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Some aspects on the effects of dissolved wood components in kraft pulping
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

During kraft cooking a significant part of the wood material, especially lignin and hemicelluloses, is degraded and dissolved in the cooking liquor, rendering a broad range of degradation products with different molecular mass and functional groups. The main part of this thesis has been devoted to clarify the role of these dissolved wood components (DWC) during kraft cooking. The investigations have covered their influence on e.g. the delignification rate, pulp yield, point of defibration, unbleached pulp c olour and pulp bleachability, i.e. the amount of bleaching chemicals consumed per kappa number or lignin unit to reach a certain brightness. Both softwood (Picea Abies) and hardwood (Eucalyptus urograndis) have been studied. During kraft cooking, many reactions occur simultaneously. Therefore emphasis has been put on separating the effects of hydroxide ions, hydrogen sulphide ions, sodium ions and DWC. This has been enabled by the use of a so called constant-composition-cooking technique, which enables the use of almost constant concentrations of the cooking chemicals during the cook and also results in a very low concentration of DWC in the cooking liquor. The presence of DWC has been controlled by the addition of industrial black liquor. To further scrutinise the role of DWC, the effect of different molecular mass fractions were studied and representative model substances were used to clarify the origin of the observed effects.

A kinetic study showed that the delignification rate was significantly affected by the presence of DWC in the cooking liquor and resulted in a rate increase in the part of the cook where the bulk phase dominates and a decreased delignification rate when the residual phase dominates. The increase in delignification rate was dependent on the concentration of DWC and was observed in softwood as well as hardwood kraft cooks. The rate increasing effect was investigated further by the use of ultra- and nanofiltra tion. This way the DWC was divided into fractions with different molecular mass distributions. The results showed that the increase in delignification rate related more strongly to the content of free phenolic groups in the DWC than on the total amount of DWC. By cooking in the presence of representative model substances the effect was further clarified. Aromatic structures with free phenolic groups gave a rate increasing effect while no visible effect could be seen from other structures. This supports the finding that the delignification rate relates to the amount of free phenols in the cooking liquor and shows that the phenolic functionality take active part in the delignification reactions. Free phenolic groups in the degraded lignin may explain a large part of the rate increasing effect seen from the presence of DWC.

Further, the presence of DWC increased the point of defibration in a eucalyptus kraft cook and made it possible to terminate the cook at a higher kappa number with the same amount of reject. By terminating the cook at a higher kappa number it was possible to noticeably increase the fully bleached pulp yield. The content of hexenuronic acids (HexA) in the eucalyptus pulp depends on the H-factor and increases with delignification, providing that the bulk phase still dominates. Therefore, by increasing the rat e of delignification and terminating the cook at a higher kappa number it was possible to significantly decrease the amount of HexA in the pulp.

The presence of DWC causes a darkening of the unbleached pulp. Bleachability in a D(EOP)DD sequence was negatively affected by the presence of DWC during pulping of softwood, while no effect was seen on the bleachability of hardwood

Place, publisher, year, edition, pages
Stockholm: KTH , 2006. , 65 p.
Series
Trita-FPT-Report, ISSN 1652-2443 ; 2006:6
Keyword [en]
Delignification, Dissolved wood components, Black liquor, Defibration point
National Category
Paper, Pulp and Fiber Technology
Identifiers
URN: urn:nbn:se:kth:diva-3868OAI: oai:DiVA.org:kth-3868DiVA: diva2:9799
Public defence
2006-03-17, Sal F3, Lindstedtsvägen 26, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20100920Available from: 2006-03-08 Created: 2006-03-08 Last updated: 2010-09-20Bibliographically approved
List of papers
1. Continuous Nano- and Ultrafiltration of Kraft Pulping Black Liquor with Ceramic Filters: A method for lowering the load on the recovery boiler while generating valuable side-products
Open this publication in new window or tab >>Continuous Nano- and Ultrafiltration of Kraft Pulping Black Liquor with Ceramic Filters: A method for lowering the load on the recovery boiler while generating valuable side-products
Show others...
2004 (English)In: Industrial crops and products (Print), ISSN 0926-6690, E-ISSN 1872-633X, Vol. 20, no 2, 143-150 p.Article in journal (Refereed) Published
Abstract [en]

Ceramic membranes coated with ZrO2 were used for the continuous separation of a well-defined low molecular weight lignin from softwood and hardwood kraft black liquors on a pilot scale. The membranes used had M-w cut-offs of 1000, 5000, and 15,000 Da, respectively. The flux (permeate flow) through the different membranes measured as L/(m(2 .)h) was studied by varying the inlet pressure and temperature. The black liquor lignins in the permeate from the filters were isolated and studied with GPC and UV spectroscopy. The low molecular weight lignin fraction was highly phenolic and could be polymerised by one-electron oxidation.

Keyword
black liquor, kraft pulping, lignin, recovery boiler, ultra-filtration
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-5431 (URN)10.1016/j.indcrop.2004.04.017 (DOI)000224636700004 ()2-s2.0-4644304536 (Scopus ID)
Note
QC 20100906Available from: 2006-03-08 Created: 2006-03-08 Last updated: 2017-11-21Bibliographically approved
2. The Effect of Sodium Ion Concentration and Dissolved Wood Components in the Kraft Cook of Softwood
Open this publication in new window or tab >>The Effect of Sodium Ion Concentration and Dissolved Wood Components in the Kraft Cook of Softwood
2004 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 19, no 3, 325-329 p.Article in journal (Refereed) Published
Abstract [en]

The effect of ionic strength and dissolved wood components (DWC) in form of industrial black liquor on the delignification rate and the brightness of the unbleached softwood kraft pulp has been investigated. A technique with a high liquor-to-wood ratio (75 L/kg) a so-called constant composition cook was used to separate the effects of the different parameters. The study showed that an increase in the ionic strength led to a decrease in the rate of delignification and gave a more coloured pulp, where as the presence of DWC gave a more coloured pulp and an increase in the delignification rate.

The influence of the ionic strength and DWC on the bleachability of the softwood kraft pulp in an ECF-sequence (D(EOP)DD) was also investigated. The results show that the bleachability i.e. consumption of bleaching chemicals to reach a certain brightness, was not affected by the ionic strength during the cook. The addition of DWC, on the other hand, increased the consumption of bleaching chemicals to reach ISO brightness 89%.

Keyword
kraft pulping, delignification rate, bleachability, softwood, black liquor
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-5432 (URN)000224636500007 ()2-s2.0-6344252669 (Scopus ID)
Note

QC 20141205

Available from: 2006-03-08 Created: 2006-03-08 Last updated: 2017-11-21Bibliographically approved
3. The influence of industrial black liquor on the delignification rate in the kraft cooking
Open this publication in new window or tab >>The influence of industrial black liquor on the delignification rate in the kraft cooking
2007 (English)In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 33, no 4, 240-245 p.Article in journal (Refereed) Published
Abstract [en]

The effect of dissolved wood components in industrial black liquor on the rate of delignification in softwood kraft cooking has been studied The results show that, when industrial black liquor was added, the delignification rate increased significantly during the bulk phase and decreased during the residual phase. A softwood black liquor was fractionated with ceramic membranes with various cut-offs, to see the way the addition of various molecular weight fractions of the black-liquor lignin affected the delignification rate. The results show that the delignification rate is dependent more on the content of phenolic groups than on the size of the lignin fragments. However, a low molecular-weight lignin fraction has a higher content of phenolic groups than a high molecular-weight fraction does. These results may explain one reason for the positive effect of adding industrial black liquor to the bulk phase of a softwood kraft cook.

Keyword
kraft pulping, delignification, black liquors, phenol groups
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-5433 (URN)000254544400009 ()2-s2.0-43049172002 (Scopus ID)
Note

Tidigare titel: The influence of industrial black liquor on the delignification rate in the kraft cook Uppdaterad från manuskript till artikel: 20100920 QC 20100920

Available from: 2006-03-08 Created: 2006-03-08 Last updated: 2017-11-21Bibliographically approved
4. Addition of Dissolved Wood Components to Improve the Delignification Rate and Pulp Yield in Hardwood Kraft Pulping
Open this publication in new window or tab >>Addition of Dissolved Wood Components to Improve the Delignification Rate and Pulp Yield in Hardwood Kraft Pulping
2006 (English)In: Appita journal, ISSN 1038-6807, Vol. 59, no 4, 317-320 p.Article in journal (Refereed) Published
Abstract [en]

This study investigates the effects on the rate of delignification, HexA content and pulp yield of dissolved wood components (DWC) in the cooking liquor during the kraft pulping of Eucalyptus urograndis. The cooking was carried out with and without the addition of 50% DWC, in the form of black liquor, and also with and without the addition of a lignin-like model compound using a so-called constant composition cooking technique.

The results show that the presence of DWC leads to an increase in the rate of delignification which makes it possible to reach kappa number 18 with an H-factor 40% less. Due to the faster delignification, 20% less HexA was formed at kappa number 18 when DWC was added than in the absence of added DWC. The presence of DWC also leads to a yield increase of up to two percentage points measured as lignin-free yield.

Keyword
kraft pulping, dissolved wood components, hexenuronic acid, delignification rate, kappa number, pulp yield, black liquor, lignin
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-5434 (URN)000238831300013 ()2-s2.0-33746224136 (Scopus ID)
Note
Uppdaterad från manuskript till artikel: 20100920 QC 20100920Available from: 2006-03-08 Created: 2006-03-08 Last updated: 2017-11-21Bibliographically approved
5. Influence of Dissolved Wood Components on the Defibration point in Hardwood Kraft Pulping
Open this publication in new window or tab >>Influence of Dissolved Wood Components on the Defibration point in Hardwood Kraft Pulping
(English)Manuscript (Other academic)
National Category
Chemical Process Engineering
Identifiers
urn:nbn:se:kth:diva-5435 (URN)
Note
QC 20100920Available from: 2006-03-08 Created: 2006-03-08 Last updated: 2010-09-20Bibliographically approved

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