Conversion of Oxygenates on H-ZSM-5 Zeolites—Effects of Feed Structure and Si/Al Ratio on the Product Quality

Abstract

The conversion of different biogenic feedstocks to hydrocarbons is a major challenge when ensuring hydrocarbon and fuel supply in spite of the heterogeneity of this feed. Flexible adaptation to changing compositions is mandatory for the respective processes. In this study, different oxygenate model feeds, such as alcohols, aldehydes, carboxylic acids and esters, were converted at 500 °C and 5 barg H2 using H-ZSM-5 zeolite catalysts with various Si/Al ratios to identify the relationship between the feed structure and the final product distribution. As the main outcome, the product distribution becomes increasingly independent of the feed structure for Al-rich H-ZSM-5 catalyst samples at low Time on Stream (ToS). Some minor exceptions are the increased formation of aromatics during ToS for carbonyl oxygenates compared to primary alcohols and the dominance of initial deoxygenation products for Si-rich H-ZSM-5 samples. This is interpreted by a multi-stage reaction sequence, which involves the initial deoxygenation of the feed and the subsequent integration of the olefin intermediates into a reaction network. The results pave the way towards the achievement of a desired product distribution in the conversion of different oxygenates simply by the adaption of the Al content of H-ZSM-5.

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“…4 , the char/coke yield decreased from 500 °C to 700 °C as the temperature increased, which is an expected trend. However, by increasing the feed-to-catalyst ratio, the char/coke yield increased, which can be attributed to the formation of coke precursors like PAHs that form at high rates when the pores are large with high acid site density [53] .…”