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Catalytic pyrolysis of crude glycerol over shaped ZSM-5/bentonite catalysts for bio-BTX synthesis

He, S., Muizebelt, I., Heeres, A., Schenk, N. J., Blees, R. & Heeres, H. J., 5-Nov-2018, In : Applied Catalysis B: Environmental. 235, p. 45-55 11 p.

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Ex-situ catalytic pyrolysis of crude glycerol for the synthesis of bio-based benzene, toluene and xylenes (bio-BTX) was performed in a tandem micro-reactor (TMR), a batch gram scale reactor and a continuous integrated bench scale unit using ZSM-5/bentonite extrudates. A bio-BTX yield of 8.1 wt.% (14.6% carbon yield) based on crude glycerol was obtained over the fresh catalysts (Cat-F) in the bench scale unit (crude glycerol feed rate of 200 g h−1, pyrolysis temperature of 520 °C and catalytic upgrading temperature of 536 °C). Catalyst activity was shown to be a function of the time on stream (TOS) and after 4.7 h the activity dropped with about 8%. After an oxidative regeneration step to remove coke, the activity of the regenerated catalysts (Cat-R1) was recovered to 95% of the original catalyst activity. After 11 reaction-regeneration cycles, the bio-BTX yield decreased to 5.4 wt.% (9.7% carbon yield) over Cat-R11. The fresh, deactivated and regenerated ZSM-5/bentonite catalysts were characterized in detail using nitrogen physisorption, XRD, ICP-AES, EA, TEM-EDX, TGA, NH3-TPD, pyridine-IR and solid MAS NMR. Coke (10.5 wt.% over Cat-D) was mostly deposited on ZSM-5 planes, and not only decreased the number of Lewis and Brönsted acid sites, but also blocked the pores, resulting in catalyst deactivation. Coke removal was effectively performed using an oxidative treatment. However, exchange of cations (e.g., Na) of the bentonite and possibly also from the crude glycerol feed with protons of ZSM-5 was observed, leading to irreversible deactivation. Furthermore, the layered structure of bentonite collapsed due to the removal of interlamellar water and dehydroxylation.

Original languageEnglish
Pages (from-to)45-55
Number of pages11
JournalApplied Catalysis B: Environmental
Volume235
Publication statusPublished - 5-Nov-2018

    Keywords

  • Bentonite, Bio-aromatics, Glycerol, Pyrolysis, ZSM-5, HZSM-5 ZEOLITES, CONVERSION, H-ZSM-5, BENTONITE, NMR, SI-29, AROMATIZATION, SPECTROSCOPY, KINETICS, METHANOL

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