Influence of ZSM-5 Crystal Size on Methanol-to-Olefin (MTO) vs. Ethanol-to-Aromatics (ETA) Conversion

Abstract

Crystal size is a key parameter of zeolites applied as catalysts. Herein, ZSM-5 crystals with similar physicochemical and acid properties, few defects, and aluminum exclusively in tetrahedral coordination are synthesized and the influence of the crystal size on the MTO and ETA conversion is investigated. Short olefins are the main products of the MTO conversion, whereas larger olefins and aromatics dominate the products after ETA conversion. In the case of both feeds, an increased crystal size decreases the catalyst’s lifetime. The MTO conversion over larger ZSM-5 altered the product distribution, which was not the case for the ETA conversion. The reason is that the instantly available aromatics during ETA conversion lead to fast coking and zeolite crystals only active in the outer layers. Thus, the different reactivity of different-sized ZSM-5 is direct proof of a different conversion mechanism for both alcohols.

Perspectives on Recent Advances in Hierarchical Zeolites for Bioethanol Conversion to Chemicals, Jet Fuels, and Carbon Nanotubes

“…130 Apart from the zeolite framework perspective, the influence of the crystal size of zeolite was also studied. Dittmann and co-workers 131 investigated the influence of HZSM-5 crystal size (2 and 60 μm) on the catalytic performance and deactivation behavior. The smaller HZSM-5 crystals exhibit a longer lifetime, showing no deactivation within 25 h. In contrast, larger HZSM-5 crystals experience rapid deactivation within the first few hours despite similar BTX selectivity (20%).…”