Oxidative cleavage of lignin aromatics during chlorine bleaching of kraft pulp

Methanol liberation and methoxyl loss during chlorine bleaching of softwood kraft pulp were quantitatively investigated to estimate the degree of structural modification of lignin aromatics. An increase in the chlorine multiple led to enhanced methoxyl loss from lignin. Our result, using pH-adjusted...

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Bibliographic Details
Published in:Journal of wood science 2001-10, Vol.47 (5), p.362-367
Main Authors: Koda, K. (Hokkaido Univ., Sapporo (Japan)), Goto, H, Shintani, H, Matsumoto, Y, Meshitsuka, G
Format: Article
Language:English
Subjects:
Applied sciences
Aromatic compounds
BLEACHING
Catalysis
CHEMICAL PULP
Chlorination
Chlorine
Cleavage
Exact sciences and technology
Infrared radiation
Kraft pulp
Lignin
LIGNINS
METHANOL
OXIDATION
Paper, paperboard, non wovens
Polymer industry, paints, wood
Pulp manufacturing
Wood. Paper. Non wovens
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Summary:Methanol liberation and methoxyl loss during chlorine bleaching of softwood kraft pulp were quantitatively investigated to estimate the degree of structural modification of lignin aromatics. An increase in the chlorine multiple led to enhanced methoxyl loss from lignin. Our result, using pH-adjusted chlorine water (pH 5.7), by which chlorination under oxidation-favorable conditions was achieved, strongly supported the importance of the oxidation reaction by chlorine during delignification and lignin degradation. It was also suggested that methanol can be produced not only via catalytic hydrolysis by chlorine but via oxidative cleavage of the ether bond as well. The infrared spectrum of chlorolignins suggested that chlorine oxidation can open aromatic rings to muconic acid derivatives without cleaving ether bonding of the methoxyl group. No straight relation between the methoxyl content and the kappa number of chlorinated pulps was shown. The methoxyl content of bleached kraft pulps subjected to successive chlorination and alkali extraction showed a good relation with the kappa number. This means that almost all the portions of the oxidatively modified lignin structure were successfully removed during these treatments, and the aromatic structures of residual lignin in chlorinated and alkali-extracted pulps were thought to remain intact.
ISSN:1435-0211
1611-4663
DOI:10.1007/BF00766786