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On the structural significance of the kappa number measurement
KTH, Tidigare Institutioner                               , Pappers- och massateknik.
KTH, Tidigare Institutioner                               , Pappers- och massateknik.
1998 (Engelska)Ingår i: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 13, nr 2, s. 153-158Artikel i tidskrift (Refereegranskat) 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.

Ort, förlag, år, upplaga, sidor
1998. Vol. 13, nr 2, s. 153-158
Nyckelord [en]
kappa number, kraft pulps, soda pulps, lignin, carbohydrates, uronic acids, permanganate consumption, HEXENEURONIC ACID GROUPS, KRAFT, PERMANGANATE, COOKING, LIGNINS, XYLAN, PULPS
Nationell ämneskategori
Teknik och teknologier
Identifikatorer
URN: urn:nbn:se:kth:diva-12988ISI: 000081970700011OAI: oai:DiVA.org:kth-12988DiVA, id: diva2:320009
Anmärkning
QC 20100521 Tillgänglig från: 2010-05-21 Skapad: 2010-05-21 Senast uppdaterad: 2017-12-12Bibliografiskt granskad
Ingår i avhandling
1. Towards an accurate determination of lignin in chemical pulps: The meaning of kappa number as a tool for analysis of oxidable groups
Öppna denna publikation i ny flik eller fönster >>Towards an accurate determination of lignin in chemical pulps: The meaning of kappa number as a tool for analysis of oxidable groups
1999 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
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.

Ort, förlag, år, upplaga, sidor
Stockholm: KTH, 1999. s. 69
Serie
Trita-PMT ; 1999:3
Nationell ämneskategori
Teknik och teknologier
Identifikatorer
urn:nbn:se:kth:diva-2780 (URN)99-2938730-7 (ISBN)
Disputation
1999-03-31, 00:00 (Engelska)
Anmärkning
QC 20100518Tillgänglig från: 2000-01-01 Skapad: 2000-01-01 Senast uppdaterad: 2010-05-21Bibliografiskt granskad

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