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  • 1.
    Brännvall, Elisabet
    et al.
    KTH, Superseded Departments, Pulp and Paper Technology.
    Hakanen, A
    Teder, Ants
    KTH, Superseded Departments, Pulp and Paper Technology.
    Strykepotentialen hos massor från polysulfidkok: Del 1. Variationer i vätesulfid- och hydroxidjonhaltReport (Other academic)
  • 2.
    Brännvall, Elisabet
    et al.
    KTH, Superseded Departments, Pulp and Paper Technology.
    Hakanen, A
    Teder, Ants
    KTH, Superseded Departments, Pulp and Paper Technology.
    Strykepotentialen hos massor från polysulfidkok: Del 2. Massa- och fiberegenskaperReport (Other academic)
  • 3.
    Gustafsson, Roland
    et al.
    KTH, Superseded Departments, Pulp and Paper Technology.
    Ek, Monica
    KTH, Superseded Departments, Pulp and Paper Technology.
    Teder, Ants
    KTH, Superseded Departments, Pulp and Paper Technology.
    Polysulphide pretreatment of softwood for increased delignification and higher pulp viscosity2004In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 30, no 5, p. 129-135Article in journal (Refereed)
    Abstract [en]

    The effect of polysulphide pretreatment under various conditions prior to a kraft cook was investigated for spruce (Picea abies) chips using a technique with a liquor:wood ratio of 67:1 to keep the liquor composition as constant as possible during the pretreatment and cooking phases. If the polysulphidepretreatment is carried out at a very high hydroxide concentration, 1.5 mol OH-/L, three independent positive effects (compared with a corresponding sulphide pretreatment without polysulphide) can be observed: more extensive delignification; higher pulp, viscosity; and higher carbohydrate yield. When the alkali change was changed in the subsequent kraft cook (in the range 0.15-0.60 mol/L), the increase in delignification extent as a result of polysulphide pretreatment was not affected but the relative carbohydrate yield increase was favoured by a higher alkali charge during cooking. On the other hand, the absolute carbohydrate yield is favoured by a intermediate alkali charge.

  • 4.
    Gustafsson, Roland
    et al.
    KTH, Superseded Departments, Pulp and Paper Technology.
    Freysoldt, Julia
    KTH, Superseded Departments, Pulp and Paper Technology.
    Teder, Ants
    KTH, Superseded Departments, Pulp and Paper Technology.
    Influence of the alkalinity in polysulphide pretreatment on results of cooking with normal liquor-to-wood ratios2004In: Paperi ja puu, ISSN 0031-1243, Vol. 86, no 3, p. 169-173Article in journal (Refereed)
    Abstract [en]

    The effect of alkalinity in a polysulphide pretreatment on the delignification rate, pulp yield and the pulp viscosity in the following kraft cook was investigated. The results were compared to those with reference pretreatments with a corresponding concentrations of hydroxide and hydrogen sulphide ions. The experiments were carried out at liquor-to-wood ratio of 4:1, and the alkalinity in the pretreatments was varied from 0 to 2.5 mole hydroxide/litre. It was found that when the polysulphide preteatment is performed at very high initial hydroxide concentrations, > 1.5 mole/litre, the delignification rate in the cook is increased. The pulp viscosity was higher than that achieved with the sulphide reference when the pulping was extended to low kappa numbers and when the initial hydroxide ion concentration in the pretreatment was high.

  • 5. Gustavsson, Catrin
    et al.
    Ek, M.
    Kadiric, J.
    Teder, Ants.
    KTH, Superseded Departments, Polymer Technology.
    Formation and dissolution/degradation of hexenuronic acids during kraft pulping of Eucalyptus Globulus2001In: 7th Brazilian Symposium on the Chemistry of Lignins and other Wood ComponentsArticle in journal (Refereed)
  • 6.
    Lindström, Mikael E.
    et al.
    KTH, Superseded Departments, Pulp and Paper Technology.
    Teder, Ants
    The Effect of Polysulfide Pretreatment when Kraft Pulping to Very Low Kappa Numbers1995In: Nordic Pulp Paper Research Journal, Vol. 10, no 1, p. 8-Article in journal (Refereed)
  • 7.
    Sjöstrom, Karin
    et al.
    KTH, Superseded Departments, Pulp and Paper Technology.
    Teder, Ants
    Changes in light absorption coefficient spectra as a result of TCF bleaching1999In: Paperi ja puu, ISSN 0031-1243, Vol. 81, no 2, p. 130-137Article in journal (Refereed)
    Abstract [en]

    Light absorption coefficient, k, spectra in the wavelength range from 200 to 700 nm have been determined for a number of modified kraft and alkaline sulfite pulps after O, OAZ and OAZQP* bleaching (O=oxygen, A=acid treatment, Z=ozone, Q=complexing agent, P*=peroxide stage with Mg addition). The different pulp types have earlier shown differences in bleachability and selectivity when bleached in an OAZQP* sequence and also in other sequences. However, the reason for the differences in bleachability are not fully understood. In this paper, the changes in k spectra after the different bleaching stages for the different pulp types are shown, and the differences are discussed, The accuracy in the determination of k is also discussed and why it is preferable to measure k rather than brightness. There were no significant differences between the shape of the k spectra for the different pulp types that could explain the known differences in bleachability between the pulp types. However, the levels of the k spectra after the oxygen stage could be correlated to the known differences in bleachability between the pulps, The k spectra for the ASAM pulp, the pulp that has shown best bleachability, was significantly lower compared to the other investigated pulps. Ozone and peroxide bleached pulps showed k spectra of approximately the same shape as the oxygen-delignified pulps. In this study, k values as high as about 10 m(2)/kg were correctly measured. At higher k values, the light scattering coefficient (s) began to deviate due to too high a light absorption. Dilution, i.e. mixing the pulp with a brighter pulp of lower and known k value so that the k value of the mixture does not exceed 10 m2/kg is a way of circumventing the problem. However, there are also some limitations with the pulp mixing method, which are discussed.

  • 8.
    Sjöstrom, Karin
    et al.
    KTH, Superseded Departments, Pulp and Paper Technology.
    Teder, Ants
    KTH, Superseded Departments, Pulp and Paper Technology.
    Changes within the modified kraft process aiming to improve TCF bleachability1999In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 25, no 5, p. 176-182Article in journal (Refereed)
    Abstract [en]

    the investigated process modifications were: presulphonation, postsulphonation, polysulphide pretreatment and polysulphide pretreatment combined with a postsulphonation. The influence of the degree of delignification in the cook, on the selectivity and bleachability, was also investigated. The pulps were produced from softwood chips and were oxygen delignified before bleaching according to an AZQP sequence. All the investigated process variants had better process selectivity (pulp viscosity at a given brightness) and the pulps produced with a postsulphonation showed better bleachability, than the reference pulp. The bleachability and the process selectivity was improved by interrupting the cook at a higher kappa number and instead extending the delignification in the oxygen stage.

  • 9.
    Teder, Ants
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Kinetics of chemical pulping and adaptation to modified processes2009In: Pulping Chemistry and Technology, Walter de Gruyter, 2009, p. 149-164Chapter in book (Refereed)
  • 10.
    Teder, Ants
    et al.
    KTH, Superseded Departments, Pulp and Paper Technology.
    Sjöstrom, Karin
    KTH, Superseded Departments, Pulp and Paper Technology.
    A comparison of bleachability in TCF sequences for alkaline sulphite and kraft pulps1996In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 22, no 8, p. J296-J300Article in journal (Refereed)
    Abstract [en]

    The bleachability in different totally chlorine-free (TCF) bleaching sequences was investigated for two types of alkaline sulphite pulps, ASAM and MSSAQ, and compared with that of pulps produced by different new and industrially applied modified kraft pulping processes. The TCF sequences included oxygen, ozone, peroxide and complexing agent stages. The alkaline sulphite pulps were found to be easier to bleach in terms of the consumption of oxidative agents required to reach a given brightness than the pulps produced by the different modified kraft pulping processes. The relationship between pulp brightness and pulp viscosity was also much better for the sulphite pulps, although the new types of kraft pulps are gradually approaching the level of the alkaline sulphite pulps in this respect. There was no significant difference between the ASAM (alkaline sulphite anthraquinone methanol) and the two-stage MSSAQ (minisulphide sulphite anthraquinone) processes.

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