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Dissociation of Phenolic Groups in Kraft Lignin at Elevated Temperatures.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.ORCID iD: 0000-0003-3407-7973
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
Responsible organisation
2000 (English)In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 54, no 5, 519-527 p.Article in journal (Refereed) Published
Abstract [en]

The dissociation of the phenolic groups in a polydisperse, low molecular weight kraft lignin (Indulin AT) was studied in alkaline aqueous solutions in the temperature interval 21-70°C, using a UV-spectrophotometric method. It was found that at a constant concentration of hydroxide ions, the degree of dissociation was decreasing when the temperature was elevated. Dissociation curves and apparent pK0 values were also calculated for the polydisperse sample at the same conditions, using the van't Hoff and the Poisson-Boltzmann equations. At degrees of dissociation exceeding α ≈ 0.4, the outcome of the theoretical approach showed to be in good agreement with the experimentally obtained results. Furthermore, calculations were performed for different molecular weights of kraft lignin and from this it was found that the apparent pK0 is shifted to higher values by increasing molecular weight, due to an increased electrostatic attraction of the hydrogen ions, which is arising from a less curved surface. Predictions of the dissociation behavior at temperatures reached in the kraft process were performed and under these conditions, higher molecular weight lignin fragments seem never to reach the point of complete dissociation. It was also found that an increase in temperature results in phase separation in kraft lignin solutions with high ionic strengths and pH values close to the pKa of the phenolic groups.

Place, publisher, year, edition, pages
2000. Vol. 54, no 5, 519-527 p.
Keyword [en]
kraft lignin, phenolic groups, pKa, dissociation, temperature, Poisson-Boltzmann equation
National Category
Chemical Engineering
Identifiers
URN: urn:nbn:se:miun:diva-1862DOI: 10.1515/HF.2000.088ISI: 000089643300014Scopus ID: 2-s2.0-0034578968Local ID: 653OAI: oai:DiVA.org:miun-1862DiVA: diva2:26894
Available from: 2008-09-30 Created: 2008-09-30 Last updated: 2016-10-11Bibliographically approved

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CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
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  • nn-NO
  • nn-NB
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  • Other locale
More languages
Output format
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