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 degrees 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 degrees 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 degrees 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.