Structure properties of pyrolytic lignin extracted from aged bio-oil

Fast pyrolysis is a promising technology that can convert biomass into liquid. Bio-oil is one such product, known not only as a greenhouse gas-neutral energy source, but also an opportunity to reduce reliance on fossil fuels. Pyrolytic lignin, a fine homogeneous powder, is the water-insoluble fraction of bio-oil and it contributes to the instability of bio-oil. Additionally, pyrolytic lignin can be used in commercial materials such as adhesives in the wood-based panel industry. This paper presents the structural characterization of pyrolytic lignin extracted from aged bio-oil and the relationship between its properties and the treatment temperature of the aged bio-oil. Pyrolytic lignin samples were characterized by Fourier transform infrared spectroscopy, gel permeation chromatography, differential scanning calorimetry, thermogravimetric analysis and proton nuclear magnetic resonance spectroscopy. The average molecular weight of pyrolytic lignin increased from 700 to 1000 g/mol with increasing aging temperature (6–50°C). Differential scanning calorimetry showed that the glass transition temperature of pyrolytic lignin increases with lower heating rate and higher treatment temperature of bio-oil. An increase in the initial decomposition temperature and the temperature at 95 wt% weight loss of the aged pyrolytic lignin in thermogravimetry were observed for the bio-oil aged at higher temperature. An increase in residue weight of aged pyrolytic lignin was found in bio-oil aged at higher temperatures.