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Oxygen delignification: Laboratory evaluation of the impact of dissolved organic matter, sodium car­bonate and sodium thiosulfate
Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013). BTG Instruments.
BTG Instruments.
Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences (from 2013).
2019 (English)In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 73, no 7, p. 645-652Article in journal (Refereed) Published
Abstract [en]

Dissolved matter (DM) in the oxygen delignification (O2Del) stage affects the lignin and carbohydrate degradation. To understand this topic better, laboratory O2Del experiments were conducted with controlled addition of either unoxidized dissolved matter (UnoxDM) originating from the cooking stage or oxidized dissolved matter (OxDM) recycled from the post-O2Del washing. The presence of UnoxDM decreased the delignification, while the presence of OxDM showed the opposite effect, both compared to a well-washed pulp and at the same alkali charge level. However, both types of DM had a negative impact on the carbohydrate degradation. The distribution between these DMs will affect the resulting lignin degradation, because the filtrate accompanying the fibers into the O2Del stage is a mixture of UnoxDM and OxDM. It is proposed that the positive impact on the delignification by OxDM is due to the high carbonate ion concentration in the filtrate. Further, the high content of thiosulfate ions in the UnoxDM was one of the reasons for the lower delignification in its presence.

Place, publisher, year, edition, pages
Walter de Gruyter, 2019. Vol. 73, no 7, p. 645-652
Keywords [en]
carbonate, carryover, COD; dissolved lignin, dissolved organic matter, filtrate, oxidized dissolved matter, oxygen delignification, thiosulfate, unoxidized dissolved matter
National Category
Chemical Engineering
Research subject
Chemical Engineering
Identifiers
URN: urn:nbn:se:kau:diva-67509DOI: 10.1515/hf-2018-0179OAI: oai:DiVA.org:kau-67509DiVA, id: diva2:1229471
Note

Artikeln ingick som manuskript i Wilkes doktorsavhandling The Impact of Dissolved Matter on Fiberline Processes.

Available from: 2018-06-30 Created: 2018-06-30 Last updated: 2019-09-12Bibliographically approved
In thesis
1. The Impact of Dissolved Matter on Fiberline Processes
Open this publication in new window or tab >>The Impact of Dissolved Matter on Fiberline Processes
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The impact of dissolved matter on the performance of four fiberline process stages was investigated: oxygen delignification, hot acid treatment, chlorine dioxide bleaching, and hydrogen peroxide reinforced alkaline extraction. In particular the impact on delignification due to dissolved lignin was studied.

The impact of unoxidized and oxidized dissolved matter on lignin and carbohydrate degradation was investigated in a laboratory oxygen delignification stage. It was concluded that the delignification was decreased by the presence of unoxidized dissolved matter but increased in the case of oxidized dissolved matter. Both types of dissolved matter comparably increased the carbohydrate degradation. Thus, the presence of unoxidized dissolved matter impaired the selectivity. In the case of oxidized dissolved matter, the selec­tiv­ity was affected in the same way as when using a higher sodium hydroxide charge.

The presence of dissolved matter reduced the efficiency of a laboratory hot acid stage, and subsequently further affected the chemical demand in a following chlorine dioxide stage. In a laboratory chlorine dioxide stage, the presence of dissolved matter reduced the delignifica­tion. The additional chemical demand required to compensate for this reduc­tion was proportional to the content of dissolved matter. Moreover, the total chemical demand was found proportional to the total kappa number of the pulp, that is the sum of the fiber and filtrate kappa numbers. Finally, the presence of dissolved matter in a laboratory hydrogen peroxide reinforced alkaline extrac­tion stage reduced both the delignification and the brightness.

Furthermore, mill studies showed that the content of dissolved lignin varied significantly, and often more than the fiber-bound lignin, in a bleaching stage. For chlorine dioxide stages, it was proposed that the chemical consumption could be reduced by controlling the chemical charge based on the sum of the fiber-bound lignin and the dissolved lignin.

Abstract [en]

Pulp mills employ different control strategies to decrease the consumption of raw materials while still maintaining high product quality. To operate a kraft pulp mill in an efficient manner, it is essential to identify the key process parameters. Residual lignin is one of the most important parameters in chemical pulping and most mills base their process control on measurements of the lignin content, analyzed as kappa number. However, they typically only determine the content of the fiber-bound lignin while the dissolved lignin in the pulp slurry is merely seen as a disturbance.

Dissolved matter, especially dissolved lignin, consumes bleaching chemicals, and any variability of the dissolved lignin content will lead to non-optimal chemical charges and subsequently higher production cost. By measuring the dissolved lignin content as well as the fiber-bound lignin content, pulp mills can however apply chemicals based on the actual total bleach load. The impact of dissolved matter was investigated in four different process stages and it was concluded that both the content and the type of dissolved matter affected the performance of the stages. Furthermore, increasing the chemical charges in the process stages could only partly compensate for the negative impact of the dissolved matter.

Place, publisher, year, edition, pages
Karlstad: Karlstads universitet, 2018. p. 104
Series
Karlstad University Studies, ISSN 1403-8099 ; 2018:29
Keywords
Bleach plant control, Carbonate, Carryover, Chlorine dioxide bleaching, COD, Dissolved lignin, Dissolved matter, Fiberline control, Filtrate, Hexenuronic acid, Hydrogen peroxide bleaching, Kappa number, Oxygen delignification, Wash loss
National Category
Chemical Engineering
Research subject
Chemical Engineering
Identifiers
urn:nbn:se:kau:diva-67511 (URN)978-91-7063-862-6 (ISBN)978-91-7063-957-9 (ISBN)
Public defence
2018-09-06, Nyquistsalen, 9C203, Karlstads universitet, Karlstad, 13:00 (Swedish)
Opponent
Supervisors
Funder
Knowledge Foundation
Note

Finansiär är även BTG Instruments. 

Artikel 4, 5 och 6 ingick som manuskript i avhandlingen, nu publicerade. 

Available from: 2018-08-17 Created: 2018-07-02 Last updated: 2019-12-13Bibliographically approved

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Wilke, CarolineGermgård, Ulf

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