Reactions of chlorine (III) and their kinetics in the chlorine dioxide bleaching of kraft pulps
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Aalto-yliopiston teknillinen korkeakoulu |
Doctoral thesis (article-based)
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Date
2010
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Mcode
Degree programme
Language
en
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Verkkokirja (646 KB, 50 s.)
Series
TKK reports in forest products technology.
Series A,
11
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.Description
Supervising professor
Vuorinen, Tapani, Prof.Thesis advisor
Vuorinen, Tapani, Prof.Keywords
chlorite, chlorous acid, chlorine dioxide, hypochlorous acid, bleaching
Other note
Parts
- [Publication 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.
- [Publication 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.
- [Publication 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.
- [Publication 4]: Tuula Lehtimaa, Susanna Kuitunen, Ville Tarvo, and Tapani Vuorinen. Reactions of aldehydes with Cl(III) in chlorine dioxide bleaching. Holzforschung, accepted for publication.
- [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.
- [Publication 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.