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Some process aspects on acid sulphite pulping of softwood
Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.ORCID iD: 0000-0003-4841-2568
Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences. (Pulp technology)
Domsjö Fabriker AB, Örnsköldsvik, Sweden.
MoRe Research, Örnsköldsvik, Sweden.
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Acid sulphite pulping is currently used for production of either paper grade pulp or dissolving grade pulp but its benefits are best seen when producing dissolving grade pulp. In this study acid sulphite pulping of either 100% pine or 100% spruce were carried out to investigate the effects of the cooking conditions on the final pulp composition. Higher cooking temperature had an impact on the delignification rate but also on the lignin condensation reactions. Lignin condensation reactions were found to have a strong negative influence on the  yield of cellulose and hemicellulose compounds in the final pulp samples. The influence of time, residual content of cooking acid and temperature on the delignification rate and on the lignin condensation reactions were analyzed and it was found that lignin condensation reactions were very frequent if the cooking acid concentration was too low.  

Keyword [en]
Acid sulphite; cellulose; extractives; hemicelluloses; lignin condensation.
National Category
Engineering and Technology
Research subject
Chemical Engineering
Identifiers
URN: urn:nbn:se:kau:diva-46908OAI: oai:DiVA.org:kau-46908DiVA: diva2:1038870
Funder
MoRe ResearchDomsjö FabrikerKnowledge FoundationThe Kempe Foundations
Available from: 2016-10-20 Created: 2016-10-20 Last updated: 2016-10-24
In thesis
1. The initial phase of sodium sulfite pulping of softwood: A comparison of different pulping options
Open this publication in new window or tab >>The initial phase of sodium sulfite pulping of softwood: A comparison of different pulping options
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Single stage and two-stage sodium sulfite cooking were carried out on either spruce, pine or pure pine heartwood chips to investigate the influence of several process parameters on the initial phase of such a cook down to about 60 % pulp yield. The cooking experiments were carried out in the laboratory with either a lab-prepared or a mill-prepared cooking acid and the temperature and time were varied. The influences of dissolved organic and inorganic components in the cooking liquor on the final pulp composition and on the extent of side reactions were investigated. Kinetic equations were developed and the activation energies for delignification and carbohydrate dissolution were calculated using the Arrhenius equation. A better understanding of the delignification mechanisms during bisulfite and acid sulfite cooking was obtained by analyzing the lignin carbohydrate complexes (LCC) present in the pulp when different cooking conditions were used. It was found that using a mill-prepared cooking acid beneficial effect with respect to side reactions, extractives removal and higher stability in pH during the cook were observed compared to a lab-prepared cooking acid. However, no significant difference in degrees of delignification or carbohydrate degradation was seen.

 The cellulose yield was not affected in the initial phase of the cook however; temperature had an influence on the rates of both delignification and hemicellulose removal. It was also found that the  corresponding activation energies increased in the order:  xylan, glucomannan, lignin and cellulose. The cooking temperature could thus be used to control the cook to a given carbohydrate composition in the final pulp. Lignin condensation reactions were observed during acid sulfite cooking, especially at higher temperatures. The LCC studies indicated the existence of covalent bonds between lignin and hemicellulose components with respect to xylan and glucomannan. LCC in native wood showed the presence of phenyl glycosides, ϒ-esters and α-ethers; whereas the α-ethers  were affected during sulfite pulping. The existence of covalent bonds between lignin and wood polysaccharides might be the rate-limiting factor in sulfite pulping.

Abstract [en]

The sulfite pulping process is today practised in only a small number of pulp mills around the globe and the number of sulfite mills that use sodium as the base (cation) is less than five. However, due to the increasing interest in the wood based biorefinery concept, the benefits of sulfite pulping and especially the sodium based variety, has recently gained a lot of interest. It was therefore considered to be of high importance to further study the sodium based sulfite process to investigate if its benefits could be better utilized in the future in the production of dissolving pulps. Of specific interest was to investigate how the pulping conditions in the initial part of the cook (≥ 60 % pulp yield) should be performed in the best way.

Thus, this thesis is focused on the initial phase of sodium based single stage bisulfite, acid sulfite and two-stage sulfite cooking of either 100 % spruce, 100 % pine or 100 % pine heartwood chips. The cooking experiments were carried out with either a lab prepared or a mill prepared cooking acid and the temperature and cooking time were varied. Activation energies for different wood components were investigated as well as side reactions concerning the formation of thiosulfate. LCC (Lignin carbohydrates complexes) studies were carried out to investigate the influence of different cooking conditions on lignin carbohydrate linkages.

Place, publisher, year, edition, pages
Karlstad: Karlstads universitet, 2016. 81 p.
Series
Karlstad University Studies, ISSN 1403-8099 ; 2016:43
Keyword
Activation energy, acid sulfite pulping, bisulfite pulping, cellulose, delignification, dissolving pulp, extractives, glucomannan, hemicelluloses, lignin, lignin condensation, lignin carbohydrate complexes, pine, spruce, thiosulfate, total SO2, xylan
National Category
Chemical Engineering
Research subject
Chemical Engineering
Identifiers
urn:nbn:se:kau:diva-46929 (URN)978-91-7063-726-1 (ISBN)
Public defence
2016-12-15, Rejmersalen, 9C204, Karlstad University, Karlstad, Sweden, 13:00 (English)
Opponent
Supervisors
Funder
Knowledge FoundationThe Kempe FoundationsMoRe ResearchDomsjö FabrikerKnut and Alice Wallenberg Foundation
Available from: 2016-11-25 Created: 2016-10-24 Last updated: 2016-11-25Bibliographically approved

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