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Valorization of lignin pyralysis vapors by iron-catalysed direct hydrodeoxygenation

Abstract : Lignin is a promising feedstock for the production of bio-based aromatic hydrocarbons (benzene, toluene, xylenes BTX) and/or phenols. In this work, the catalytic hydrotreatment of lignin pyrolysis vapours was studied. Lignin pyrolysis vapors are a complex mixture of unstable oxygenated molecules. Our goal was to hydrogenate selectively the Caromatic-O bond lignin vapours, before their condensation, to produce higher yield of useful molecules (BTX, phenol). The conversion of a model molecule (guaiacol) was studied (350-450°C, 1 atm, 90%mol. H2). Commercial Cobalt-based catalyst was not selective and converted guaiacol into CH4. Inexpensive Fe-silica catalyst was active and selective for the conversion of guaiacol into benzene and toluene. H2 molar fraction showed no effect on the 20-90%mol. range. The effect of H2O, CO, CO2 and CH4 on guaiacol conversion with Fe-silica catalyst was studied separately. These gases are also present in lignin pyrolysis vapors. H2O inhibits Car-O bond hydrogenolysis. CO increases deactivation. CH4 has no effect and CO2 decreases deactivation. Under a mixture of gases that mimics lignin pyrolysis vapors with H2, Fe-silica is still active and very selective for the production of Benzene and Toluene (66% carbon yield). Fe-Activated carbon is selective for the production of phenol and cresol that are also useful chemicals. Real lignin pyrolysis vapors were generated with a discontinuous pyrolysis reactor. Products were mixed with H2 and directly introduced into a catalytic fixed bed reactor. The enhancement of oil quality was remarkable both for Fe-silica or Fe-Activated Carbon catalyst. A kinetic model for the conversion of guaiacol in model pyrolysis vapor with Fe-silica catalyst was developed. The resulting kinetics was implemented in an Aspen plus model that handles the entire lignin to BTX process including pyrolysis, catalytic reactor, heat exchanger and products recovery. The benzene + toluene (BT) carbon yield is 7.5% based on lignin. Char and lignin oligomers yields of existing lignin pyrolysis technology are too high and reduce carbon yield in BT
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Roberto Nicolas Olcese. Valorization of lignin pyralysis vapors by iron-catalysed direct hydrodeoxygenation. Food and Nutrition. Université de Lorraine, 2012. English. ⟨NNT : 2012LORR0107⟩. ⟨tel-01751014⟩



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