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Dithionite impregnation combined with mild steam explosion of spruce wood – an improved version of kraft pulping
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
Chalmers University of Technology.
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.ORCID iD: 0000-0002-2900-4713
Chalmers University of Technology.
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(English)Manuscript (preprint) (Other (popular science, discussion, etc.))
Abstract [en]

Norway spruce (Picea abies) wood chips were impregnated with water or sodium dithionite (Na2S2O4) and were subsequently subjected to a mild steam explosion (STEX) treatment at four or seven bar for ten minutes. In order to evaluate the combined effect of Na2S2O4 and STEX, kraft cooking was performed on samples pre-treated with different combinations of impregnation and STEX. Carbohydrate composition, Klason lignin content, kappa number, intrinsic viscosity, pulp yield, brightness and tensile strength (on pulp sheets) were tested and compared. The results showed that an impregnation with Na2S2O4 combined with mild STEX had a good effect on the delignification during kraft pulping, shown by lower kappa numbers and lower Klason lignin content. The viscosity of the pulp samples of Na2S2O4 plus STEX was lower than the water impregnated and non-STEX pulps. However, the lower viscosity did not influence the strength of the pulp since the tensile index was still high. The Na2S2O4 plus STEX pulp sheets also showed the highest brightness value.

Keyword [en]
sodium dithionite, mild steam explosion, kraft pulping, peeling, enhanced delignification
National Category
Polymer Technologies
Research subject
Fibre and Polymer Science
Identifiers
URN: urn:nbn:se:kth:diva-150394OAI: oai:DiVA.org:kth-150394DiVA: diva2:742769
Funder
Knut and Alice Wallenberg Foundation, 8102
Note

QS 2014

Available from: 2014-09-02 Created: 2014-09-02 Last updated: 2014-09-03Bibliographically approved
In thesis
1. Pretreatment and Enzymatic Treatment of Spruce: A functional designed wood components separation for a future biorefinery
Open this publication in new window or tab >>Pretreatment and Enzymatic Treatment of Spruce: A functional designed wood components separation for a future biorefinery
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The three main components of wood, namely, cellulose, hemicellulose, and lignin, can be used in various areas. However, since lignin covalently crosslinks with wood polysaccharides creating networks that is an obstacle for extraction, direct extraction of different wood components in high yield is not an easy matter. One potential approach to overcome such obstacles is to treat the wood with specific enzymes that degrade the networks by specific catalysis. However, the structure of wood is so compact that the penetration of the wood fibers by large enzyme molecules is hindered. Thus, the pretreatment of wood prior to the application of enzymes is necessary, for “opening” the structure.

One pretreatment method that was performed in this thesis is based on kraft pulping, which is a well-established and industrialized technique. For untreated wood, the wood fibers cannot be attacked by the enzymes. A relatively mild pretreatment was sufficient for wood polysaccharides hydrolyzed by a culture filtrate. A methanol-alkali mixture extraction was subsequently applied to the samples that were pretreated with two types of hemicellulases, Gamanase and Pulpzyme HC, respectively. The extraction yield increased after enzymatic treatment, and the polymers that were extracted from monocomponent enzyme-treated wood had a higher degree of polymerization. Experiments with in vitro prepared lignin polysaccharide networks suggested that the increased extraction was due to the enzymatic untying. However, the relatively large loss of hemicellulose, particularly including (galacto)glucomannan (GGM), represents a problem with this technique. To improve the carbohydrate yield, sodium borohydride (NaBH4), polysulfide and anthraquinone were used, which increased the yields from 76.6% to 89.6%, 81.3% and 80.0%, respectively, after extended impregnation (EI). The additives also increased the extraction yield from approximately 9 to 12% w/w wood. Gamanase treatment prior to the extraction increased the extraction yield to 14% w/w wood.

Sodium dithionite (Na2S2O4) is an alternative reducing agent for the preservation of hemicelluloses because it is less expensive than metal hydrides and only contains sodium and sulfur, which will not introduce new elements to the recovery system. Moreover, Na2S2O4has the potential to be generated from black liquor. Na2S2O4 has some preservation effect on hemicelluloses, and the presence of Na2S2O4 also contributed to delignification. The extraction yield increased to approximately 15% w/w wood. Furthermore, Na2S2O4 has been applied in the kraft pulping process of spruce. The yield and viscosity increased, while the Klason lignin content and kappa number decreased, which represents a beneficial characteristic for kraft pulp. The brightness and tensile strength of the resulting sheets also improved. However, the direct addition of Na2S2O4 to white liquor led to greater reject content. This problem was solved by pre-impregnation with Na2S2O4 and/or mild steam explosion (STEX) prior to the kraft pulping process. Following Na2S2O4 pre-impregnation and mild STEX, the obtained kraft pulp had substantially better properties compared with the properties exhibited after direct addition of Na2S2O4 to the white liquor.

The wood structure opening efficiency of mild STEX alone was also tested. The accessibility of the wood structure to enzymes was obtained even at very modest STEX conditions, according to a reducing sugar analysis, and was not observed in untreated wood chips, which were used as a reference. The mechanical effect of STEX appears to be of great importance at lower temperatures, and both chemical and mechanical effects occur at higher STEX temperatures. 

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2014. 59 p.
Series
TRITA-CHE-Report, ISSN 1654-1081 ; 2014:28
Keyword
kraft cooking; extended impregnation; enzymes; chemo-enzymatic separation process; peeling reaction; sodium borohydride; polysulfide; anthraquinone; sodium dithionite; mild steam explosion; biorefinery.
National Category
Chemical Engineering Polymer Chemistry Paper, Pulp and Fiber Technology
Research subject
Fibre and Polymer Science
Identifiers
urn:nbn:se:kth:diva-150395 (URN)978-91-7595-206-2 (ISBN)
Public defence
2014-09-24, F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
Knut and Alice Wallenberg Foundation, 8102
Note

QC 20140903

Available from: 2014-09-03 Created: 2014-09-02 Last updated: 2014-09-03Bibliographically approved

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Lindström, Mikael E.

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