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EP0433138B1 - Process for bleaching chemical cellulose pulps - Google Patents

Process for bleaching chemical cellulose pulps Download PDF

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Publication number
EP0433138B1
EP0433138B1 EP90403462A EP90403462A EP0433138B1 EP 0433138 B1 EP0433138 B1 EP 0433138B1 EP 90403462 A EP90403462 A EP 90403462A EP 90403462 A EP90403462 A EP 90403462A EP 0433138 B1 EP0433138 B1 EP 0433138B1
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EP
European Patent Office
Prior art keywords
treatment
poa
sequence
alkaline
acid
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EP90403462A
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German (de)
French (fr)
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EP0433138A1 (en
Inventor
Alain M. Siohan
Jean-Claude M. Doignie
Jean-Claude M. Pommier
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TARTAS S.A.
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Cellulose du Pin SA
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Classifications

    • 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

  • the invention relates to the bleaching of chemical cellulosic pulps, in particular bisulphite pulps in order to obtain bleached pulps, absorbents in particular fluff pulps, having the desired whiteness and hydrophilicity.
  • Industrial processes for bleaching chemical cellulosic pulps generally use different sequences corresponding to different successive treatments, and generally among these at least one treatment using chlorine or chlorine derivatives.
  • H2O2 hydrogen peroxides
  • NaoCl sodium hypochlorite
  • chlorinated products Cl2, ClO2, NaOCl
  • Cl2, ClO2, NaOCl chlorinated products
  • chlorinated organic compounds chlorine level: AOX. TOCl
  • Most of these products are generated at the chlorination stage. By the use of chlorine dioxide one can decrease their formation.
  • the invention as described in claim 1, provides a process for bleaching a chemical cellulose pulp, in particular a bisulphite pulp, which not only avoids the use of chlorinated products, but which, in addition, by l elimination of the resins makes it possible to obtain a hydrophilic paste, having the desired absorption properties.
  • bleaching process therefore means, according to the invention, a process which not only makes it possible to bleach the chemical pulp, but which also makes this pulp hydrophilic.
  • the method according to the invention comprises at least one treatment with a bleaching agent that does not contain chlorine, at least two alkaline treatments and at least one acid treatment of a duration at least equal to 15 minutes, interleaved between the two alkaline treatments .
  • alkaline treatment is meant according to the invention either a treatment with sodium hydroxide or equivalent, or a treatment in an alkaline medium, that is to say a treatment combining the action of sodium hydroxide, or equivalent, with another agent , especially oxygen or hydrogen peroxide.
  • acid treatment means, according to the invention, either a treatment with an acid, or a treatment in an acid medium, that is to say combining the action of the acid with another agent, in particular oxygen, hydrogen peroxide, ozone.
  • the hydrophilicity of the dough is obtained thanks to treatments allowing the elimination of hydrophobic extractable products which are resin substances of wood.
  • This elimination is carried out according to the invention by preceding at least one alkaline treatment with an acid treatment. It has been found according to the invention in particular in the case of bisulfite pastes that this acid treatment predisposes the resin to better dissolution by the alkali and therefore promoting its elimination thereafter. But for this acid treatment to be the desired effectiveness, this treatment must be carried out for a duration of at least 15 minutes.
  • the sequence of successive treatments begins with an alkaline treatment.
  • the whitening process according to the invention can use the following treatment sequences, the letters representing the treatments explained below: O - a - P O - a - P - P O - a - P - a - P O - a - P - a - P - a - P O - POa - P O- POa - P - P O - POa - Pa - P O - Pa- O - Pa O - Pa O - POa - POa - POa - POa - POa - POa - POa - POa - POa - PO - P O - POa - PO - P O - POa - PO - P O - POa - PO - PO - PO - PO - PO - PO - PO - PO - PO - - - PO - PO - PO - - - PO - - PO - - PO - - PO
  • This treatment is equivalent to POa treatment.
  • the degree of whiteness is determined according to the ISO 2470 method.
  • the HV8 measurement is determined according to the following method:
  • bleached dry paste test pieces are prepared which have been aged for 8 hours at 105 ° C and conditioned at 20 ° C and 65% relative humidity. These test pieces have the shape of a cylinder 52 mm in diameter and they have a mass of 3 grams.
  • the HV8 measurement is carried out by placing the underside of the test piece in contact with water at 20 ° C and determining the time required for complete wetting of the test piece by capillary rise, under a constant pressure of 2.5 kPa .
  • the method according to the invention makes it possible to reach a degree of whiteness greater than 70 for all the chemical pastes treated and an HV8 value of less than 5 seconds.
  • This HV8 value of 5 seconds corresponds approximately to a content of the resin paste of approximately 0.05%.
  • This example describes the whitening of a bisulphite paste by the use of a sequence e a1P1 / O a2P2
  • I - treatment e it is a treatment with soda.
  • the dough is then washed with water on a rotary filter. The washing juices are eliminated. The dough goes to the next stage.
  • the paste is diluted by the return water from the same stage. Simultaneously adding acid (H2SO4 or water sulfurous).
  • the dough is then sent to a washing filter. Wash with water.
  • III - P1 / O treatment it is a mixed peroxide-oxygen treatment.
  • the dough is pumped after dilution by the return water. It is washed with water on a filter. The dough goes to the next stage.
  • IV - a2 treatment this is an acid treatment.
  • This treatment is identical to treatment a1
  • V - P2 treatment it is a peroxide treatment in an alkaline medium.
  • the paste taken out of the tower by overflow, is diluted with return water and washed with water on a filter.
  • the pulp is sent to the following facilities (purification and Press Pulp).
  • the degree of whiteness measured on the pulp treated according to the example is 80.
  • the resin content, measured by DCM extract is approximately 0.03.
  • the HV8 measurement is 3.5.
  • this example describes the whitening of a bisulfite paste by the use of an O - a1 - P1O - a2 - P2 sequence
  • treatment e is replaced by treatment O.
  • I- O treatment this is an oxygen treatment in the alkaline phase.
  • a pressure regulating valve lets out the dough which is diluted by return juice and sent by pump on a washing filter (water).
  • the treated paste has a degree of whiteness of 82.
  • the HV8 measurement is 3.5.
  • This example describes the whitening of a Kraft pulp by the implementation of an Oa1P1 / Oa2P2 sequence (a2P3)
  • This sequence up to P2 can be modeled on the sequence identical to that described for the bisulfite paste in Example 2.
  • the treated pulp has a whiteness degree of 81.
  • the resin content measured by DCM extract is 0.03%.
  • the HV8 measurement is 3.4.
  • Treatment a3 is identical to treatment a2 and the P3 treatment is identical to the P2 treatment.
  • the whiteness obtained is 83.
  • Example 2 A difference between this example and Example 2 concerns the washing juices.
  • P3 last stage washing
  • the juices are then brought up to O through all the stages of the exit of O, the juices instead of being put in the gutter are used for washing the unbleached dough. They will then be brought up to the boiler via evaporation.
  • a bisulphite paste is treated by the use of an O - P - O - P sequence, that is to say without an acid treatment preceding an alkaline treatment.
  • the treated pulp has a degree of whiteness of 76, which is satisfactory, but the resin content measured by DCM extract is 0.1% and the HV8 measurement is 9 seconds. These values are too high for an absorbent paste, in particular a fluff paste.
  • a bisulphite paste is treated by the use of a PO - PO a - P sequence as described in the publication Das Textil Vol 40, n ° 6, June 1986, pages 258-263, the duration of the acid treatment PO a being of 4 minutes.
  • the treated pulp has a degree of whiteness of 83.
  • the HV8 measurement is 9 seconds and the resin content measured by DCM extract is 0.1%. These values are too high for an absorbent paste.
  • the same bisulfite paste is treated by using a PO - PO a - P sequence as in Comparative Example 2, except that the duration of the acid treatment PO a is 15 minutes.
  • the treated pulp has a degree of whiteness of 83.
  • the HV8 measurement is 4.9 seconds and the resin content measured by DCM extract is 0.04%. These values are suitable for an absorbent paste.

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  • Life Sciences & Earth Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Wood Science & Technology (AREA)
  • Paper (AREA)
  • Polysaccharides And Polysaccharide Derivatives (AREA)
  • Solid-Sorbent Or Filter-Aiding Compositions (AREA)
  • Noodles (AREA)

Abstract

Process for bleaching chemical cellulose pulps with a view to obtaining absorbent, bleached pulps, without using chlorine. The process for bleaching chemical pulps employs a sequence of different treatments comprising at least one treatment with a bleaching agent not containing chlorine, at least two alkaline treatments and at least one acidic treatment, lasting at least 5 minutes, inserted between the two alkaline treatments.

Description

L'invention concerne le blanchîment des pâtes cellulosiques chimiques, en particulier des pâtes bisulfites en vue d'obtenir des pâtes blanchies, absorbantes notamment des pâtes fluff, ayant la blancheur et l'hydrophilie désirées.The invention relates to the bleaching of chemical cellulosic pulps, in particular bisulphite pulps in order to obtain bleached pulps, absorbents in particular fluff pulps, having the desired whiteness and hydrophilicity.

Les procédés industriels de blanchîment des pâtes cellulosiques chimiques utilisent généralement différentes séquences correspondant à différents traitements successifs, et généralement parmi ceux-ci au moins un traitement à l'aide de chlore ou de dérivés chlorés.Industrial processes for bleaching chemical cellulosic pulps generally use different sequences corresponding to different successive treatments, and generally among these at least one treatment using chlorine or chlorine derivatives.

Ainsi, le procédé de blanchîment généralement utilisé jusqu'à présent met en oeuvre successivement :

  • a) un traitement de délignification à l'oxygène,
  • b) un traitement de chloration (Cl₂) dans lequel le taux de substitution de Cl₂ par le bioxyde de chlore (ClO₂) peut atteindre 50 % à 100 %,
  • c) un traitement d'extraction alcaline à l'aide de soude (NaOH) souvent renforcé par un traitement oxygène,
  • d) un traitement au bioxyde de chlore,
  • e) un traitement d'extraction alcaline,
  • f) à nouveau un traitement au bioxyde de chlore.
Thus, the bleaching process generally used until now implements successively:
  • a) an oxygen delignification treatment,
  • b) a chlorination treatment (Cl₂) in which the rate of substitution of Cl₂ by chlorine dioxide (ClO₂) can reach 50% to 100%,
  • c) an alkaline extraction treatment using sodium hydroxide (NaOH) often reinforced by an oxygen treatment,
  • d) a treatment with chlorine dioxide,
  • e) an alkaline extraction treatment,
  • f) again treatment with chlorine dioxide.

D'autres traitements associés à des traitements utilisant des produits ou dérivés chlorés peuvent être mis en oeuvre, notamment des traitements au peroxydes d'hydrogène (H₂O₂) et/ou des traitements à l'hypochlorite de sodium (NaoCl).Other treatments associated with treatments using chlorinated products or derivatives can be used, in particular treatments with hydrogen peroxides (H₂O₂) and / or treatments with sodium hypochlorite (NaoCl).

Dans la plupart des cas, des produits chlorés : Cl₂, ClO₂, NaOCl, sont utilisés et on ne connait pas dans l'industrie des pâtes chimiques, des techniques efficaces permettant d'obtenir des pâtes chimiques blanchies, absorbantes, sans l'utilisation de ces produits.In most cases, chlorinated products: Cl₂, ClO₂, NaOCl, are used and we do not know in chemical pulp industry, effective techniques for obtaining bleached, absorbent chemical pulps without the use of these products.

Récemment, les contraintes d'environnement de plus en plus fortes ont amené les fabricants de pâtes cellulosiques à modifier les séquences de blanchîment.Recently, increasing environmental constraints have led manufacturers of cellulose pulps to modify the bleaching sequences.

Les effluents rejetés par les usines fabricant les pâtes cellulosiques sont contrôlés et des limites sont imposées en ce qui concerne les composés organiques chlorés (taux de chlore : AOX. TOCl). Ces produits sont générés en majorité au stade de la chloration. Par l'utilisation de bioxyde de chlore on peut diminuer leur formation.The effluents discharged by the factories manufacturing the cellulose pulps are controlled and limits are imposed with regard to the chlorinated organic compounds (chlorine level: AOX. TOCl). Most of these products are generated at the chlorination stage. By the use of chlorine dioxide one can decrease their formation.

D'autre part, très récemment, il a été démontré que l'action du chlore avec certains composés de la pâte de bois fournissant la pâte fluff pouvait être susceptible de former de la dioxine, le bioxyde de chlore étant quant à lui moins néfaste dans ce sens.On the other hand, very recently, it has been shown that the action of chlorine with certain compounds of the wood pulp supplying the fluff pulp could be capable of forming dioxin, chlorine dioxide being meanwhile less harmful in that Sens.

La plus grande sensibilité aux problèmes de l'environnement impose donc aux fabricants de pâtes de profondes modifications des techniques de blanchîment et en particulier l'action de l'oxygène est intensifié, l'utilisation de chlore gazeux est réduite au profit du bioxyde de chlore, l'utilisation d'hypochlorite est supprimée.The greater sensitivity to environmental problems therefore imposes on pulp manufacturers profound modifications of bleaching techniques and in particular the action of oxygen is intensified, the use of chlorine gas is reduced in favor of chlorine dioxide , the use of hypochlorite is suppressed.

Mais jusqu'à aujourd'hui, s'il est possible d'éliminer le chlore gazeux et l'hypochlorite, il n'était pas envisageable industriellement de se passer du bioxyde de chlore.But until today, if it is possible to eliminate chlorine gas and hypochlorite, it was not conceivable industrially to do without chlorine dioxide.

Des procédés utilisant de l'ozone ou du peroxyde d'hydrogène en tant qu'agent de blanchîment pour une pâte chimique ont déjà été décrits, par exemple dans la publication de brevet FR-A-2 474 550. Mais de tels procédés ne procurent pas à la fois la blancheur et l'hydrophilie désirées.Methods using ozone or hydrogen peroxide as a bleaching agent for a chemical pulp have already been described, for example in patent publication FR-A-2 474 550. But such methods do not provide not both the whiteness and the hydrophilicity desired.

Un des problèmes rencontrés dans la préparation des pâtes absorbantes, surtout à partir des pâtes bisulfites, est la difficulté d'élimination des substances résiniques du bois. Ces produits, hydrophobes, doivent être extraits de la pâte afin de rendre les fibres hydrophiles.One of the problems encountered in the preparation of absorbent pastes, especially from bisulphite pastes, is the difficulty of removing resin substances from the wood. These hydrophobic products must be extracted from the pulp in order to make the fibers hydrophilic.

Pour qu'une pâte chimique puisse être considérée comme absorbante on estime que sa teneur en résine, mesurée d'après la méthode de l'extraction au dichlorométhane (DCM) selon la norme ISO 624, doit être inférieure à 0,1 % et de préférence inférieure à 0,05 %.For a chemical paste to be considered absorbent, it is estimated that its resin content, measured according to the dichloromethane (DCM) extraction method according to ISO 624, must be less than 0.1% and preferably less than 0.05%.

Dans la publication Das Papier, vol. 40 n°6, Juin 1986, DARMSTADT DE, pages 258-263, on a décrit un traitement de délignification d'une pâte sulfite qui utilise une séquence comprenant une étape rapide de traitement avec du peroxyde d'hydrogène en présence d'oxygène dans des conditions acides. Cette séquence présente une efficacité vis-à-vis de l'élimination de la lignine. En revanche, l'élimination des résines procurant finalement une pâte hydrophile n'est pas satisfaisante.In the publication Das Papier, vol. 40 no. 6, June 1986, DARMSTADT DE, pages 258-263, a delignification treatment of a sulphite paste has been described which uses a sequence comprising a rapid stage of treatment with hydrogen peroxide in the presence of oxygen in acidic conditions. This sequence is effective in eliminating lignin. On the other hand, the elimination of the resins ultimately providing a hydrophilic paste is not satisfactory.

L'invention, comme décrite dans la revendication 1, propose un procédé de blanchîment d'une pâte cellulosique chimique, en particulier d'une pâte bisulfite, qui non seulement évite l'utilisation de produits chlorés, mais qui, en outre, par l'élimination des résines, permet d'obtenir une pâte hydrophile, ayant les propriétés d'absorption désirées.The invention, as described in claim 1, provides a process for bleaching a chemical cellulose pulp, in particular a bisulphite pulp, which not only avoids the use of chlorinated products, but which, in addition, by l elimination of the resins makes it possible to obtain a hydrophilic paste, having the desired absorption properties.

Par procédé de blanchîment, on entend donc selon l'invention un procédé qui non seulement permet de blanchir la pâte chimique, mais qui en outre rend cette pâte hydrophile.The term “bleaching process” therefore means, according to the invention, a process which not only makes it possible to bleach the chemical pulp, but which also makes this pulp hydrophilic.

Le procédé selon l'invention comprend au moins un traitement par un agent de blanchîment ne contenant pas de chlore, au moins deux traitements alcalins et au moins un traitement acide d'une durée au moins égale à 15 minutes, intercalaire entre les deux traitements alcalins.The method according to the invention comprises at least one treatment with a bleaching agent that does not contain chlorine, at least two alkaline treatments and at least one acid treatment of a duration at least equal to 15 minutes, interleaved between the two alkaline treatments .

Par traitement alcalin, on entend selon l'invention soit un traitement par la soude ou équivalent, soit un traitement en milieu alcalin, c'est-à-dire un traitement combinant l'action de la soude, ou équivalent, avec un autre agent, notamment l'oxygène ou le peroxyde d'hydrogène.By alkaline treatment is meant according to the invention either a treatment with sodium hydroxide or equivalent, or a treatment in an alkaline medium, that is to say a treatment combining the action of sodium hydroxide, or equivalent, with another agent , especially oxygen or hydrogen peroxide.

Par traitement acide, on entend selon l'invention soit un traitement par un acide, soit un traitement en milieu acide, c'est-à-dire combinant l'action de l'acide avec un autre agent, notamment l'oxygène, le peroxyde d'hydrogène, l'ozone.The term “acid treatment” means, according to the invention, either a treatment with an acid, or a treatment in an acid medium, that is to say combining the action of the acid with another agent, in particular oxygen, hydrogen peroxide, ozone.

L'hydrophilie de la pâte est obtenue grâce à des traitements permettant l'élimination des produits extractibles hydrophobes qui sont des substances résiniques du bois.The hydrophilicity of the dough is obtained thanks to treatments allowing the elimination of hydrophobic extractable products which are resin substances of wood.

Cette élimination est réalisée selon l'invention en faisant précéder au moins un traitement alcalin par un traitement acide. On a trouvé selon l'invention en particulier dans le cas des pâtes bisulfites que ce traitement acide prédisposait la résine à une meilleure dissolution par l'alcalin et donc favorisant son élimination par la suite. Mais pour que ce traitement acide est l'efficacité recherchée, il faut que ce traitement s'opère pendant une durée d'au moins 15 minutes.This elimination is carried out according to the invention by preceding at least one alkaline treatment with an acid treatment. It has been found according to the invention in particular in the case of bisulfite pastes that this acid treatment predisposes the resin to better dissolution by the alkali and therefore promoting its elimination thereafter. But for this acid treatment to be the desired effectiveness, this treatment must be carried out for a duration of at least 15 minutes.

Les réactifs et les traitements mis en oeuvre sont choisis parmi les suivants :

  • oxygène en milieu alcalin,
  • peroxyde d'hydrogène soit en milieu alcalin, soit en milieu acide,
  • soude,
  • combinaison d'oxygène et de peroxyde, soit en milieu alcalin, soit en phase acide,
  • acide sulfurique, anhydride sulfureux, ou tout autre acide ne contenant pas de chlore et permettant l'obtention du pH désiré, inférieur à 5.
The reagents and treatments used are chosen from the following:
  • oxygen in an alkaline medium,
  • hydrogen peroxide either in an alkaline medium or in an acid medium,
  • welded,
  • combination of oxygen and peroxide, either in an alkaline medium or in the acid phase,
  • sulfuric acid, sulfur dioxide, or any other acid that does not contain chlorine and allows the desired pH to be obtained, less than 5.

Selon une caractéristique du procédé selon l'invention, la séquence des traitements successifs commence par un traitement alcalin.According to a characteristic of the method according to the invention, the sequence of successive treatments begins with an alkaline treatment.

Le procédé de blanchîment selon l'invention peut utiliser les séquences de traitements suivantes, les lettres représentant les traitements explicités par la suite :
   O - a - P
   O - a - P - P
   O - a - P - a - P
   O - a - P - a - P - P
   O - a - P - a - P - a - P
   O - POa - P
   O- POa - P - P
   O - POa - P-a - P
   O - Pa- O - Pa
   O - POa - POa
   O - POa - POa - P
   O - POa - PO - P
   O - POa - PO - a - P
   O - a - PO - P
   O - a - PO - a - P
   O - a - PO - a - P - P
   O - a - PO - a - P - a - P
   O - a - O - P
   O - a - O - a - P
   O - a - O - a - P - P
   O - a - O - a - P - a - P
   P - a - P
   P - a - P - a - P
   e - P - a - P
   e - P - a - P - a - P
   e - a - P - a - P
   e - a - P - P
   e - a - P - a - P - P
   e - a - P - a - P - a - P
   e - a - PO - P
   e - a - PO - a - P
   e - a - PO - a - P - P
   e - a - Po - a - P - a - P
   e - POa - P
   e - a - O - P
   e - a - O - P - P
   e - a - O - a - P
   e - a - O - a - P - P
   e - a - O - a - P - a - PThe whitening process according to the invention can use the following treatment sequences, the letters representing the treatments explained below:
O - a - P
O - a - P - P
O - a - P - a - P
O - a - P - a - P - P
O - a - P - a - P - a - P
O - POa - P
O- POa - P - P
O - POa - Pa - P
O - Pa- O - Pa
O - POa - POa
O - POa - POa - P
O - POa - PO - P
O - POa - PO - a - P
O - a - PO - P
O - a - PO - a - P
O - a - PO - a - P - P
O - a - PO - a - P - a - P
O - a - O - P
O - a - O - a - P
O - a - O - a - P - P
O - a - O - a - P - a - P
P - a - P
P - a - P - a - P
e - P - a - P
e - P - a - P - a - P
e - a - P - a - P
e - a - P - P
e - a - P - a - P - P
e - a - P - a - P - a - P
e - a - PO - P
e - a - PO - a - P
e - a - PO - a - P - P
e - a - Po - a - P - a - P
e - POa - P
e - a - O - P
e - a - O - P - P
e - a - O - a - P
e - a - O - a - P - P
e - a - O - a - P - a - P

Les traitements désignés par des lettres et utilisés dans les séquences précédentes, sont les suivants, les concentrations étant exprimées en poids par rapport aux poids des pâtes sèches.The treatments designated by letters and used in the preceding sequences are as follows, the concentrations being expressed by weight relative to the weight of the dry pasta.

O : Traitement oxygène en phase alcaline O: Oxygen treatment in alkaline phase

  • concentration en pâte 6 à 12 % ,paste concentration 6 to 12%,
  • quantité d'oxygène mise en oeuvre 0,5 à 3 % en poids des pâtes sèches,amount of oxygen used 0.5 to 3% by weight of the dry pasta,
  • quantité de soude ou d'une base équivalente mise en oeuvre : 0,5 à 4,5 %quantity of soda or equivalent base used work: 0.5 to 4.5%
  • température de 60°C à 120°C,temperature from 60 ° C to 120 ° C,
  • pression : 1 à 5 barspressure: 1 to 5 bars
  • durée de la réaction : 15 minutes à 120 minutesreaction time: 15 minutes to 120 minutes
a : Traitement acide a: Acid treatment

  • réactifs H₂SO₄ ou SO₂ ou H₃PO₄, ou tout autre acide ne contenant pas de chlore et permettant d'obtenir un pH de 2 à 5,H₂SO₄ or SO₂ or H₃PO₄ reagents, or any other acid that does not contain chlorine and allows a pH of 2 to 5 to be obtained,
  • concentration en pâte : 2 à 12 %pulp concentration: 2 to 12%
  • durée : 15 minutes à 60 minutes,duration: 15 minutes to 60 minutes,
  • température : 30°C à 80°Ctemperature: 30 ° C to 80 ° C
P : Traitement peroxyde d'hydrogène (H₂O₂) en milieu alcalin P: Treatment of hydrogen peroxide (H₂O₂) in an alkaline medium

  • quantité de peroxyde mis en oeuvre : 0,5 à 4 %,amount of peroxide used: 0.5 to 4%,
  • NaOH ou équivalent : 1,0 à 2,5 %NaOH or equivalent: 1.0 to 2.5%
  • D T P A (diéthylènetétrapentacétique acide) : 0,05 à 0,2% (ou autre agent qui empêche la décomposition de H₂O₂),D T P A (diethylenetetrapentacetic acid): 0.05 to 0.2% (or other agent which prevents the decomposition of H₂O₂),
  • concentration en pâte : 5 à 30 %paste concentration: 5 to 30%
  • température : 55 à 85°Ctemperature: 55 to 85 ° C
  • durée de la réaction : de 60 minutes à 180 minutesreaction time: 60 minutes to 180 minutes
PO ou P/O : Traitement mixte peroxyde-oxygène en phase alcaline PO or P / O: Mixed peroxide-oxygen treatment in alkaline phase

  • quantité de réactifs mis en oeuvre :
    • oxygène : 0,5 à 2,5 %
    • peroxyde : 0,5 à 2 %
    • NaOH ou équivalent : 0,5 à 4,5 %
    • MgSO₄ : 0,05 à 0,5 %
    quantity of reagents used:
    • oxygen: 0.5 to 2.5%
    • peroxide: 0.5 to 2%
    • NaOH or equivalent: 0.5 to 4.5%
    • MgSO₄: 0.05 to 0.5%
  • température : 0 à 100°C,temperature: 0 to 100 ° C,
  • pression : 1 à 5 bars,pressure: 1 to 5 bars,
  • concentration en pâte : 6 à 12 %,paste concentration: 6 to 12%,
  • durée de la réaction : 15 minutes à 120 minutesreaction time: 15 minutes to 120 minutes
POa : Traitement mixte peroxyde-oxygène en milieu acide POa: Mixed peroxide-oxygen treatment in an acid medium

  • quantité de réactifs mis en oeuvre :
    • oxygène : 0,5 à 2,5 %
    • peroxyde : 0,5 à 2,0 %
    • H₂SO₄ ou tout autre acide équivalent, ne contenant pas de chlore et non réducteur en quantité suffisante pour pH initial de 1,5 à 3,5
    quantity of reagents used:
    • oxygen: 0.5 to 2.5%
    • peroxide: 0.5 to 2.0%
    • H₂SO₄ or any other equivalent acid, not containing chlorine and not reducing in sufficient quantity for an initial pH of 1.5 to 3.5
  • température : 60°C à 100°C,temperature: 60 ° C to 100 ° C,
  • pression : 1 à 5 barspressure: 1 to 5 bars
  • durée de la réaction : 30 minutes à 180 minutesreaction time: 30 minutes to 180 minutes
  • concentration en pâte : 6 à 12 %paste concentration: 6 to 12%
e - Traitement à la soude NaOH ou avec une base équivalente en quantité suffisante pour porter la pâte à un pH > 10,5.e - Treatment with NaOH soda or with an equivalent base in sufficient quantity to bring the paste to a pH> 10.5. Pa - Traitement peroxyde en milieu acide Pa - Peroxide treatment in an acid medium

Ce traitement est équivalent au traitement POa.This treatment is equivalent to POa treatment.

Dans le tableau ci-après, on a indiqué les résultats obtenus par la mise en oeuvre de quelques séquences possibles selon le procédé de l'invention qui s'applique ici à une pâte bisulfite.In the table below, the results obtained are indicated by the use of a few possible sequences according to the process of the invention which is applied here to a bisulfite paste.

Ces résultats concernent le degré de blancheur et la mesure HV₈ qui correspond au temps de montée capillaire qui est directement lié à la teneur en résine de la pâte. Plus la mesure HV₈ est basse et plus faible est la teneur en résine.These results relate to the degree of whiteness and the HV₈ measurement which corresponds to the capillary rise time which is directly linked to the resin content of the paste. The lower the HV₈ measurement, the lower the resin content.

Le degré de blancheur est déterminé d'après la méthode ISO 2470.The degree of whiteness is determined according to the ISO 2470 method.

La mesure HV₈ est déterminée d'après la méthode suivante :The HV₈ measurement is determined according to the following method:

Pour déterminer HV₈, on prépare des éprouvettes de pâte sèche blanchie que l'on a fait vieillir durant 8 heures à 105°C et conditionnées à 20°C et à 65 % d'humidité relative. Ces éprouvettes présentent la forme d'un cylindre de 52 mm de diamètre et elles ont une masse de 3 grammes.To determine HV₈, bleached dry paste test pieces are prepared which have been aged for 8 hours at 105 ° C and conditioned at 20 ° C and 65% relative humidity. These test pieces have the shape of a cylinder 52 mm in diameter and they have a mass of 3 grams.

La mesure HV₈ s'effectue en plaçant la face inférieure de l'éprouvette au contact d'eau à 20°C et en déterminant le temps nécessaire au mouillage complet de l'éprouvette par montée capillaire, sous une pression constante de 2,5 kPa.

Figure imgb0001
The HV₈ measurement is carried out by placing the underside of the test piece in contact with water at 20 ° C and determining the time required for complete wetting of the test piece by capillary rise, under a constant pressure of 2.5 kPa .
Figure imgb0001

Le procédé selon l'invention permet d'atteindre un degré de blancheur supérieur à 70 pour toutes les pâtes chimiques traitées et une valeur HV₈ inférieure à 5 secondes. Cette valeur HV₈ de 5 secondes correspond approximativement à une teneur de la pâte en résine de 0,05 % environ.The method according to the invention makes it possible to reach a degree of whiteness greater than 70 for all the chemical pastes treated and an HV₈ value of less than 5 seconds. This HV₈ value of 5 seconds corresponds approximately to a content of the resin paste of approximately 0.05%.

Par la suite, on décrit plusieurs exemples du procédé de blanchîment selon l'invention.In the following, several examples of the bleaching process according to the invention are described.

EXEMPLE 1EXAMPLE 1

Cet exemple décrit le blanchîment d'une pâte Bisulfite par la mise en oeuvre d'une séquence e a₁P₁/O a₂P₂This example describes the whitening of a bisulphite paste by the use of a sequence e a₁P₁ / O a₂P₂

I - traitement e : c'est un traitement à la soude.I - treatment e : it is a treatment with soda.

La pâte écrue lavée est triturée dans des défibreurs en présence de soude :

  • temps de passage (mn) : 2 à 5
  • température (°C) : 20
  • Concentration pâte (%) : 10
  • NaOH (% de la pâte sèche) : 1 à 2,5
  • pH final : > 11
The washed unbleached pulp is crushed in shredders in the presence of soda:
  • passage time (min): 2 to 5
  • temperature (° C): 20
  • Dough concentration (%): 10
  • NaOH (% of dry paste): 1 to 2.5
  • final pH:> 11

La pâte est ensuite lavée à l'eau sur un filtre rotatif. Les jus de lavage sont éliminés. La pâte va au stade suivant.The dough is then washed with water on a rotary filter. The washing juices are eliminated. The dough goes to the next stage.

II - traitement a₁ : c'est un traitement acide.II - a₁ treatment : it is an acid treatment.

La pâte est diluée par les eaux de retour du même stade. Simultanément on ajoute de l'acide (H₂SO₄ ou eau sulfureuse).The paste is diluted by the return water from the same stage. Simultaneously adding acid (H₂SO₄ or water sulfurous).

La pâte est pompée et introduite à la base d'une tour ascendante :

  • temps de passage (mn) : 15 à 30
  • température (°C) : 20 à 50
  • concentration pâte (%) : 3
  • pH initial : < 4
  • acide/pâte : quantité pour pH désiré.
The dough is pumped and introduced at the base of an ascending tower:
  • passage time (min): 15 to 30
  • temperature (° C): 20 to 50
  • dough concentration (%): 3
  • initial pH: <4
  • acid / paste: quantity for desired pH.

Par débordement et pompage, la pâte est ensuite envoyée sur un filtre laveur. Lavage à l'eau.By overflow and pumping, the dough is then sent to a washing filter. Wash with water.

III - traitement P₁/O : c'est un traitement mixte peroxydeoxygène.III - P₁ / O treatment: it is a mixed peroxide-oxygen treatment.

La pâte sortie du traitement a₁ est envoyée par une pompe MC (Moyenne Concentration) à la base d'un réacteur à travers un mixer. Les réactifs liquides (soude, peroxyde, DTPA) sont introduit en amont de la pompe. L'oxygène est injecté au refoulement de la pompe, avant le mixage, les conditions du traitement sont les suivantes :

  • temps de passage (mn) : 12 à 15
  • température (°C) : 75 à 85
  • concentration pâte (%) : 10
  • pH sortie réacteur : 11
  • pression (Bar) : 4 à 6
  • oxygène (%) : 0,5 à 1,0
  • peroxyde (%) : 2,0
  • NaOH (%) : quantité pour pH désiré
  • DTPA (%) : 0,2
The paste leaving the a₁ treatment is sent by an MC (Medium Concentration) pump to the base of a reactor through a mixer. Liquid reagents (soda, peroxide, DTPA) are introduced upstream of the pump. Oxygen is injected at the pump discharge, before mixing, the treatment conditions are as follows:
  • passage time (min): 12 to 15
  • temperature (° C): 75 to 85
  • dough concentration (%): 10
  • reactor outlet pH: 11
  • pressure (Bar): 4 to 6
  • oxygen (%): 0.5 to 1.0
  • peroxide (%): 2.0
  • NaOH (%): quantity for desired pH
  • DTPA (%): 0.2

La pâte tombe ensuite dans une tour descendante au travers d'une vanne régulatrice de pression.

  • temps de passage (mn) : 60 à 120
  • température (°C) : 75 à 85
  • concentration (%) : 10
The dough then falls into a descending tower through a pressure regulating valve.
  • passage time (min): 60 to 120
  • temperature (° C): 75 to 85
  • concentration (%): 10

A la base de la tour, la pâte est pompée après dilution par les eaux de retour. Elle est lavée par de l'eau sur un filtre. La pâte va vers le stade suivant.At the base of the tower, the dough is pumped after dilution by the return water. It is washed with water on a filter. The dough goes to the next stage.

IV - traitement a₂ : c'est un traitement acide.IV - a₂ treatment : this is an acid treatment.

Ce traitement est identique au traitement a₁This treatment is identical to treatment a₁

V - traitement P₂ : c'est un traitement peroxyde en milieu alcalin.V - P₂ treatment : it is a peroxide treatment in an alkaline medium.

La pâte sortie a₂ est envoyée par une pompe MC à la base d'une tour ascendante. Les réactifs sont introduits en amont de la pompe.

  • temps de passage (mn) : 120
  • température (°C) : 75
  • concentration (%) : 10
  • pH initial : 11
  • peroxyde (%) : 2
  • NaOH (%) : quantité suffisante pour pH désiré
  • DTPA (%) : 0,2
The output paste a₂ is sent by an MC pump to the base of an ascending tower. Reagents are introduced upstream of the pump.
  • passage time (min): 120
  • temperature (° C): 75
  • concentration (%): 10
  • initial pH: 11
  • peroxide (%): 2
  • NaOH (%): sufficient quantity for desired pH
  • DTPA (%): 0.2

La pâte, sortie de la tour par débordement est diluée par des eaux de retour et lavée à l'eau sur un filtre. La pâte est envoyée dans les installations suivantes (épuration et Presse Pâte).The paste, taken out of the tower by overflow, is diluted with return water and washed with water on a filter. The pulp is sent to the following facilities (purification and Press Pulp).

Le degré de blancheur mesuré sur la pâte traitée selon l'exemple est de 80. La teneur en résine, mesurée par extrait DCM est de 0,03 environ. La mesure HV₈ est de 3,5.The degree of whiteness measured on the pulp treated according to the example is 80. The resin content, measured by DCM extract is approximately 0.03. The HV₈ measurement is 3.5.

Remarques: Notes :

  • Les filtres laveurs peuvent être remplacés par tout autre instrument de lavage (diffuseur, presse, etc . . .)The washing filters can be replaced by any other washing instrument (diffuser, press, etc.).
  • Les jus de lavage de chaque stade peuvent être utilisés à la place de l'eau sur le filtre du stade précédent.Wash juices from each stage can be used in place of water on the filter from the previous stage.
EXEMPLE 2EXAMPLE 2

cet exemple décrit le blanchîment d'une pâte bisulfite par la mise en oeuvre d'une séquence O - a₁ - P₁O - a₂ - P₂this example describes the whitening of a bisulfite paste by the use of an O - a₁ - P₁O - a₂ - P₂ sequence

Les différents traitements utilisés dans cette séquence sont les mêmes que pour ceux utilisés dans la séquence e - a₁ - P₁O - a₂ - P excepté pour le premier stade: le traitement e est remplacé par un traitement O.The different treatments used in this sequence are the same as those used in the sequence e - a₁ - P₁O - a₂ - P except for the first stage: treatment e is replaced by treatment O.

I- traitement O : c'est un traitement oxygène en phase alcaline.I- O treatment : this is an oxygen treatment in the alkaline phase.

La pâte écrue lavée est envoyée à la base d'une tour ascendante par une pompe MC à travers un mixer. La soude est introduite avant la pompe. L'oxygène est injecté au refoulement de la pompe, avant le mixer.

  • temps de passage (mn): 60
  • concentration (%) : 10
  • température (°C) : 85 à 100
  • pH sortie réacteur : 10
  • pression (Bar) : 4 à 6
  • oxygène (%) : 1,5
  • NaOH (%) : quantité suffisante pour pH.
The washed unbleached pulp is sent to the base of an ascending tower by an MC pump through a mixer. Soda is introduced before the pump. Oxygen is injected at the pump discharge, before the mixer.
  • passage time (min): 60
  • concentration (%): 10
  • temperature (° C): 85 to 100
  • reactor outlet pH: 10
  • pressure (Bar): 4 to 6
  • oxygen (%): 1.5
  • NaOH (%): sufficient quantity for pH.

Au sommet de la tour, une vanne régulatrice de pression laisse sortir la pâte qui est diluée par des jus de retour et envoyée par pompe sur un filtre laveur (eau).At the top of the tower, a pressure regulating valve lets out the dough which is diluted by return juice and sent by pump on a washing filter (water).

Les jus de lavage, en partie recyclés à la sortie de la tour, vont finalement au caniveau. La pâte va vers le stade suivant (a₁).The washing juices, partly recycled at the exit of the tower, finally go to the gutter. The dough goes to the next stage (a₁).

Les autres stades se déroulent comme dans l'exemple 1.The other stages proceed as in Example 1.

La pâte traitée présente un degré de blancheur de 82.The treated paste has a degree of whiteness of 82.

La mesure HV₈ est de 3,5.The HV₈ measurement is 3.5.

Bien que le procédé selon l'invention procure les meilleurs résultats lorsqu'il s'agit du blanchîment d'une pâte bisulfite, il peut néanmoins s'appliquer avec avantage également au blanchîment d'une pâte kraft comme le montre l'exemple 3.Although the process according to the invention provides the best results when it comes to bleaching a bisulfite paste, it can nevertheless also be applied with advantage to the bleaching of a kraft paste as shown in Example 3.

EXEMPLE 3EXAMPLE 3

Cet exemple décrit le blanchîment d'une pâte Kraft par la mise en oeuvre d'une séquence Oa₁P₁/Oa₂P₂ (a₂P₃)This example describes the whitening of a Kraft pulp by the implementation of an Oa₁P₁ / Oa₂P₂ sequence (a₂P₃)

Cette séquence jusqu'à P₂ peut être calquée sur la séquence identique à celle décrite pour la pâte bisulfite dans l'exemple 2.This sequence up to P₂ can be modeled on the sequence identical to that described for the bisulfite paste in Example 2.

La pâte traitée présente un degré de blancheur de 81. La teneur en résine mesurée par extrait DCM est de 0,03 %. La mesure HV₈ est de 3,4.The treated pulp has a whiteness degree of 81. The resin content measured by DCM extract is 0.03%. The HV₈ measurement is 3.4.

Si on veut encore améliorer la blancheur, on peut ensuite continuer la séquence jusqu'à P₃. Dans ce cas :If we still want to improve the whiteness, we can then continue the sequence until P₃. In that case :

Le traitement a₃ est identique au traitement a₂ et
   le traitement P₃ est identique au traitement P₂. La blancheur obtenue est de 83.Treatment a₃ is identical to treatment a₂ and
the P₃ treatment is identical to the P₂ treatment. The whiteness obtained is 83.

Une différence entre cet exemple et l'exemple 2 concerne les jus de lavage. Dans le cas de la pâte kraft, on se doit de ne mettre de l'eau que sur le lavage du dernier stade (P₃). Les jus sont ensuite remontés jusqu'à O à travers tous les stades de la sortie de O, les jus au lieu d'être mis au caniveau sont utilisés pour le lavage de la pâte écrue. Ils seront donc ensuite remontés jusqu'à la chaudière via l'évaporation.A difference between this example and Example 2 concerns the washing juices. In the case of kraft dough, you should only put water on the last stage washing (P₃). The juices are then brought up to O through all the stages of the exit of O, the juices instead of being put in the gutter are used for washing the unbleached dough. They will then be brought up to the boiler via evaporation.

EXEMPLES COMPARATIFSCOMPARATIVE EXAMPLES EXEMPLE COMPARATIF 1COMPARATIVE EXAMPLE 1

On traite une pâte bisulfite par la mise en oeuvre d'une séquence O - P - O - P, c'est-à-dire sans qu'un traitement acide ne précède un traitement alcalin.A bisulphite paste is treated by the use of an O - P - O - P sequence, that is to say without an acid treatment preceding an alkaline treatment.

La pâte traitée présente un degré de blancheur de 76, ce qui est satisfaisant, mais la teneur en résine mesurée par extrait DCM est de 0,1 % et la mesure HV₈ est de 9 secondes. Ces valeurs sont trop élevées pour une pâte absorbante, en particulier une pâte fluff.The treated pulp has a degree of whiteness of 76, which is satisfactory, but the resin content measured by DCM extract is 0.1% and the HV₈ measurement is 9 seconds. These values are too high for an absorbent paste, in particular a fluff paste.

EXEMPLE COMPARATIF 2COMPARATIVE EXAMPLE 2

On traite une pâte bisulfite par la mise en oeuvre d'une séquence PO - POa - P comme décrit dans la publication Das Papier Vol 40, n° 6, Juin 1986, pages 258-263, la durée du traitement acide POa étant de 4 minutes.A bisulphite paste is treated by the use of a PO - PO a - P sequence as described in the publication Das Papier Vol 40, n ° 6, June 1986, pages 258-263, the duration of the acid treatment PO a being of 4 minutes.

La pâte traitée présente un degré de blancheur de 83.The treated pulp has a degree of whiteness of 83.

La mesure HV₈ est de 9 secondes et la teneur en résine mesurée par extrait DCM est de 0,1 %. Ces valeurs sont trop élevées pour une pâte absorbante.The HV₈ measurement is 9 seconds and the resin content measured by DCM extract is 0.1%. These values are too high for an absorbent paste.

EXEMPLE 4EXAMPLE 4

On traite la même pâte bisulfite par la mise en oeuvre d'une séquence PO - POa - P comme dans l'exemple comparatif 2, sauf que la durée du traitement acide POa est de 15 minutes.The same bisulfite paste is treated by using a PO - PO a - P sequence as in Comparative Example 2, except that the duration of the acid treatment PO a is 15 minutes.

La pâte traitée présente un degré de blancheur de 83.The treated pulp has a degree of whiteness of 83.

La mesure HV₈ est de 4,9 secondes et la teneur en résine mesurée par extrait DCM est de 0,04 %. Ces valeurs conviennent pour une pâte absorbante.The HV₈ measurement is 4.9 seconds and the resin content measured by DCM extract is 0.04%. These values are suitable for an absorbent paste.

Claims (10)

  1. Method of whitening chemical cellulosic pulps in accordance with a sequence of different treatments for the purpose of producing whitened, absorbent pulps having a degree of whiteness, measured according to Standard ISO 2470, greater than 70, the sequence of treatments comprising at least one treatment by a whitening agent containing no chlorine, at least two alkaline treatments and at least one acid treatment intermediate between the two alkaline treatments, characterized in that the acid treatment has a duration of at least 15 minutes, in such a way as to obtain a pulp having a residual resin content, measured by DCM extract according to Standard ISO 624, of less than 0.05%.
  2. Method according to Claim 1, characterized in that the sequence starts with an alkaline treatment.
  3. Method according to one of Claims 1 to 2, characterized in that one of the following sequences is used:
    O - a - P
    O - a - P - P
    O - a - P - a - P
    O - a - P - a - P - P
    O - a - P - a - P - a - P
    O - POa - P
    O - POa - P - P
    O - POa - P-a - P
    O - Pa - O - Pa
    O - POa - POa
    O - POa - POa - P
    O - POa - PO - P
    O - POa - PO - a - P
    O - a - PO - P
    O - a - PO - a - P
    O - a - PO - a - P - P
    O - a - PO - a - P - a - P
    O - a - O - P
    O - a - O - a - P
    O - a - O - a - P - P
    O - a - O - a - P - a - P
    P - a - P
    P - a - P - a - P
    e - P - a - P
    e - P - a - P - a - P
    e - a - P - a - P
    e - a - P - P
    e - a - P - a - P - P
    e - a - P - a - P - a - P
    e - a - PO - P
    e - a - PO - a - P
    e - a - PO - a - P - P
    e - a - PO - a - P - a - P
    e - POa - P
    e - a - O - P
    e - a - O - P - P
    e - a - O - a - P
    e - a - O - a - P - P
    e - a - O - a - P - a - P
    where
    O :   oxygen treatment in alkaline phase,
    a :   acid treatment,
    P :   hydrogen peroxide treatment in alkaline medium,
    PO:   mixed peroxide-oxygen treatment in alkaline phase,
    POa:   mixed peroxide-oxygen treatment in acid medium,
    Pa:   hydrogen peroxide treatment in acid medium,
    e :   soda treatment.
  4. Method according to Claim 3, characterized in that one of the following sequences is used:
    P - a - P - a - P
    P - a - P - a - P - a - P
    e - P - a - P
    O - Pa - O - Pa
    O - POa - P - a - P
    e - a - P - a - P
    e - a - PO - a - P
    O - a - PO - a - P
    O - a - P
    a - PO - a - P
  5. Method according to one of Claims 1 to 4, characterized in that it is applicable to the whitening of a bisulphite pulp.
  6. Method according to Claim 5, characterized in that it uses the sequence:
    e - a - PO - a - P.
  7. Method according to Claim 5, characterized in that it uses the sequence:
    O - a - PO - a - P.
  8. Method according to one of Claims 1 to 4, characterized in that it is applicable to the whitening of a Kraft pulp.
  9. Method according to Claim 8, characterized in that it uses a sequence chosen from among the sequences:
    O - a - PO - a - P, or
    O - a - PO - a - P - a - P.
  10. Whitened cellulosic pulpsobtained by using the method according to one of Claims 1 to 9, characterized in that they have a whiteness degree greater than 70 and a capillary ascent time HV₈ less than 5 seconds.
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DE69011636T2 (en) 1995-01-26
NO905333D0 (en) 1990-12-10
ES2062463T3 (en) 1994-12-16
NO176809C (en) 1995-05-31
FR2655668B1 (en) 1995-06-09
FI906076A0 (en) 1990-12-10
DE69011636D1 (en) 1994-09-22
ATE110129T1 (en) 1994-09-15
NO176809B (en) 1995-02-20
FI96784B (en) 1996-05-15
NO905333L (en) 1991-06-12
DK0433138T3 (en) 1994-12-05

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