSM-5 at 160 °C, compared to that of 37% crystallinity from the solid state alone. Highly dispersed ZSM-5 zeolite with adjustable SiO2/Al2O3 ratio is prepared by steam-assisted crystallization of grinding solid raw materials. The catalytic activity of ZSM-5 catalyst from this combination strategy for the acetalization of cyclohexanone is superior to that of the solid-state method alone. This sustainable and green synthesis method provides a potential way for the preparation of zeolites in an industrial scale.