EP0464110B1 - Procede de blanchiment servant a la production de pulpes tres claires - Google Patents

Procede de blanchiment servant a la production de pulpes tres claires Download PDF

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Publication number
EP0464110B1
EP0464110B1 EP90905400A EP90905400A EP0464110B1 EP 0464110 B1 EP0464110 B1 EP 0464110B1 EP 90905400 A EP90905400 A EP 90905400A EP 90905400 A EP90905400 A EP 90905400A EP 0464110 B1 EP0464110 B1 EP 0464110B1
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EP
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Prior art keywords
pulp
bleaching
stage
sodium
consistency
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Expired - Lifetime
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EP90905400A
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German (de)
English (en)
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EP0464110A1 (fr
Inventor
Michel Barbe
Carole Gagne
Céline LEDUC
Claude Daneault
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Kvaerner Hymac Inc
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Kvaerner Hymac Inc
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    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
    • D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
    • D21C9/10—Bleaching ; Apparatus therefor
    • D21C9/1057—Multistage, with compounds cited in more than one sub-group D21C9/10, D21C9/12, D21C9/16

Definitions

  • This invention relates to a multistage bleaching process in which reducing agents and oxidizing agents are used sequentially to bleach mechanical and chemimechanical pulps to high brightness levels and partially remove their yellow shade.
  • the process is usually carried out in an aqueous phase at 3 to 5% consistency, a pH of 4.5 to 6.0, a temperature of about 60 ° C and a retention time of up to one hour.
  • a chelating or sequestering agent such as sodium tripolyphosphate (STPP) to remove naturally occuring trace metals is recommended. This agent is being added to the pulp prior to the addition of the reducing agent or is incorporated in the bleaching solution.
  • peroxide (P) is the most commonly employed oxidizing agent for bleaching mechanical and chemimechanical pulps. This alkaline process is normally carried out in a single stage or in a double stage. In both cases, the bleaching is done at a pulp consistency of 15 to 35%, moderate temperatures of 50 to 70 ° C, and retention times of 2 to 3 hours for each stage.
  • stabilizers such as sodium silicate and magnesium sulfate are added to the bleach liquor to prevent decomposition of the oxidizing agent.
  • Sodium hydroxide is also used to maintain an alkaline pH of 9.5 to 11 so as to increase the concentration of the perhydroxyl ion OOH- which is beleived to be the active bleaching agent.
  • pulps are normally pretreated at low consistency with organic chelating agents such as sodium diethylenetriamine penta-acetate (DTPA) to remove naturally occuring trace metals. Additional quantities are added in the bleach liquor to complex trace metals that are desorbed from the pulp as a result of the reaction of the bleaching agents with the chromophores of the pulp.
  • organic chelating agents such as sodium diethylenetriamine penta-acetate (DTPA)
  • DTPA sodium diethylenetriamine penta-acetate
  • a method for the bleaching of high yield or ultra high yield pulp which comprises the steps of sequentially treating the lignocellulosic fibres with a reducing compound and subsequently treating the same fibres with peroxide in two successive stages.
  • the method or process includes three stages where the wood pulp is subjected to bleaching operations.
  • the wood pulp which may be utilized is any high yield or ultra yield pulp such as mechanical, chemimechanical, chemithermomechanical, groundwood, refiner mechanical pulp, thermomechanical pulp, high yield and ultra high yield sulfite pulps.
  • the wood pulp is treated with a reducing compound which may be chosen from many such reducing compounds known to those skilled in the art.
  • a reducing compound which may be chosen from many such reducing compounds known to those skilled in the art.
  • preferred reaction conditions include:
  • the pulp is bleached with a peroxygen compound.
  • Preferred conditions of bleaching include:
  • a peroxygen compound is utilized which is similar to the one used in the second stage.
  • the preferred reaction conditions include:
  • the compounds utilized in the process of the present invention may be selected from among these well known to those skilled in the art.
  • the reducing compounds may be chosen from commercially inorganic reducing agents such as sodium or zinc hydrosulfite (dithionite), sodium or magnesium bisulfite, sodium borohydride, Borol * (a solution of sodium borohydride and sodium hydroxide), thiourea dioxide, ammonium borohydride, hydrazine and organic reducing agents such as amine-boranes and phosphine- boranes. It will be noted that some of these reducing agents are sold commercially with a chelating agent mixed therewith.
  • Examples of the peroxide compound utilized in the second and third stages may include conventional inorganic peroxides such as hydrogen and sodium peroxide and also organic peroxides such as benzyl peroxide, ditertiary-butyl peroxide and peracetic acid.
  • the process flow diagram of figure 1 illustrates the various steps of a continuous operation in which pulps are bleached in multistage according to the present invention.
  • the pulp is first washed with a dewatering device (1) such as, but not exclusively, a standard screw press, a displacement washing screw press, a twin wire press, a disc filter or a twin roll press.
  • a dewatering device (1) such as, but not exclusively, a standard screw press, a displacement washing screw press, a twin wire press, a disc filter or a twin roll press.
  • These devices allow for water removal from the pulp slurry as well as for washing of contaminants such as sodium sulfite, metal ions, organic extractives, dissolved solids, etc., which are known to impair on the bleaching reactions between the bleaching agents and lignocellulosic fibres.
  • the pulp is mixed with the bleaching liquor containing the reducing agent.
  • Mixing devices (2) such as single or double shaft mixers, refiner type mixers, high shear mixers and medium or low consistency pumps can be used. It is important in this stage of the process to disperse the bleaching liquor uniformly onto the fibre surface so that bleaching reactions can prevail over darkening reactions that also occur when lignocellulosic fibres are submitted to high temperature. After this pulp mixing stage the reducing agent reacts with the pulp in an upflow tower or steaming tube (3). A chemical charge of 0.75 to 1.25% sodium hydrosulfite and of 0.3 to 0.5% of sodium borohydride by weight of oven dried pulp are the preferred charges.
  • the efficiency of the mixer is important at this stage of the process to disperse the bleaching liquor uniformly onto the fibre surface so that oxidizing bleaching reactions of the chromophoric groups on the lignocellulosic fibres occur and prevail over darkening reactions that also occur when pulps are submitted to high temperatures.
  • a mixer (5) which allows for the addition of steam and the peroxide bleaching liquor simultaneously.
  • the pulp is transferred to a bleaching tower (6).
  • the most preferred charge of the peroxygen compound in this second stage bleaching is in amount equal to the charge of the last bleaching tower or to one third of the charge of the last bleaching tower.
  • Sodium hydroxide, sodium silicate and magnesium sulfate are preferably added in charge ranges of 0.5-3.0%, 0.0 to 3.0% and 0.01-0.05% respectively. It is also preferable to add small amounts of DTPA between 0.1-0.4%. All these components stabilize the peroxygen compound, in the form of the perhydroxyl ion, initiate and maintain a stable bleaching reaction.
  • the peroxide bleaching liquor mixed with the pulp at this stage can be either prepared from fresh commercial components dissolved in water in separate tanks or it can be a residual bleaching liquor solution from the last stage bleaching tower (9). We have found from mass balance calculations that this latter is preferable to minimize the operating and bleaching cost of the process disclosed in this application.
  • the size of the second bleaching tower (6) is to be determined considering the production rate, reaction time and pulp consistency selected or desired. We have found that a consistency in the 10-12% range, a retention time of 60 to 90 minutes and a temperature of 65 to 70 ° C are preferable to minimize the bleaching cost of the process disclosed.
  • figure 1 we show a schematic of a tower which is discharged with a medium consistency pump so as to have an operation with an efficient control over the bleaching conditions.
  • the pulp is dewatered and washed with a dewatering device (7) such as those described previously and used in position (1) and (4).
  • the purpose is to wash the byproducts produced from the bleaching reactions which occured in the second stage bleaching tower, avoid their carry over to the next bleaching stage and eliminate these from the bleach plant with an adequate white water recirculation strategy.
  • the pulp is mixed with the peroxide bleaching liquor in a mixer (8).
  • the mixer used and its efficiency are important at this stage for the same reasons as those elaborated previously above.
  • the pulp is transferred to a bleaching tower (9).
  • the preferred charge of the peroxygen compound in this third stage bleaching is 3 to 10% by weight of oven dried pulps.
  • Sodium hydroxide, sodium silicate and magnesium sulfate are preferably added in charge ranges of 0.25-0.3%, 0.01% to 3.0% and 0.01-0.05% respectively. It is also preferable to add small amounts of DTPA between 0.2-0.4%.
  • This bleaching liquor is normally prepared from fresh commercial components which are dissolved in water in separate tanks. In addition to this fresh liquor, a small quantity of the residual bleaching liquor solution from the same tower (9) can also be used. The residual bleaching liquor is recovered with the last pair of dewatering presses (11 and 12). We have found that high charges of peroxide are required in this last bleaching tower to achieve high brightness levels.
  • the size of the third bleaching tower (9) is to be determined considering the production rate, reaction time and pulp consistency selected or desired. We have found that a consistency in the 20-35% range is preferable to have high effective concentrations of the oxidizing agents so as to minimize the bleaching cost of the process disclosed.
  • figure 1 we show a schematic of a tower which is discharged in a transfer chest (10) with a screw conveyer. This device allows for a positive displacement out of the tower so as to provide an efficient control over the operating and bleaching conditions of the pulp in the tower.
  • the bleaching chemicals were mixed by hand with a 20-g pulp sample, while the pulp consistency was simultaneously adjusted with demineralized water. Subsequently, the bags were sealed and immersed in a thermostatically controlled bath for the bleaching reactions to occur. After bleaching, the pulps were neutralized to destroy the bleaching agents and to adjust the pulp pH to minimize brightness reversion. For hydrogen peroxide bleaching, sodium metabisulfide was used, while sulfuric acid was used for the other bleaching agents.
  • the pulps were neutralized by diluting the pulp to 3% consistency with the neutralizing agent, mixing the slurry for 5 minutes, and pressing the pulp to 18% consistency. After neutralization, two samples of 3.5g each were used to make the handsheets. The pulps were disintegrated for 2 minutes at a consistency of approximately 0.3%.
  • the sheets were made with demineralized water on a British handsheet machine following the procedures prescribed by the Canadian Pulp and Paper Association. The sheets were pressed for 2 minutes at 345kPag (50 psig) and dried for 24 h at 23 ° C and 50% RH. The brightness was measured with an Elrepho spectrophotometer. Reflectance measurements with Filter Nos. 8, 9, 10, and 11 were made and used to calculate the color coordinates (CIE LAB) reference system. ISO brightness reported are the reflectance values at 457 nm using filter No. 8.
  • each stage was similar to the single stage. However, the two- stage experiments were carried out with 30-g pulp samples, and 40-g samples were used for three stages. In all cases, a 7-g sample was taken at the end of each stage and was processed to obtain brightness values.

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  • Life Sciences & Earth Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Wood Science & Technology (AREA)
  • Paper (AREA)
  • Treatment Of Fiber Materials (AREA)
  • Detergent Compositions (AREA)

Claims (20)

1. Procédé de blanchiment de pâtes mécaniques et chimicomécaniques, qui englobe les étapes consistant à traiter, dans une première étape, la pâte avec un agent réducteur et à traiter ensuite, dans une seconde étape, la même pâte avec un composé peroxygéné, puis à la traiter à nouveau avec un composé peroxygéné dans une troisième étape.
2. Procédé selon la revendication 1, dans lequel l'agent réducteur est l'hydrosulfite de sodium.
3. Procédé selon la revendication 2, dans lequel le traitement de la pâte, dans la première étape, emploie une charge chimique de 0,75 à 1,25% d'hydrosulfite de sodium en poids de pâte séchée au four, en présence d'un agent chélateur, à une température réactionnelle comprise entre 65 et 85 °C, une consistance comprise entre 3,5 et 5%, une durée de réaction comprise entre 1 et 40 minutes et un pH de fin de réaction d'environ 4,5 à 5,0.
4. Procédé selon la revendication 1, dans lequel l'agent réducteur est le borohydrure de sodium.
5. Procédé selon la revendication 4, dans lequel le traitement de la pâte dans la première étape emploie une charge chimique de 0,3 à 0,5% de borohydrure de sodium en poids de pâte séchée au four, en présence d'un agent chélateur, à une température réactionnelle comprise entre 65 et 85 °C, une consistance comprise entre 10 et 12%, une durée de réaction comprise entre 1 et 40 minutes et un pH de fin de réaction de 10,0 à 10,5.
6. Procédé selon la revendication 3 ou 5, dans lequel la pâte de la tour de blanchiment de la première étape et/ou la pâte de la tour de blanchiment de la seconde étape est égouttée et lavée pour éliminer les sous-produits résultant des réactions de blanchiment.
7. Procédé selon la revendication 6, dans lequel on disperse dans la pâte 3 à 10% de peroxygène en poids de la pâte séchée au four, en utilisant un malaxeur, et on transfère la pâte et le liquide de blanchiment dans une tour de blanchiment.
8. Procédé selon la revendication 7, dans lequel on ajoute de l'hydroxyde de sodium, du silicate de sodium et du silicate de magnésium pour stabiliser le composé peroxygéné respectivement dans des gammes de 0,5-3,0%, 0,0 à 3,0% et 0,01 à 0,05%.
9. Procédé selon la revendication 8, dans lequel on ajoute au liquide de blanchiment de petites quantités de DTPA, entre 0,1 - 0,4%.
10. Procédé selon la revendication 9, dans lequel la consistance de la pâte est dans la gamme de 10-12%, la température est de 65 à 70 ° C et le temps de rétention est de 60 à 90 minutes.
11. Procédé selon la revendication 8, dans lequel la consistance de la pâte est dans la gamme de 20-35% et des peroxygènes essentiellement frais sont mélangés à la pâte.
12. Procédé selon la revendication 11, dans lequel la pâte est lavée et égouttée après le blanchiment de la troisième étape.
13. Procédé selon la revendication 12, dans lequel on ajoute à la pâte de l'acide sulfurique après son lavage et son égouttage, pour abaisser le pH de la solution aqueuse à environ 6.
14. Procédé selon la revendication 1, dans lequel le composé réducteur est choisi dans le groupe constitué par le bisulfite de sodium, le bisulfite de magnésium, l'hydrosulfite de zinc, le BOROL@, le dioxyde de thio-urée, le borohydrure d'ammonium et l'hydrazine.
15. Procédé selon la revendication 1, dans lequel le traitement de la pâte avec l'agent réducteur emploie une charge d'environ 0,01 à environ 1,5% en poids, en présence d'un agent chélateur, à une température réactionnelle comprise entre 60 ° C et 100°C, pendant une durée comprise entre 4 et 120 minutes, à une consistance de la pâte de 3% à 35% et à un pH de fin de réaction compris entre 3,5 et environ 11,0; le procédé étant caractérisé en outre par un lavage de ladite pâte après le traitement.
16. Procédé selon la revendication 15, dans lequel le composé peroxygéné est choisi dans le groupe constitué par le peroxyde d'hydrogène, le peroxyde de sodium, le peroxyde de benzyle, le peroxyde de di-t-butyle et l'acide peracétique.
17. Procédé selon la revendication 16, dans lequel le traitement de la pâte avec un composé peroxygéné, dans la seconde étape, emploie une charge comprise entre 0,01% et environ 5,0% en poids, à une température comprise entre 60 ° C et 100°C, pendant une durée comprise entre 4 minutes et 180 minutes, à une consistance de la pâte comprise entre 4% et 40% et à un pH de fin de réaction d'environ 0,5 à 10,5.
18. Procédé selon la revendication 17, dans lequel le traitement avec ledit composé peroxygéné, dans la troisième étape, emploie une charge comprise entre 0,1 et environ 12% en poids, par rapport à la pâte séchée au four, à une température comprise entre 60 °C et 100°C, pendant une durée comprise entre 4 minutes et 250 minutes, à une consistance de la pâte comprise entre 4% et 40% et à un pH de fin de réaction de 7,5 à environ 10,0.
19. Procédé selon la revendication 18, dans lequel le traitement de la pâte avec les composés peroxygé- nés est réalisé en présence d'hydroxyde de sodium, de silicate de sodium, de sulfate de magnésium et de DTPA.
20. Procédé selon la revendication 1, dans lequel la pâte est choisie dans le groupe des pâtes constituées par les pâtes à haut rendement et les pâtes à ultra-haut rendement, que l'on appelle pâtes mécaniques, chimico-mécaniques, chimico-thermomécaniques, pâtes de bois broyé, pâtes au sulfite à haut rendement et à ultra-haut rendement.
EP90905400A 1989-03-23 1990-03-22 Procede de blanchiment servant a la production de pulpes tres claires Expired - Lifetime EP0464110B1 (fr)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
CA000594763A CA1340348C (fr) 1989-03-23 1989-03-23 Procede de blanchiment pour la production de pates tres blanches
CA594763 1989-03-23
PCT/CA1990/000097 WO1990011403A1 (fr) 1989-03-23 1990-03-22 Procede de blanchiment servant a la production de pulpes tres claires

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Publication Number Publication Date
EP0464110A1 EP0464110A1 (fr) 1992-01-08
EP0464110B1 true EP0464110B1 (fr) 1994-06-08

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EP90905400A Expired - Lifetime EP0464110B1 (fr) 1989-03-23 1990-03-22 Procede de blanchiment servant a la production de pulpes tres claires

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EP (1) EP0464110B1 (fr)
AT (1) ATE106961T1 (fr)
CA (1) CA1340348C (fr)
DE (1) DE69009750D1 (fr)
WO (1) WO1990011403A1 (fr)

Families Citing this family (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
USH1690H (en) * 1995-07-20 1997-11-04 Nye; Jeffrey Process for bleaching kraft pulp
FI105932B (fi) * 1996-05-30 2000-10-31 Kemira Chemicals Oy Menetelmä korkeasaanto- tai kierrätysmassan valkaisemiseksi
US20030062138A1 (en) * 2001-05-09 2003-04-03 Hache Maurice Joseph Albert Method for brightening mechanical pulps
EP1418269B1 (fr) * 2002-11-05 2009-02-11 Rohm And Haas Company Procédé de blanchiment des pates mecaniques
FI122239B (fi) * 2004-02-25 2011-10-31 Kemira Oyj Menetelmä kuitumateriaalin käsittelemiseksi ja uusi koostumus
FI120201B (fi) 2004-05-12 2009-07-31 Kemira Oyj Uusi koostumus ja menetelmä kuitumateriaalin käsittelemiseksi
US7967948B2 (en) * 2006-06-02 2011-06-28 International Paper Company Process for non-chlorine oxidative bleaching of mechanical pulp in the presence of optical brightening agents
US20100224333A1 (en) 2009-03-09 2010-09-09 Prasad Duggirala Method and chemical composition to improve efficiency of mechanical pulp
US9932709B2 (en) 2013-03-15 2018-04-03 Ecolab Usa Inc. Processes and compositions for brightness improvement in paper production
CN104237211B (zh) * 2014-09-23 2016-09-28 中国科学院长春应用化学研究所 一种鲁米诺化学发光体系和鲁米诺、二氧化硫脲、钴离子浓度的测定方法

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CA1249402A (fr) * 1984-12-21 1989-01-31 Pulp And Paper Research Institute Of Canada Avivage multi-etage des pates a fort et tres fort rendement
SE8600615L (sv) * 1985-02-15 1986-08-16 Kamyr Ab Hog ljushet astadkommes genom blekning av mekanisk massa, sasom kemisk-mekanisk massa (cmp), kemisk-termisk-mekanisk massa (ctmp) och liknande

Also Published As

Publication number Publication date
DE69009750D1 (de) 1994-07-14
WO1990011403A1 (fr) 1990-10-04
ATE106961T1 (de) 1994-06-15
CA1340348C (fr) 1999-01-26
EP0464110A1 (fr) 1992-01-08

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