Effects of the component interaction on the formation of aromatic structures during the pyrolysis of bio-oil at various temperatures and heating rates

This study focuses on the effects of interactions among bio-oil components on the formation of aromatic structures of bio-oil during its thermal treatment processes at various temperatures and heating rates. A bio-oil sample and its extracted fractions were pyrolyzed in a fixed-bed reactor at 300-800 °C at different temperatures and heating rates. The results show that the pyrolytic products (including the yields and aromatic structures) from raw bio-oil and its extracted fractions are significantly different, which proves the existence of the interactions between the aromatic components and light components of the bio-oil. Additionally, those interactions are determined by the pyrolysis temperature and heating rate to different extents, which further leads to the evolution of aromatic structures during the pyrolysis of bio-oil. For example, owing to the presence of the aromatic-poor fraction, the aromatic compounds (especially ≥ 2 rings) from the pyrolysis of bio-oil are less than that of the aromatic-rich fraction at relatively low temperatures (≤ 500 °C), especially at slow heating rates. This is because the polymerization, as the main interactions, promotes the transformation of more aromatic compounds (over wide range of ring sizes) into coke at these conditions. At fast heating rates, among the complex interactions, the self-gasification of bio-oil is intensified at high temperatures (≥ 700 °C), resulting in lower secondary coke yields and tar yields as well as the concentration of aromatic compounds (especially ≥ 2 rings).