Hydrodeoxygenation of Bio-Oils (Eugenol, Vanillin, and Syringol)

Lignocellulosic residues such as agricultural wastes and energy crops have been a promising feedstock for production of pyrolysis liquid (bio-oil) for industrial burners recently. However, liquid product from pyrolysis process (400–650°C in an inert environment) containing hundreds of organic compounds is unsuitable for use in the transport industry due to their chemical and thermal instability, high acidity (pH 2–3) and water content (up to 30–40 wt%). The upgrading of biomass-derived oxygenated compounds into valuable chemicals via hydrodeoxygenation has been considering a potential pathway in recent years. The hydrodeoxygenation of pyrolysis liquid (bio-oil) is an intricate chemical involving the removal of oxygen from oxygenated molecules, leading to the generation of water. This transformation takes place as bio-oil molecules react with hydrogen within a range of temperature of 250–450°C and under hydrogen partial pressures of up to 300 bar. The elucidation of the precise reaction mechanism governing bio-oil hydrodeoxygenation (HDO) remains challenging due to the wide array of organic compounds found in bio-oil. To enhance our understanding of this mechanism and mitigate complexity, model compounds are frequently employed. This chapter aims to provide a comprehensive understanding of hydrodeoxygenation processes of three specific compounds in bio-oil: (i) eugenol, (ii) vanillin, and (iii) syringol.