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Towards an accurate determination of lignin in chemical pulps: The meaning of kappa number as a tool for analysis of oxidable groups
KTH, Superseded Departments, Pulp and Paper Technology.
1999 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Lignin content is the most important parameter in chemicalpulping. At present, kappa number is the most common parameterfor determination of lignin content and the base for otheron-line methods and for industrial automation (Chapter 1). However, a substantial portion of the kappa number originates from non-lignin structures, for example from pulp xylan, whichhas been severely degraded and modified during the kraft cook (Chapter 2).

During a systematic research about the hexenuronic acid (HUA) structure, one of the most important structures derivedfrom carbohydrates, a new, simple, fast and sensitivecolorimetric method has been developed for the quantificationof the HUA group (Chapter 3). Furthermore, it has been demonstrated that the quantitative contribution of the HUAgroups to the kappa number is 0.84-0.86 kappa units per 10µmol of HUA (Chapter 4).

In systematic work about the reactions involved in the kappanumber determination, it was found that an addition of permanganate onto all the double bonds in the aromatic rings of lignin takes place, resulting in a reduction of permanganate toMnO2. The present standard method should therefore beimproved by rejecting or modifying the iodometric titrationmethod, correcting the concept of remaining permanganate, resetting the applicable region of permanganate consumption andshortening the reaction time (Chapter 5).

The quantitative fundament for the kappa numberdetermination has been found to be a consumption of 11-12equivalents of KMnO4 per mole of C9units from any wood lignin structure. Besides HUA,any other non-lignin but oxidizable structure will, more or less, influence the accuracy of the kappa number determination;the most noticeable structures being double bonds, aldehydes orα-keto carboxylic acids (Chapter 6).

Based on the above fundamental research, anoxymercuration-demercuration-kappa (Ox - Dem kappa) numberdetermination has been developed. All the noticeably interfering non-lignin structures are eliminated by one Ox -Dem procedure before a conventional kappa number determination so that a more accurate determination of aromatic (Klason) lignin content in pulps then can be easily, quickly and directly obtained (Chapter 7).

For industrial and laboratory made unbleached chemicalpulps, it has been revealed that for different pine kraft orsoda pulps 2.9 - 4.8 kappa units were from non-ligninstructures, corresponding to 13-26% of the observed kappanumber. For birch kraft pulps, these data are much higher: 8.2-9.4 units, 60 - 80 % of the observed kappa number! Among these non-lignin contributions, approximately 30-60% are caused by HUA structure while the others are from double bonds, aldehydes or α-keto carboxylicacid structures, except forpine soda pulps where the non-lignin contributions are mainlyfrom the latter types of structures. Preliminary application ofthe Ox - Dem kappa number has resulted in brand new delignification curves for kraft cooking and OQP bleaching of birch pulp. A possible reformation of "lignin" in kraft cookingand a higher bleach-ability after low alkalinity and lowtemperature cooking have been noticed (Chapter 8).

The easy and more accurate determination of lignin contentdescribed in this thesis suggests a promising future for better control of cooking and bleaching and for further optimizationand modification of present chemical pulping procedures.

Place, publisher, year, edition, pages
Stockholm: KTH , 1999. , 69 p.
Series
Trita-PMT, 1999:3
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:kth:diva-2780ISBN: 99-2938730-7 OAI: oai:DiVA.org:kth-2780DiVA: diva2:8493
Public defence
1999-03-31, 00:00 (English)
Note
QC 20100518Available from: 2000-01-01 Created: 2000-01-01 Last updated: 2010-05-21Bibliographically approved
List of papers
1. Xylan degradation products from birch kraft pulp
Open this publication in new window or tab >>Xylan degradation products from birch kraft pulp
1995 (English)In: Proceedings of the 8th International Symposium on Wood and Pulping Chemistry, Helsinki: Vol. I, 1995, 533-540 p.Conference paper, Published paper (Other academic)
Identifiers
urn:nbn:se:kth:diva-12896 (URN)
Note
QC 20100518Available from: 2010-05-18 Created: 2010-05-18 Last updated: 2010-05-21Bibliographically approved
2. An HPLC method for the quantitative determination of hexeneuronic acid groups in chemical pulps
Open this publication in new window or tab >>An HPLC method for the quantitative determination of hexeneuronic acid groups in chemical pulps
1996 (English)In: Carbohydrate Research, ISSN 0008-6215, E-ISSN 1873-426X, Vol. 294, 41-51 p.Article in journal (Refereed) Published
Abstract [en]

It has recently been demonstrated that 4-deoxy-L-threo-hex-4-enopyranosyluronic acid (''hexeneuronic acid'') is present in kraft pulps and linked to the xylan backbone. An analytical method for the quantitative determination of hexeneuronic acid groups has now been developed. The procedure involves a selective hydrolysis with mercuric acetate of the glucosidic linkage between the hexeneuronic acid group and the xylan chain, followed by oxidation with periodate to form P-formyl pyruvic acid. The latter is reacted with thiobarbituric acid, and the red-coloured adduct formed is separated by reverse phase HPLC and quantified by measuring the absorbance at 549 nm, Some kraft pulps have been analysed to illustrate the contribution of hexeneuronic acid groups to the total amount of oxidizable structures present in such pulps.

Keyword
4-deoxy-L-threo-hex-4-enopyranosyluronic acid, xylan, quantitative analysis, colorimetry, kraft pulps, PINE KRAFT PULP, RESIDUES
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-12909 (URN)A1996VV08500004 ()
Note
QC 20100518Available from: 2010-05-18 Created: 2010-05-18 Last updated: 2010-05-21Bibliographically approved
3. The contribution to kappa number from hexeneuronic acid groups in pulp xylan
Open this publication in new window or tab >>The contribution to kappa number from hexeneuronic acid groups in pulp xylan
1997 (English)In: Carbohydrate Research, ISSN 0008-6215, E-ISSN 1873-426X, Vol. 302, no 3-4, 213-218 p.Article in journal (Refereed) Published
Abstract [en]

The kappa number of chemical pulps is widely used both in mill operation and in laboratory work as a measure of the degree of delignification in pulping, oxygen delignification, and prebleaching. Recently, it has been shown that the kappa number reflects not only lignin but also carbohydrate structures sensitive to oxidation by permanganate, notably hexeneuronic acid groups linked to xylan. In the present work, the kappa number units originating from hexeneuronic acid groups calculated on a molar basis have been determined in two different ways, viz. by permanganate oxidation of model compounds and by selective elimination of hexeneuronic acid groups from a series of kraft pulps. The results are in good agreement with each other and demonstrate that 10 mu mol of hexeneuronic acid correspond to 0.84-0.86 kappa units. From kappa number determinations combined with hydrolysis of the pulp with mercuric acetate, it is possible to calculate the amount of hexeneuronic acid groups present in a pulp.

Keyword
4-deoxy-L-threo-hex-4-enopyranosyluronic acid, kappa number, kraft pulps, xylan, KRAFT
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-12986 (URN)A1997XR58000011 ()
Note
QC 20100521 Available from: 2010-05-21 Created: 2010-05-21 Last updated: 2010-05-21Bibliographically approved
4. Kinetics and mechanism of kappa number determination
Open this publication in new window or tab >>Kinetics and mechanism of kappa number determination
1998 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, Vol. 13, no 2, 147-152 p.Article in journal (Refereed) Published
Abstract [en]

The kinetics and mechanism involved in the kappa number determination have been studied using a spectrophotometric method to monitor the oxidation of pine kraft pulp as well as of model compounds for lignin and carbohydrates. It was found that, during the kappa number determination, the permanganate oxidation proceeds stepwise, forming manganese dioxide which is then reduced to manganous ions. Lignin is oxidized by the addition of permanganate to all the double bonds in the aromatic rings followed by a rupture of the rings. The predominant part of the oxidation of lignin is completed within one minute whereas the oxidation of e.g. glucose is slow but proceeds at an accelerating rate during the kappa number determination time (10 min). The spectrophotometric determination of per manganate remaining after the reaction has advantages over the traditional iodometric method.

Keyword
kappa number, kraft pulps, permanganate consumption, kinetics, reaction mechanism, lignin, HEXENEURONIC ACID GROUPS, PERMANGANATE
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-12987 (URN)000081970700010 ()
Note
QC 20100521Available from: 2010-05-21 Created: 2010-05-21 Last updated: 2010-05-21Bibliographically approved
5. On the structural significance of the kappa number measurement
Open this publication in new window or tab >>On the structural significance of the kappa number measurement
1998 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, Vol. 13, no 2, 153-158 p.Article in journal (Refereed) Published
Abstract [en]

The structural significance of a kappa number has been studied by quantifying the permanganate consumption of various isolated pine, birch and poplar lignins, of lignin model compounds and of carbohydrate and other aliphatic compounds under kappa number measurement conditions. It was found that the average permanganate consumption for the different lignins was 11-12 equivalents per phenylpropane unit. This value is in accordance with the addition of permanganate ion to all three double bonds in the aromatic rings regardless of whether these are phenolic or non-phenolic or whether they belong to a guaiacyl or a syringyl unit. It was further found that permanganate can be consumed by other types of oxidizable structures like aliphatic double bonds, aldehyde groups and alpha-keto-carboxylic acid groups. For unbleached kraft pulp samples, the combined consumption of permanganate by lignin and hexenuronic acid groups from xylan was found to be fairly close to the measured kappa number. The small discrepancies found indicate, however, that other types of structures may contribute to the kappa number.

Keyword
kappa number, kraft pulps, soda pulps, lignin, carbohydrates, uronic acids, permanganate consumption, HEXENEURONIC ACID GROUPS, KRAFT, PERMANGANATE, COOKING, LIGNINS, XYLAN, PULPS
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-12988 (URN)000081970700011 ()
Note
QC 20100521 Available from: 2010-05-21 Created: 2010-05-21 Last updated: 2010-05-21Bibliographically approved
6. Oxymercuration-demercuration kappa number: An accurate estimation of the lignin content in chemical pulps
Open this publication in new window or tab >>Oxymercuration-demercuration kappa number: An accurate estimation of the lignin content in chemical pulps
2002 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, Vol. 17, no 4, 410-414 p.Article in journal (Refereed) Published
Abstract [en]

In the kappa number determination, it has been found that non-lignin structures contribute to the consumption of permanganate, and thus make it difficult to estimate the lignin content in the pulp. In order to improve the accuracy of the determination, a two-step pretreatment with mercury acetate - sodium borohydride prior to a conventional kappa number determination is proposed. It has been found that such a pretreatment eliminates all interfering structures in the pulp except a, P-unsaturated carboxylic acid groups. and thus permits a very accurate estimation of the lignin content. The method has been termed "oxymercuration - demercuration (Ox-Dem) kappa number" and can be used to obtain information not only about the lignin content but also about the quantity of other oxidizable structures present in a chemical pulp. New information concerning the delignification reactions taking place in pulping and bleaching can thus be obtained.

Keyword
kappa number, oxymercuration, demercuration, kraft pulps, permanganate consumption, lignin determination, HEXENEURONIC ACID GROUPS, HEXENURONIC ACID, SOFTWOOD, XYLAN
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-12989 (URN)000180616600009 ()
Note
QC 20100521Available from: 2010-05-21 Created: 2010-05-21 Last updated: 2010-05-21Bibliographically approved

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