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Mild alkaline treatment activates spruce wood for enzymatic processing: A possible stage in bio-refinery processes
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), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.ORCID iD: 0000-0002-2900-4713
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
2011 (English)In: BioResources, ISSN 1930-2126, Vol. 6, no 3, 2425-2434 p.Article in journal (Refereed) Published
Abstract [en]

The structure of wood is so compact that enzymes are too large to penetrate into the structure and thereby attack the wood components for modifications that can be valuable for various purposes. Here we present a pretreatment method based on traditional kraft pulping, which opens the wood structure, so that enzymes are able to attack the wood components. To study this kind of chemical pretreatment, spruce wood samples were treated at similar conditions used in kraft cooking at varying intensities (H-factors). To verify if the structure was "opened" for enzymes, the pretreated wood samples were incubated with a cellulolytic culture filtrate, and the released reducing sugar concentration after the enzymatic hydrolysis was measured. The results indicated that un-pretreated wood fibers could not be attacked by the enzymes, but already relatively mild pretreatment was sufficient for letting the culture filtrate attack wood polysaccharides, and more intensive treatments opened the structure further. The mildest treatments did not cause any significant yield losses of lignin (Klason lignin). Some galactoglucomannans were however lost during the pretreatments. The mechanisms behind the effect and the technical significance of the method are discussed.

Place, publisher, year, edition, pages
2011. Vol. 6, no 3, 2425-2434 p.
Keyword [en]
Wood structure, Kraft pulping, Enzymatic treatment, Lignin-polysaccharide networks, Bio-refinery
National Category
Polymer Chemistry
URN: urn:nbn:se:kth:diva-48525ISI: 000295864500012ScopusID: 2-s2.0-80051559058OAI: diva2:458283
QC 20111122Available from: 2011-11-22 Created: 2011-11-21 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.
TRITA-CHE-Report, ISSN 1654-1081 ; 2014:28
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
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)
Knut and Alice Wallenberg Foundation, 8102

QC 20140903

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

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