Template-Free ZSM-5 Synthesis Using Bio-Sourced Waste Materials

Abstract

Hydrochars synthesized from lignocellulosic waste (rice husk and exhausted black wattle bark) through hydrothermal carbonization were used as pore-forming agents in template-free ZSM-5 zeolites. The influence of the amount of hydrochar added to the zeolite synthesis and the nature of the hydrochar on the zeolite features and catalytic performance were evaluated. It was observed that the hydrochar had little influence on the textural properties and Si/Al ratio of the zeolites. However, the hydrochar was able to enhance the number of Brønsted acid sites in the zeolite and led to different ZSM-5 crystal morphologies (french-fries and twinned crystals). The latter zeolites exhibited a higher cracking activity of n-hexane, favoring the formation of light olefins, due to the presence of Brønsted sites and suitable shape selectivity. In contrast, they exhibited a lower conversion of methanol into hydrocarbons (MTH), favoring the formation of dimethylether due to rapid deactivation. The hydrochars acted therefore, in the synthesis of template-free ZSM-5 zeolite, as a mean to both raise the acidity and control the aggregation of zeolite crystals.