Sustainable production of liquid biofuels and value-added platform chemicals by hydrodeoxygenation of lignocellulosic bio-oil over a carbon–neutral Mo2C/CNF catalyst

Abstract

For the first time, this work addresses the hydrodeoxygenation (HDO) of lignocellulosic bio-oil over a carbon–neutral Mo2C/CNF catalyst for the production of liquid biofuels and value-added chemicals, thoroughly examining the effect of the temperature, initial H2 pressure, reaction time and catalyst/bio-oil ratio. These variables had a significant influence on the process, allowing the transformation of the original bio-oil into different fractions in varying yields, including an upgraded bio-oil (17–72%), a solid product (4–44%), an aqueous phase (5–39%) and a gaseous stream (1–15%). The upgraded bio-oil comprised a mix of phenols (56–78%), cyclic ketones (7–30%), carboxylic acids (2–8%), esters (0–9%) and aromatic compounds (0–20%). The relative amounts of C, H and O of this product shifted by 34–78 wt%, 3–8 wt% and 13–62 wt%, while its HHV ranged between 9 and 35 MJ/kg. Process optimisation revealed that using a temperature of 350 °C, an initial H2 pressure of 40 bar and 0.19 g cat/g bio-oil for 1 h, it was possible to convert 65% of the organic content of the bio-oil into a liquid bio-fuel with a HHV of 30 MJ/kg (twice the value of the original feedstock), which represents a deoxygenation degree of 70% and an energy efficiency of 62%. Besides, all the bio-oil organic content can be converted into a liquid product with a high proportion of phenols (79%) at 250 °C, applying an initial H2 pressure of 20 bar and 0.14 g cat/g bio-oil for around 0.5 h. This liquid can be used as a sustainable phenolic-rich antioxidant additive as well as a bio-based source of aromatic compounds. Therefore, these results are a step forward in the biomass conversion over carbon–neutral catalysts.