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EP0293309A1 - Process for producing chemithermomechanical pulps - Google Patents

Process for producing chemithermomechanical pulps Download PDF

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Publication number
EP0293309A1
EP0293309A1 EP88420160A EP88420160A EP0293309A1 EP 0293309 A1 EP0293309 A1 EP 0293309A1 EP 88420160 A EP88420160 A EP 88420160A EP 88420160 A EP88420160 A EP 88420160A EP 0293309 A1 EP0293309 A1 EP 0293309A1
Authority
EP
European Patent Office
Prior art keywords
sodium
cooking
sulfite
reducing agent
lignocellulosic material
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
EP88420160A
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German (de)
French (fr)
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EP0293309B1 (en
Inventor
Michel Devic
Robert Angelier
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Arkema France SA
Original Assignee
Atochem SA
Elf Atochem SA
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Publication of EP0293309A1 publication Critical patent/EP0293309A1/en
Application granted granted Critical
Publication of EP0293309B1 publication Critical patent/EP0293309B1/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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Classifications

    • DTEXTILES; PAPER
    • D21PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21CPRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
    • D21C3/00Pulping cellulose-containing materials
    • D21C3/22Other features of pulping processes
    • D21C3/222Use of compounds accelerating the pulping processes

Definitions

  • the present invention relates to a process for the manufacture of chemothermal mechanical pulps and more particularly of chemothermal mechanical pulps having a high ability to be bleached using hydrogen peroxide in an alkaline aqueous medium.
  • cellulosic material like wood in the form of chips, is subjected to separate or associated actions of mechanical, chemical or thermal origin.
  • Mechanical type pulps or high yield pulps are produced by mechanical defibration of the lignocellulosic material, for example in a grindstone shredder or a disc shredder or refiner.
  • the chemothermal-mechanical pastes whose manufacture is covered by the invention, designated in all that follows by CTMP pastes, are obtained by adding to the above process a non-destructive cooking of material carried out at a temperature equal to or greater than 100 ° C. under pressure saturated water vapor in the presence of sodium sulfite, or sodium bisulfite or more generally a mixture of sulfur dioxide SO2 and sodium hydroxide NaOH, indistinctly referred to in all that follows by sulfite, unless otherwise specified .
  • CTMP pastes are of definite interest for the industry because they achieve a valid compromise between mechanical and chemical pulps themselves.
  • the yield of CTMP pulp, weight of pulp in the dry state relative to the weight of starting material in the dry state is generally greater than 85% and most often at least equal to about 90%, this which makes them very close to the pastes of purely mechanical origin and which is translated here by the expression non-destructive cooking of the material.
  • the present invention aims to obtain CTMP pastes which bleaching using hydrogen peroxide brings, except in special cases of interest understandable by those skilled in the art, to a degree of white generally greater than 80%, or 80 °, when it is measured in the usual way today at the wavelength of 457 nm with magnesium oxide as standard of reference using the spectrophotometer of the General Electric or Elrepho type.
  • the French patent published under the number 1150451 recommends baking at a temperature of up to 150 ° C., using sulfite and hydrosulfite, in an acid medium. Any bleaching of the defibrated pulp would be facilitated, but no details are provided in this regard.
  • the invention is first of all a process for manufacturing CTMP pastes in which sodium sulfite or sodium bisulfite or a mixture of sulfur dioxide and sodium hydroxide are involved, and a reducing agent which is more electronegative than ion.
  • sulfite which consists in adding to a mechanical defibration of the cellulosic material a non-destructive cooking of said material at a temperature equal to or greater than 100 ° C.
  • the reducing agent is most often chosen from thiourea dioxide or formamidinesulfinic acid, sodium borohydride and sodium hydrosulfite or sodium dithionite.
  • the amount of reducing agent used can vary depending on the nature thereof. It is generally between 0.1 and 5% in the case of thiourea dioxide or dithionite. This quantity, like any quantity in all that follows, is expressed in percent by weight relative to the weight of lignocellulosic material in the dry state, unless indicated or evident.
  • Sodium borohydride is used in an amount of about 0.01% to 0.5%.
  • This reducing agent is conveniently used in the form of an aqueous solution such as for example the solution containing 12% by weight of sodium borohydride marketed under the name of BOROL® by the company VENTRON Corporation.
  • the cooking temperature according to the invention can reach 200 ° C. It is most frequently chosen between around 120 ° C and 160 ° C.
  • the pressure is practically equal to that corresponding to the pressure of the steam at the cooking temperature.
  • the amount of molecular oxygen, such as oxygen in the air, especially that included in the lignocellulosic material must obviously be minimized. This is carried out in a known manner for example using steam or by compression as indicated inter alia the already cited work of James P. CASEY, p 213, which further describes, p 219 - 229 , equipment, in particular pressure resistant, suitable for the production of CTMP pastes.
  • the committed amount of sulphite is that usually used in processes which do not incorporate the invention and which are known to be suitable for the preparation of CTMP pastes. It is therefore between approximately 0.1% and 10%, most often between 1% and 6% by expressing it in SO2.
  • the cooking according to the invention can be carried out before, during or after a defibering or mechanical refining action.
  • cooking according to the invention of the starting lignocellulosic material can precede a mechanical defibration which continues the action started or which is carried out at low temperature at atmospheric pressure.
  • wood shavings can be impregnated in a known manner when cold using an aqueous solution of the reagents necessary for carrying out the invention, then cooked according to the invention and finally defibrated as indicated in the preceding paragraph.
  • cooking according to the invention begins in the mechanical defibrator or refiner which is fed by the starting lignocellulosic material, for example wood shavings, or said material already formed in the form of a paste by defibration, to be completed at- beyond if necessary.
  • starting lignocellulosic material for example wood shavings, or said material already formed in the form of a paste by defibration
  • the cooking according to the invention can be applied to a paste after defibering-refining of the starting lignocellulosic material, for example wood chips.
  • the consistency, percentage by weight of lignocellulosic material counted in the dry state in the medium, is not a critical factor for the implementation of the invention. In practice, and depending on the methods of execution adopted, it is between approximately 5% and 50%, in general between 5% and 25% in the case of a material already defibrated.
  • the duration of the cooking according to the invention depends on the other performance parameters including the type of equipment used. It usually does not exceed approximately 1 hour and is generally between a few tens of seconds and 30 minutes.
  • the invention is also the bleaching of the pulp produced as described just above, which comprises washing said pulp in order to remove therefrom the sulphite ions and the reducing agent and the action on this washed pulp of peroxide. hydrogen in an alkaline aqueous medium.
  • Washing is carried out in a known manner, for example in a repeated or non-repeated sequence of diluting the dough with water and reconcentrating the dough by pressing or filtration.
  • Bleaching is for example carried out by using an amount of hydrogen peroxide of between approximately 0.5% and 10%, preferably between 2% and 6%, in the presence of approximately 1% to 6% of a solution of sodium silicate of density 1.33, at pH between about 9 and 11, at a temperature between 40 ° C and 100 ° C for about 0.5 hour to 2 hours, with a consistency between 10% and 30% .
  • the bleaching solution may contain additives such as essentially one or more complexing or sequestering agents such as, for example, diethylenetriaminepentaacetic and ethylenediaminetetraacetic acids in the form of sodium salts in an amount generally between approximately 0.1% and 1%.
  • the pulp to be bleached can also be subjected before bleaching to a treatment with, in kind and in quantity, the complexing or sequestering agents as above, at a temperature between 20 ° C and 100 ° C, preferably between 50 ° C and 100 ° C, preferably between 50 ° C and 95 ° C so as not to have to work under pressure while keeping a sufficiently rapid complexing or sequestration rate, at a consistency of between approximately 5% and 30% during periods of time can vary between about 5 minutes and 2 hours, and preferably followed by washing, for example by pressing.
  • the cooking according to the invention can itself be preceded by a treatment of the lignocellulosic material using a complexing or sequestering agent, of the type described above.
  • the consistency can then be between approximately 5% and 50% without generally being greater than approximately 25% to 30% when the treated material has previously been subjected to a mechanical defibration action.
  • Such treatment contributes to further increasing the intrinsic effect of the invention on the degree of white after bleaching and on the action efficiency of hydrogen peroxide.
  • the quantities are expressed in percent by weight relative to the lignocellulosic matter in the dry state, unless specified or evident, - when, before cooking, a treatment is applied using a complexing or sequestering agent, designated by sequestering treatment, it is carried out, unless otherwise specified, at 90 ° C for 15 minutes, at a consistency of 10%, at using 0.5% of an aqueous solution at 40% by weight of sodium salt of diethylenetriaminepentaacetic acid, designated by DTPA the initial pH of the cooking medium according to and, where appropriate, that of the aqueous impregnation solution containing the sulphite and the reducing agent, is between 7 and 12.5, - sodium borohydride is applied in the form of BOROL® and the quantity indicated is that of this presentation, - by silicate is designated an aqueous sodium dilicate solution with a density equal to 1.33, - the degree of white is measured (457 nm) using the ELREPHO type spectrophotometer
  • Defibrated softwood shavings with a white degree of 53.7% are autoclaved under saturated steam pressure at 120 ° C for 0.5 hours at a consistency of 20% , in the presence, jointly, of 5.9% of sodium sulfite Na2SO3, 2.5% of sodium hydrosulfite and of 2% of sodium hydroxide.
  • CTMP paste obtained is then bleached at 90 ° C for 2 hours, at a consistency of 20%, using 5% hydrogen peroxide H2O2, 2% sodium hydroxide, 4% silicate and 0.5 % of DTPA.
  • the degree of white thus obtained is equal to 82.8%.
  • Example 1 The same starting lignocellulosic material as in Example 1 is subjected to the sequestering treatment and then to washing with water. It is then treated as in Example 1.
  • the degree of white finally obtained is 83.3% when the cooking before blanching involves the joint action of the hydrosulfite with the sulfite. It is only 81% by adopting the cooking conditions defined for comparison in Example 1 with in addition a consumption of H2O2 being multiplied by 1.12.
  • Example 2 is repeated in the case of the joint action of hydrosulfite with sulfite but with a cooking temperature of 140 ° C instead of 120 ° C.
  • the degree of whiteness thus achieved is always high and equal to 82.6%.
  • the lignocellulosic starting material of Example 1 is successively subjected to the sequestering treatment, to washing with water, to baking carried out under saturated steam pressure at 120 ° for 0.5 hour, the consistency being 20%, in the presence, jointly, of 1.5% of BOROL® and of 5.9% of sodium sulfite, finally to a washing with water to remove the sulfite and the reducing agent.
  • the CTMP paste obtained is then bleached as after the joint action of the hydrosulfite with the sulfite in Example 1.
  • the degree of white achieved then is equal to 84.5%.
  • Example 4 is modified in that the amount of BOROL® goes from 1.5% to 1% and in that the sodium bisulfite, used at the rate of 5%, replaces the sodium sulfite.
  • the CTMP paste obtained is bleached as after the joint action of the hydrosulfite with the sulfite in Example 1.
  • the degree of white achieved after bleaching is equal to 82.7%.
  • Example 5 is repeated but with 3% of BOROL® instead of 1%. The degree of white is then equal to 83.8%.
  • the degree of whiteness is no longer equal to only 77%, yet engaging 5.4% of H2O2, and the rupture length only to 3,290 m.
  • the starting chips have, after defibering-refining in the absence of any chemical reagent, a degree of whiteness equal to 55.5% and a rupture length equal to 2,755 m.
  • the CTMP pulp bleached as in Example 7 but using only 4.7% of H2O2 has a degree of whiteness equal to 78.5% and a breaking length of 3,525 m.
  • Example 2 The same starting lignocellulosic material as in Example 1 is subjected to the sequestering treatment and then to washing with water. It is then subjected to cooking according to the invention at 120 ° C. for 0.5 h, at a consistency of 20%, in the joint presence of 1% of thiourea dioxide and 5.9% of sodium sulfite.
  • Cooking is followed by washing with water to remove the sulfite ions and the reducing agent.
  • the washed paste obtained is then bleached as after the joint action of the hydrosulfite with the sulfite in Example 1, at 90 ° C for 2 hours, at a consistency of 20%, using 5% H deO2, 2% d sodium hydroxide, 4% silicate and 0.5% DTPA.
  • the degree of white thus obtained is equal to 83.5%.
  • Defibrated hardwood shavings with a whiteness level of 59.9% are subjected to autoclaving under saturated steam pressure at 120 ° C for 0.5 hours at a consistency of 20% , in the presence, jointly, of 1.5% of BOROL® and 5.9% of sodium sulfite, followed by washing with water to remove the sulfite and the reducing agent.
  • the washed paste obtained is then bleached at 90 ° C for 2 hours, at a consistency of 20%, using 5% H2O2, 4% silicate and 0.5% DTPA.
  • the degree of white achieved is equal to 86.6%.
  • 250 kg / h of defibered softwood chips are treated by impregnation with 0.5% DTPA at 90 ° C at a consistency of 20%, washed with diluted water tions and successive pressings, then subjected to cooking under saturated steam pressure at 120 ° C. during the stay of a duration of approximately 30 seconds in a mechanical defibrator at a consistency of 28% by joint action of 1, 5% BOROL® and 3% SO2 in a mixture of pH 8.4 with sodium hydroxide, extending at 100 ° C for 30 minutes.
  • the dough washed with water after cooking by successive dilutions and pressings to remove the sulfite ions and the reducing agent, is finally bleached at 80 ° C for 2 hours at a consistency of 26.5% using 5.2% of H2O2, 2% NaOH, 4% silicate and 0.5% DTPA.
  • the whiteness of the bleached washed pulp is 83.6%.
  • the degree of whiteness of the bleached dough is only 80.1% by consuming 1.05 times more H2O2.
  • Example 11 The procedure is as in Example 11, but starting from hardwood chips and cooking under saturated steam pressure with, together with BOROL®, 2.45% SO2 in a mixture of pH 11.5 with sodium hydroxide.
  • the degree of white in the bleached pulp obtained is equal to 87.3%, the length of the break, in meters, equal to 3,235, and the tear index to 352.
  • the degree of white is only 86%, the breaking length, in meters, is only 2,885 m and the tear index 310 , with identical degree of refinement.
  • Example 4 is repeated on defibred softwood shavings with a degree of white equal to 62% except that the sequestering treatment is not carried out before cooking but that the latter is carried out in the presence, in addition to sulfite and BOROL ®, 0.5% DTPA.
  • the degree of white of the bleached pulp obtained is equal to 86% while it is only 84% by operating as above but without using BOROL®.
  • coniferous wood shavings are impregnated, by immersion and draining, simultaneously with 3% sodium sulfite, 3% sodium bisulfite, 1.5% BOROL®, 0.5 % of DTPA and are autoclaved under saturated steam pressure for 4 minutes at 190 ° C before undergoing mechanical defibration by sudden ejection from the autoclave through a die and refining in a disc refiner.
  • the dough thus obtained is bleached, after washing to remove the sulphite and, at 90 ° C for 2 hours at a consistency of 20% using 5% H2O2, 2% sodium hydroxide, 4% silicate and 0 , 5% DTPA.
  • the degree of whiteness of the paste thus finally obtained is equal to 71% while the refined starting chips had only a degree of whiteness equal to 56%.
  • the invention makes it possible not only to manufacture CTMP bleached pulps of high white level from both softwood and hardwood with reduced consumption of H2O2 but also to conserve and even improve the mechanical properties of the pulps. usual bleached.

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Abstract

Process for the manufacture of CTMP pulps, in which a mechanical grinding of the lignocellulosic material is added to a cooking of the said material at a temperature equal to or higher than 100 DEG C, under saturated steam pressure, with the aid of Na2SO3 or NaHSO3 or SO2NaOH and of a reducing agent more electronegative than the SO3<=> ion, used together and in a medium of initial pH between 7 and 12.5, and bleaching of the manufactured pulp with the aid of H2O2 in an alkaline aqueous medium.

Description

La présente invention concerne un procédé de fabrica­tion de pâtes chimicothermomécaniques et plus particulièrement de pâtes chimicothermomécaniques présentant une aptitude élevée à être blanchies à l'aide de peroxyde d'hydrogène en milieu aqueux alcalin.The present invention relates to a process for the manufacture of chemothermal mechanical pulps and more particularly of chemothermal mechanical pulps having a high ability to be bleached using hydrogen peroxide in an alkaline aqueous medium.

Pour obtenir une pâte, la matière cellulosique, comme le bois sous forme de copeaux, est soumise à des actions sépa­rées ou associées d'origine mécanique, chimique ou thermique.To obtain a pulp, cellulosic material, like wood in the form of chips, is subjected to separate or associated actions of mechanical, chemical or thermal origin.

Les pâtes de type mécanique ou pâtes à haut rendement sont fabriquées par défibrage mécanique de la matière lignocellulosique, par exemple dans un défibreur à meule ou un défibreur ou raffineur à disques.Mechanical type pulps or high yield pulps are produced by mechanical defibration of the lignocellulosic material, for example in a grindstone shredder or a disc shredder or refiner.

Les pâtes chimicothermomécaniques dont la fabrication est visée par l'invention, désignées dans tout ce qui suit par pâtes CTMP, sont obtenues en adjoignant au processus ci-dessus une cuisson non destructrice de matière réalisée à température égale ou supérieure à 100°C sous pression de vapeur d'eau saturée en présence de sulfite de sodium, ou de bisulfite de sodium ou plus généralement d'un mélange de dioxyde de soufre SO₂ et d'hydroxyde de sodium NaOH, indistinctement désignés dans tout ce qui suit par sulfite, sauf précision.The chemothermal-mechanical pastes whose manufacture is covered by the invention, designated in all that follows by CTMP pastes, are obtained by adding to the above process a non-destructive cooking of material carried out at a temperature equal to or greater than 100 ° C. under pressure saturated water vapor in the presence of sodium sulfite, or sodium bisulfite or more generally a mixture of sulfur dioxide SO₂ and sodium hydroxide NaOH, indistinctly referred to in all that follows by sulfite, unless otherwise specified .

Les pâtes CTMP sont d'un intérêt certain pour l'industrie car elles réalisent un compromis valable entre les pâtes mécaniques et les pâtes chimiques proprement dites.CTMP pastes are of definite interest for the industry because they achieve a valid compromise between mechanical and chemical pulps themselves.

Par exemple, le rendement en pâte CTMP, poids de pâte à l'état sec par rapport au poids de matière de départ à l'état sec, est généralement supérieur à 85 % et le plus souvent au moins égal à environ 90 %, ce qui les rend en cela très proches des pâtes d'origine purement mécanique et ce qui est traduit ici par l'expression cuisson non destructrice de la matière.For example, the yield of CTMP pulp, weight of pulp in the dry state relative to the weight of starting material in the dry state, is generally greater than 85% and most often at least equal to about 90%, this which makes them very close to the pastes of purely mechanical origin and which is translated here by the expression non-destructive cooking of the material.

Toutefois le blanchiment des pâtes CTMP, nécessité par la qualité requise en ce domaine des produits marchands qui en dérivent, pose problème. En effet ce blanchiment, par exemple au moyen de peroxyde d'hydrogène en milieu alcalin , conduit à des résultats encore insuffisamment élevés, vraisemblablement à cause d'effets thermiques néfastes subis préalablement par la matière lignocellulosique notamment au cours de la cuisson définie plus haut.However, the bleaching of CTMP pasta, which is necessary because of the quality required in this field of market products derived therefrom, poses a problem. Indeed, this bleaching, for example by means of hydrogen peroxide in an alkaline medium, leads to results which are still insufficiently high, probably because of harmful thermal effects previously suffered by the lignocellulosic material, in particular during the cooking defined above.

L'exposé ci-dessus est développé par exemple dans l'ouvrage de James P. CASEY, "Pulp and Paper Chemistry and Chemical Technology",3ème ed. vol.I, 1980, p.242-250, 654, 655.The above discussion is developed for example in the work of James P. CASEY, "Pulp and Paper Chemistry and Chemical Technology", 3rd ed. vol.I, 1980, p.242-250, 654, 655.

La présente invention vise à obtenir des pâtes CTMP qu'un blanchiment à l'aide de peroxyde d'hydrogène amène, sauf cas particulier d'intérêt compréhensible par l'homme du métier, à un degré de blanc généralement supérieur à 80 %, ou 80°, quand il est mesuré de façon aujourd'hui usuelle à la longueur d'onde de 457 nm avec l'oxyde de magnésium comme standard de référence à l'aide du spectrophotomètre de type General Electric ou Elrepho.The present invention aims to obtain CTMP pastes which bleaching using hydrogen peroxide brings, except in special cases of interest understandable by those skilled in the art, to a degree of white generally greater than 80%, or 80 °, when it is measured in the usual way today at the wavelength of 457 nm with magnesium oxide as standard of reference using the spectrophotometer of the General Electric or Elrepho type.

Diverses solutions ont déjà été proposées pour obtenir des pâtes de degré de blanc suffisamment élevé avec l'aide du sulfite.Various solutions have already been proposed for obtaining pastes with a sufficiently high degree of whiteness with the aid of sulfite.

Par exemple le brevet français publié sous le n°1150451 préconsise une cuisson à une température allant jusqu'à 150°C, au moyen de sulfite et d'hydrosulfite, en milieu acide. Un blanchiment éventuel de la pâte défibrée en serait facilité mais aucune précision n'est fournie à ce propos.For example, the French patent published under the number 1150451 recommends baking at a temperature of up to 150 ° C., using sulfite and hydrosulfite, in an acid medium. Any bleaching of the defibrated pulp would be facilitated, but no details are provided in this regard.

Le brevet français publié sous le n°1389308 note qu'une amélioration du blanchiment peut être attendue quand on fait suivre un traitement au moyen d'une solution acide de l'ion bisulfite SO₃H⁻, d'un traitement, en milieu acide aussi, et sans pression de vapeur d'eau saturée, au moyen de sulfite en présence de borohydrure de sodium qui est préféré à l'hydrosulfite. La présence du borohydrure de sodium avec le sulfite dans le premier traitement est nuisible et conduit même à un résultat inférieur à celui procuré lorsque le sulfite est employé seul dans les deux traitements.Le blanchiment par H₂O₂ d'une pâte raffinée obtenue selon le mode recommandé coinduit à des degrés de blanc nettement inférieurs à 80 %.The French patent published under the number 1389308 notes that an improvement in bleaching can be expected when a treatment is followed by means of an acid solution of the bisulfite ion SO₃H⁻, of a treatment, also in acid medium, and without saturated steam pressure, using sulfite in the presence of sodium borohydride which is preferred to hydrosulfite. The presence of sodium borohydride with the sulphite in the first treatment is harmful and even leads to a lower result than that obtained when the sulphite is used alone in the two treatments. Bleaching by H₂O₂ of a refined paste obtained according to the recommended method co-induced at degrees of white significantly less than 80%.

Enfin le brevet des Etats Unis d'Amérique, publié sous le n°3981765, qui précise et complète le brevet français correspondant publié sous le numéro 2186984, enseigne que lorsque l'intervention du borohydrure de sodium a lieu en milieu alcalin, avec ou sans sulfite, elle est réalisée néces­sairement en milieu de pH initial supérieur à 13, et doit être suivie ou, de préférence, précédée de celle d'une solution aqueuse acide telle qu'une solution de SO₂ ou de bisulfite. Le procédé décrit ne présente d'intérêt en pratique que pour le bois de feuillus. Aucune indication n'est donnée sur ce que pourrait être l'effet sur la pâte du cumul du traitement alcalin décrit et d'un traitement alcalin en présence de peroxyde d'hydrogène.Finally, the patent of the United States of America, published under the number 3981765, which specifies and supplements the corresponding French patent published under the number 2186984, teaches that when the intervention of sodium borohydride takes place in an alkaline medium, with or without sulphite, it is necessarily carried out in a medium with an initial pH greater than 13, and must be followed or, preferably, preceded by that of a solution aqueous acid such as a solution of SO₂ or bisulfite. The process described is of interest in practice only for hardwoods. No indication is given on what could be the effect on the dough of the combination of the alkaline treatment described and an alkaline treatment in the presence of hydrogen peroxide.

Il ressort de la technique connue que, dans un procé­dé d'élaboration d'une pâte avant blanchiment qui comprend l'in­tervention du sulfite et d'un agent tel que l'hydrosulfite ou le borohydrure, une phase d'acidification est tenue de façon constante pour une nécessité.It is apparent from the known technique that, in a process for preparing a pulp before bleaching which comprises the intervention of the sulfite and an agent such as hydrosulfite or borohydride, an acidification phase is held so constant for a necessity.

Depuis que l'usage de H₂O₂ permet de blanchir jusqu'à un haut niveau de blanc des pâtes obtenues avec l'aide du sul­fite, l'industrie s'est désintéressée de l'action combinée de ce dernier avec des agents comme l'hydrosulfite ou le borohy­drure. Telle que connue, celle-ci entraine en effet pour le moins une complication du processus, une consommation supplé­mentaire de SO₂ ou de bisulfite, une augmentation de la charge polluante. L'invention évite les inconvénients des procédés passés tout en améliorant le résultat des procédés actuels de fabrication de pâtes blanchies jusqu'à un haut niveau de blanc à l'aide de peroxyde d'hydrogène.Since the use of H₂O₂ makes it possible to whiten pulps obtained with the aid of sulfite to a high level of white, the industry has lost interest in the combined action of the latter with agents such as hydrosulfite. or borohydride. As known, this causes in fact at least a complication of the process, an additional consumption of SO₂ or bisulfite, an increase in the pollutant load. The invention avoids the drawbacks of past methods while improving the result of current methods of making bleached pasta up to a high level of white using hydrogen peroxide.

L'invention est d'abord un procédé de fabrication de pâtes CTMP dans lequel interviennent le sulfite de sodium ou le bisulfite de sodium ou un mélange de dioxyde de soufre et d'hydroxyde de sodium,et un agent réducteur plus électronégatif que l'ion sulfite, qui consiste à ajoindre à un défibrage mécanique de la matière cellulosique une cuisson non destructrice de ladite matière à température égale ou supérieure à 100°C sous pression de vapeur d'eau saturée, à l'aide desdits sulfite, bisulfite ou mélange et dudit agent réductuer, caractérisé en ce que lesdits sulfite, bisulfite ou mélange, et ledit agent réducteur interviennent sur la matière lignocellulosique conjointement et en milieu de pH initial compris entre 7 et 12,5, pour conduire à une pâte fabriquée apte au blanchiment à l'aide de peroxyde d'hydrogène en milieu aqueux alcalin.The invention is first of all a process for manufacturing CTMP pastes in which sodium sulfite or sodium bisulfite or a mixture of sulfur dioxide and sodium hydroxide are involved, and a reducing agent which is more electronegative than ion. sulfite, which consists in adding to a mechanical defibration of the cellulosic material a non-destructive cooking of said material at a temperature equal to or greater than 100 ° C. under saturated steam pressure, using said sulfite, bisulfite or mixture and of said reducing agent, characterized in that said sulphite, bisulphite or mixture, and said reducing agent intervene on the lignocellulosic material jointly and in a medium of initial pH between 7 and 12.5, to lead to a paste made capable of bleaching using hydrogen peroxide in an alkaline aqueous medium.

L'agent réducteur est le plus souvent choisi parmi le dioxyde de thiourée ou acide formamidinesulfinique, le borohydrure de sodium et l'hydrosulfite de sodium ou dithionite de sodium.The reducing agent is most often chosen from thiourea dioxide or formamidinesulfinic acid, sodium borohydride and sodium hydrosulfite or sodium dithionite.

On peut se reporter par exemple à la thèse soutenue le 6 décembre 1985 à l'Université Claude Bernard-Lyon-1 par Odile CHALMIN LOUIS-ANDRE : "Propriétés réductrices du dithionite de sodium dans des conditions de transfert de phase" pour juger de l'électronégativité du dithionite et du dioxyde de thiourée.We can refer for example to the thesis defended on December 6, 1985 at the University Claude Bernard-Lyon-1 by Odile CHALMIN LOUIS-ANDRE: "Reducing properties of sodium dithionite under phase transfer conditions" to judge the electronegativity of dithionite and thiourea dioxide.

La quantité d'agent réducteur mis en oeuvre peut varier selon la nature de celui-ci. Elle est en général compri­se entre 0,1 et 5 % dans le cas du dioxyde de thiourée ou du dithionite. Cette quantité comme toute quantité dans tout ce qui suit est exprimée en pour cent en poids par rapport au poids de matière lignocellulosique à l'état sec, sauf indica­tion ou évidence. Le borohydrure de sodium est employé à raison d'environ 0,01 % à 0,5 %. Ce réducteur est commodément utilisé sous forme d'une solution aqueuse comme par exemple la solution renfermant 12 % en poids de borohydrure de sodium commerciali­sée sous le nom de BOROL® par la Société VENTRON Corporation.The amount of reducing agent used can vary depending on the nature thereof. It is generally between 0.1 and 5% in the case of thiourea dioxide or dithionite. This quantity, like any quantity in all that follows, is expressed in percent by weight relative to the weight of lignocellulosic material in the dry state, unless indicated or evident. Sodium borohydride is used in an amount of about 0.01% to 0.5%. This reducing agent is conveniently used in the form of an aqueous solution such as for example the solution containing 12% by weight of sodium borohydride marketed under the name of BOROL® by the company VENTRON Corporation.

La température de cuisson selon l'invention peut atteindre 200°C. Elle est le plus fréquemment choisie entre environ 120°C et 160°C.The cooking temperature according to the invention can reach 200 ° C. It is most frequently chosen between around 120 ° C and 160 ° C.

La pression est pratiquement égale à celle corres­pondant à la pression de la vapeur d'eau à la température de cuisson.The pressure is practically equal to that corresponding to the pressure of the steam at the cooking temperature.

Pendant la cuisson, la quantité d'oxygène moléculaire, comme l'oxygène de l'air, en particulier celui inclus dans la matière lignocellulosique doit être évidemment minimisée. Ceci est réalisé de façon connue par exemple à l'aide de la vapeur d'eau ou par compression comme l'indique entre autres l'ouvrage déjà cité de James P. CASEY, p 213, qui décrit en outre, p 219 - 229, des équipements, en particulier résistant à la pression, convenant à l'élaboration de pâtes CTMP.During cooking, the amount of molecular oxygen, such as oxygen in the air, especially that included in the lignocellulosic material must obviously be minimized. This is carried out in a known manner for example using steam or by compression as indicated inter alia the already cited work of James P. CASEY, p 213, which further describes, p 219 - 229 , equipment, in particular pressure resistant, suitable for the production of CTMP pastes.

La quantité engagée de sulfite est celle habituelle­ment mise en oeuvre dans les procédés n'incorporant pas l'invention et connus pour convenir à l'élaboration de pâtes CTMP. Elle est comprise en conséquence entre environ 0,1 % et 10 %, le plus souvent entre 1 % et 6 % en l'exprimant en SO₂.The committed amount of sulphite is that usually used in processes which do not incorporate the invention and which are known to be suitable for the preparation of CTMP pastes. It is therefore between approximately 0.1% and 10%, most often between 1% and 6% by expressing it in SO₂.

La cuisson selon l'invention peut être réalisée avant, pendant ou après une action de défibrage ou raffinage mécanique.The cooking according to the invention can be carried out before, during or after a defibering or mechanical refining action.

Par exemple une cuisson selon l'invention de la matière lignocellulosique de départ, comme des copeaux de bois, peut précéder un défibrage mécanique qui poursuit l'action commencée ou qui est exécuté à basse température à pression atmosphérique.For example, cooking according to the invention of the starting lignocellulosic material, such as wood chips, can precede a mechanical defibration which continues the action started or which is carried out at low temperature at atmospheric pressure.

Par exemple des copeaux de bois peuvent être imprégnés de façon connue à froid à l'aide d'une solution aqueuse des réactifs nécessaires à la réalisation de l'invention puis cuits selon l'invention et enfin défibrés comme indiqué au paragraphe précédent.For example, wood shavings can be impregnated in a known manner when cold using an aqueous solution of the reagents necessary for carrying out the invention, then cooked according to the invention and finally defibrated as indicated in the preceding paragraph.

Par exemple la cuisson selon l'invention débute dans le défibreur ou raffineur mécanique qu'alaimente la matière lignocellulosique de départ, par exemple des copeaux de bois, ou ladite matière déjà mise sous forme d'une pâte par défibrage, pour être achevée au-delà si nécessaire.For example, cooking according to the invention begins in the mechanical defibrator or refiner which is fed by the starting lignocellulosic material, for example wood shavings, or said material already formed in the form of a paste by defibration, to be completed at- beyond if necessary.

Par exemple la cuisson selon l'invention peut être appliquée à une pâte après défibrage-raffinage de la matière lignocellulosique de départ, par exemple des copeaux de bois.For example, the cooking according to the invention can be applied to a paste after defibering-refining of the starting lignocellulosic material, for example wood chips.

La consistance, pourcentage en poids de matière lignocellulosique comptée à l'état sec dans le milieu, n'est pas un facteur critique pour la réalisation de l'invention. Pratiquement, et selon les modes d'exécution adoptés, elle est comprise entre environ 5 % et 50 %,en général entre 5 % et 25 % dans le cas d'une matière déjà défibrée.The consistency, percentage by weight of lignocellulosic material counted in the dry state in the medium, is not a critical factor for the implementation of the invention. In practice, and depending on the methods of execution adopted, it is between approximately 5% and 50%, in general between 5% and 25% in the case of a material already defibrated.

La durée de la cuisson selon l'invention dépend des autres paramètres d'exécution y compris du type d'équipment utilisé. Elle n'excède pas le plus souvent environ 1 heure et est généralement comprise entre quelques dizaines de secondes et 30 minutes.The duration of the cooking according to the invention depends on the other performance parameters including the type of equipment used. It usually does not exceed approximately 1 hour and is generally between a few tens of seconds and 30 minutes.

L'invention est encore le blanchiment de la pâte fabriquée comme décrit juste ci-dessus, qui comprend le lavage de ladite pâte pour en éliminer au mieux les ions sulfite et l'agent réducteur et l'action sur celle pâte lavée du peroxyde d'hydrogène en milieu aqueux alcalin.The invention is also the bleaching of the pulp produced as described just above, which comprises washing said pulp in order to remove therefrom the sulphite ions and the reducing agent and the action on this washed pulp of peroxide. hydrogen in an alkaline aqueous medium.

L'avantage dont l'invention est la cause, l'amélio­ration de l'aptitude au blanchiment jusqu'à un niveau de blanc élevé, est ainsi constaté.The advantage of which the invention is the cause, the improvement of the whitening ability up to a high white level, is thus observed.

Le lavage est réalisé de façon connue par exemple dans une séquence répétée ou non de dilution de la pâte par l'eau et de reconcentration de la pâte par pressage ou filtration.Washing is carried out in a known manner, for example in a repeated or non-repeated sequence of diluting the dough with water and reconcentrating the dough by pressing or filtration.

On pourra se reporter par exemple à l'article de H.KRUGER, H.U.SUSS - Tappi, 1982 International Sulfite Pulping Conference, Toronto, 20-22 octobre 1982, 143-148 -pour juger de l'importance attribuée à ce lavage.We can refer, for example, to the article by H. Kruger, H.U.SUSS - Tappi, 1982 International Sulfite Pulping Conference, Toronto, October 20-22, 1982, 143-148 - to judge the importance attributed to this washing.

Le blanchiment est par exemple réalisé en engageant une quantité de peroxyde d'hydrogène comprise entre environ 0,5 % et 10 %, de préférence entre 2 % et 6 %, en présence d'environ 1 % à 6 % d'une solution de silicate de sodium de densité 1,33, à pH compris entre environ 9 et 11, à une température compise entre 40°C et 100°C durant environ 0,5 heure à 2 heures, avec une consistance comprise entre 10 % et 30 %. La solution de blanchiment peut contenir des additifs comme essentiellement un ou plusieurs agents complexants ou séquestrants comme par exemple les acides diéthylènetriamine­pentaacétique et éthylènediaminetétraacétique sous forme de sels de sodium en quantité généralement comprise entre environ 0,1 % et 1 %. La pâte à blanchir peut encore être soumise avant blanchiment à un traitement avec,en nature et en quantité,les agents complexants ou séquestrants tels que ci-dessus, à une température comprise entre 20°C et 100°C, de préférence entre 50°C et 100°C, de préférence entre 50°C et 95°C pour ne pas avoir à travailler sous pression en gardant une vitesse de complexation ou séquestration suffisamment rapide, à une consistance comprise entre environ 5 % et 30 % durant des périodes de temps pouvant varier entre environ 5 minutes et 2 heures, et suivie de préférence d'un lavage, par exemple par pressage.Bleaching is for example carried out by using an amount of hydrogen peroxide of between approximately 0.5% and 10%, preferably between 2% and 6%, in the presence of approximately 1% to 6% of a solution of sodium silicate of density 1.33, at pH between about 9 and 11, at a temperature between 40 ° C and 100 ° C for about 0.5 hour to 2 hours, with a consistency between 10% and 30% . The bleaching solution may contain additives such as essentially one or more complexing or sequestering agents such as, for example, diethylenetriaminepentaacetic and ethylenediaminetetraacetic acids in the form of sodium salts in an amount generally between approximately 0.1% and 1%. The pulp to be bleached can also be subjected before bleaching to a treatment with, in kind and in quantity, the complexing or sequestering agents as above, at a temperature between 20 ° C and 100 ° C, preferably between 50 ° C and 100 ° C, preferably between 50 ° C and 95 ° C so as not to have to work under pressure while keeping a sufficiently rapid complexing or sequestration rate, at a consistency of between approximately 5% and 30% during periods of time can vary between about 5 minutes and 2 hours, and preferably followed by washing, for example by pressing.

La cuisson selon l'invention peut être elle-même précédée d'un traitement de la matière lignocellulosique à l'aide d'un agent complexant ou séquestrant, du type de celui décrit ci-dessus. La consistance peut alors être comprise entre environ 5 % et 50 % sans généralement être supérieure à environ 25 % à 30 % quand la matière traitée a au préalable été soumise à une action de défibrage mécanique. Un tel traitement contribue à accroître encore l'effet intrinsèque de l'inven­tion sur le degré de blanc après blanchiment et sur l'effica­cité d'action du peroxyde d'hydrogène.The cooking according to the invention can itself be preceded by a treatment of the lignocellulosic material using a complexing or sequestering agent, of the type described above. The consistency can then be between approximately 5% and 50% without generally being greater than approximately 25% to 30% when the treated material has previously been subjected to a mechanical defibration action. Such treatment contributes to further increasing the intrinsic effect of the invention on the degree of white after bleaching and on the action efficiency of hydrogen peroxide.

Il est encore possible de mettre la matière ligno­cellulosique en présence de l'agent complexant ou séquestrant au moment de la cuisson selon l'invention.It is also possible to put the lignocellulosic material in the presence of the complexing or sequestering agent at the time of cooking according to the invention.

Les exemples suivants, donnés à titre indicatif mais non limitatif permettent de juger de l'invention et de ses avantages.The following examples, given as an indication but not limiting, make it possible to judge of the invention and of its advantages.

Dans ces exemples :
    - les quantités sont exprimées en pour cent en poids par rapport à la matière lignocellulosique à l'état sec, sauf précision ou évidence,
    - quand, avant cuisson, est appliqué un traitement à l'aide d'un agent complexant ou séquestrant, désigné par trai­tement séquestrant, il est réalisé sauf exception précisée, à 90°C durant 15 minutes, à une consistance de 10 %, à l'aide de 0,5 % d'une solution aqueuse à 40 % en poids de sel de sodium de l'acide diéthylènetriaminepentaacétique, désignée par DTPA
    - le pH initial du milieu de cuisson selon et, le cas échéant, celui de la solution aqueuse d'imprégnation contenant le sulfite et l'agent réducteur, est compris entre 7 et 12,5,
    - le borohydrure de sodium est appliqué sous forme de BOROL® et la quantité indiquée est celle de cette présentation,
    - par silicate est désignée une solution aqueuse de dilicate de sodium de densité égale à 1,33,
    - le degré de blanc est mesuré (457 nm) à l'aide du spectrophotomètre de type ELREPHO, fabriqué par KARL ZEISS.
In these examples:
- the quantities are expressed in percent by weight relative to the lignocellulosic matter in the dry state, unless specified or evident,
- when, before cooking, a treatment is applied using a complexing or sequestering agent, designated by sequestering treatment, it is carried out, unless otherwise specified, at 90 ° C for 15 minutes, at a consistency of 10%, at using 0.5% of an aqueous solution at 40% by weight of sodium salt of diethylenetriaminepentaacetic acid, designated by DTPA
the initial pH of the cooking medium according to and, where appropriate, that of the aqueous impregnation solution containing the sulphite and the reducing agent, is between 7 and 12.5,
- sodium borohydride is applied in the form of BOROL® and the quantity indicated is that of this presentation,
- by silicate is designated an aqueous sodium dilicate solution with a density equal to 1.33,
- the degree of white is measured (457 nm) using the ELREPHO type spectrophotometer, manufactured by KARL ZEISS.

Exemple 1Example 1

Des copeaux de bois de résineux défibrés présentant un degré de blanc égal à 53,7 % sont soumis à une cuisson en autoclave sous pression de vapeur d'eau saturée, à 120°C durant 0,5 heure, à une consistance de 20 %, en présence, conjointement, de 5,9 % de sulfite de sodium Na₂SO₃, 2,5 % d'hydrosulfite de sodium et de 2 % d'hydroxyde de sodium.Defibrated softwood shavings with a white degree of 53.7% are autoclaved under saturated steam pressure at 120 ° C for 0.5 hours at a consistency of 20% , in the presence, jointly, of 5.9% of sodium sulfite Na₂SO₃, 2.5% of sodium hydrosulfite and of 2% of sodium hydroxide.

La cuisson est suivie d'un lavage à l'eau pour élimi­ ner les ions sulfite et le réducteur. La pâte CTMP obtenue est alors blanchie à 90°C durant 2 heures,à une consistance de 20 %, au moyen de 5 % de peroxyde d'hydrogène H₂O₂, 2 % d'hydroxyde de sodium, 4 % de silicate et 0,5 % de DTPA.Cooking is followed by washing with water to remove ner sulphite ions and reducer. The CTMP paste obtained is then bleached at 90 ° C for 2 hours, at a consistency of 20%, using 5% hydrogen peroxide H₂O₂, 2% sodium hydroxide, 4% silicate and 0.5 % of DTPA.

Le degré de blanc ainsi atteint est égal à 82,8 %.The degree of white thus obtained is equal to 82.8%.

En procédant comme ci-dessus à l'exception de la cuisson qui est réalisée, dans un but de comparaison, sans hy­drosulfite, à l'aide d'une quantité de bisulfite de sodium égale à 5 % et d'une quantité de NaOH égale à 1,2 %, soit un rapport SO₂/NaOH considéré comme pratiquement optimal en un tel cas, le degré de blanc attaint n'est que de 81 %, en consommant en outre 1,05 fois plus de H₂O₂.By proceeding as above with the exception of the cooking which is carried out, for comparison purposes, without hydrosulfite, using an amount of sodium bisulfite equal to 5% and an equal amount of NaOH at 1.2%, ie a SO₂ / NaOH ratio considered to be practically optimal in such a case, the degree of whiteness attained is only 81%, while consuming 1.05 times more H₂O₂.

Exemple 2Example 2

La même matière lignocellulosique de départ que dans l'exemple 1 est soumise au traitement séquestrant puis à un lavage à l'eau. Elle est ensuite traitée comme dans l'exemple 1.The same starting lignocellulosic material as in Example 1 is subjected to the sequestering treatment and then to washing with water. It is then treated as in Example 1.

Le degré de blanc finalement obtenu est de 83,3 % lorsque la cuisson avant blanchiment comporte l'action conjointe de l'hydrosulfite avec le sulfite. Il est de 81 % seulementt en adoptant les conditions de cuisson définies pour comparaison dans l'exemple 1 avec de plus une consommation de H₂O₂ se trouvant multipliée par 1,12.The degree of white finally obtained is 83.3% when the cooking before blanching involves the joint action of the hydrosulfite with the sulfite. It is only 81% by adopting the cooking conditions defined for comparison in Example 1 with in addition a consumption of H₂O₂ being multiplied by 1.12.

Exemple 3Example 3

L'exemple 2 est répété dans le cas de l'action conjointe de l'hydrosulfite avec le sulfite mais avec une température de cuisson de 140°C au lieu de 120°C.Example 2 is repeated in the case of the joint action of hydrosulfite with sulfite but with a cooking temperature of 140 ° C instead of 120 ° C.

Le degré de blanc ainsi atteint est toujours élevé et égal à 82,6 %.The degree of whiteness thus achieved is always high and equal to 82.6%.

Exemple 4Example 4

La matière lignocellulosique de départ de l'exemple 1 est successivement soumise au traitement séquestrant, à un lavage à l'eau, à une cuisson effectuée sous pression de vapeur d'eau saturée à 120° durant 0,5 heure, la consistance étant de 20 %, en présence, conjointement, de 1,5 % de BOROL® et de 5,9 % de sulfite de sodium, enfin à un lavage à l'eau pour éliminer le sulfite et le réducteur. La pâte CTMP obtenue est alors blanchie comme après action conjointe de l'hydrosulfite avec le sulfite dans l'exemple 1.The lignocellulosic starting material of Example 1 is successively subjected to the sequestering treatment, to washing with water, to baking carried out under saturated steam pressure at 120 ° for 0.5 hour, the consistency being 20%, in the presence, jointly, of 1.5% of BOROL® and of 5.9% of sodium sulfite, finally to a washing with water to remove the sulfite and the reducing agent. The CTMP paste obtained is then bleached as after the joint action of the hydrosulfite with the sulfite in Example 1.

Le degré de blanc atteint alors est égal à 84,5 %.The degree of white achieved then is equal to 84.5%.

Il est encore de 82 % lorsque le blanchiment est modi­fié en ce qui concerne les quantités de H₂O₂, de NaOH et de si­licate qui deviennent égales respectivement à 2 %, 1 % et 3 %.It is still 82% when the bleaching is modified as regards the amounts of H₂O₂, NaOH and silicate which become equal to 2%, 1% and 3% respectively.

Exemple 5Example 5

L'exemple 4 est modifié en ce que la quantité de BOROL® passe de 1,5 % à 1 % et en ce que le bisulfite de sodium, engagé à raison de 5 %, remplace le sulfite de sodium.Example 4 is modified in that the amount of BOROL® goes from 1.5% to 1% and in that the sodium bisulfite, used at the rate of 5%, replaces the sodium sulfite.

La pâte CTMP obtenue est blanchie comme après action conjointe de l'hydrosulfite avec le sulfite dans l'exemple 1. Le degré de blanc atteint après blanchiment est égal à 82,7 %.The CTMP paste obtained is bleached as after the joint action of the hydrosulfite with the sulfite in Example 1. The degree of white achieved after bleaching is equal to 82.7%.

Exemple 6Example 6

L'exemple 5 est répété mais avec 3 % de BOROL® au lieu de 1 %. Le degré de blanc est égal alors à 83,8 %.Example 5 is repeated but with 3% of BOROL® instead of 1%. The degree of white is then equal to 83.8%.

Exemple 7Example 7

250 kg/h de copeaux de bois de résineux défibrés sont soumis à un traitement complexant à 90°C à l'aide de 0,5 % de DTPA, la consistance étant de 40 %, puis lavés par pressage et cuits en autoclave sous pression de vapeur d'eau saturée par action conjointe de 1,5 % de BOROL® avec 2,5 % de bisulfite de sodium neutralisé à l'aide d'hydroxyde de sodium. La cuisson est commencée à une température de 140°C durant 5 minutes puis ache­vée à une température de 100°C durant 1 heure. Après lavage à l'eau pour éliminer les ions sulfite et le réducteur, la pâte CTMP obtenue est blanchie à une consistance de 28 %, à 80°C du­rant 1 heure au moyen de 5,1 % de H₂O₂, 2 % de NaOH, 4 % de si­licate et 0,5 % de DTPA.250 kg / h of defibred softwood chips are subjected to a complexing treatment at 90 ° C. using 0.5% DTPA, the consistency being 40%, then washed by pressing and cooked in an autoclave under pressure of saturated steam by joint action of 1.5% of BOROL® with 2.5% of sodium bisulphite neutralized with sodium hydroxide. Cooking is started at a temperature of 140 ° C for 5 minutes and then completed at a temperature of 100 ° C for 1 hour. After washing with water to remove the sulfite ions and the reducing agent, the CTMP paste obtained is bleached at a consistency of 28%, at 80 ° C. for 1 hour using 5.1% H deO₂, 2% NaOH, 4% silicate and 0.5% DTPA.

Après raffinage dans un raffineur à disques et clas­sage le degré de blanc de la pâte CTMP obtenue est égal à 80 %. La résistance à la traction, ou longueur de rupture en mètres est de 3 835.After refining in a disc refiner and classifying the degree of white of the CTMP paste obtained is equal to 80%. The tensile strength, or rupture length in meters is 3,835.

En répétant le processus décrit ci-dessus mais en omettant le BOROL®, le degré de blanc n'est plus égal qu'à 77 %, en engageant pourtant 5,4 % de H₂O₂, et la longueur de rupture qu'à 3 290 m.By repeating the process described above but omitting the BOROL®, the degree of whiteness is no longer equal to only 77%, yet engaging 5.4% of H₂O₂, and the rupture length only to 3,290 m.

Les copeaux de départ présentent, après défibrage-­raffinage en l'absence de tout réactif chimique, un degré de blanc égal à 55,5 % et une longueur de rupture égale à 2 755 m.The starting chips have, after defibering-refining in the absence of any chemical reagent, a degree of whiteness equal to 55.5% and a rupture length equal to 2,755 m.

Exemple 8Example 8

En répétant le procédé selon l'invention tel qu'il est décrit dans l'exemple 7 mais en réalisant la cuisson selon l'invention par action conjointe de 2,5 % d'hydrosulfite de sodium avec 5 % de bisulfite de sodium neutralisé à l'aide de NaOH et de 1 % de NaOH, la pâte CTMP blanchie comme dans l'exemple 7 mais en n'engageant que 4,7 % de H₂O₂ a un degré de blanc égal à 78,5 % et une longueur de rupture de 3 525 m.By repeating the process according to the invention as it is described in Example 7 but by cooking according to the invention by the joint action of 2.5% sodium hydrosulfite with 5% sodium bisulfite neutralized using NaOH and 1% NaOH, the CTMP pulp bleached as in Example 7 but using only 4.7% of H₂O₂ has a degree of whiteness equal to 78.5% and a breaking length of 3,525 m.

Exemple 9Example 9

La même matière lignocellulosique de départ que dans l'exemple 1 est soumise au traitement séquestrant puis à un lavage à l'eau. Elle est ensuite soumise à une cuisson selon l'invention à 120°C durant 0,5 h, à une consistance de 20 %, en présence conjointement de 1 % de dioxyde de thiourée et de 5,9 % de sulfite de sodium.The same starting lignocellulosic material as in Example 1 is subjected to the sequestering treatment and then to washing with water. It is then subjected to cooking according to the invention at 120 ° C. for 0.5 h, at a consistency of 20%, in the joint presence of 1% of thiourea dioxide and 5.9% of sodium sulfite.

La cuisson est suivie d'un lavage à l'eau pour éli­miner les ions sulfite et le réducteur. La pâte lavée obtenue est alors blanchie comme après action conjointe de l'hydrosul­fite avec le sulfite dans l'exemple 1, à 90°C durant 2 heures, à une consistance de 20 %, au moyen de 5 % de H₂O₂, 2 % d'hydroxyde de sodium, 4 % de silicate et 0,5 % de DTPA.Cooking is followed by washing with water to remove the sulfite ions and the reducing agent. The washed paste obtained is then bleached as after the joint action of the hydrosulfite with the sulfite in Example 1, at 90 ° C for 2 hours, at a consistency of 20%, using 5% H deO₂, 2% d sodium hydroxide, 4% silicate and 0.5% DTPA.

Le degré de blanc ainsi atteint est égal à 83,5 %.The degree of white thus obtained is equal to 83.5%.

Exemple 10Example 10

Des copeaux de bois de feuillu défibrés présentant un degré de blanc égal à 59,9 % sont soumis à une cuisson en auto­clave sous pression de vapeur d'eau saturée, à 120°C durant 0,5 heure, à une consistance de 20 %, en présence, conjointement, de 1,5 % de BOROL® et de 5,9 % de sulfite de sodium, suivie d'un lavage à l'eau pour éliminer le sulfite et le réducteur. La pâte lavée obtenue est alors blanchie à 90°C durant 2 heu­res, à une consistance de 20 %, au moyen de 5 % de H₂O₂, 4 % de silicate et 0,5 % de DTPA.Defibrated hardwood shavings with a whiteness level of 59.9% are subjected to autoclaving under saturated steam pressure at 120 ° C for 0.5 hours at a consistency of 20% , in the presence, jointly, of 1.5% of BOROL® and 5.9% of sodium sulfite, followed by washing with water to remove the sulfite and the reducing agent. The washed paste obtained is then bleached at 90 ° C for 2 hours, at a consistency of 20%, using 5% H₂O₂, 4% silicate and 0.5% DTPA.

Le degré de blanc atteint est égal à 86,6 %.The degree of white achieved is equal to 86.6%.

En procédant comme ci-dessus sauf pour la cuisson qui est réalisée, dans un but de comparaison, sans BOROL®, le degré de blanc atteint n'est plus que de 84,1 % en consommant de plus 1,05 fois plus de H₂O₂.By proceeding as above except for the cooking which is carried out, for the purpose of comparison, without BOROL®, the degree of whiteness achieved is only 84.1% by consuming 1.05 times more H₂O₂ .

Example 11Example 11

250 kg/h de copeaux de bois de résineux ayant subi un défibrage sont traités par imprégnation à l'aide de 0,5 % de DTPA à 90°C à une consistance de 20 %, lavés à l'eau par dilu­ tions et pressages successifs, puis soumis à une cuisson sous pression de vapeur d'eau saturée, à 120°C pendant le séjour d'une durée de 30 secondes environ dans un défibreur mécanique à une consistance de 28 % par action conjointe de 1,5 % de BOROL® et de 3 % de SO₂ en mélange de pH 8,4 avec de l'hydroxyde de sodium, se prolongeant à 100°C durant 30 minutes. La pâte, lavée à l'eau après cuisson par dilutions et pressages successifs pour éliminer les ions sulfite et le réducteur, est enfin blanchie à 80°C durant 2 heures à une consistance de 26,5 % au moyen de 5,2 % de H₂O₂, 2 % de NaOH, 4 % de silicate et 0,5 % de DTPA.250 kg / h of defibered softwood chips are treated by impregnation with 0.5% DTPA at 90 ° C at a consistency of 20%, washed with diluted water tions and successive pressings, then subjected to cooking under saturated steam pressure at 120 ° C. during the stay of a duration of approximately 30 seconds in a mechanical defibrator at a consistency of 28% by joint action of 1, 5% BOROL® and 3% SO₂ in a mixture of pH 8.4 with sodium hydroxide, extending at 100 ° C for 30 minutes. The dough, washed with water after cooking by successive dilutions and pressings to remove the sulfite ions and the reducing agent, is finally bleached at 80 ° C for 2 hours at a consistency of 26.5% using 5.2% of H₂O₂, 2% NaOH, 4% silicate and 0.5% DTPA.

Après raffinage en raffineur à double disque et clas­sage, le degré de blanc de la pâte lavée blanchie est de 83,6 %.After refining in a double disc refiner and grading, the whiteness of the bleached washed pulp is 83.6%.

En opérant comme ci-dessus mais en ommettant le BOROL® dans la cuisson, le degré de blanc de la pâte blanchie n'est plus que de 80,1 % en consommant 1,05 fois plus de H₂O₂.By operating as above but omitting the BOROL® in cooking, the degree of whiteness of the bleached dough is only 80.1% by consuming 1.05 times more H₂O₂.

Exemple 12Example 12

On opère comme dans l'exemple 11 mais en partant de copeaux de bois de feuillu et en réalisant la cuisson sous pression de vapeur d'eau saturée avec, conjointement au BOROL®, 2,45 % de SO₂ en mélange de pH 11,5 avec de l'hydro­xyde de sodium.The procedure is as in Example 11, but starting from hardwood chips and cooking under saturated steam pressure with, together with BOROL®, 2.45% SO₂ in a mixture of pH 11.5 with sodium hydroxide.

Le degré de blanc de la pâte blanchie obtenue est égal à 87,3 % la longueur de la rupture, en mètres, égale à 3 235, et l'indice de déchirure à 352.The degree of white in the bleached pulp obtained is equal to 87.3%, the length of the break, in meters, equal to 3,235, and the tear index to 352.

En opérant comme ci-dessus mais sans mettre en oeuvre le BOROL® le degré de blanc n'est plus que de 86 %, la longueur de rupture, en mètres, est égale a seulement 2 885 m et l'indice de déchirure à 310,à degré de raffinage identique.By operating as above but without using BOROL®, the degree of white is only 86%, the breaking length, in meters, is only 2,885 m and the tear index 310 , with identical degree of refinement.

Exemple 13Example 13

On répète l'exemple 4 sur des copeaux de bois de rési­neux défibrés de degré de blanc égal à 62 % sauf que le traite­ment séquestrant n'est pas effectué avant cuisson mais que cette dernière est réalisée en présence, en plus du sulfite et du BOROL®, de 0,5 % de DTPA.Example 4 is repeated on defibred softwood shavings with a degree of white equal to 62% except that the sequestering treatment is not carried out before cooking but that the latter is carried out in the presence, in addition to sulfite and BOROL ®, 0.5% DTPA.

Le degré de blanc de la pâte blanchie obtenue est égal à 86 % tandis qu'il n'est que de 84 % en opérant comme ci-­dessus mais sans mettre en oeuvre le BOROL®.The degree of white of the bleached pulp obtained is equal to 86% while it is only 84% by operating as above but without using BOROL®.

Exemple 14Example 14

Après préchauffage à la vapeur d'eau, des copeaux de bois de résineux sont imprégnés, par immersion et égouttage, simultanément de 3 % de sulfite de sodium, 3 % de bisulfite de sodium, 1,5 % de BOROL®, 0,5 % de DTPA et sont cuits en autoclave sous pression de vapeur d'eau saturée durant 4 minutes à 190°C avant de subir un défibrage mécanique par éjection brutale hors de l'autoclave à travers une filière et un raffinage en raffineur à disques.After preheating with steam, coniferous wood shavings are impregnated, by immersion and draining, simultaneously with 3% sodium sulfite, 3% sodium bisulfite, 1.5% BOROL®, 0.5 % of DTPA and are autoclaved under saturated steam pressure for 4 minutes at 190 ° C before undergoing mechanical defibration by sudden ejection from the autoclave through a die and refining in a disc refiner.

La pâte ainsi obtenue est blanchie, après lavage pour éliminer le sulfite et, à 90°C durant 2 heures à une consistance de 20 % au moyen de 5 % de H₂O₂, 2 % d'hydroxyde de sodium, 4 % de silicate et 0,5 % de DTPA.The dough thus obtained is bleached, after washing to remove the sulphite and, at 90 ° C for 2 hours at a consistency of 20% using 5% H₂O₂, 2% sodium hydroxide, 4% silicate and 0 , 5% DTPA.

Le degré de blanc de la pâte ainsi finalement obtenue est égal à 71 % tandis que les copeaux de départ raffinés n'avaient qu'un degré de blanc égal à 56 %.The degree of whiteness of the paste thus finally obtained is equal to 71% while the refined starting chips had only a degree of whiteness equal to 56%.

En opérant comme ci-dessus mais sans mettre en oeuvre le BOROL®, le degré de blanc atteint n'est égal qu'à 66 % et la longueur de rupture, en mètres, est plus faible, 3 755 au lieu de 3 900, pour un indice de rupture pratiquement inchangé.By operating as above but without using BOROL®, the degree of white achieved is only equal to 66% and the breaking length, in meters, is lower, 3,755 instead of 3,900, for a practically unchanged rupture index.

L'invention permet non seulement de fabriquer des pâtes CTMP blanchies de haut niveau de blanc à partir aussi bien de bois de résineux que de bois de feuillus avec une consommation réduite de H₂O₂ mais encore de conserver et même d'améliorer les propriétés mécaniques des pâtes blanchies usuelles.The invention makes it possible not only to manufacture CTMP bleached pulps of high white level from both softwood and hardwood with reduced consumption of H₂O₂ but also to conserve and even improve the mechanical properties of the pulps. usual bleached.

Claims (14)

1. Procédé de fabrication de pâtes CTMP dans lequel interviennent le sulfite de sodum ou le bisulfite de sodium ou un mélange de dioxyde de soufre et d'hydroxyde de sodium, et un agent réducteur plus électronégatif que l'ion sulfite, qui consiste à adjoindre à un défibrage mécanique de la matière lignocellulosique une cuisson non destructrice de ladite matière à température égale ou supérieure à 100°C sous pression de vapeur d'eau saturée, à l'aide desdits sulfite, bisulfite ou mélange et dudit agent réducteur, caractérisé en ce que lesdits sulfite, bisulfite ou mél;ange, et ledit agent réducteur interviennent sur la matière lignocellulosique conjointement et en milieu de pH initial compris entre 7 et 12,5, pour conduire à une pâte fabriquée apte au blanchiment à l'aide de peroxyde d'hydrogène en milieu aqueux alcalin.1. Process for manufacturing CTMP pastes in which sodium sulfite or sodium bisulfite or a mixture of sulfur dioxide and sodium hydroxide are involved, and a reducing agent more electronegative than sulfite ion, which consists in adding mechanical defibration of the lignocellulosic material non-destructive cooking of said material at a temperature equal to or greater than 100 ° C. under saturated steam pressure, using said sulfite, bisulfite or mixture and said reducing agent, characterized in that said sulfite, bisulfite or mel; angel, and said reducing agent intervene on the lignocellulosic material jointly and in medium of initial pH between 7 and 12.5, to lead to a paste made suitable for bleaching using peroxide of hydrogen in an alkaline aqueous medium. 2. Procédé selon la revendication 1, caractérisé en ce que l'agent réducteur est choisi parmi le dioxyde de thiourée, le borohydrure de sodium ou le dithionite de sodium.2. Method according to claim 1, characterized in that the reducing agent is chosen from thiourea dioxide, sodium borohydride or sodium dithionite. 3. Procédé selon la revendication 2, caractérisé en ce que le dioxyde de thiourée ou l'hydrosulfite de sodium sont engagés à raison de 0,1 % à 5 %.3. Method according to claim 2, characterized in that the thiourea dioxide or sodium hydrosulfite are used in an amount of 0.1% to 5%. 4. Procédé selon la revendication 2, caractérisé en ce que le borohydrure de sodium est engagé à raison de 0,01 % à 0,5 %.4. Method according to claim 2, characterized in that the sodium borohydride is engaged in an amount of 0.01% to 0.5%. 5. Procédé selon l'une quelconque des revendications 1 à 4, caractérisé en ce que la température de cuisson n'excède pas 200°C.5. Method according to any one of claims 1 to 4, characterized in that the cooking temperature does not exceed 200 ° C. 6. Procédé selon la revendication 5, caractérisé en ce que la température de cuisson est comprise entre 120°C et 160°C.6. Method according to claim 5, characterized in that the cooking temperature is between 120 ° C and 160 ° C. 7. Procédé selon l'une quelconque des revendications 1 à 6, caractérisé en ce que la quantité de sulfite de sodium, ou de bisulfite de sodium ou de mélange dioxyde de soufre-hydroxyde de sodium est telle qu'elle soit comprise entre 0,1 % et 10 % exprimée en dioxyde de soufre.7. Method according to any one of claims 1 to 6, characterized in that the quantity of sodium sulfite, or of sodium bisulfite or of mixture of sulfur dioxide and sodium hydroxide is such that it is between 0, 1% and 10% expressed as sulfur dioxide. 8. Procédé selon l'une quelconque des revendications 1 à 7, caractérisé en ce que la matière lignocellulosique est traitée à l'aide d'un agent complexant ou séquestrant avant cuisson.8. Method according to any one of claims 1 to 7, characterized in that the lignocellulosic material is treated with a complexing or sequestering agent before cooking. 9. Procédé selon l'une quelconque des revendications 1 à 7, caratcérisé en ce que la matière lignocellulosique est mise en présence d'un agent complexant ou séquestrant au moment de la cuisson.9. Method according to any one of claims 1 to 7, characterized in that the lignocellulosic material is placed in the presence of a complexing or sequestering agent at the time of cooking. 10. Procédé selon l'une des revendications 8 ou 9, caractérisé en ce que l'agent complexant ou séquestrant est le DTPA.10. Method according to one of claims 8 or 9, characterized in that the complexing or sequestering agent is DTPA. 11. Procédé selon l'une quelconque des revendications 1 à 10, caractérisé en ce que la cuisson est réalisée avant, pendant ou après le défibrage mécanique.11. Method according to any one of claims 1 to 10, characterized in that the cooking is carried out before, during or after the mechanical defibration. 12. Blanchiment de la pâte fabriquée selon l'une des revendications 1 à 11 qui comprend le lavage de ladite pâte pour en éliminer les ions sulfite et l'agent réducteur, puis l'action sur cette pâte lavée du peroxyde d'hydrogène en milieu aqueux alcalin.12. Bleaching of the pulp produced according to one of claims 1 to 11 which comprises washing said pulp to remove the sulfite ions and the reducing agent, then the action on this washed pulp of hydrogen peroxide in the medium aqueous alkaline. 13. Procédé selon la revendication 12, caractérisé en ce que le peroxyde d'hydrogène est engagé en milieu de pH compris entre 9 et 11.13. The method of claim 12, characterized in that the hydrogen peroxide is used in a medium of pH between 9 and 11. 14. Procédé selon l'une des revendications 12 et 13, caractérisé en ce que le peroxyde d'hydrogène est engagé à raison de 2 % à 6 %.14. Method according to one of claims 12 and 13, characterized in that the hydrogen peroxide is used in an amount of 2% to 6%.
EP88420160A 1987-05-25 1988-05-17 Process for producing chemithermomechanical pulps Expired - Lifetime EP0293309B1 (en)

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EP0446110A1 (en) * 1990-03-07 1991-09-11 Elf Atochem S.A. Process for producing bleached high-yield pulps
WO1992020855A1 (en) * 1991-05-24 1992-11-26 Sunds Defibrator Industries Aktiebolag A method for the manufacture of chemithermomechanical pulp
US7198695B2 (en) 2001-02-28 2007-04-03 Rhodia Acetow Gmbh Method for separating hemicelluloses from a biomass containing hemicelluloses and biomass and hemicelluloses obtained by said method
CN111549552A (en) * 2020-05-25 2020-08-18 广西大学 High-yield chemi-mechanical pulp making method for recycling alkali in waste water

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FR2634233B1 (en) * 1988-07-12 1995-04-14 Atochem PROCESS FOR PRODUCING BLANCHED CHEMICOTHERMOMECHANICAL PASTES
RU2649301C2 (en) * 2012-12-12 2018-03-30 Басф Се Use of sodium dithionite in a cellulose pulping process
EP2924166A1 (en) 2014-03-25 2015-09-30 Basf Se Method for the manufacture of bleached wood fibre

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FR1150451A (en) * 1956-05-04 1958-01-14 Saint Gobain Improvement in the manufacturing processes of semi-chemical cellulose pulps
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EP0172135A1 (en) * 1984-07-17 1986-02-19 Rudy Vit Method, process and apparatus for converting wood, wood residue, vegetable fibre and biomass into pulp

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FR1389308A (en) * 1964-02-17 1965-02-12 Fmc Corp High gloss cellulose pastes
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FR2389712A1 (en) * 1977-05-02 1978-12-01 Mo Och Domsjoe Ab
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Cited By (5)

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Publication number Priority date Publication date Assignee Title
EP0446110A1 (en) * 1990-03-07 1991-09-11 Elf Atochem S.A. Process for producing bleached high-yield pulps
FR2659363A1 (en) * 1990-03-07 1991-09-13 Atochem PROCESS FOR PREPARING BLANKED HIGH PERFORMANCE PASTES.
WO1992020855A1 (en) * 1991-05-24 1992-11-26 Sunds Defibrator Industries Aktiebolag A method for the manufacture of chemithermomechanical pulp
US7198695B2 (en) 2001-02-28 2007-04-03 Rhodia Acetow Gmbh Method for separating hemicelluloses from a biomass containing hemicelluloses and biomass and hemicelluloses obtained by said method
CN111549552A (en) * 2020-05-25 2020-08-18 广西大学 High-yield chemi-mechanical pulp making method for recycling alkali in waste water

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NZ224749A (en) 1989-08-29
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