T. Kishimoto, A. Ueki, Y. Sano
Delignification Mechanism during High-Boiling Solvent Pulping Part 3. Structural Changes in Lignin Analyzed by 13C-NMR Spectroscopy
Summary
Milled wood lignin as well as wood meal from todo fir (Abies sachalinensis MAST) was treated
with 70% aqueous 1,4-butanediol solution at 220°C without acid catalyst in order to elucidate the
delignification mechanism during high-boiling solvent (HBS) pulping. HBS lignin was recovered
from black liquor by precipitation, and was subjected to gel permeation chromatography and
quantitative 13C-NMR study. The average molecular weight of MWL decreased. The content of
phenolic hydroxyl groups in MWL increased from 0.28 to 0.68/OMe. The decrease in the content
of ?-O-4 substructures was evident, which may be attributed to the homolytic cleavage of phenolic
?-aryl ethers. The changes in the content of ?-5 and ?-? substructures were rather small. The benzyl
ether formation of ?-O-4 structures with 1,4-butanediol was also confirmed by 13C-NMR. However,
the signals corresponding to Hibbert's ketones were not observed, which suggests that acidolysis
was not an important degradation pathway during HBS pulping.
Holzforschung, Walter de Gruyter
Print ISSN: 0018-3830
Volume: 57, 10/2003
Pages: 602 - 610
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