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Catalytic fast pyrolysis of biomass: superior selectivity of hierarchical zeolite to aromatics


The catalytic fast pyrolysis of oak over two zeolites (microporous and hierarchical) was investigated in a microfluidized bed reactor (MFBR) at 500 °C and as a function of biomass-to-catalyst ratio. A hierarchical zeolite was produced by desilication with NaOH solution of a conventional HZSM-5 zeolite. The outlet of the MFBR was connected to a single photoionization mass spectrometer (SPI-MS) for on-line analysis of volatiles. The formation of products was assessed on-line by SPI-MS during stepwise injections of wood particles within the MFBR. Heavy compounds present in bio-oils were analyzed by laser desorption ionization (LDI) combined with high resolution mass spectrometry. Strikingly the selectivity in targeted mono-aromatic compounds (quantified by gas chromatography) is doubled after desilication of the zeolite. The coked zeolites were characterized by TEM-EDX, digestion in fluoric acid, MALDI-TOFMS, etc. Three different types of coke are evidenced: (1) coke trapped inside micropores, (2) external coke formed on the outer surface of the crystals and (3) coke precursors deposited in the mesoporous. The latter two cokes are much less toxic than the micropores coke. The open mesopores produced after desilication can be seen as “highways” where big molecules (such as levoglucosan) can diffuse to more accessible pore mouths. Brønsted acid sites present on micropores mouths can be active for the conversion of bigger molecules to small fragments. These fragments diffuse and form aromatics in the micropores (shape selectivity). The mesopores also promote the evacuation of catalytic products thus enhancing the selectivity in mono-aromatic hydrocarbons. Desilicated zeolite presents much higher selectivity to mono-aromatics and stability upon coke deposit than microporous zeolite.

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Publication details

The article was received on 31 Jul 2017, accepted on 04 Sep 2017 and first published on 04 Sep 2017

Article type: Paper
DOI: 10.1039/C7GC02309J
Citation: Green Chem., 2017, Accepted Manuscript
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    Catalytic fast pyrolysis of biomass: superior selectivity of hierarchical zeolite to aromatics

    L. Jia, M. Raad, S. Hamieh, J. Toufaily, T. Hamieh, M. Bettahar, G. mauviel, M. Tarrighi, L. Pinard and A. Dufour, Green Chem., 2017, Accepted Manuscript , DOI: 10.1039/C7GC02309J

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