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Pretreatment and Enzymatic Treatment of Spruce: A functional designed wood components separation for a future biorefinery
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. (WWSC)
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 [en]
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: urn:nbn:se:kth:diva-150395ISBN: 978-91-7595-206-2 (print)OAI: oai:DiVA.org:kth-150395DiVA: diva2:742794
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
List of papers
1. Mild alkaline treatment activates spruce wood for enzymatic processing: A possible stage in bio-refinery processes
Open this publication in new window or tab >>Mild alkaline treatment activates spruce wood for enzymatic processing: A possible stage in bio-refinery processes
2011 (English)In: BioResources, ISSN 1930-2126, E-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.

Keyword
Wood structure, Kraft pulping, Enzymatic treatment, Lignin-polysaccharide networks, Bio-refinery
National Category
Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-48525 (URN)000295864500012 ()2-s2.0-80051559058 (Scopus ID)
Note
QC 20111122Available from: 2011-11-22 Created: 2011-11-21 Last updated: 2017-12-08Bibliographically approved
2. Extraction of polymers from enzyme-treated softwood
Open this publication in new window or tab >>Extraction of polymers from enzyme-treated softwood
Show others...
2011 (English)In: BioResources, ISSN 1930-2126, E-ISSN 1930-2126, Vol. 6, no 4, 4606-4614 p.Article in journal (Refereed) Published
Abstract [en]

In a biorefinery context it is an advantage to fractionate and extract different wood components in a relatively pure form. However, one major obstacle for efficient extraction of wood polymers (lignin, polysaccharides etc.) is the covalent lignin-polysaccharide networks present in lignified cell walls. Enzymatic catalysis might be a useful tool for a controlled degradation of these networks, thereby enhancing the extraction of high molecular weight polymers. In this work, a methanol-alkali mixture was used to extract two different wood samples treated with endoxylanase and gammanase, respectively. Wood chips were pretreated with alkali prior to enzymatic treatment to enhance the cell-wall accessibility to enzymes. Extractions were also carried out on non-enzyme-treated samples to evaluate the enzymatic effects. Results showed that the enzymatic treatment increased the extraction yield, with gammanase as the more efficient of the two enzymes. Furthermore, polymers extracted from xylanase-treated wood had a higher degree of polymerization than the reference.

National Category
Engineering and Technology
Research subject
SRA - Production
Identifiers
urn:nbn:se:kth:diva-49731 (URN)000298119500071 ()2-s2.0-84863040860 (Scopus ID)
Funder
XPRES - Initiative for excellence in production research
Note
QC 20111130Available from: 2011-11-29 Created: 2011-11-29 Last updated: 2017-12-08Bibliographically approved
3. Stabilisation of polysaccharides during alkaline pretreatment of wood combined with enzyme-supported extractions in a biorefinery
Open this publication in new window or tab >>Stabilisation of polysaccharides during alkaline pretreatment of wood combined with enzyme-supported extractions in a biorefinery
2015 (English)In: Journal of wood chemistry and technology, ISSN 0277-3813, E-ISSN 1532-2319, Vol. 35, no 2, 91-101 p.Article in journal (Refereed) Published
Abstract [en]

Specific enzymes have been demonstrated to increase the possibilities for extracting wood polymers. Enzymatic treatment requires an open wood structure, which was achieved by extended impregnation of the wood. However, some of the hemicelluloses, primarily glucomannan, and lignin were lost during the impregnation. To improve the carbohydrate yield, three glucomannan modification agents: sodium borohydride, polysulphide and anthraquinone, were used, which increased the yields of the impregnated materials from 76.6% to 89.6%, 81.3% and 80.0%, respectively. Through the use of additives, most of the glucomannan could be retained in the wood while still allowing the enzymes to penetrate the wood and attack the polymers. The additives also increased the extraction yield from 9 to 12% w/w wood. Gamanase treatment prior to the extraction increased the extraction yield to 14%. Of the three stabilising agents, sodium borohydride was the most efficient, providing the highest extraction yields.

Keyword
extended impregnation, peeling reaction, sodium borohydride (NaBH4), polysulphide (PS), anthraquinone (AQ), extraction, biorefinery
National Category
Polymer Technologies
Research subject
Fibre and Polymer Science
Identifiers
urn:nbn:se:kth:diva-150392 (URN)10.1080/02773813.2013.875041 (DOI)000345585100001 ()2-s2.0-84913587206 (Scopus ID)
Funder
Knut and Alice Wallenberg Foundation, 8102
Note

Updated from manuscript to article in journal.

QC 20150115

Available from: 2014-09-02 Created: 2014-09-02 Last updated: 2017-12-05Bibliographically approved
4. Mild steam explosion: A way to activate wood for enzymatic treatment, chemical pulping and biorefinery processes
Open this publication in new window or tab >>Mild steam explosion: A way to activate wood for enzymatic treatment, chemical pulping and biorefinery processes
Show others...
2012 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 27, no 5, 828-835 p.Article in journal (Refereed) Published
Abstract [en]

Industrially chipped wood chips of Norway spruce (Picea abies) were subjected to mild steam explosion (115 - 160°C) in a small-scale steam explosion reactor. This was followed by kraft cooking or extraction in alkali at 130°C for two hours, or by an enzymatic treatment with a culture filtrate in order to investigate the efficiency of the process in opening wood structure. The results demonstrated that mild explosion has an effect on opening wood structure, shown by increased release of glucomannans during alkaline extraction and faster delignification in kraft cooks for steam-exploded samples. The effect was also shown by analysis of the released reducing sugars of enzymatic treated wood chips, which showed that the wood structure became accessible for enzymes even at very modest mild steam explosion conditions. This was not observed in untreated wood chips, used as reference. The enzyme activity increased with increased temperature during mild steam explosion, and the effect did not seem to be linear. The mechanical effect of steam explosion seems to be of great importance at lower temperatures, and both chemical and mechanical effects are important at higher steam explosion temperatures. Samples for enzymatic treatment were taken both from the edges of wood chips as well as from the middle part of the chips, and the effect of steam explosion was somewhat greater in samples from the middle parts.

Keyword
Enzymatic activity, Kraft cooking, Mild steam explosion, Norway spruce
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-115485 (URN)10.3183/NPPRJ-2012-27-05-p828-835 (DOI)000313375400001 ()2-s2.0-84871743517 (Scopus ID)
Funder
Knut and Alice Wallenberg Foundation
Note

QC 20130116

Available from: 2013-01-16 Created: 2013-01-15 Last updated: 2017-12-06Bibliographically approved
5. A method for studying effects on lignin-polysaccharide networks during degradation and technical processing of wood
Open this publication in new window or tab >>A method for studying effects on lignin-polysaccharide networks during degradation and technical processing of wood
(English)Manuscript (preprint) (Other academic)
Identifiers
urn:nbn:se:kth:diva-149642 (URN)
Note

QS 2014

Available from: 2014-08-25 Created: 2014-08-25 Last updated: 2014-09-03Bibliographically approved
6. Improved yield and pulp properties by adding sodium dithionite in kraft pulping of spruce
Open this publication in new window or tab >>Improved yield and pulp properties by adding sodium dithionite in kraft pulping of spruce
Show others...
(English)Manuscript (preprint) (Other academic)
Abstract [en]

The reductive effect of sodium dithionite (Na2S2O4) on sugar model compounds was investigated. Results revealed that parts of open aldehyde forms in the sugars were reduced to the corresponding alditols by Na2S2O4. The possibilities to improve yield and other properties of spruce kraft pulp by addition of Na2S2O4 were also investigated. The yield, carbohydrate compositions, Klason lignin, intrinsic viscosity, kappa number of pulp, tensile strength and optical properties of resultant paper sheets were analysed. Compare with the normal kraft pulp without Na2S2O4 addition, yield together with viscosity were increased, while Klason lignin and kappa number were decreased. The brightness and tensile strength of paper sheet were also improved. The only drawback for adding sodium dithionite to white liquor was higher reject content. This could be overcome by pre-impregnation with Na2S2O4 before kraft pulping process. The possibility of applying Na2S2O4 in industrial kraft pulp mill was discussed, including how to generate Na2S2O4 from black liquor thereby closing the process.

Keyword
sodium dithionite, reductive reaction, peeling reaction, kraft pulping, pulp quality
National Category
Polymer Technologies
Research subject
Fibre and Polymer Science
Identifiers
urn:nbn:se:kth:diva-150393 (URN)
Funder
Knut and Alice Wallenberg Foundation, 8102
Note

QS 2014

Available from: 2014-09-02 Created: 2014-09-02 Last updated: 2015-04-14Bibliographically approved
7. Dithionite impregnation combined with mild steam explosion of spruce wood – an improved version of kraft pulping
Open this publication in new window or tab >>Dithionite impregnation combined with mild steam explosion of spruce wood – an improved version of kraft pulping
Show others...
(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
sodium dithionite, mild steam explosion, kraft pulping, peeling, enhanced delignification
National Category
Polymer Technologies
Research subject
Fibre and Polymer Science
Identifiers
urn:nbn:se:kth:diva-150394 (URN)
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

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