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On the structure of residual lignin in kraft pulping
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
2005 (English)Licentiate thesis, comprehensive summary (Other scientific)
Place, publisher, year, edition, pages
Stockholm: KTH , 2005. , 41 p.
Series
Trita-FPT-Report, ISSN 1652-2443 ; 2005:43
Keyword [en]
biphenyl structures, kappa number, kraft pulping, phenols, radical coupling, residual delignificaiton, residual lignin, softwood
National Category
Paper, Pulp and Fiber Technology
Identifiers
URN: urn:nbn:se:kth:diva-3855OAI: oai:DiVA.org:kth-3855DiVA: diva2:9723
Presentation
2006-02-09, E2, KTH, Lindstedtsvägen 3, Stockholm, 10:00
Note
QC 20101213Available from: 2006-02-14 Created: 2006-02-14 Last updated: 2010-12-13Bibliographically approved
List of papers
1. Towards a new concept of lignin condensation in kraft pulping. Initial results
Open this publication in new window or tab >>Towards a new concept of lignin condensation in kraft pulping. Initial results
2004 (English)In: Comptes rendus. Biologies, ISSN 1631-0691, E-ISSN 1768-3238, Vol. 327, no 9-10, 817-826 p.Article in journal (Refereed) Published
Abstract [en]

In kraft pulping, a comparatively large amount of lignin remains in the fibres after the cook. Based on various analytical techniques for lignin, such as thioacidolysis, GPC and NMR, it is suggested that lignin condensation reactions take place during the cook. The reaction seems, however, not to involve ionic intermediates as has been suggested previously but rather a one-electron mechanism with elemental sulphur as the initiator. Support for such a reaction has been found through kraft cooks in the presence of an added phenol, 2,6-xylenol, as well as through NMR analysis of kraft lignin. It was found that the added phenol is incorporated in the pulp lignin with linkages indicative of radical coupling. Furthermore, kraft lignin was found to contain substantial amounts of chemically linked fatty acids. By complementary analyses of sulphur and polysulphide in an industrial black liquor, the presence of these compounds throughout a kraft cook was demonstrated.

Keyword
Condensation, Electron transfer reactions, Fatty acids, GPC, Kraft pulping, NMR analysis, Phenols, Thioacidolysis
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-5372 (URN)10.1016/j.crvi.2004.03.011 (DOI)000225355200007 ()2-s2.0-9244265580 (Scopus ID)
Note
QC 20101004Available from: 2006-02-14 Created: 2006-02-14 Last updated: 2017-11-21Bibliographically approved
2. Radical coupling - A major obstacle to delignification in kraft pulping
Open this publication in new window or tab >>Radical coupling - A major obstacle to delignification in kraft pulping
2006 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 21, no 1, 129-134 p.Article in journal (Refereed) Published
Abstract [en]

Lignin dissolution is very slow in the final delignification phase of kraft pulping whereas carbohydrate degradation and dissolution proceeds at a rate that is about the same as that in the bulk phase. The reason for the change in lignin reactivity has been studied by the addition of selected phenols to laboratory kraft cooks of spruce. A substantial formation of new biphenyl bonds between the added phenol and lignin was found both in the residual fiber lignin and in the dissolved kraft lignin, as revealed by GC-MS of thioacidolysis products and complementary NMR analysis of isolated lignins. The formation of biphenyl structures can be explained by a radical coupling mechanism between the added phenol and free aromatic C-5 positions in phenolic lignin units, possibly involving sulfur/polysulfide as radical initiator. The possibility that similar radical coupling reactions may take place between dissolved low molecular mass phenols of lignin origin and polymeric lignin is discussed and it is suggested that this may be the reason for the slow delignification in the final phase.

Keyword
Biphenyl structures, Kappa number, Kraft pulping, Lignin, Phenols, Picea abies, Radical coupling
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-5373 (URN)10.3183/NPPRJ-2006-21-01-p129-134 (DOI)000236358800020 ()2-s2.0-33645666410 (Scopus ID)
Note
QC 20100928. Uppdaterad från Submitted till Published (20100928).Available from: 2006-02-14 Created: 2006-02-14 Last updated: 2017-11-21Bibliographically approved

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