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The influence of high temperature on the discoloration and degradation of carbohydrates and on hydrogen peroxide bleaching of spruce TMP
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics. (FSCN – Fibre Science and Communication Network)
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

When processing wood to obtain pulp, the fibers are subjected to high temperatureat moisture levels and to the influence of metal ions. Many process developmentshave resulted in utilization of higher temperatures that induce chemical reactionsin the wood fibers. This thesis deals with some aspects of using high temperaturesin pulping processes. The first part of this work concerns how carbohydrates areaffected, in terms of discoloration and degradation, by high temperature, moisture,and the presence of metal ions. The next part deals with the metal ion profiles inthermomechanical pulp (TMP) processes and the effects of the high temperaturetreatment of native wood under TMP processing conditions. The third sectionconcerns processing conditions present in the high‐temperature hydrogenperoxide bleaching of TMP.In experiments using cotton linter sheets impregnated with glucuronic acid anddifferent metal ions, increased 5‐(hydroxymethyl)furfural and 2‐furaldehydeconcentrations were accompanied by decreased viscosity and increaseddiscoloration when Mg2+ ions and, to some extent, Ca2+ ions were present. Thisindicates that under certain conditions, in this case, dry heat‐induced ageing underslightly acidic conditions and with access to oxygen, the presence of alkaline earthmetals can cause substantial degradation and discoloration of cellulose. Thisindicates that Mg2+ ions can promote the Lewis‐acid‐catalyzed degradation ofcellulose. When glucuronic acid was added to the cotton linter sheets, the presenceof Ca2+ or Mg2+ ions decreased the discoloration caused by the dry heat‐inducedageing of glucuronic acid and also led to a smaller decrease in viscosity comparedto that in cotton linter sheets containing only Ca2+ or Mg2+ ions. This may explainwhy the negative effect of Ca2+ or Mg2+ ions on viscosity is less pronounced incertain pulps.

In mechanical pulping processes, the addition of sodium silicate and kaolin clayand re‐circulation of water from the paper machines increased the levels of ironand aluminum ions. In a mill using dithionite bleaching, the levels of iron andaluminum ions in the final pulp were approximately ten times higher than in a millusing hydrogen peroxide bleaching. This was probably due to extraction of moreiron and aluminum ions from the clay to the water due to low pH and to thecorrosion of process equipment induced by thiosulfate ions derived fromdecomposed dithionite. In laboratory trials, it was impossible to completelyremove iron from these pulps using diethylenetriaminepentaacetic acid orextraction with hydrochloric acid. This was probably due to the strong binding ofiron to the wood fiber or its presence as oxide/hydroxide clusters. The mostimportant issue is to avoid contaminating the pulp with iron ions; process waterand process chemicals with low iron contents should therefore be used. Especiallyin the dithionite bleaching process, iron contamination increases thedecomposition of the dithionite, causing corrosion of the process equipment andadding further iron to the pulp.The shavings method is a straightforward method for studying the formation andelimination of chromophores in wood. Light absorption coefficients, lightscattering coefficients, and brightness can easily be obtained using this method.The method was used for studying how temperature in the absence of mechanicalenergy affects wood brightness. This provided useful information about the effectof process conditions in mechanical pulping and its relationship to chromophoreformation. An advantage of using thin shavings is the rapid penetration ofchemicals into the fibers. The shavings method was therefore also used in studyingthe kinetics of hydrogen peroxide bleaching at high temperature.The high‐temperature (HT) hydrogen peroxide bleaching of a thermomechanicalpulp was carried out in a pressurized laboratory‐scale wing defibrator. Theexperiments demonstrate two ways to obtain high brightness under HT conditions.One way is two‐stage peroxide bleaching with a low total alkali/peroxide ratio inthe first stage to avoid alkaline darkening. The second way is to pre‐impregnatethe pulp with hydrogen peroxide before adding alkali in two stages. Themaximum brightness was reached after only 2.5 minutes at low alkali charge.Thus, the bleaching time can be short and the total alkali charge low under hightemperatureperoxide bleaching conditions. To achieve very high brightness usingHT hydrogen peroxide bleaching, other measures than increasing the alkali chargeand prolonging the bleaching time are necessary.

Place, publisher, year, edition, pages
Sundsvall: Mid Sweden University , 2008. , 80 p.
Series
Mid Sweden University doctoral thesis, ISSN 1652-893X ; 46
Keyword [en]
Temperature, metal ions, cellulose, glucuronic acid, UV-Vis spectroscopy, spruce, TMP, hydrogen peroxide bleaching, spectroscopy, optical properties
National Category
Chemical Engineering
Identifiers
URN: urn:nbn:se:miun:diva-7780ISBN: 978-91-85317-86-8 (print)OAI: oai:DiVA.org:miun-7780DiVA: diva2:128282
Public defence
(English)
Supervisors
Available from: 2008-12-15 Created: 2008-12-15 Last updated: 2009-06-08Bibliographically approved
List of papers
1. The influence of temperature and moisture on the optical properties of cellulose in the presence of metal chlorides and glucuronic acid
Open this publication in new window or tab >>The influence of temperature and moisture on the optical properties of cellulose in the presence of metal chlorides and glucuronic acid
2008 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, Vol. 23, no 1, 72-80 p.Article in journal (Refereed) Published
Abstract [en]

The influence of Mg2+, Ca2+, Fe3+ ions and glucuronic acid on the dry and humid heat-induced (120180C) discoloration of cotton linter sheets was investigated. The quantity of the added metal ions was similar to that of metal ions found in wood and pulp. Heat-induced ageing (120150C, pH 5) under dry conditions caused only slight discoloration of the reference sheets and of the sheets impregnated with the metal ions. However, during ageing at 180C, the presence of Mg2+ ions accelerated the discoloration. An initial pH in the range of 38 had no great influence on the discoloration of the reference sheets, but a low pH in combination with Mg2+ ions increased the discoloration drastically. Under humid ageing conditions at 180C (<30 min), the sheets discolored approximately twice as much as under dry conditions; the difference in discoloration caused by the metal ions was less than in dry ageing. Adding glucuronic acid to the sheets caused extensive discoloration under dry ageing conditions (120180°C), while Ca2+ and Mg2+ ions decreased the glucuronic acid induced discoloration. Under humid conditions (180°C), however, Mg2+ and Ca2+ ions did not prevent the discoloration caused by glucuronic acid. An increase in the absorption coefficient was observed at 285 nm, most likely due to the formation of 5-hydroxy-2-methyl-furaldehyde (HMF) and 2-furaldehyde (furfural). GC-MS analysis reveals increased formation of HMF in the sheets impregnated with Mg2+ ions. Degradation of the cellulose in which the alkaline earth metals act as Lewis acids is proposed.

Keyword
Cellulose, Discoloration, Temperature, Calcium, Magnesium, Iron, HMF, Furfural
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:miun:diva-982 (URN)10.3183/NPPRJ-2008-23-01-p072-080 (DOI)000255491400012 ()2-s2.0-50949125887 (Scopus ID)5157 (Local ID)5157 (Archive number)5157 (OAI)
Available from: 2008-11-19 Created: 2008-11-19 Last updated: 2011-04-04Bibliographically approved
2. The influence of temperature and moisture on the physical properties of cellulose in the presence of metal chlorides and glucuronic acid
Open this publication in new window or tab >>The influence of temperature and moisture on the physical properties of cellulose in the presence of metal chlorides and glucuronic acid
2008 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, Vol. 23, no 1, 81-86 p.Article in journal (Refereed) Published
Abstract [en]

We investigated the influence of Mg2+, Ca2+, and Fe3+ ions and glucuronic acid on the viscosity, after dry or humid ageing, of two different cellulosic materials, cotton linters and dissolving pulp. The quantity of added metal ions was similar to that found in pulp. In the cotton linters sheets, especially in those containing Mg2+, increased 5-hydroxy-2-methyl furfural (HMF) and 2-furaldehyde (furfural) concentrations were accompanied by decreased viscosity under dry conditions at 180C (pH 5). This indicates that Mg2+ ions can promote the Lewis-acidcatalyzed degradation of cellulose. For cotton linters and dissolving pulp sheets, adding Ca2+ and Mg2+ ions is detrimental when ageing at 180C under dry conditions (pH 5). Adding glucuronic acid increases the viscosity of cotton linters sheets, especially when Ca2+ and Mg2+ ions are present. Due to formation of complexes between the Ca2+ and Mg2+ ions and glucuronic acid, these ions reduce pulp viscosity to a smaller degree.

Keyword
Cellulose, High temperature, Metal ions, Glucuronic acid, Viscosity
National Category
Chemical Engineering
Identifiers
urn:nbn:se:miun:diva-4323 (URN)10.3183/NPPRJ-2008-23-01-p081-086 (DOI)000255491400013 ()2-s2.0-50949083981 (Scopus ID)5158 (Local ID)5158 (Archive number)5158 (OAI)
Available from: 2008-11-19 Created: 2008-11-19 Last updated: 2011-04-04Bibliographically approved
3. Comparison of metal profiles in thermomechanical pulping processes in which either hydrogen peroxide or dithionite bleaching is used
Open this publication in new window or tab >>Comparison of metal profiles in thermomechanical pulping processes in which either hydrogen peroxide or dithionite bleaching is used
2003 (English)In: Paperi ja Puu/Paper and timber, ISSN 0031-1243, Vol. 85, no 6, 334-339 p.Article in journal (Refereed) Published
Keyword
Metals in pulp
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:miun:diva-1597 (URN)2-s2.0-0142228676 (Scopus ID)808 (Local ID)808 (Archive number)808 (OAI)
Available from: 2008-12-16 Created: 2008-12-16 Last updated: 2016-09-28Bibliographically approved
4. A study of the formation and elimination of chromophores in wood under mechanical pulping conditions using spectroscopy
Open this publication in new window or tab >>A study of the formation and elimination of chromophores in wood under mechanical pulping conditions using spectroscopy
2010 (English)In: Paperi ja puu - Paper and timber, ISSN 0031-1243, Vol. 92, no 5, 35-39 p.Article in journal (Refereed) Published
Abstract [en]

Thin sections of wood, i.e., shavings, were used in spectroscopic measurements studying the formation and elimination of chromophores under mechanical pulping conditions. Light absorption coefficients, light scattering coefficients, and brightness were monitored.The method was applied to study how temperature in the absence of mechanical energy affects wood brightness. An increase in absorption coefficient at 420 nm indicates formation of ortho-quinone structures. By applying mechanical pulp processing conditions, the light absorption coefficient increased in the 400-500-nm wavelength region, probably due to the formation of chromophores in the lignin. Comparison of heat treated wood shavings with mechanical pulps indicated that additional chromophores were created during the mechanical pulping processes.The method was also used in studying how high-temperature hydrogen peroxide bleaching of the wood shavings affects the light absorption coefficients. The light absorption spectra reveal information about chromophore elimination in wood chemical components during hydrogen peroxide bleaching at slightly pressurized conditions. This is relevant to processes, such as the alkaline peroxide mechanical pulp process, in which the wood chips are impregnated with bleaching chemicals before refining. The easy penetration of chemicals into the wood shavings ensures rapid and even distribution of the treatment chemicals. A change in light absorption coefficient at shorter wavelengths (400-500 nm) was observed.

Keyword
Light scattering coefficient, light absorption coefficient, brightness, wood, chromophore
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:miun:diva-7770 (URN)000282459000011 ()2-s2.0-84862667135 (Scopus ID)
Available from: 2008-12-15 Created: 2008-12-15 Last updated: 2013-02-18Bibliographically approved
5. High-Temperature Bleaching of Mechanical Pulps from Spruce
Open this publication in new window or tab >>High-Temperature Bleaching of Mechanical Pulps from Spruce
(English)Manuscript (Other academic)
Abstract [en]

High-temperature (HT)-peroxide bleaching of a thermomechanical pulp made of Norwegian spruce was investigated; to that end, one-stage reference bleaching at 70°C and one- and two-stage bleaching at 105°C at different total alkali charges (TAs) using a wing defibrator as a mixer were performed. Two-stage HT peroxide bleaching produces a brighter pulp than one-stage HT peroxide bleaching does. The TA should be kept low (10�15 kg/t) and the total alkali/peroxide ratio should be low in the first stage to minimize the COD load and obtain higher residual peroxide. Increased TA does not improve brightness. The bleaching time in HT bleaching at 105°C can be short, since the maximum brightness is reached after only 2.5 min.Preimpregnation of the pulp with hydrogen peroxide before a two-stage alkali addition can produce a pulp with a brightness and residual peroxide comparable to those obtained in conventional one-stage peroxide bleaching at the same hydrogen peroxide charge and at a low TA. The COD load was, however, higher than in conventional bleaching

Keyword
Hydrogen peroxide bleaching TMP
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:miun:diva-6476 (URN)5161 (Local ID)5161 (Archive number)5161 (OAI)
Note
Submitted to Journal of Pulp and Paper Science (JPPS)(ISSN 0826-6220)Available from: 2008-12-07 Created: 2008-12-07 Last updated: 2011-04-04Bibliographically approved

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