Fast pyrolysis of Kraft lignins fractionated by ultrafiltration

The pyrolysis behavior of different lignin samples fractionated by ultrafiltration membrane technology was investigated by pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). Results indicated that the predominant products derived from pyrolysis of lignin fractions with different molecular weights changed in the relative content, but not in the compound species. At 500 °C, high molecular weight lignin favored the generation of guaiacol-type compounds (57.33%), and low molecular weight lignin produced more syringol-type compounds (34.33%). As temperature increased to 650 °C, methoxy groups in S and G units were easier to cleave from the benzene ring of the high molecular weight lignin leading to an increase in the relative content of phenol-type compounds. High molecular weight lignin was found to produce the highest amounts of phenol-type compounds (46.22%) and aromatic hydrocarbons (17.25%) at 800 °C, while low molecular weight lignin favored the generation of guaiacol-type and syingol-type compounds. The reveal of relevance between specific lignin fractions and pyrolysis behaviour is meaningful for the efficient transformation of lignin to specific aromatic compounds.