Impact of dissolved sodium salts on kraft cooking reactions
Journal article, 2009

This study examined the effects of inactive ions - ions not reacting with wood - during kraft cooking, which thus far have received modest attention. Six different sodium salts were added to kraft cooking liquors at two different levels of alkalinities. Delignification as well as the formation and degradation of hexenuronic acid (HexA) were observed of Scots pine sapwood meal. The delignification rate was greatly affected by the presence of additional anions. Chloride ions had the greatest retarding effect, while the addition of polyacrylate ions had almost no effect. When carbonate, sulphate and lactate ions were added to the liquors, the delignification rates were in-between the series with chloride and polyacrylates ions. We suggest that the anions affect the solubility of lignin fragments in analogy to the Hofmeister effect observed in various macromolecular systems in the presence of dissolved salts. When the reactions involving HexA were examined, the opposite results were obtained. In that case, the highest reaction rates were in the presence of chloride ions, and the lowest rates were obtained when no extra ions were added, and the second lowest rates were obtained in the presence of polyacrylate ions. As for delignification, the cooking series containing carbonate, sulphate and lactate ions had a reaction rate in-between the series with the highest and lowest rates. The differences obtained with various inorganic ions can be qualitatively explained by the Donnan equilibrium theory and by the variation in activity coefficients of hydroxide ions. Findings imply that knowledge of kraft cooking is far from complete. The effects of inactive ions on reaction kinetics should also receive more attention. © 2009 by Walter de Gruyter.

Author

Johannes Bogren

Chalmers, Chemical and Biological Engineering, Forest Products and Chemical Engineering

Harald Brelid

Chalmers, Chemical and Biological Engineering, Forest Products and Chemical Engineering

Marta Anna Bialik

Chalmers, Chemical and Biological Engineering, Forest Products and Chemical Engineering

Hans Theliander

Wallenberg Wood Science Center (WWSC)

Chalmers, Chemical and Biological Engineering, Forest Products and Chemical Engineering

Holzforschung

0018-3830 (ISSN) 1437-434X (eISSN)

Vol. 63 2 226-231

Subject Categories

Chemical Process Engineering

DOI

10.1515/HF.2009.032

More information

Latest update

8/27/2018