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Improved Usage of Wood Raw Material through Modification of the Kraft Process
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology. (Pulp Technology)ORCID iD: 0000-0002-0003-9242
2015 (English)Licentiate 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.
Place, publisher, year, edition, pages
Stockholm, Sweden: Kungliga Tekniska högskolan, 2015. , xii, 72 p.
Series
TRITA-CHE-Report, ISSN 1654-1081 ; 2015:25
Keyword [en]
kraft process, impregnation, xylan, spruce
National Category
Chemical Process Engineering Other Chemical Engineering
Research subject
Chemical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-167491ISBN: 978-91-7595-586-5 (print)OAI: oai:DiVA.org:kth-167491DiVA: diva2:813354
Presentation
2015-06-10, Rånbyrummet, Teknikringen 56, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20150525

Available from: 2015-05-25 Created: 2015-05-22 Last updated: 2015-05-25Bibliographically approved
List of papers
1. Impact of Differing Time and Temperature during Impregnation on Kraft Cooking of Softwood Chips
Open this publication in new window or tab >>Impact of Differing Time and Temperature during Impregnation on Kraft Cooking of Softwood Chips
(English)Manuscript (preprint) (Other academic)
National Category
Chemical Process Engineering
Identifiers
urn:nbn:se:kth:diva-167989 (URN)
Note

QS 2015

Available from: 2015-05-25 Created: 2015-05-25 Last updated: 2015-05-25Bibliographically approved
2. Influence of spruce xylan characteristics on tensile strength of spruce kraft pulp
Open this publication in new window or tab >>Influence of spruce xylan characteristics on tensile strength of spruce kraft pulp
2015 (English)In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 69, no 1, 1-7 p.Article in journal (Refereed) Published
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.

Keyword
kraft cooking, spruce, tensile strength, uronic acid, xylan
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-159109 (URN)10.1515/hf-2014-0010 (DOI)000346764600001 ()2-s2.0-84920088278 (Scopus ID)
Funder
VINNOVA
Note

QC 20150129

Available from: 2015-01-29 Created: 2015-01-22 Last updated: 2017-12-05Bibliographically approved
3. Xylan from Agro Waste As a Strength Enhancing Chemical in Kraft Pulping of Softwood
Open this publication in new window or tab >>Xylan from Agro Waste As a Strength Enhancing Chemical in Kraft Pulping of Softwood
2014 (English)In: Industrial & Engineering Chemistry Research, ISSN 0888-5885, E-ISSN 1520-5045, Vol. 53, no 23, 9738-9742 p.Article in journal (Refereed) Published
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.

National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-147942 (URN)10.1021/ie5006806 (DOI)000337337000024 ()2-s2.0-84902477720 (Scopus ID)
Funder
Vinnova
Note

QC 20140714

Available from: 2014-07-14 Created: 2014-07-10 Last updated: 2017-12-05Bibliographically approved

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