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  • 1.
    Tavast, Daniel
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Improved Usage of Wood Raw Material through Modification of the Kraft Process2015Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

       The kraft process is a complex system with many variables, and though the process is fairly well understood, there is still much we do not know.

     

       This thesis examines some aspects of the kraft process that could prove to be of interest for the pulp and paper industry, specifically, the impact of wood chip impregnation and of the chemical structure of xylan on spruce kraft pulp. The intent is to suggest modifications to the kraft process as it is used today.

     

       The effect of wood chip impregnation varies with the prevalent conditions, and increases the effect of the subsequent kraft cook. Longer impregnation at a lower temperature was found to increase screened pulp yield, reduce shives content, make it possible to reach a certain kappa number at a lower H-factor, and make it possible to reach a certain kappa number at a lower total alkali consumption.

     

       Xylan has previously been found to have a strength-enhancing effect on pulp, and the chemical structure of the xylan in question was found to be the main strength-enhancing factor. For spruce xylan, the structure that provides the largest increase in strength is not the same as the structure that increases the yield the most. Removing xylan was determined to have a negative impact on pulp strength.

     

       Xylan extracted from agro waste can be used as an additive to increase pulp strength. This could be viable, especially when combined with the production of green plastics from hemicelluloses extracted from the agro waste.

     

       A suggested configuration of a future pulp mill is presented, incorporating the following modifications to the now standard kraft cooking system:

    • impregnation at a lower temperature for a longer time;
    • extracting xylan-enriched black liquor at an early stage of the impregnation or cook, and adding this liquor at a late stage of the cook;
    • terminating the cook at a higher kappa number;
    • increasing oxygen delignification to compensate for the increased kappa number at the end of the cook, keeping the kappa number constant going into the bleaching plant; and
    • adding agro-waste xylan during oxygen delignification.
  • 2.
    Tavast, Daniel
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Brännvall, Elisabet
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Impact of Differing Time and Temperature during Impregnation on Kraft Cooking of Softwood ChipsManuscript (preprint) (Other academic)
  • 3.
    Tavast, Daniel
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Brännvall, Elisabet
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Increased pulp yield by prolonged impregnation in softwood kraft pulping2017In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 32, no 1, p. 14-20Article in journal (Refereed)
    Abstract [en]

    The effect on kraft cooking proceeded by an impregnation stage performed at 130 degrees C for 30 min was compared to kraft cooking following prolonged impregnation at 105 degrees C for 60-120 min. The alkali consumed during impregnation varied depending on the temperature and time of the impregnation stage. In order to study the impact of the impregnation stage on the subsequent kraft cook, the initial concentration of effective alkali was adjusted to be initially the same in all cooks before cooking for 180-290 min. The alkali consumed in the impregnation stage affected the alkali profile of the cooking stage. The more alkali consumed in impregnation, the lower the demand in cooking. Higher alkali consumption in the impregnation stage also led to faster delignification in the cooking stage. Prolonged impregnation resulted in 1-1.5 percentage points higher yield compared to the reference case. The yield increment was due to a higher cellulose retention. Although the impregnation time was prolonged from 30 min up to 2 h, the higher delignification rate and higher yield only decreased the production rate with 11% compared to the reference.

  • 4.
    Tavast, Daniel
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Brännvall, Elisabeth
    KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center. KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Lindström, Mikael E.
    KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center. KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Henriksson, Gunnar
    KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center. KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Selectiveness and efficiency of combined peracetic acid and chlorine dioxide bleaching stage for kraft pulp in removing hexeuronic acid2011In: Cellulose Chemistry and Technology, ISSN 0576-9787, Vol. 45, no 1-2, p. 89-95Article in journal (Refereed)
    Abstract [en]

    Combined peracetic acid and chlorine dioxide bleaching stages of unbleached and oxygen delignified hardwood and softwood kraft pulps were compared with conventional chlorine dioxide and peracetic acid stages as to kappa number and viscosity reduction, selectivity and reduction of hexenuronic acid content. The combined stages were more efficient in kappa number reduction than those with only chlorine dioxide. Part of the increased kappa number reduction was due to an improved degradation of hexenuronic acid. The stages where chlorine dioxide was added before the peracetic acid (DT) showed a higher selectivity than those in which the chemicals were added simultaneously (D+T); in turn, the latter were more efficient than the "pure" chlorine dioxide (D, D-0) and peracetic acid stages (T). However, peracetic acid and chlorine dioxide seemed to react with each other, leading to the degradation of both bleaching chemicals. The mechanisms and practical implementation of these bleaching sequences are discussed.

  • 5.
    Tavast, Daniel
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Li Jansson, Zheng
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Brännvall, Elisabet
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Designing spruce xylan for higher tensile strength2011Manuscript (preprint) (Other academic)
  • 6.
    Tavast, Daniel
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Li Jansson, Zheng
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Brännvall, Elisabet
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Influence of spruce xylan characteristics on tensile strength of spruce kraft pulp2015In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 69, no 1, p. 1-7Article in journal (Refereed)
    Abstract [en]

    The aim of the study was to investigate the possibility to use spruce xylan more efficiently by possible relocation of dissolved xylan with certain characteristics from the first part of the kraft cooking to the later part, when precipitation occur. The characteristics of re-located xylan was controlled by replacing half the black liquor (BL) at a late stage of a kraft cook, with the same amount of black liquor containing spruce xylan with known molecular weight and content of uronic acid (UA). Pulp with addition of xylan with high amount of UA groups responded strongly on beating, resulting in improved tensile strength. It is proposed that the best effect of xylan on tensile strength occurs when the xylan penetrates some distance into the subsurface of the fiber wall. Both low molecular weight (M-w) and a high degree of substitution decreases the tendency of xylan to aggregate, which enables the dissolved xylan to penetrate some distance into the exposed fiber surface. Upon beating, this xylan will be exposed thus facilitating improved fiber-fiber joint formation, which leads to increased tensile strength.

  • 7.
    Tavast, Daniel
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Mansoor, Zaheer Ahmad
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Brännvall, Elisabet
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Xylan from Agro Waste As a Strength Enhancing Chemical in Kraft Pulping of Softwood2014In: Industrial & Engineering Chemistry Research, ISSN 0888-5885, E-ISSN 1520-5045, Vol. 53, no 23, p. 9738-9742Article in journal (Refereed)
    Abstract [en]

    The possibility to use xylan from agro waste in order to improve the strength properties of spruce kraft pulp was examined. Xylan was extracted from wheat straw and rice husks, by subjecting the agro waste to kraft cooking. The extracted xylan was subsequently used at the end of a kraft cooking process of spruce, by replacing half of the black liquor with dissolved spruce xylan with white liquor containing agro waste xylan. The strength tests performed on the obtained softwood kraft pulps showed that even a small amount of rice husk or wheat straw xylan deposited on softwood fibers had a positive effect on the tensile index of the paper at given sheet density.

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