Effect of autohydrolysis on the lignin structure and the kinetics of delignification of birch wood

Tiina Rauhala, Alistair W.T. King, Gerhard Zuckerstätter, Simopekka Suuronen, Herbert Sixta

Research output: Contribution to journalArticleScientificpeer-review

23 Citations (Scopus)

Abstract

The first aim of this study was to investigate the delignification kinetics of alkaline cooking for autohydrolyzed birch wood (Betula pendula). A series of cooking trials, at temperatures ranging between 130°C and 170°C were performed on untreated (P-factor 0) and autohydrolyzed (P-factor 200) wood. The results of carbohydrate and lignin analyses were fitted to a kinetic model and it was observed that autohydrolysis doubles the delignification rate, during bulk delignification. However, a slight decrease was noticed in the delignification rate during residual pulping. Thus, the second aim of this study was to elucidate the reasons behind accelerated delignification. For this purpose two different autohydrolysis treatments (P-factors 200 and 750) were applied to birch wood. Lignin was isolated from both the native and autohydrolyzed wood and subjected to elemental analysis, methoxyl group determination, carbohydrate analysis and quantitative 1H, 13C and 31P nuclear magnetic resonance (NMR) spectroscopy. The results indicate that, during autohydrolysis, P-O-4 linkages were cleaved, the methoxyl group content was reduced and the syringyl/guaiacyl (S/G) ratio decreased. In addition, a decrease in primary and secondary aliphatic hydroxyl groups and an increase in phenolic hydroxyl groups were detected. It could be concluded that condensation reactions were also occurring during autohydrolysis. Although lignin reactions such as the cleavage of (i-O-4-cleavages and the increase in phenolic hydroxyl groups partly account for the pulping behaviour the reason behind the significantly accelerated bulk delignification is not entirely explained through this study. More research concerning reactions during autohydrolysis is needed.

Original languageEnglish
Pages (from-to)386-391
Number of pages6
JournalNordic Pulp and Paper Research Journal
Volume26
Issue number4
DOIs
Publication statusPublished - 2011
MoE publication typeA1 Journal article-refereed

Keywords

  • Autohydrolysis
  • Birch
  • Delignification kinetics
  • Kraft pulping
  • Lignin structure
  • MWL

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