Reducing bio-oil oxygen content via in-situ deoxygenation and hydrogen production

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Date
2020
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University of New Brunswick
Abstract
Crude bio-oil produced through biomass thermal decomposition processes such as pyrolysis needs to be upgraded via hydroprocessing to remove oxygen. This requires hydrogen gas which is problematic as it represents an additional cost and sustainability issues as most hydrogen is produced from non-renewable sources. Therefore, hydrogen requirements need to be reduced. The options for reducing hydrogen requirements that have been explored include increasing hydrogen efficiency via selective deoxygenation, using water-gas-shift reaction (WGSR) to regenerate hydrogen, and reducing oxygen content during the biomass decomposition. To initially demonstrate biomass thermal decomposition with in-situ deoxygenation, glucose was decomposed in the presence of monometallic and bimetallic catalysts on SiO2 with small amounts of hydrogen gas at 350°C for 1-hour. As glucose decomposed, intermediates/products underwent deoxygenation. The catalysts that were dominant in furanic compound deoxygenation selectivity were 4%Co/SiO2, 0.5%Ni4%Fe/SiO2, and 0.5%Co4%Fe/SiO2. Catalysts were shown to influence glucose decomposition. Catalysts with exposed Ni helped reduce solid residue. NiFe catalysts supported on ceria-zirconia were developed for the purpose of performing both WGSR and deoxygenation. These catalysts were used to deoxygenate guaiacol in the presence of CO and H2O instead of H2 at 350°C. Nano-casting ceria-zirconia on MCM-41 produced an active support good for oxygen storage with comparatively high surface area (to other ceria-zirconia catalysts), CZ-41. Sequentially prepared 2%Ni4%Fe/CZ-41 was capable of producing H2 internally and using it to convert guaiacol to products such as phenol. Adding 0.5 wt% Co to the Fe phase improved hydrogen production. The aforementioned CZ-41 catalysts were used for the decomposition of glucose with internal hydrogen production and deoxygenation without the addition of H2. The trimetallic NiCoFe/CZ-41 catalyst provided superior yields of liquid product. The addition of Co to Fe as an alloy improves reducibility of Fe and improves metal-support interactions. Future work should focus on reactor design without the use of a solvent and mild reforming to improve H2 generation all along with continued catalyst development.
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