Effects of hot water extraction in a batch reactor on the delignification of birch wood

Marc Borrega (Corresponding Author), Kaarlo Nieminen, Herbert Sixta

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68 Citations (Scopus)


The amount of residual lignin in birch wood after a hot water extraction in a batch reactor was investigated as a function of extraction temperature and time. A kinetic model fitting the experimental data was then developed to explain delignification of wood during a hot water treatment. Results showed that delignification kinetics involves simultaneous degradation and condensation reactions, with degradation of lignin being much faster than its condensation. Native lignin in wood was successfully modeled as the sum of two fractions with different degradation rates. The rates of degradation and condensation increased along with increasing extraction temperature. The proportion of acidsoluble lignin to acid-insoluble (Klason) lignin in the wood residue decreased with increasing extraction temperature and time, probably due to chemical and structural changes in the lignin during the hot water treatment. Condensed lignin was predominantly determined as Klason lignin. On the other hand, the amount of soluble lignin in the extraction liquor increased slightly with temperature, but remained mostly constant after any extraction time. An insoluble fraction in the liquor that originated from precipitated lignin fragments is believed to contain traces of degradation products from carbohydrates or other degradation compounds.

Original languageEnglish
Pages (from-to)1890-1903
Number of pages14
Issue number2
Publication statusPublished - May 2011
MoE publication typeA1 Journal article-refereed


  • Autohydrolysis
  • Birch
  • Delignification kinetics
  • Hot water extraction
  • Lignin condensation
  • Wood fractionation


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