Roles of furfural during the thermal treatment of bio-oil at low temperatures

The reactive O-containing species in bio-oil could induce the polymerization of bio-oil during its thermal treatment, which affects the relevant utilization of bio-oil significantly. Furans, as the highly reactive O-containing species in bio-oil, play important roles during the thermal treatment of bio-oil. In this study, furfural was chosen as the representative of the furans in bio-oil to investigate its roles during the thermal treatment of bio-oil. The raw bio-oil with and without the addition of extra furfural (10 wt% of bio-oil) and pure furfural were pyrolyzed in a fixed-bed reactor at 200–500°C. The results show that the interactions among furfural and bio-oil components can take place prior to the evaporation of furfural (< 140°C) to form the intermediates, then these intermediates could be further polymerized to form large molecular compounds, and coke can be formed via the interactions at temperatures ≥ 300°C. At temperatures ≤ 300°C, furfural mainly interacts with anhydrosugars. As the temperature further increases, the aromatics are involved in the interactions to form coke. The increased percentage of the coke formed via the interactions is in a linear relation with the conversion of furfural during the pyrolysis at 300–500°C (no coke formed at 200°C). Meanwhile, more non-aromatic light components (≤ C6) and less aromatics in the tars could be formed due to the interactions.