June 16-21, 2019
Fast pyrolysis is an advanced thermochemical conversion technology developed to produce bio-oil from biomass. With lignocellulosic biomass, high product yields (65-75 wt.%) can be attained. Yet, certain unfavorable characteristics of bio-oil impede its utilization prospects. High water content, high oxygen content, together with instability and acidity are the recognized adverse features of bio-oil. Tackling these issues is possible by reducing the oxygen content and/or steering the oxygen functionality of bio-oils.
Electrochemical hydrogenation (ECH) is a recently proposed approach targeting the reduction of the reactive compounds in bio-oil (aldehydes, ketones etc.) to their corresponding alcohols, diols . In this attractive approach, the water present in bio-oil acts as the hydrogen source for reduction reactions. Production of alcohols/diols leads to an upgraded/stabilized bio-oil product. Performing the upgrading at ambient temperature, pressure and providing a means to store intermittently available renewable energy (e.g. solar, wind) are clear advantages of the ECH process.
In this work, we have investigated electrochemical upgrading of bio-oil using water soluble bio-oil (WSBO) as feed. The ECH experiments, carried out in an electrochemical reactor at a current density of 44 mA cm-2, focused on comparison of several cathode materials. Separated by a cation exchange membrane, cathode and anode chambers of the reactor were filled with WSBO (ca. 20 wt.% bio-oil in aqueous solution) and 1M H2SO4, respectively. The tested cathode materials included Ti, Ru-coated Ti (Ru), Pt-coated Ti (Pt), stainless steel (SS) and CuZn (brass) electrodes. All electrodes converted the carbonyl groups present in bio-oil to a certain extent following the order CuZn>>SS>Ti>Pt>Ru. The trend is explained in close relation with the hydrogen evolution reaction, the preferred pathway especially with Pt and Ru electrodes. Despite the high conversions achieved for some compounds, the selectivity towards desired alcohols and diols was not very high (e.g. 15 – 49% ethylene glycol selectivity for glycolaldehyde conversion) for the electrodes tested in this study. Low Faradaic efficiencies obtained are considered as another challenge keeping the conversion costs high.
Nevertheless, electrochemical hydrogenation appears to be a promising technology to upgrade/stabilize bio-oil that deserves further investigation. Next to the experimental results obtained, possible future improvements in catalytic cathode selection and processing options will be discussed as well.
 Z. Li, S. Kelkar, L. Raycraft, M. Garedew, J.E. Jackson, D.J. Miller, C.M. Saffron, Green Chem., 2014, 16, 844.
Mehmet Pala, Kun Guo, Wolter Prins, Frederik Ronsse, Korneel Rabaey, and Antonin Prévoteau, "Electrochemical upgrading of bio-oil: A proof-of-principle investigation" in "Pyroliq 2019: Pyrolysis and Liquefaction of Biomass and Wastes", Franco Berruti, ICFAR, Western University, Canada Anthony Dufour, CNRS Nancy, France Wolter Prins, University of Ghent, Belgium Manuel Garcia-Pérez, Washington State University, USA Eds, ECI Symposium Series, (2019). https://dc.engconfintl.org/pyroliq_2019/21