EP0018287B1 - Process for the delignification of unbleached chemical paper pulp - Google Patents

Process for the delignification of unbleached chemical paper pulp Download PDF

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Publication number
EP0018287B1
EP0018287B1 EP80400516A EP80400516A EP0018287B1 EP 0018287 B1 EP0018287 B1 EP 0018287B1 EP 80400516 A EP80400516 A EP 80400516A EP 80400516 A EP80400516 A EP 80400516A EP 0018287 B1 EP0018287 B1 EP 0018287B1
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EP
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Prior art keywords
pulp
pressing
oxidation
unbleached
oxidized
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EP80400516A
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German (de)
French (fr)
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EP0018287A1 (en
Inventor
Jacques Carles
Henri Lemoyne
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LA CELLULOSE DES ARDENNES
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LA CELLULOSE DES ARDENNES
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Priority claimed from FR7909642A external-priority patent/FR2454479A1/en
Priority claimed from FR8007170A external-priority patent/FR2479295A2/en
Application filed by LA CELLULOSE DES ARDENNES filed Critical LA CELLULOSE DES ARDENNES
Priority to AT80400516T priority Critical patent/ATE2232T1/en
Publication of EP0018287A1 publication Critical patent/EP0018287A1/en
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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
    • D21C9/16—Bleaching ; Apparatus therefor with per compounds
    • D21C9/163—Bleaching ; Apparatus therefor with per compounds with peroxides

Definitions

  • the first stage of bleaching typically consists of treatment with a chlorine reagent: chlorine, chlorine dioxide, sodium hypochlorite, etc.
  • a chlorine reagent chlorine, chlorine dioxide, sodium hypochlorite, etc.
  • this type of treatment has certain drawbacks; in particular, it leads to effluents polluted by corrosive chlorides which it is not possible to recycle in the recovery circuit for unitized chemicals for pulping wood (cooking), due to the high risks associated with the presence of chlorides.
  • peroxides have also recently been proposed as bleaching agents, also leading to a recoverable effluent.
  • Peroxides are bleaching agents known as lignin preservation, that is to say that they make it possible to obtain a lightening of the dough without reduction of material weight, by oxidizing the chromophoric groups attached to the large lignin molecules. , but they do not attack the main structure of lignin itself.
  • the peroxides are reserved for the bleaching of paper pulps (mechanical pulps, thermomechanical pulps, michemical pulps) said to have a high lignin content or a high yield (yield> 6596) for which no delignification is sought, but a lightening without reduction of material weight.
  • step a) of oxidation of the unbleached pulp an amount of peroxide is used which is adapted to the lignin level of the pulp to be treated so as to have a ratio of% peroxide / pulp relative to the Kappa index of the paste to be treated between 0.01 and 0.1 (in other words, the weight ratio peroxide / paste expressed in% and divided by the Kappa index of the paste must be between 0.01 and 0.1).
  • the alkaline medium (sodium hydroxide, in particular) used in this oxidation step must be in sufficient quantity to maintain the pH of the paste to be treated at a value of 9 to 12, preferably 10 to 11, in order to cause swelling of the cellulose fibers of the pulp and make lignin adsorbed on the surface of said cellulose fibers, or trapped in the pores of these fibers, more accessible to the action of peroxides, action which results in oxidation and in the fragmentation of lignin into smaller molecules which can be eliminated from the system by solubilization.
  • the advantages conferred by the present process are multiple: the dissolved materials contained in the recycling effluents being made up in part of carboxylic acid salts (oxidized lignin) having a buffering effect, it is therefore no longer necessary to use buffers inorganic and / or cellulose protectors (no sodium silicate or magnesium sulfate in particular), in the peroxide oxidation step.
  • mechanical pressing allows better extraction and better elimination of oxidized lignins and other dissolved materials, and therefore, it is possible to obtain a reduction in the pollution rejected during the final bleaching phases much greater than the reduction. that can be expected from simple delignification with peroxide.
  • Pressing can be carried out using any known material, provided that a high pulp concentration is obtained, if possible of the order of 30% or more, for example by means of presses or washing presses.
  • Such a process applies to chemical pulps in general, whether they are produced by an alkaline process (example Kraft process) or by an acid process (bisulfitic processes).
  • mechanical pressing is carried out so as to obtain an expression of the oxidized paste corresponding to a concentration (or density) of the paste of 10 to 60%, preferably from 30 to 40%.
  • the prior dilution of the oxidized pulp before pressing is adjusted so as to have a pulp concentration of 1 to 5%, immediately before pressing.
  • the partial recycling of the extraction effluents from the pressing step upstream from the oxidation step is adjusted so as to obtain a dissolved matter rate of 0.5 to 5% by weight per compared to the dough.
  • the juices contained in the dough are preferably displaced by a washing liquor, immediately after pressing.
  • the step of oxidizing the unbleached pulp is carried out with hydrogen peroxide in the presence of soda.
  • the temperature in the oxidation step is between 40 and 95 ° C, preferably between 70 and 90 ° C.
  • the duration of the oxidation step is between 10 min and 5 hours, and preferably between 20 min and 3 hours.
  • the peroxide / soda by weight ratio is between 0.1 and 0.8 and preferably between 0.4 and 0.6.
  • the oxidized, pressed and possibly washed pulp is subjected to a sequence of subsequent bleaching operations.
  • the inventors have found that when this oxidation is carried out in a closed enclosure (closed oxidation reactor, that is to say one not open to the atmosphere) it a slight overpressure develops in the column and pulp relative to the vapor pressure of the water in the liquid phase of the pulp, probably due to the formation of very active nascent oxygen by decomposition of the peroxide, and that, in these conditions, the delignification rate of the dough is significantly improved.
  • a slight overpressure in the pulp column is maintained in the peroxide oxidation step with respect to atmospheric pressure and with respect to the water vapor pressure of the phase dough liquid to be treated.
  • Such an overpressure is limited to a value less than or equal to 2 kg / cm 2 (2 bar) and preferably to a value between 100 and 500 g / cm 2 (0.5 bar).
  • This overpressure in the pulp column can advantageously be maintained by closing the reactor and by the hydraulic pressure of the pulp column in the case of an upward flow.
  • the oxidation step is carried out with peroxide in a closed reactor in which the progression of the dough is done either in the downward direction, or in the upward direction.
  • Figures 2 and 3 show variants of the installation of Figure 1, using a descending tower with closed oxidation reactor ( Figure 2), or an ascending tower with closed oxidation reactor ( Figure 3) respectively.
  • the unbleached dough (1 ton) from cooking and containing 4.5 t of residual liquor is introduced via line 1 into the last washing zone 2 supplied with a mixture of water (4 tonnes) brought in through line 3 and of a part of the pressing effluent (2.5 tonnes) supplied by line 4, via the supply line 5.
  • the water and the pressing effluent are at a temperature of 65 ° C.
  • a 6.5 ton washing effluent is sent to the first washing stage and / or to recovery (combustion) via line 6.
  • the paste-reagents-pressing effluent mixture enters an oxidation reactor 10 to undergo an oxidation reaction there (temperature 70 ° C., duration 2 hours).
  • the oxidized mixture then passes into a dilution zone 11 to receive there another part of the pressing effluent (15 t) supplied by line 12.
  • the oxidized and diluted pulp leaving the dilution zone via line 13 and containing 24 tonnes of mixture of water and pressing effluent is sent to a press 14 and expressed at a pulp concentration of 32.9%. Leaving the press, the delignified paste at 32.9% concentration is obtained via line 15 (ie 2 t of liquid per tonne of dough).
  • a Kraft (unbleached) pulp of various hardwoods (oak, beech) of Kappa index 19.4 is delignified according to the method of the invention, with pressing followed by washing, and recycling, and according to a bleaching control test with peroxide with a simple spin, without recycling.
  • a Kraft (unbleached) pulp of various hardwoods (beech, oak) of index Kappa 17 is treated according to the method of Figure 1, with the following conditions:
  • the properties of the paste are also improved, be it the mechanical characteristics or the optical characteristics (white and white stability).
  • Example 3 The pulp of Example 3 is preoxidized according to the conditions indicated in Table IV below, then bleached at a high level of whiteness by limiting the number of stages to 4 according to 2 sequences CEHD and CEPD (the first step of treatment with dioxide chlorine is removed).
  • Table IV shows that the pre-oxidation according to the process of the invention makes it possible to achieve a quality of pulp superior to that of pulp bleached with conventional CEDE H D bleaching.
  • a Kraft pulp of various hardwoods (beech, oak, etc.) preoxidized according to the invention and the same untreated pulp are bleached in a conventional manner according to a CEDED sequence.
  • Table V below shows that this same pre-oxidized pulp with the conditions indicated can be completely bleached with a sequence reduced to 3 stages C D HD (deletion of 2 conventional stages).
  • C D HD discharge of 2 conventional stages
  • a hardwood pulp (oak / beech) prepared by the cooking process with sodium bisulfite and Kappa index 20.2 is preoxidized according to the process of the invention and bleached at a high level of whiteness.
  • the results in Table VI above show the advantages of the process compared to the DEHD sequence conventionally used for a bisulphite paste (whiteness, cleanliness, consumption of chemicals).
  • This example shows the advantage of pressing after the peroxide treatment according to the invention.
  • a Kraft pulp of various hardwoods with a Kappa index of 19.4 is oxidized with peroxide and then pressed according to the process of the invention (P + Press).
  • the unbleached dough from cooking and containing residual liquor is introduced via line 1 into the last washing zone 2 supplied with a mixture of water supplied via line 3 and part of the pressing effluent supplied via line 4, via supply line 5.
  • the water and the pressing effluent are at a temperature of 95 ° C.
  • a washing effluent is sent to the first washing stage and / or to recovery (combustion) via line 6.
  • the pulp-reactants-pressing effluent mixture enters a descending tower at the top of an oxidation reactor 10a of the closed type to undergo an oxidation reaction there. Said mixing progresses from top to bottom inside said reactor and a slight overpressure of 300 g / cm 2 (0.3 bar) is maintained in the dough column.
  • the oxidized mixture then passes into a dilution zone 11a formed in the extension of the lower part of the reactor 10a in order to receive there another part of the pressing effluent supplied by line 12.
  • the reactor-dilution zone assembly constitutes a descending tower with a closed reactor.
  • the oxidized and diluted pulp leaving the lower part of the dilution zone via line 13 and containing a mixture of water and pressing effluent is sent to a press 14 and expressed at a pulp concentration of 33%. Leaving the press, the delignified paste at 33% concentration is obtained via line 15.
  • the washing water can also be introduced at the outlet of the press through the pipe 17 (instead of the pipe 4 at the inlet of the washing zone 2).
  • the method of the invention is implemented in the installation shown in FIG. 3.
  • Such an installation comprises an ascending tower with closed reactor 10b and a separate dilution zone 11b.
  • the rest of the installation is identical to that shown in Figure 2.
  • the unbleached pulp to be treated is a Kraft softwood pulp with a Kappa index of 19.
  • the oxidized mixture leaves through the upper part of the reactor, via line 18, and then passes into the dilution zone 11b to receive there another part of the pressing effluent brought in through line 12.
  • the pressing of the oxidized and diluted pulp and the recycling of the pressing effluent are carried out as described for the installation of FIG. 2.
  • a control test is also carried out in an open reactor.

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  • Life Sciences & Earth Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Wood Science & Technology (AREA)
  • Paper (AREA)

Description

La fabrication de pâte à papier dite "chimique" comporte deux phases essentielles, à savoir;

  • - une phase de cuisson de matériaux lignocellulosiques à l'aide de réactifs chimiques (tels que soude caustique, bisulfite de calcium, mélange sulfure de sodium-soude caustique, etc.), destinée à dissoudre la plus grande partie de la lignine et à libérer les fibres de cellulose, conduisant à une pâte écrue et à des liqueurs résiduaires de cuisson, qui sont généralement récupérées et brûlées;
  • - une phase de blanchiment de la pâte écrue comprenant généralement plusieurs étapes de traitement permettant d'éclacir la pâte de d'éliminer la lignine résiduelle laissée dans la pâte écrue après la cuisson.
The manufacture of so-called "chemical" pulp has two essential phases, namely;
  • - a phase of cooking lignocellulosic materials using chemical reagents (such as caustic soda, calcium bisulfite, sodium sulfide-caustic soda mixture, etc.), intended to dissolve most of the lignin and to release cellulose fibers, leading to an unbleached pulp and residual cooking liquors, which are generally recovered and burned;
  • - a bleaching phase of the unbleached dough generally comprising several treatment steps making it possible to remove the dough and eliminate the residual lignin left in the unbleached dough after cooking.

La première étape du blanchiment consiste de façon classique en un traitement à l'aide d'un réactif chloré: chlore, bioxyde de chlore, hypochlorite de sodium, etc. Ce type de traitement présente cependant certains inconvénients; notamment, il conduit à des effluents pollués par des chlorures corrosifs qu'il n'est pas possible de recycler dans le circuit de récupération des produits chimiques unitisés pour la mise en pâte du bois (cuisson), du fait des risques élevés associés à la présence de chlorures.The first stage of bleaching typically consists of treatment with a chlorine reagent: chlorine, chlorine dioxide, sodium hypochlorite, etc. However, this type of treatment has certain drawbacks; in particular, it leads to effluents polluted by corrosive chlorides which it is not possible to recycle in the recovery circuit for unitized chemicals for pulping wood (cooking), due to the high risks associated with the presence of chlorides.

En vue de limiter la pollution, on a proposé récemment un procédé de blanchiment consistant à traiter la pâte chimique à blanchir par l'oxygène sous pression et en milieu alcalin. Ce dernier procédé conduit à un effluent, compatible avec la circuit de récupération de l'atelier de cuisson, qui est éliminé par combustion. Un tel procédé requiert cependant des investissements lourds.In order to limit pollution, a bleaching process has recently been proposed which consists in treating the chemical pulp to be bleached with oxygen under pressure and in an alkaline medium. This latter process leads to an effluent, compatible with the recovery circuit of the cooking workshop, which is eliminated by combustion. However, such a process requires heavy investments.

Par ailleurs, on a également proposé récemment les peroxydes comme agents de blanchiment conduisant aussi à un effluent récupérable.Furthermore, peroxides have also recently been proposed as bleaching agents, also leading to a recoverable effluent.

Toutefois, le mécanisme de l'action de blanchiment aux peroxydes est entièrement différent des mécanismes des agents de blanchiment discutés ci-dessus.However, the mechanism of the peroxide bleaching action is entirely different from the mechanisms of the bleaching agents discussed above.

Les peroxydes sont des agents de blanchiment dits à préservation de lignine, c'est-à-dire qu'ils permettent d'obtenir un éclaircissement de la pâte sans réduction de poids de matière, en oxydant les groupes chromophores rattachés aux grosses molécules de lignine, mais ils n'attaquent pas la structure principale de la lignine elle-même.Peroxides are bleaching agents known as lignin preservation, that is to say that they make it possible to obtain a lightening of the dough without reduction of material weight, by oxidizing the chromophoric groups attached to the large lignin molecules. , but they do not attack the main structure of lignin itself.

De ce fait, on réserve les peroxydes au blanchiment des pâtes à papier (pâtes mécaniques, pâtes thermomécaniques, pâtes michimiques) dites à haute teneur en lignine ou à haut rendement (rendement > 6596) pour lesquelles on ne recherche pas une délignification, mais un éclaircissement sans réduction de poids de matière.Therefore, the peroxides are reserved for the bleaching of paper pulps (mechanical pulps, thermomechanical pulps, michemical pulps) said to have a high lignin content or a high yield (yield> 6596) for which no delignification is sought, but a lightening without reduction of material weight.

Or, less inventeurs ont découvert qu'il était possible de réaliser une délignification des pâtes chimiques écrues (c'est-à-dire des pâtes à bas rendement (<65%) et à faible teneur en lignine) à l'aide des peroxydes (peroxyde d'hydrogène, peroxyde de sodium et autres peroxydes alcalins) dont les propriétés délignifiantes ne sont pas connues à ce jour,

  • - en adaptant la quantité de peroxyde employée à la teneur en lignine de la pâte écrue à traiter,
  • - en conduisant le traitement par un peroxyde en milieu alcalin,
  • - en combinant ledit traitement avec un pressage mécanique à haute densité,
  • - et en recyclant les effluents de ce pressage vers l'amont et vers l'aval dudit traitement au peroxyde avant ledit pressage mécanique.
However, the inventors have discovered that it is possible to carry out delignification of unbleached chemical pulps (that is to say pulps with low yield (<65%) and with low lignin content) using peroxides (hydrogen peroxide, sodium peroxide and other alkaline peroxides) whose delignifying properties are not known to date,
  • - by adapting the amount of peroxide used to the lignin content of the unbleached pulp to be treated,
  • - by conducting the treatment with a peroxide in an alkaline medium,
  • - by combining said treatment with high density mechanical pressing,
  • - And by recycling the effluents from this pressing upstream and downstream of said peroxide treatment before said mechanical pressing.

La présente invention a donc pour objet un procédé de délignification de pâte à papier dite "chimique" écrue comportant la combinaison des étapes suivantes:

  • a) une étape d'oxydation de la pâte écrue par un peroxyde, en milieu alcalin, suivie de,
  • b) une étape de pressage mécanique de la pâte oxydée, avec recyclage des effluents d'extraction de l'étape de pressage
    • - en partie vers l'amont de l'étape d'oxydation
    • - en partie en aval de cette étape d'oxydation en vue d'assurer une dilution préalable de la pâte oxydée avant le pressage
    • - et éventuellement en partie vers le lavage de la pâte écrue, et/ou à la récupération.
The subject of the present invention is therefore a process for the delignification of so-called "chemical" unbleached paper pulp comprising the combination of the following steps:
  • a) an oxidation step of the unbleached pulp with a peroxide, in an alkaline medium, followed by,
  • b) a mechanical pressing step of the oxidized pulp, with recycling of the extraction effluents from the pressing step
    • - partly upstream of the oxidation stage
    • - partly downstream of this oxidation step in order to ensure a prior dilution of the oxidized dough before pressing
    • - and possibly partly towards washing the unbleached dough, and / or recovering it.

Dans l'étape a) d'oxydation de la pâte écrue, on emploie une quantité de peroxyde adaptée au taux de lignine de la pâte à traiter de façon à avoir un rapport en % de peroxyde/pâte par rapport à l'indice Kappa de la pâte à traiter compris entre 0,01 et 0,1 (autrement dit, le rapport pondéral peroxyde/pâte exprimé en % et divisé par l'indice Kappa de la pâte doit être compris entre 0,01 et 0,1 ).In step a) of oxidation of the unbleached pulp, an amount of peroxide is used which is adapted to the lignin level of the pulp to be treated so as to have a ratio of% peroxide / pulp relative to the Kappa index of the paste to be treated between 0.01 and 0.1 (in other words, the weight ratio peroxide / paste expressed in% and divided by the Kappa index of the paste must be between 0.01 and 0.1).

De plus, le milieu alcalin (soude, notamment) employé dans cette étape d'oxydation doit être en quantité suffisante pour maintenir le pH de la pâte à traiter à une valeur de 9 à 12, de préférence de 10 à 11, afin de provoquer un gonflement des fibres de cellulose de la pâte et rendre la lignine adsorbée sur la surface desdites fibres de cellulose, ou emprisonnée dans les pores de ces fibres, plus accessible à l'action des peroxydes, action qui se traduit par une oxydation et par une fragmentation de la lignine en molécules plus petites qui peuvent être éliminées du système par solubilisation.In addition, the alkaline medium (sodium hydroxide, in particular) used in this oxidation step must be in sufficient quantity to maintain the pH of the paste to be treated at a value of 9 to 12, preferably 10 to 11, in order to cause swelling of the cellulose fibers of the pulp and make lignin adsorbed on the surface of said cellulose fibers, or trapped in the pores of these fibers, more accessible to the action of peroxides, action which results in oxidation and in the fragmentation of lignin into smaller molecules which can be eliminated from the system by solubilization.

Les avantages que confère le présent procédé sont multiples: les matières dissoutes contenues dans les effluents de recyclage étant constituées en partie de sels d'acides carboxyliques (lignine oxydée) ayant un effet tampon, il n'est donc plus nécessaire d'utiliser des tampons inorganiques et/ou des protecteurs de la cellulose (pas de silicate de sodium ni de sulfate de magnésium en particulier), dans l'étape d'oxydation au peroxyde. De plus, la pressage mécanique permet une meilleure extraction et une meilleure élimination des lignines oxydées et autres matières dissoutes, et de ce fait, il est possible d'obtenir une réduction de la pollution rejetée lors des phases de blanchiment finales bien supérieure à la réduction qu'on peut attendre d'une simple délignification au peroxyde.The advantages conferred by the present process are multiple: the dissolved materials contained in the recycling effluents being made up in part of carboxylic acid salts (oxidized lignin) having a buffering effect, it is therefore no longer necessary to use buffers inorganic and / or cellulose protectors (no sodium silicate or magnesium sulfate in particular), in the peroxide oxidation step. In addition, mechanical pressing allows better extraction and better elimination of oxidized lignins and other dissolved materials, and therefore, it is possible to obtain a reduction in the pollution rejected during the final bleaching phases much greater than the reduction. that can be expected from simple delignification with peroxide.

Il est préférable de ne pas presser la pâte tout de suite après l'addition des réactifs mais plutôt de laisser agir les réactifs et d'effectuer le pressage en fin d'oxydation après la rétention; le pressage de la pâte à haute densité en vue d'obtenir une extraction en fin d'oxydation par le peroxyde alcalin conduit à des résultats nettement supérieurs à ceux obtenus avec un simple essorage destiné à faciliter l'imprégnation et permet une réduction sensible de la pollution rejetée.It is preferable not to press the paste immediately after the addition of the reagents but rather to let the reactants act and to press at the end of oxidation after retention; pressing the high density dough in order to obtain an extraction at the end of oxidation with alkaline peroxide leads to results clearly superior to those obtained with a simple spin intended to facilitate impregnation and allows a significant reduction in the pollution released.

Le pressage peut être réalisé au moyen de tout matériel connu pour autant que l'on obtienne une concentration en pâte élevée, si possible de l'ordre de 30% ou plus, par exemple au moyen de presses ou de presses-laveuses.Pressing can be carried out using any known material, provided that a high pulp concentration is obtained, if possible of the order of 30% or more, for example by means of presses or washing presses.

Un tel procédé s'applique aux pâtes chimiques en général, qu'elles soient produites par un procédé alcalin (exemple procédé Kraft) ou par un procédé acide (procédés bisulfitiques).Such a process applies to chemical pulps in general, whether they are produced by an alkaline process (example Kraft process) or by an acid process (bisulfitic processes).

C'est également un procédé conservateur d'énergie thermique et le pressage de la pâte permet de récupérer non seulement une grande quantité de filtrats, mais aussi les thermies de ces filtrats. L'excédent de filtrats peut ainsi non seulement être recyclé à la phase d'oxydation, mais aussi être utilisé pour le lavage de la pâte en amont de l'oxydation, c'est-à-dire après la cuisson. Ceci constitue un avantage supplémentaire sur les procédés conventionnels, dans lesquels la pâte issue du traitement au peroxyde est simplement lavée à l'eau et les effluents, dilués, sont directement soumis à une évaporation et à une concentration des matières dissoutes avant d'être brûlés. L'absence de pressage ne permet donc pas, dans un tel cas, d'obtenir le gain optimal d'extraction et de pollution; l'absence de recyclage ne permet pas une protection de la pâte et une économie de produits chimiques et de thermies.It is also a thermal energy conserving process and the pressing of the dough makes it possible to recover not only a large quantity of filtrates, but also the therms of these filtrates. The excess filtrates can thus not only be recycled to the oxidation phase, but also be used for washing the dough before oxidation, that is to say after cooking. This constitutes an additional advantage over conventional processes, in which the pulp resulting from the peroxide treatment is simply washed with water and the effluents, diluted, are directly subjected to evaporation and to a concentration of the dissolved materials before being burnt. . The absence of pressing therefore does not make it possible, in such a case, to obtain the optimal gain in extraction and pollution; the absence of recycling does not allow a protection of the dough and a saving of chemicals and thermals.

Selon une autre caractéristique de l'invention, le pressage mécanique est effectué de façon à obtenir un exprimage de la pâte oxydée correspondant à une concentration (ou densité) de la pâte de 10 à 60%, de préférence de 30 à 40%.According to another characteristic of the invention, mechanical pressing is carried out so as to obtain an expression of the oxidized paste corresponding to a concentration (or density) of the paste of 10 to 60%, preferably from 30 to 40%.

De plus, la dilution préalable de la pâte oxydée avant le pressage est réglée de façon à avoir une concentration en pâte de 1 à 5%, immédiatement avant pressage.In addition, the prior dilution of the oxidized pulp before pressing is adjusted so as to have a pulp concentration of 1 to 5%, immediately before pressing.

De même, le recyclage en partie des effluents d'extraction de l'étape de pressage vers l'amont de l'étape d'oxydation est réglé de façon à obentir un taux de matières dissoutes de 0,5 à 5% en poids par rapport à la pâte.Likewise, the partial recycling of the extraction effluents from the pressing step upstream from the oxidation step is adjusted so as to obtain a dissolved matter rate of 0.5 to 5% by weight per compared to the dough.

En outre, les jus contenus dans la pâte sont de préférence déplacés par une liqueur de lavage, immédiatement après le pressage.In addition, the juices contained in the dough are preferably displaced by a washing liquor, immediately after pressing.

Selon une autre caractéristique encore de l'invention, l'étape d'oxydation de la pâte écrue est conduite par du peroxyde d'hydrogène en présence de soude.According to yet another characteristic of the invention, the step of oxidizing the unbleached pulp is carried out with hydrogen peroxide in the presence of soda.

La température dans l'étape d'oxydation est comprise entre 40 et 95°C, de préférence entre 70 et 90°C.The temperature in the oxidation step is between 40 and 95 ° C, preferably between 70 and 90 ° C.

De plus, la durée de l'étape d'oxydation est comprise entre 10 mn et 5 heures, et de préférence entre 20 mn et 3 heures.In addition, the duration of the oxidation step is between 10 min and 5 hours, and preferably between 20 min and 3 hours.

En outre, le rapport pondéral peroxyde/soude d'appoint est compris entre 0,1 et 0,8 et, de préférence, entre 0,4 et 0,6.In addition, the peroxide / soda by weight ratio is between 0.1 and 0.8 and preferably between 0.4 and 0.6.

Selon une autre caractéristique encore, la pâte oxydée, pressée, et éventuellement lavée, est soumise à une séquence d'opérations ultérieures de blanchiment.According to yet another characteristic, the oxidized, pressed and possibly washed pulp is subjected to a sequence of subsequent bleaching operations.

Par ailleurs, lors de l'étape d'oxydation au peroxyde, les inventeurs ont constaté que lorsque cette oxydation est conduite dans une enceinte fermée (réacteur d'oxydation fermé, c'est-à-dire non ouvert à l'atmosphère) il se développe une légère surpression dans la colonne et pâte par rapport à la tension de vapeur de l'eau de la phase liquide de la pâte, probablement du fait de la formation d'oxygène naissant très actif par décomposition du peroxyde, et que, dans ces conditions, le taux de délignification de la pâte est amélioré de façon significative.Furthermore, during the peroxide oxidation step, the inventors have found that when this oxidation is carried out in a closed enclosure (closed oxidation reactor, that is to say one not open to the atmosphere) it a slight overpressure develops in the column and pulp relative to the vapor pressure of the water in the liquid phase of the pulp, probably due to the formation of very active nascent oxygen by decomposition of the peroxide, and that, in these conditions, the delignification rate of the dough is significantly improved.

Ainsi, selon une nouvelle caractéristique de l'invention, on maintient dans l'étape d'oxydation au peroxyde une légère surpression dans la colonne de pâte par rapport à la pression atmosphérique et par rapport à la tension de vapeur d'eau de la phase liquide de la pâte à traiter.Thus, according to a new characteristic of the invention, a slight overpressure in the pulp column is maintained in the peroxide oxidation step with respect to atmospheric pressure and with respect to the water vapor pressure of the phase dough liquid to be treated.

Une telle surpression est limitée à une valeur inférieure ou égale à 2 kg/cm2 (2 bar) et de préférence à une valeur comprise entre 100 et 500 g/cm2 (0,5 bar).Such an overpressure is limited to a value less than or equal to 2 kg / cm 2 (2 bar) and preferably to a value between 100 and 500 g / cm 2 (0.5 bar).

Cette surpression dans la colonne de pâte peut être maintenue avantageusement par la fermeture du réacteur et par la pression hydraulique de la colonne de pâte dans le cas d'un écoulement ascendant.This overpressure in the pulp column can advantageously be maintained by closing the reactor and by the hydraulic pressure of the pulp column in the case of an upward flow.

Pour la mise en oeuvre de ce perfectionnement selon l'invention, on conduit l'étape d'oxydation au peroxyde dans un réacteur fermé dans lequel la progression de la pâte se fait soit dans le sens descendant, soit dans le sens ascendant.For the implementation of this improvement according to the invention, the oxidation step is carried out with peroxide in a closed reactor in which the progression of the dough is done either in the downward direction, or in the upward direction.

On illustre l'invention par des exemples non limitatifs qui suivent.The invention is illustrated by the following nonlimiting examples.

La mise en oeuvre du procédé selon l'invention peut être faite dans une installation représentée schématiquement à la figure 1 du dessin.The implementation of the method according to the invention can be done in an installation shown schematically in Figure 1 of the drawing.

Les figures 2 et 3 représentent des variantes de l'installation de la figure 1, utilisant une tour descendante avec réacteur d'oxydation fermé (figure 2), ou une tour ascendante avec réacteur d'oxydation fermé (figure 3) respectivement.Figures 2 and 3 show variants of the installation of Figure 1, using a descending tower with closed oxidation reactor (Figure 2), or an ascending tower with closed oxidation reactor (Figure 3) respectively.

Exemple 1Example 1

Une pâte (écrue) Kraft de feuillus divers (hêtre, chêne, etc.) d'indice Kappa 19,5 est oxydée par le peroxyde d'hydrogène:

  • -d'une part, selon le procédé de l'invention,
  • - d'autre part, à titre de comparaison, selon le procédé d'oxydation au moyen du peroxyde d'hydrogène en milieu alcalin, sans pressage.
A Kraft (unbleached) pulp of various hardwoods (beech, oak, etc.) with a Kappa index of 19.5 is oxidized by hydrogen peroxide:
  • on the one hand, according to the method of the invention,
  • - on the other hand, by way of comparison, according to the oxidation process using hydrogen peroxide in an alkaline medium, without pressing.

Le procédé selon l'invention est mis en oeuvre dans l'installation représentée schématiquement à la figure 1 du dessin.The method according to the invention is implemented in the installation shown schematically in Figure 1 of the drawing.

LavageWashing

La pâte écrue (1 tonne) provenant de la cuisson et contenant 4,5 t de liqueur résiduaire est introduite par la conduite 1 dans la dernière zone de lavage 2 alimentée par un mélange d'eau (4 tonnes) amenée par la conduite 3 et d'une partie de l'effluent de pressage (2,5 tonnes) amenée par la conduite 4, via la conduite d'alimentation 5. L'eau et l'effluent de pressage sont à une température de 65°C. Un effluent de lavage de 6,5 tonnes est envoyé au premier stade de lavage et/ou à la récupération (combustion) par la conduite 6.The unbleached dough (1 ton) from cooking and containing 4.5 t of residual liquor is introduced via line 1 into the last washing zone 2 supplied with a mixture of water (4 tonnes) brought in through line 3 and of a part of the pressing effluent (2.5 tonnes) supplied by line 4, via the supply line 5. The water and the pressing effluent are at a temperature of 65 ° C. A 6.5 ton washing effluent is sent to the first washing stage and / or to recovery (combustion) via line 6.

OxydationOxidation

La pâte lavée sortant de la zone de lavage par la conduite 7 et contenant 4,5 tonnes d'un mélange d'eau et d'effluent de pressage reçoit simultanément

  • - d'une part, les réactifs d'oxydation peroxyde d'hydrogène (0,005 t) et soude (0,005 t) et leur eau de dilution (0,01 t) provenant de la conduite 8,
  • - d'autre part, une autre partie de l'effluent de pressage (4,5 t) amenée par la conduite 9.
The washed dough leaving the washing zone via line 7 and containing 4.5 tonnes of a mixture of water and pressing effluent receives simultaneously
  • on the one hand, the hydrogen peroxide (0.005 t) and sodium hydroxide (0.005 t) oxidation reagents and their dilution water (0.01 t) coming from line 8,
  • - on the other hand, another part of the pressing effluent (4.5 t) supplied by line 9.

La mélange pâte-réactifs-effluent de pressage pénètre dans un réacteur d'oxydation 10 pour y subir une réaction d'oxydation (température 70°C, durée 2 heures).The paste-reagents-pressing effluent mixture enters an oxidation reactor 10 to undergo an oxidation reaction there (temperature 70 ° C., duration 2 hours).

DilutionDilution

Le mélange oxydé passe ensuite dans une zone de dilution 11 pour y recevoir une autre partie de l'effluent de pressage (15 t) amenée par la conduite 12.The oxidized mixture then passes into a dilution zone 11 to receive there another part of the pressing effluent (15 t) supplied by line 12.

PressagePressing

La pâte oxydée et diluée sortant de la zone de dilution par la conduite 13 et contenant 24 tonnes de mélange d'eau et d'effluent de pressage est envoyée dans une presse 14 et exprimée à une concentration de pâte de 32,9%. On obtient à la sortie de la presse la pâte délignifiée à 32,9% de concentration par la conduite 15 (soit 2 t de liquid par tonne de pâte).The oxidized and diluted pulp leaving the dilution zone via line 13 and containing 24 tonnes of mixture of water and pressing effluent is sent to a press 14 and expressed at a pulp concentration of 32.9%. Leaving the press, the delignified paste at 32.9% concentration is obtained via line 15 (ie 2 t of liquid per tonne of dough).

RecyclageRecycling

Par ailleurs, on recycle un effluent de pressage (22 t) par la conduite 16:

  • - d'une part, à l'entrée du réacteur d'oxydation (4,5 t),
  • - d'autre part, dans la zone de dilution (15 t),
  • - et également dans la zone de lavage (2,5 t).
Furthermore, a pressing effluent (22 t) is recycled through line 16:
  • - on the one hand, at the inlet of the oxidation reactor (4.5 t),
  • - on the other hand, in the dilution zone (15 t),
  • - and also in the washing area (2.5 t).

Les résultats des essais sont groupés dans le tableau I ci-après. Ils montrent que, dans les conditions ajustées de façon à obtenir un même taux de délignification (indice Kappa) et une même qualité de pâte (degré de polymérisation), le procédé selon l'invention, grâce au pressage mécanique de la pâte après oxydation et au recyclage de l'effluent de pressage en amont et en aval du réacteur d'oxydation et éventuellement vers la zone de lavage de la pâte écrue, permet de réaliser d'importantes économies en ce que concerne la consommation des réactifs d'oxydation (consommation réduite de moitié par rapport à l'essai témoin sans pressage), et la consommation d'énergie thermique (consommation réduite de moitié environ par rapport à l'essai témoin).The results of the tests are grouped in Table I below. They show that, under the conditions adjusted so as to obtain the same delignification rate (Kappa index) and the same quality of dough (degree of polymerization), the process according to the invention, thanks to the mechanical pressing of the dough after oxidation and the recycling of the press effluent upstream and downstream of the oxidation reactor and possibly towards the washing area of the unbleached pulp, makes it possible to make significant savings as regards the consumption of the oxidation reagents (consumption halved compared to the control test without pressing), and thermal energy consumption (consumption reduced by about half compared to the control test).

Exemple 2Example 2

Une même pâte (écrue) Kraft de feuillus d'indice Kappa 19,5 est traitée selon le procédé de l'invention, avec 1% de H2O2, et selon le procédé classique de délignification à l'oxygène sous pression. Les résultats mentionnés dans le tableau Il ci-après montrent que le procédé selon l'invention permet en travaillant sans pression et à plus faible température d'obtenir des résultats équivalents au procédé à l'oxygène (qui nécessite des réacteurs pressurisés, coûteux et peu maniables).

Figure imgb0001
Figure imgb0002
 The same (unbleached) Kraft hardwood pulp of Kappa index 19.5 is treated according to the method of the invention, with 1% H 2 O 2 , and according to the conventional method of delignification with oxygen under pressure. The results mentioned in table II below show that the process according to the invention makes it possible, by working without pressure and at a lower temperature, to obtain results equivalent to the oxygen process (which requires pressurized reactors, which are expensive and inexpensive). handy).
Figure imgb0001
Figure imgb0002

Exemple 3Example 3

Une pâte (écrue) Kraft de feuillus divers (chêne, hêtre) d'indice Kappa 19,4 est délignifiée selon la procédé de l'invention, avec pressage suivi d'un lavage, et recyclage, et selon un essai témoin de blanchiment au peroxyde avec un simple essorage, sans recyclage.A Kraft (unbleached) pulp of various hardwoods (oak, beech) of Kappa index 19.4 is delignified according to the method of the invention, with pressing followed by washing, and recycling, and according to a bleaching control test with peroxide with a simple spin, without recycling.

Les résultats ci-après montrent que le pressage/lavage selon l'invention permet un gain de délignification par rapport à l'essai témoin, avec moitié moins de soude, pour un temps de rétention court, et moins d'eau de lavage.

Figure imgb0003
The results below show that the pressing / washing according to the invention allows a gain in delignification compared to the control test, with half less sodium hydroxide, for a short retention time, and less washing water.
Figure imgb0003

Exemple 4Example 4

Une pâte (écrue) Kraft de feuillus divers (hêtre, chêne) d'indice Kappa 17 est traitée selon le procédé de la figure 1, avec les conditions suivantes:

Figure imgb0004
Figure imgb0005
 A Kraft (unbleached) pulp of various hardwoods (beech, oak) of index Kappa 17 is treated according to the method of Figure 1, with the following conditions:
Figure imgb0004
Figure imgb0005

La pâte ainsi traitée et la pâte non traitée (témoin) sont blanchies selon une séquence classique de blanchiment complet CEDEHD selon les conditions du tableau III ci-après (C=chloration; E=extraction alcaline; D=traitement du bioxyde de chlore; EH=extraction à l'hypochlorite en milieu alcalin).The pulp thus treated and the untreated pulp (control) are bleached according to a conventional complete bleaching sequence CEDE H D according to the conditions in Table III below (C = chlorination; E = alkaline extraction; D = treatment of chlorine dioxide ; E H = extraction with hypochlorite in an alkaline medium).

Outre l'économie de produits chimiques et d'énergie thermique (température), on constate des gains importants sur la pollution. Ces gains sont encore accrus si la phase de pressage est accompagnée d'un déplacement des jus contenus dans la pâte par un jus de lavage (eau chaude) au moyen par exemple de presse-laveuse (essai 2), lavage à fond.In addition to saving chemicals and thermal energy (temperature), there are significant gains in pollution. These gains are further increased if the pressing phase is accompanied by a displacement of the juices contained in the dough by a washing juice (hot water) by means for example of washer-presser (test 2), washing thoroughly.

Les propriétés de la pâte sont également améliorées que ce soit les caractéristiques mécaniques ou les caractéristiques optiques (blanc et stabilité de blanc).The properties of the paste are also improved, be it the mechanical characteristics or the optical characteristics (white and white stability).

Exemple 5Example 5

La pâte de l'exemple 3 est préoxydée selon les conditions indiquées au tableau IV ci-après, puis blanchie à un haut niveau de blancheur en limitant le nombre des stades à 4 selon 2 séquences CEHD et CEPD (la première étape de traitement au bioxyde de chlore est supprimée).The pulp of Example 3 is preoxidized according to the conditions indicated in Table IV below, then bleached at a high level of whiteness by limiting the number of stages to 4 according to 2 sequences CEHD and CEPD (the first step of treatment with dioxide chlorine is removed).

Le tableau IV montre que la préoxydation selon le procédé de l'invention permet d'arriver à une qualité de pâte supérieure à celle de la pâte blanchie avec un blanchiment conventionnel CEDEHD.Table IV shows that the pre-oxidation according to the process of the invention makes it possible to achieve a quality of pulp superior to that of pulp bleached with conventional CEDE H D bleaching.

Exemple 6Example 6

Une pâte Kraft de feuillus divers (hêtre, chêne, etc.) préoxydée selon l'invention et la même pâte non traitée sont blanchies de façon conventionnelle selon une séquence CEDED. Le tableau V ci-après montre que cette même pâte préoxydée avec les conditions indiquées peut être totalement blanchie avec une séquence réduite à 3 stades CDHD (suppression de 2 étapes conventionnelles). On notera de plus le gain important réalisé ainsi sur la pollution (couleur) des effluents rejetés.

Figure imgb0006
Figure imgb0007
Figure imgb0008
Figure imgb0009
 A Kraft pulp of various hardwoods (beech, oak, etc.) preoxidized according to the invention and the same untreated pulp are bleached in a conventional manner according to a CEDED sequence. Table V below shows that this same pre-oxidized pulp with the conditions indicated can be completely bleached with a sequence reduced to 3 stages C D HD (deletion of 2 conventional stages). We also note the significant gain made in this way on the pollution (color) of the effluents discharged.
Figure imgb0006
Figure imgb0007
Figure imgb0008
Figure imgb0009

Exemple 7Example 7

Une pâte de feuillus (chêne/hêtre) préparée par le procédé de cuisson au bisulfite de sodium et d'indice Kappa=20,2 est préoxydée selon le procédé de l'invention et blanchie à haut niveau de blancheur. Les résultats du tableau VI ci-avant montrent les avantages de procédé par rapport à la séquence DEHD utilisée de façon classique pour une pâte bisulfitique (blancheur, propreté, consommation de produits chimiques).A hardwood pulp (oak / beech) prepared by the cooking process with sodium bisulfite and Kappa index = 20.2 is preoxidized according to the process of the invention and bleached at a high level of whiteness. The results in Table VI above show the advantages of the process compared to the DEHD sequence conventionally used for a bisulphite paste (whiteness, cleanliness, consumption of chemicals).

Exemple 8Example 8

Cet exemple montre l'intérêt du pressage après le traitement au peroxyde selon l'invention.This example shows the advantage of pressing after the peroxide treatment according to the invention.

Une pâte Kraft de feuillus divers d'indice Kappa 19,4 est oxydée au peroxyde puis pressée selon le procédé de l'invention (P+Presse).A Kraft pulp of various hardwoods with a Kappa index of 19.4 is oxidized with peroxide and then pressed according to the process of the invention (P + Press).

Conditions du traitement au peroxyde d'hydrogène (P):

Figure imgb0010
Conditions for treatment with hydrogen peroxide (P):
Figure imgb0010

Conditions de pressage (Presse):

Figure imgb0011
Pressing conditions (Press):
Figure imgb0011

A titre d'essais comparatifs: la pâte est soumise d'abord à un pressage, puis à l'oxydation au peroxyde (Presse+P); dans un autre essai, la pâte est soumise à un pressage seul, sans oxydation (presse seule); les résultats sont mentionnés dans le tableau VII ci-après.By way of comparative tests: the dough is first subjected to pressing, then to peroxide oxidation (Press + P); in another test, the dough is subjected to pressing alone, without oxidation (press alone); the results are listed in Table VII below.

Seul le procédé selon l'invention a permis d'obtenir une économie importante de consommation des réactifs, de consommation d'énergie thermique et une diminution importante de la pollution.

Figure imgb0012
Only the process according to the invention has made it possible to obtain a significant saving in consumption of reagents, in consumption of thermal energy and a significant reduction in pollution.
Figure imgb0012

Exemple 9Example 9

Une pâte écrue Kraft de feuillus divers (hêtre, chêne, etc.) d'indice Kappa 20,5 est oxydée par le peroxyde d'hydrogène:

  • - d'une part, selon le procédé de l'invention, en tour descendante avec réacteur fermé,
  • - d'autre part, à titre de comparaison, selon le procédé d'oxydation au moyen du peroxyde d'hydrogène en milieu alcalin, en tour descendante avec réacteur ouvert.
An unbleached Kraft pulp of various hardwoods (beech, oak, etc.) with a Kappa index of 20.5 is oxidized by hydrogen peroxide:
  • on the one hand, according to the method of the invention, in a descending tower with the reactor closed,
  • - on the other hand, by way of comparison, according to the oxidation process using hydrogen peroxide in an alkaline medium, in a descending tower with an open reactor.

Le procédé selon l'invention est mis en oeuvre dans l'installation représentée schématiquement à la figure 2 du dessin.The method according to the invention is implemented in the installation shown schematically in Figure 2 of the drawing.

LavageWashing

La pâte écrue provenant de la cuisson et contenant de la liqueur résiduaire est introduite par la conduite 1 dans la dernière zone de lavage 2 alimentée par un mélange d'eau amenée par la conduite 3 et d'une partie de l'effluent de pressage amenée par la conduite 4, via la conduite d'alimentation 5. L'eau et l'effluent de pressage sont à une température de 95°C. Un effluent de lavage est envoyé au premier stade de lavage et/ou à la récupération (combustion) par la conduite 6.The unbleached dough from cooking and containing residual liquor is introduced via line 1 into the last washing zone 2 supplied with a mixture of water supplied via line 3 and part of the pressing effluent supplied via line 4, via supply line 5. The water and the pressing effluent are at a temperature of 95 ° C. A washing effluent is sent to the first washing stage and / or to recovery (combustion) via line 6.

OxydationOxidation

La pâte lavée sortant de la zone de lavage par la conduite 7 et contenant un mélange d'eau et d'effluent de pressage, reçoit simultanément:

  • - d'une part, les réactifs d'oxydation peroxyde d'hydrogène et soude et leur eau de dilution provenant de la conduite 8,
  • ­-d'autre part, une autre partie de l'effluent de pressage amenée par la conduite 9.
The washed dough leaving the washing zone via line 7 and containing a mixture of water and pressing effluent, simultaneously receives:
  • on the one hand, the hydrogen peroxide and sodium hydroxide oxidation reagents and their dilution water coming from line 8,
  • on the other hand, another part of the pressing effluent brought in through line 9.

Le mélange pâte-réactifs-effluent de pressage pénètre dans une tour descendante, à la partie supérieure d'un réacteur d'oxydation 10a du type fermé pour y subir une réaction d'oxydation. Ledit mélange progresse de haut en bas à l'intérieur dudit réacteur et une légère surpression de 300 g/cm2 (0,3 bar) est maintenue dans la colonne de pâte.The pulp-reactants-pressing effluent mixture enters a descending tower at the top of an oxidation reactor 10a of the closed type to undergo an oxidation reaction there. Said mixing progresses from top to bottom inside said reactor and a slight overpressure of 300 g / cm 2 (0.3 bar) is maintained in the dough column.

Elle est probablement due à la formation d'oxygène naissant par décomposition du peroxyde d'hydrogène dans les conditions de mise en oeuvre du procédé.It is probably due to the formation of nascent oxygen by decomposition of hydrogen peroxide under the conditions of implementation of the process.

DilutionDilution

Le mélange oxydé passe ensuite dans une zone de dilution 11 a ménagée dans le prolongement de la partie inférieure du réacteur 10a pour y recevoir une autre partie de l'effluent de pressage amenée par la conduite 12.The oxidized mixture then passes into a dilution zone 11a formed in the extension of the lower part of the reactor 10a in order to receive there another part of the pressing effluent supplied by line 12.

L'ensemble réacteur-zone de dilution constitue une tour descendante à réacteur fermé.The reactor-dilution zone assembly constitutes a descending tower with a closed reactor.

PressagePressing

La pâte oxydée et diluée sortant de la partie inférieure de la zone de dilution par la conduite 13 et contenant un mélange d'eau et d'effluent de pressage est envoyée dans une presse 14 et exprimée à une concentration de pâte de 33%. On obtient à la sortie de la presse la pâte délignifiée à 33% de concentration par la conduite 15.The oxidized and diluted pulp leaving the lower part of the dilution zone via line 13 and containing a mixture of water and pressing effluent is sent to a press 14 and expressed at a pulp concentration of 33%. Leaving the press, the delignified paste at 33% concentration is obtained via line 15.

RecyclageRecycling

Par ailleurs, on recycle un effluent de pressage par la conduite 16,

  • -d'une part, à l'entré du réacteur d'oxydation (par la conduite 9),
  • - d'autre part, dans la zone de dilution (par la conduite 12),
  • - et également dans la zone de lavage (par la conduite 4).
Furthermore, a pressing effluent is recycled via line 16,
  • on the one hand, at the inlet of the oxidation reactor (via line 9),
  • - on the other hand, in the dilution zone (via line 12),
  • - and also in the washing area (via line 4).

L'eau de lavage peut également être introduite à la sortie de la presse par la conduite 17 (au lieu de la conduite 4 à l'entrée de la zone de lavage 2).The washing water can also be introduced at the outlet of the press through the pipe 17 (instead of the pipe 4 at the inlet of the washing zone 2).

Les résultats des essais sont groupés dans le tableau VIII ci-après. Ils montrent que, dans les conditions préconisées selon l'invention (oxydation au peroxyde d'hydrogène en tour descendante avec réacteur fermé, avec une légère surpression de 300 g/cm2), on a obtenu un taux de dilignification correspondant à un indice Kappa final de 9,6, contre un indice Kappa final de 12, 1, lorsqu'on opère en réacteur ouvert (pression atmosphérique), soit une amélioration significative de ce taux de délignification.

Figure imgb0013
The results of the tests are grouped in Table VIII below. They show that, under the conditions recommended according to the invention (oxidation with hydrogen peroxide in descending tower with closed reactor, with a slight overpressure of 300 g / cm 2 ), a dilignification rate corresponding to a Kappa index was obtained. final of 9.6, against a final Kappa index of 12.1 when operating in an open reactor (atmospheric pressure), a significant improvement in this delignification rate.
Figure imgb0013

Exemple 10Example 10

Le procédé de l'invention est mis en oeuvre dans l'installation représentée à la figure 3. Une telle installation comporte une tour ascendante avec réacteur fermé 10b et une zone de dilution séparée 11 b. Le reste de l'installation est identique à celle représentée à la figure 2.The method of the invention is implemented in the installation shown in FIG. 3. Such an installation comprises an ascending tower with closed reactor 10b and a separate dilution zone 11b. The rest of the installation is identical to that shown in Figure 2.

La pâte écrue à traiter est une pâte Kraft de bois résineux ayant un indice Kappa de 19.The unbleached pulp to be treated is a Kraft softwood pulp with a Kappa index of 19.

OxydationOxidation

La pâte écrue lavée sortant de la zone de lavage par la conduite 7 et contenant:

  • -d'une par, les réactifs d'oxydation (peroxyde d'hydrogène et soude) amenés par la conduite 8, et
  • ­-d'autre part, une partie de l'effluent de pressage amenée par la conduite 9,

est introduite à la partie inférieure d'un réacteur ascendant fermé 10b pour y subir une réaction d'oxydation. Le mélange remonte de bas en haut à l'intérieur du réacteur à mesure que progresse la réaction d'oxydation. Une légère surpression de 100 g/cmz (0,1 bar) est maintenue dans la colonne de pâte.The washed unbleached paste leaving the washing zone via line 7 and containing:
  • on the one hand, the oxidation reagents (hydrogen peroxide and soda) supplied via line 8, and
  • on the other hand, part of the pressing effluent supplied by line 9,

is introduced to the lower part of a closed ascending reactor 10b to undergo an oxidation reaction there. The mixture rises from bottom to top inside the reactor as the oxidation reaction. A slight overpressure of 100 g / cm z (0.1 bar) is maintained in the dough column.

DilutionDilution

Le mélange oxydé sort par la partie supérieure du réacteur, par la conduite 18, et passe ensuite dans la zone de dilution 11b pour y recevoir une autre partie de l'effluent de pressage amenée par la conduite 12.The oxidized mixture leaves through the upper part of the reactor, via line 18, and then passes into the dilution zone 11b to receive there another part of the pressing effluent brought in through line 12.

Le pressage de la pâte oxydée et diluée et le recyclage de l'effluent de pressage se font comme décrit pour l'installation de la figure 2.The pressing of the oxidized and diluted pulp and the recycling of the pressing effluent are carried out as described for the installation of FIG. 2.

Un essai témoin est également conduit en réacteur ouvert.A control test is also carried out in an open reactor.

Les résultats des essais sont groupés dans le tableau IX ci-après. Ils montrent que dans les conditions préconisées selon l'invention (oxydation en tour ascendante avec réacteur fermé, avec une légère surpression de 100 g/cm2 (0,1 bar) on a obtenu une amélioration significative du taux de délignification de la pâte; en effet, l'indice Kappa final de la pâte obtenue est de 13,1, contre un indice Kappa de 15,1 pour l'essai témoin conduit en réacteur ouvert.

Figure imgb0014
The results of the tests are grouped in Table IX below. They show that under the conditions recommended according to the invention (oxidation in ascending tower with closed reactor, with a slight overpressure of 100 g / cm 2 (0.1 bar), a significant improvement in the degree of delignification of the dough was obtained; indeed, the final Kappa index of the pulp obtained is 13.1, against a Kappa index of 15.1 for the control test conducted in an open reactor.
Figure imgb0014

Claims (18)

1. A process for the delignification of unbleached chemical wood pulp characterized in that it comprises the combination of the following steps:
a) a step of oxidation of the unbleached pulp with a peroxide, in an alkaline medium with a % peroxide/pulp ratio with respect to the Kappa index of said pulp of from 0.01 to 0.1, and with a pH kept at a value of from 9 to 12, the said oxidation being followed by
b) a step of mechanical pressing of the oxidized pulp with recycling of the extraction effluents from the pressing step,
- partly upstream the oxidation step,
- partly downstream the oxidation step with a view to ensure the prior dilution of the pulp oxidized before the pressing,
- and if necessary partly towards the wash of the unbleached pulp.
2. The process of claim 1, characterized in that the mechanical pressing of the oxidized pulp is conducted in such a way as to obtain a squeezing of the pulp corresponding to a pulp concentration or density of 10 to 60%.
3. The process of claim 1 or 2, characterized in that the prior dilution of the pulp oxidized before the pressing is adjusted in such a way as to obtain a pulp concentration of from 1 to 5% by weight immediately before pressing.
4. The process of claim 1, 2 or 3, characterized in that the recycling of part of the extraction effluents from the pressing step upstream of the oxidation step is adjusted so as to obtain a quantity of dissolved materials of from 0.5% to 5% by weight with respect to the pulp.
5. The process of claim 1, 2, 3 or 4, characterized in that immediately after pressing, the juices contained in the pulp are moved by a washing liquor.
6. The process of claim 1, characterized in that the oxidation of the unbleached pulp is conducted with hydrogen peroxide in the presence of sodium hydroxide.
7. The process of claim 1 or 6, characterized in that the duration of the oxidation step is from 10 minutes to 5 hours.
8. The process of claim 1 or 6, characterized in that the temperature is from 40 to 95°C during the oxidation step.
9. The process of claim 2, characterized in that the pulp concentration or density after pressing is from 30 to 40%.
10. The process of claim 8, characterized in that the oxidation of the unbleached pulp is conducted at a temperature of from 70 to 90°C.
11. The process of claim 7, characterized in that the duration of the oxidation step is from 20 minutes to 3 hours.
12. The process of claim 1, characterized in that the pH is kept at 10 to 11 in the oxidation step.
13. The process of claim 1, characterized in that the oxidized, pressed and if necessary washed pulp, is subjected to a sequence of subsequent bleaching operations.
14. The process of claim 1, characterized in that during the oxidation step a slight overpressure is kept in the column of pulp compared with the atmospheric pressure and with the pressure of the steam of the liquid phase of the pulp to be treated, the said overpressure being limited to a value below or equal to 2 kg/cm2 (2 bars).
15. The process of claim 14, characterized in that the said overpressure is limited to a value of from 100 to 500 g/cm2 (0,1 to 0,5 bar).
16. The process of claim 14, characterized in that the oxidation step is conducted in a closed reactor inside which the pulp progresses downwards.
17. The process of claim 14, characterized in that the oxidation stage is conducted in a closed reactor inside which the pulp progresses upwards.
18. The process of any one of the preceding claims characterized in that the unbleached chemical pulp is an unbleached Kraftpulp.
EP80400516A 1979-04-17 1980-04-16 Process for the delignification of unbleached chemical paper pulp Expired EP0018287B1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AT80400516T ATE2232T1 (en) 1979-04-17 1980-04-16 PROCESS FOR DELIGNIFICATION OF UNBLEACHED CHEMICAL PAPER PULP.

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
FR7909642A FR2454479A1 (en) 1979-04-17 1979-04-17 Delignification of chemical pulp - by peroxide oxidation in alkaline medium followed by mechanical pressing
FR7909642 1979-04-17
FR8007170A FR2479295A2 (en) 1980-03-31 1980-03-31 Delignification of chemical pulp - by peroxide oxidation in alkaline medium followed by mechanical pressing
FR8007170 1980-03-31

Publications (2)

Publication Number Publication Date
EP0018287A1 EP0018287A1 (en) 1980-10-29
EP0018287B1 true EP0018287B1 (en) 1983-01-12

Family

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Application Number Title Priority Date Filing Date
EP80400516A Expired EP0018287B1 (en) 1979-04-17 1980-04-16 Process for the delignification of unbleached chemical paper pulp

Country Status (9)

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US (1) US4462864A (en)
EP (1) EP0018287B1 (en)
AU (1) AU539108B2 (en)
BR (1) BR8002356A (en)
CA (1) CA1151363A (en)
DE (1) DE3061582D1 (en)
FI (1) FI67242B (en)
NZ (1) NZ193456A (en)
OA (1) OA06515A (en)

Families Citing this family (25)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
SE445051B (en) * 1980-04-10 1986-05-26 Sca Development Ab SET FOR MANUFACTURING MECHANICAL, MAINLY HEART-FREE CELLULOSAMASSA
US4559103A (en) * 1982-08-05 1985-12-17 Honshu Seishi Kabushiki Kaisha Packaging paper and packaging material for packaging metallic material and method of producing the same
SE451606B (en) * 1982-09-14 1987-10-19 Sca Development Ab VIEW WHITENING OF HOG REPLACEMENT MASSES AVERAGE PEROXIDES
US4806475A (en) * 1983-12-28 1989-02-21 The United States Of America As Represented By The Secretary Of Agriculture Alkaline peroxide treatment of agricultural byproducts
US4649113A (en) * 1983-12-28 1987-03-10 The United States Of America As Represented By The Secretary Of Agriculture Alkaline peroxide treatment of nonwoody lignocellulosics
SE444825B (en) * 1984-09-10 1986-05-12 Mo Och Domsjoe Ab PROCEDURE FOR THE PREPARATION OF IMPROVED HOG REPLACEMENT MASS
US4568420B1 (en) * 1984-12-03 1999-03-02 Int Paper Co Multi-stage bleaching process including an enhanced oxidative extraction stage
US4793898A (en) * 1985-02-22 1988-12-27 Oy Keskuslaboratorio - Centrallaboratorium Ab Process for bleaching organic peroxyacid cooked material with an alkaline solution of hydrogen peroxide
US4826567A (en) * 1985-08-05 1989-05-02 Interox (Societe Anonyme) Process for the delignification of cellulosic substances by pretreating with a complexing agent followed by hydrogen peroxide
US4826568A (en) * 1985-08-05 1989-05-02 Interox (Societe Anonyme) Process for delignification of cellulosic substances by pretreating with a complexing agent followed by peroxide prior to kraft digestion
US4965086A (en) * 1988-01-04 1990-10-23 Degussa Aktiengesellschaft Chemical-mechanical treatment of lignocellulosics to improve nutritive value
US5023097A (en) * 1988-04-05 1991-06-11 Xylan, Inc. Delignification of non-woody biomass
US4842877A (en) * 1988-04-05 1989-06-27 Xylan, Inc. Delignification of non-woody biomass
US4859282A (en) * 1988-04-15 1989-08-22 E. I. Du Pont De Nemours And Company Acid purification of product from alkaline peroxide processing of nonwoody lignocellulosic substrates
EP0337653A3 (en) * 1988-04-15 1991-10-02 E.I. Du Pont De Nemours And Company Improved alkaline peroxide treatment of nonwoody lignocellulosic substrates
US4957599A (en) * 1988-04-15 1990-09-18 E. I. Du Pont De Nemours And Company Alkaline extraction, peroxide bleaching of nonwoody lignocellulosic substrates
US4859283A (en) * 1988-04-15 1989-08-22 E. I. Du Pont De Nemours And Company Magnesium ions in a process for alkaline peroxide treatment of nonwoody lignocellulosic substrates
US4915785A (en) * 1988-12-23 1990-04-10 C-I-L Inc. Single stage process for bleaching of pulp with an aqueous hydrogen peroxide bleaching composition containing magnesium sulphate and sodium silicate
CA2082557C (en) * 1992-02-24 1997-03-11 Charles W. Hankins Integrated pulping process of waste paper yielding tissue-grade paper fibers
BE1008751A3 (en) * 1994-07-26 1996-07-02 Solvay Xylanase, the producing microorganisms, dna molecules, methods of preparation of this xylanase and uses thereof.
US5770010A (en) * 1995-04-20 1998-06-23 R-J Holding Company Pulping process employing nascent oxygen
US7747434B2 (en) * 2000-10-24 2010-06-29 Speech Conversion Technologies, Inc. Integrated speech recognition, closed captioning, and translation system and method
US8138106B2 (en) 2005-09-30 2012-03-20 Rayonier Trs Holdings Inc. Cellulosic fibers with odor control characteristics
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
WO2008137517A1 (en) * 2007-05-07 2008-11-13 Hydrite Chemical Co. Systems, compositions, and/or methods for depolymerizing cellulose and/or starch

Family Cites Families (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CA558246A (en) * 1958-06-03 L. Mcewen Robert High temperature pulp bleaching
US3313678A (en) * 1962-02-14 1967-04-11 Svenska Cellulose Aktiebolaget Bleaching of cellulose pulp in towers in completely filled and closed system
DE1203592B (en) * 1962-02-23 1965-10-21 Rudolf Bott Dipl Ing Process for the bleaching of cellulosic fibers
DE2219505C3 (en) * 1972-04-21 1974-10-17 Deutsche Gold- Und Silber-Scheideanstalt Vormals Roessler, 6000 Frankfurt Chlorine-free multi-stage bleaching of cellulose
SE413684C (en) * 1974-09-23 1987-05-18 Mo Och Domsjoe Ab PROCEDURE FOR PREPARING CELLULOSAMASSA IN THE REPLACEMENT AREA 65-95%
SE415581B (en) * 1977-04-18 1980-10-13 Mo Och Domsjoe Ab PROCEDURE FOR PEROCID WHITING OF HOG REPLACEMENT MASS
SE422818B (en) * 1978-03-31 1982-03-29 Modo Chemetrics Ab PROCEDURE FOR PROCESSING ALLULOSAMASSA BY BLACKING OR EXTRACTING

Also Published As

Publication number Publication date
BR8002356A (en) 1980-12-02
OA06515A (en) 1981-07-31
EP0018287A1 (en) 1980-10-29
DE3061582D1 (en) 1983-02-17
FI67242B (en) 1984-10-31
FI801211A (en) 1980-10-18
CA1151363A (en) 1983-08-09
AU539108B2 (en) 1984-09-13
NZ193456A (en) 1982-06-29
US4462864A (en) 1984-07-31
AU5745080A (en) 1980-10-23

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