Pyrolytic lignin

the water-insoluble fraction in bio-oil

often shows a high content and has strong intermolecular interactions with other compounds in bio-oil. In order to obtain pure pyrolytic lignin and facilitate the utilization of aqueous phase obtained fromwater extraction of bio-oil

methanol-water extraction method was employed to further separate the bio-oil water-insoluble phase in this paper. Different technologies

including Fourier transform infrared spectroscopy

gel permeation chromatography

and nuclear magnetic resonance

were adopted to characterize the structures of pyrolytic lignins with different activities obtained through this method. Both the heating value and the polymerization degree of high-molecular-weight pyrolytic lignin were higher than those of low-molecular-weight pyrolytic lignin. The molecularweight distribution of high-molecular-weight pyrolytic ligninwas relatively wider

among which the contents of dimers to pentamers all accounted for 12%-18%

while the low-molecular-weight pyrolytic lignin mainly consisted of trimers (75.38%). The pyrolytic lignins had similar basic structures

both ofwhich contained syringyl and guaiacyl units

whereas the low-molecular-weight pyrolytic lignin had more abundant syringyl units

reactive carbonyl groups and hydroxyl groups. Meanwhile

thermogravimetric study revealed that the final char residue yield of low-molecular-weight pyrolytic lignin was lower than that of high-molecular-weight pyrolytic lignin.