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Energy efficient refining of Black spruce TMP by using acid hydrogen peroxide: Part 2. Washing, chelating and bleaching studies
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics. (FSCN)
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics. (FSCN)
Eka Chemicals AB, Bohus, Sweden.
2009 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, Vol. 24, no 3, 266-272 p.Article in journal (Refereed) Published
Abstract [en]

The acid hydrogen peroxide system has the potential to significantly

reduce the specific energy consumption in the production of softwood

thermomechanical pulps (TMPs). A drawback of the chemical system is

discoloration of the pulp during refining. The work presented in this

study evaluates the possibility to regain the lost brightness by

washing, chelating and sodium dithionite or hydrogen peroxide bleaching

of the treated pulps.

A washing or chelating procedure can reduce the metal ion content of

the chemically treated TMPs considerably, though brightness can be

increased by a maximum of two ISO units. The amount of iron can be

further reduced to a level similar to that of untreated pulps by

performing a reducing agent-assisted chelating stage (Q(Y)) with

dithionite. The discoloration cannot,, however, be completely

eliminated. The brightness decrease-of the treated pulps is thus not

only caused by higher iron content in the pulp, but is also dependent

on the type of iron compound and/or other coloured compounds connected

with the acid hydrogen peroxide treatment.

Oxidative bleaching with hydrogen peroxide (P) is more effective than

reductive bleaching with sodium dithionite in regaining the brightness

lost during the energy reductive treatment. By using a Q(Y) P sequence,

a hydrogen peroxide charge of 3.8% was needed to reach an ISO

brightness of 75% for the chemically treated pulps. The corresponding

hydrogen peroxide charge for the untreated TMP reference was 2.5%.

 

Place, publisher, year, edition, pages
Stockholm: SPCI , 2009. Vol. 24, no 3, 266-272 p.
Keyword [en]
TMP, Black spruce, Energy reduction, Bleaching, Hydrogen peroxide, Sodium dithionite, Brightness, Metals
National Category
Paper, Pulp and Fiber Technology
Identifiers
URN: urn:nbn:se:miun:diva-8825DOI: 10.3183/NPPRJ-2009-24-03-p266-272ISI: 000270862100002Scopus ID: 2-s2.0-72749097945OAI: oai:DiVA.org:miun-8825DiVA: diva2:213797
Projects
Mechanical Pulp Industrial Research College
Available from: 2009-04-29 Created: 2009-04-29 Last updated: 2013-12-16Bibliographically approved
In thesis
1. Influence of acid hydrogen peroxide treatment on refining energy and TMP properties
Open this publication in new window or tab >>Influence of acid hydrogen peroxide treatment on refining energy and TMP properties
2009 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The potential of using acid hydrogen peroxide under Fenton conditions to lower the electrical energy consumed during the production of Black spruce (Picea mariana) thermomechanical pulp (TMP) was investigated. The chemical system, which consisted of ferrous sulphate, hydrogen peroxide and optionally an enhancer (3,4-dimethoxybenzyl alcohol, ethylenediaminetetraacetic acid or oxalic acid/sodium oxalate), was evaluated as an inter-stage treatment where the primary refiner was used as a mixer. The produced TMPs were thoroughly characterised in order to explain the effect of the chemical system on fibre development and to be able to propose a mechanism for the impact on refining energy reduction. The possibility to improve the optical properties by washing, chelating and sodium dithionite or hydrogen peroxide bleaching the treated pulps was evaluated.

 

The results obtained in a pilot plant trial show that it is possible to significantly reduce the comparative specific energy consumption by approximately 20% and 35% at a freeness value of 100 ml CSF or a tensile index of 45 Nm/g by using 1% and 2% hydrogen peroxide respectively. The energy reduction is obtained without any substantial change in the fractional composition of the pulp, though tear strength is slightly reduced, as are brightness and pulp yield. No major differences between the reference pulp and the chemically treated pulps were found with respect to fibre length, width or cross-sectional dimensions. However, the acid hydrogen peroxide-treated pulps tend to have more collapsed fibres, higher flexibility, a larger specific surface area and a lower coarseness value. The yield loss accompanying the treatment is mainly a consequence of degraded hemicelluloses. It was also found that the total charge of the chemically treated pulps is higher compared to the reference pulps, something that may have influenced the softening behaviour of the fibre wall.

 

A washing or chelating procedure can reduce the metal ion content of the chemically treated TMPs considerably. The amount of iron can be further reduced to a level similar to that of untreated pulps by performing a reducing agent-assisted chelating stage (QY) with dithionite. The discoloration cannot, however, be completely eliminated. The brightness decrease of the treated pulps is thus not only caused by higher iron content in the pulp, but is also dependent on the type of iron compound and/or other coloured compounds connected with the acid hydrogen peroxide treatment. Oxidative bleaching with hydrogen peroxide (P) is more effective than reductive bleaching with sodium dithionite in regaining the brightness lost during the energy reductive treatment. Using a QY P sequence, a hydrogen peroxide charge of 3.8% was needed to reach an ISO brightness of 75% for the chemically treated pulps. The corresponding hydrogen peroxide charge for the untreated TMP reference was 2.5%.

 

The radicals generated in the Fenton reaction will probably attack and weaken/soften the available outer fibre wall layers. This could facilitate fibre development and consequently lower the electrical energy demand for a certain degree of refinement.

Place, publisher, year, edition, pages
Sundsvall: FSCN - Fibre Science and Communication Network, 2009. 69 p.
Series
Mid Sweden University licentiate thesis, ISSN 1652-8948 ; 37
Keyword
TMP, Black Spruce, Energy reduction, Hydrogen peroxide, Ferrous sulphate, Refining, Inter-stage treatment, Pulp and paper properties, Fenton´s reagent, Bleaching, Sodium dithionite, Brightness, Metals, Fibre dimensions, Cross-sectional dimensions, Chemical composition
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:miun:diva-9207 (URN)978-91-86073-40-4 (ISBN)
Presentation
O102, Mittuniversitetet, Sundsvall (Swedish)
Opponent
Supervisors
Available from: 2009-06-24 Created: 2009-06-23 Last updated: 2009-11-18Bibliographically approved
2. The use of Fenton chemistry for reducing the refining energy during TMP production: the effect of free ferrous and free or chelated ferric ions
Open this publication in new window or tab >>The use of Fenton chemistry for reducing the refining energy during TMP production: the effect of free ferrous and free or chelated ferric ions
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The potential of using acid hydrogen peroxide under Fenton conditions to lowerthe electrical energy consumed during the production of Black spruce (Piceamariana) thermomechanical pulp (TMP) was investigated in pilot scale. Thechemical system, which consisted of ferrous sulphate, hydrogen peroxide andoptionally an enhancer (such as a chelating agent), was evaluated as an inter-stagetreatment. The produced TMPs were thoroughly characterised in order to explainthe effect of the chemical system on fibre development and to be able to propose amechanism for the impact on refining energy reduction. The possibility to improvethe optical properties by washing, chelating and sodium dithionite or hydrogenperoxide bleaching the treated pulps was evaluated. The system of lignocellulosicmaterial, a Norway spruce (Picea abies) TMP, and Fenton chemistry was alsoevaluated in a model study to understand more about how conditions such as e.g.initial pH, dissolved organic material and reaction time affect the reactions.Ferrous and ferric ions (free and chelated) and different anions were evaluated.Moreover, it was examined whether hydroxyl radicals could be detected andmonitored.The results obtained in pilot scale showed that it is possible to significantly reducethe specific energy consumption by approximately 20% and 35% at a freenessvalue of 100 ml CSF or a tensile index of 45 Nm/g by using 1% and 2% hydrogenperoxide respectively. The energy reduction was obtained without any substantialchange to the fractional composition of the pulp, although tear strength wasslightly reduced, as were brightness and pulp yield. No major differences betweenthe reference pulp and the chemically treated pulps were found with respect tofibre length, width or cross-sectional dimensions. However, the acid hydrogenperoxide-treated pulps tended to have more collapsed fibres, higher flexibility, alarger specific surface area and a lower coarseness value. The yield lossiiiaccompanying the treatment was mainly a consequence of degradedhemicelluloses. It was also found that the total charge of the chemically treatedpulps was higher compared to the reference pulps; something that may haveinfluenced the softening behaviour of the fibre wall.A washing or chelating procedure could significantly reduce the metal ion contentof the chemically treated TMPs. The amount of iron could be further reduced to alevel similar to that of untreated pulps by performing a reducing agent-assistedchelating stage with dithionite. The discoloration could not, however, becompletely eliminated. The brightness decrease of the treated pulps was thereforenot only caused by the greater iron content in the pulp, but was also dependent onthe type of iron compound and/or other coloured compounds connected with theacid hydrogen peroxide treatment. Oxidative bleaching using hydrogen peroxidewas more effective than reductive bleaching using sodium dithionite in regainingthe brightness that was lost during the energy reductive treatment.From the model study and by using a chemiluminescence method, it could beconcluded that hydroxyl radicals were present in the system of Fenton chemicalsand lignocellulosic material (TMP). Initial pH, retention time, pulp consistency,type of catalyst (free or chelated) and dissolved organic material had an impact onthe reactions between TMP and acid hydrogen peroxide. Different anions(sulphate, nitrate and chloride) of ferric ion salt gave a similar catalytic effect.There appeared to be more reactions with the TMP when there was less dissolvedorganic material in the liquid phase from the start. A catalyst of ferrous sulphatehad a greater impact on the pulp (increased total fibre charge and carbonyl groups,more dissolved organic material in filtrate) than ferric ions chelated withethylenediaminetetraacetic acid at an initial pH of about 3-7. If using ferric-EDG(ethanol diglycinic acid) as catalyst, the measured effect on the pulp was similar orless compared to using ferrous sulphate. Ferric-EDG, however, gave higherhydrogen peroxide consumption and more detectable hydroxyl radicals than usingferrous sulphate (initial pH 5-8). It is likely that the iron catalyst must bind to theTMP, or be in close proximity to it, for the hydroxyl radicals to be able to react withthe material.A mechanism was proposed: the hydroxyl radicals generated in the Fentonreaction will probably attack and oxidise the available outer fibre surfaces,weakening these layers, and simultaneously dissolve some of the organic material.This can facilitate fibre development, give a better bonding pulp and reduce theelectrical energy required during refining.

Place, publisher, year, edition, pages
Sundsvall: Mid Sweden University, 2013. 102 p.
Series
Mid Sweden University doctoral thesis, ISSN 1652-893X ; 169
National Category
Chemical Engineering
Identifiers
urn:nbn:se:miun:diva-20737 (URN)978-91-87557-15-6 (ISBN)
Supervisors
Available from: 2013-12-16 Created: 2013-12-16 Last updated: 2013-12-16Bibliographically approved

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