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Kinetics and mechanism of kappa number determination
1998 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, Vol. 13, no 2, 147-152Article 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 [en]
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 (ISI)oai:DiVA.org:kth-12987 (OAI)diva2:320008 (DiVA)
Note
QC 20100521Available from2010-05-21 Created:2010-05-21 Last updated:2010-05-21Bibliographically approved
In thesis
1. Towards an accurate determination of lignin in chemical pulps
Open this publication in new window or tab >>Towards an accurate determination of lignin in chemical pulps : The meaning of kappa number as a tool for analysis of oxidable groups
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.

Publisher, range
Stockholm: KTH, 1999. 69 p.
Series
Trita-PMT, 1999:3
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-2780 (URN)99-2938730-7 (ISBN)
Public defence
1999-03-31, 00:00 (English)
Note
QC 20100518Available from2000-01-01 Created:2000-01-01 Last updated:2010-05-21Bibliographically approved

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