The doctoral dissertations of the former Helsinki University of Technology (TKK) and Aalto University Schools of Technology (CHEM, ELEC, ENG, SCI) published in electronic format are available in the electronic publications archive of Aalto University - Aaltodoc.
Aalto

Reactions of Chlorine (III) and Their Kinetics in the Chlorine Dioxide Bleaching of Kraft Pulps

Tuula Lehtimaa

Doctoral dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the Faculty of Chemistry and Materials Sciences for public examination and debate in Auditorium Puu II at the Aalto University School of Science and Technology (Espoo, Finland) on the 21st of June 2010 at 12 noon.

Overview in PDF format (ISBN 978-952-60-3203-0)   [646 KB]
Dissertation is also available in print (ISBN 978-952-60-3202-3)

Abstract

The reactions of Cl(III) were investigated utilizing iodometric titration in combination with DMSO and EDTA to prevent undesired side reactions. Among a large group of suggested Cl(III) decomposition reactions, two reactions were found to be adequate to describe the Cl(III) decomposition in the absence of metals and HOCl. The rate parameters (k – rate coefficient, Ea – activation energy) were determined for these reactions.

The reaction between Cl(III) and HOCl is known to start with the formation of a Cl2O2 intermediate. The Cl2O2 intermediate was found to be formed through both, hypochlorous acid and chlorine. The kinetic parameters were obtained for the reaction between chlorous acid and hypochlorous acid. The reaction rate between chlorine and chlorite was found to be restricted by the kinetics of the HOCl/Cl2 equilibrium. The extremely fast Cl2O2 consuming reactions were identified among a group of suggested reactions and their relative rates were determined.

Kinetic parameters were identified for several aldehydes with Cl(III). Aldehyde groups were shown to be present in kraft pulps and a considerable amount of aldehydes was found to be formed during chlorine dioxide bleaching. These aldehydes seemed to originate both from carbohydrates and lignin and the amount was dependent on the ClO2 dosage used. According to the results obtained, it was concluded that the reaction between Cl(III) and aldehydes may contribute substantially to the overall Cl(III) consumption during chlorine dioxide bleaching.

Chlorine dioxide prebleaching (D0-stage) experiments were conducted to gain more knowledge of the rate of the different reactions and on the time-dependent behavior of various components. Kappa number reduction, hexenuronic acid depletion, chlorination and chlorine dioxide consumption were all found to be fast reactions, with almost everything occurring during the first minute of bleaching. Cl(III) was an exception. The amount of Cl(III) first increased rapidly and then decreased slowly.

This thesis consists of an overview and of the following 6 publications:

  1. Tuula Lehtimaa, Ville Tarvo, Gérard Mortha, Susanna Kuitunen, and Tapani Vuorinen. 2008. Reactions and kinetics of Cl(III) decomposition. Industrial & Engineering Chemistry Research, volume 47, number 15, pages 5284-5290.
  2. Ville Tarvo, Tuula Lehtimaa, Susanna Kuitunen, Ville Alopaeus, Tapani Vuorinen, and Juhani Aittamaa. 2009. The kinetics and stoichiometry of the reaction between hypochlorous acid and chlorous acid in mildly acidic solutions. Industrial & Engineering Chemistry Research, volume 48, number 13, pages 6280-6286.
  3. Tuula Lehtimaa, Susanna Kuitunen, Ville Tarvo, and Tapani Vuorinen. 2010. Kinetics of aldehyde oxidation by chlorous acid. Industrial & Engineering Chemistry Research, volume 49, number 6, pages 2688-2693.
  4. Tuula Lehtimaa, Susanna Kuitunen, Ville Tarvo, and Tapani Vuorinen. Reactions of aldehydes with Cl(III) in chlorine dioxide bleaching. Holzforschung, accepted for publication.
  5. Tuula Lehtimaa, Ville Tarvo, Susanna Kuitunen, Anna-Stiina Jääskeläinen, and Tapani Vuorinen. 2010. The effect of process variables in chlorine dioxide prebleaching of birch kraft pulp. Part 1. Inorganic chlorine compounds, kappa number, lignin, and hexenuronic acid content. Journal of Wood Chemistry and Technology, volume 30, number 1, pages 1-18.
  6. Tuula Lehtimaa, Ville Tarvo, Susanna Kuitunen, Anna-Stiina Jääskeläinen, and Tapani Vuorinen. 2010. The effect of process variables in chlorine dioxide prebleaching of birch kraft pulp. Part 2. AOX and OX formation. Journal of Wood Chemistry and Technology, volume 30, number 1, pages 19-30.

Keywords: chlorite, chlorous acid, chlorine dioxide, hypochlorous acid, bleaching

This publication is copyrighted. You may download, display and print it for Your own personal use. Commercial use is prohibited.

© 2010 Aalto University School of Science and Technology

Last update 2011-05-26