EP0578304A1 - Process for bleaching a chemical paper pulp - Google Patents
Process for bleaching a chemical paper pulp Download PDFInfo
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- EP0578304A1 EP0578304A1 EP93201886A EP93201886A EP0578304A1 EP 0578304 A1 EP0578304 A1 EP 0578304A1 EP 93201886 A EP93201886 A EP 93201886A EP 93201886 A EP93201886 A EP 93201886A EP 0578304 A1 EP0578304 A1 EP 0578304A1
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- pulp
- hydrogen peroxide
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- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
- D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
- D21C9/10—Bleaching ; Apparatus therefor
- D21C9/1057—Multistage, with compounds cited in more than one sub-group D21C9/10, D21C9/12, D21C9/16
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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 invention relates to a process for bleaching cellulosic paper pulps belonging to the chemical pulp category.
- the first step of a conventional chemical pulp bleaching sequence aims to complete the delignification of the unbleached pulp as it occurs after the cooking operation.
- This first significant step is traditionally carried out by treating the unbleached pulp with chlorine in an acid medium or by a chlorine-chlorine dioxide association, in mixture or in sequence, so as to react with the residual lignin of the pulp and give rise to chlorolignins which can be extracted from the pulp by dissolving these chlorolignins in an alkaline medium in a subsequent treatment step.
- the invention remedies these drawbacks of known methods by providing a new method for delignification and / or bleaching of chemical paper pulps which makes it possible to achieve high levels of whiteness without degrading the cellulose too much.
- the invention relates to a process for bleaching a chemical paper pulp making it possible to obtain high whiteness levels of at least 89 ° ISO according to which the pulp is subjected to a sequence of treatment steps comprising a final step with hydrogen peroxide in an alkaline medium, the final step with hydrogen peroxide being carried out in the presence of at least one stabilizing agent and at a paste consistency of at least 25%, the paste subjected to the final step with hydrogen peroxide having been purified in the preceding steps so that its manganese content does not exceed 3 ppm by weight relative to the dry matter and having been delignified to a kappa number (measured according to SCAN C1-59) not exceeding 5.
- chemical paper pulp the pulp which has already undergone a delignifying treatment in the presence of chemical reagents such as sodium sulfide in alkaline medium (kraft or sulfate cooking), sulfur dioxide or a metallic salt of sulfurous acid in an acid medium (cooking with sulfite or bisulfite).
- chemical reagents such as sodium sulfide in alkaline medium (kraft or sulfate cooking), sulfur dioxide or a metallic salt of sulfurous acid in an acid medium (cooking with sulfite or bisulfite).
- pulps such as those where cooking was carried out using a sulfurous acid salt in a neutral medium (cooking with neutral sulfite also called NSSC cooking), as well as pasta obtained by processes using solvents, such as ORGANOSOLV, ALCELL®, ORGANOCELL® and ASAM pastes described in ULLMANN's Encyclopedia of Industrial Chemistry, 5th Edition, Vol. A18, 1991, pages 568 and 569.
- solvents such as ORGANOSOLV, ALCELL®, ORGANOCELL® and ASAM pastes described in ULLMANN's Encyclopedia of Industrial Chemistry, 5th Edition, Vol. A18, 1991, pages 568 and 569.
- the bleaching process comprises a final bleaching step with hydrogen peroxide in an alkaline medium which is carried out at the end of the bleaching sequence.
- the final bleaching step with hydrogen peroxide ends this sequence.
- This final step with hydrogen peroxide is carried out, in accordance with the invention, in the presence of at least one stabilizing agent.
- the known stabilizing agents for peroxygenated products are very suitable.
- examples of such stabilizing agents are the alkaline earth metal salts, in particular the soluble magnesium salts, the silicates, the phosphates and inorganic polyphosphates such as the alkali metal silicates, pyrophosphates and metaphosphates, the polycarboxylates and the aminopolycarboxylates.
- organic such as tartaric, citric, gluconic, ethylenediaminetetraacetic diethylenetriaminepentaacetic, cyclohexanediaminetetraacetic and their salts, poly- ⁇ -hydroxyacrylic acids and their salts and phosphonic acids such as ethylenediaminetetra (methylenephosphonic), diethylenethanephosphonic) ) and their salts.
- phosphonic acids such as ethylenediaminetetra (methylenephosphonic), diethylenethanephosphonic) ) and their salts. It is also possible to combine several of these stabilizing agents in a mixture.
- silicates, polycarboxylates or phosphonic acids are very suitable, in particular when they are combined with at least one magnesium salt. Sodium silicate has given good results.
- the amount of stabilizing agent to be used in the final step with hydrogen peroxide varies according to the type of wood used for the manufacture of the paste as well as the operating conditions of the cooking which prevailed during the pulping of the type of wood used and the effectiveness of the bleaching stages which preceded the final stage with hydrogen peroxide. In some cases, it is possible to use only a reduced amount of stabilizing agent. Preferably, however, the amount of stabilizing agent will be at least 0.1% by weight expressed relative to the dry paste. Most often, it will not exceed 5% and preferably not 4% of the weight of the dry dough.
- the final step with hydrogen peroxide is carried out at a paste consistency of at least 25% dry matter.
- paste consistency is meant the percentage by weight of the dry matter relative to the total weight of the dry matter and the aqueous solution of reagents.
- the final step with hydrogen peroxide will be carried out at a consistency of at least 30% in dry matter.
- the dough subjected to the final step with hydrogen peroxide is selected from the doughs which have been delignified, in the steps which precede the final step, up to a high level of delignification corresponding to an index kappa not exceeding 5.
- the dough subjected to the final step will have a kappa index not exceeding 3.
- the dough subjected to the final step has a kappa index of at least 0.1. Any treatment sequence which makes it possible to delignify the dough to such a value of the kappa index is according to the invention.
- sequences include sequences using steps using at least one chlorinated reagent such as chlorine in an acid medium, chlorine dioxide, the combination of chlorine and chlorine dioxide in mixture or in sequence, hypochlorite of an alkali or alkaline-earth metal or alternatively, and preferably, sequences free from chlorinated reagents comprising at least one step with oxygen, with ozone, or with an inorganic peroxyacid such as, for example example, peroxymonosulfuric acid or Caro acid, or also with an organic peroxyacid such as peroxyformic, peroxyacetic, peroxypropionic or peroxybutyric acid.
- chlorinated reagent such as chlorine in an acid medium, chlorine dioxide, the combination of chlorine and chlorine dioxide in mixture or in sequence, hypochlorite of an alkali or alkaline-earth metal or alternatively, and preferably, sequences free from chlorinated reagents comprising at least one step with oxygen, with ozone, or with an inorganic peroxyacid such as, for
- the pulp subjected to the final step with hydrogen peroxide has been purified in the preceding steps so that its manganese content does not exceed 3 ppm by weight relative to the dry matter.
- Any treatment sequence capable of purifying the manganese paste is in accordance with the invention. Examples of such sequences include sequences using steps using at least one acid reagent such as sulfuric acid, sulfurous acid or chlorine, or a sequestering agent in acidic medium at controlled pH. These different reagents can also be used in an acidic medium at a controlled pH during the washing of the pulp which is carried out between the delignification and / or bleaching steps.
- the manganese content of the pulp subjected to the final step with hydrogen peroxide will not exceed 2 ppm by weight relative to the dry matter.
- any pulp treatment sequence preceding the final step with hydrogen peroxide can be put used to prepare the dough for the bleaching operation by the final step with hydrogen peroxide.
- sequences using chlorine reagents such as chlorine in an acid medium, chlorine dioxide in an acid medium or the association of chlorine and chlorine dioxide in an acid medium in a mixture or in sequence, or alternatively the hypochlorites of alkali or alkaline earth metals in an alkaline medium.
- sequences which do not use chlorinated reagents or, at least, limiting the quantity of chlorinated reagents such as the sequences comprising at least one step using gaseous oxygen.
- ozone an acid reagent, an alkaline reagent or a peroxygen compound in an acid or alkaline medium.
- peroxygen compound is meant to denote any inorganic or organic chemical compound comprising the group -OO- in its molecule. Examples of such compounds are hydrogen peroxide, inorganic peroxyacids such as peroxymonosulfuric acid or Caro acid and inorganic persalts such as perborates, percarbonates and perphosphates of alkali or alkaline earth metals.
- peroxygen compounds are organic carboxylic peroxyacids such as formic, acetic and propionic peracids as well as organic hydroperoxides such as tert-butyl hydroperoxide.
- Organic carboxylic peroxyacids are preferred.
- peracetic acid has given excellent results. It is also possible to design treatment sequences which combine steps using chlorinated reagents with steps free of such reagents.
- this first embodiment of the method according to the invention is carried out by carrying out step Ep of the bleaching sequence in the presence of an agent sequestering metal ions.
- agent sequestering metal ions All metal ion sequestering agents are suitable. Sequestering agents having a particular affinity for iron and manganese ions are particularly suitable.
- silicates examples include silicates, inorganic phosphates and polyphosphates such as silicates, pyrophosphates and metaphosphates of alkali metals, polycarboxylates and organic aminopolycarboxylates such as tartaric, citric, gluconic, ethylenediaminetetraacetic, diethylenetriaminepentaacetic cyclohexanediaminetetraacetic and their salts, poly- ⁇ -hydroxyacrylic acids and their salts and phosphonic acids such as ethylenediaminetetra (methylenephosphonic), diethylenetriaminepenta (methylenephosphonic), cyclohexanediaminetetra (methylenephosphonic) acids and their salts.
- silicates inorganic phosphates and polyphosphates
- polyphosphates such as silicates, pyrophosphates and metaphosphates of alkali metals
- polycarboxylates and organic aminopolycarboxylates such as tartaric, citric
- Phosphonic acids and their salts have given the best results for sequestering metal ions in the Ep step.
- Step Q of treatment with an acid or with a sequestering acid comprises treatment with anhydrides or inorganic acids such as sulfur dioxide and sulfuric, sulfurous, hydrochloric, and nitric acids or their acid salts, as well as the acids organic such as carboxylic or phosphonic acids or their acid salts.
- Sulfur dioxide or alkali or alkaline earth metal bisulfites are well suited.
- bisulfite is intended to denote the acid salts of sulfurous acid corresponding to the formula Me (HSO3) n, in which Me symbolizes a metal atom of valence n, n being an integer equal to 1 or 2.
- It also comprises the treatment with at least one sequestering agent in an acid medium such as an inorganic phosphate or polyphosphate in an acid medium, such as, for example, a pyrophosphate or an alkali metal metaphosphate, a polycarboxylate or an organic aminopolycarboxylate such as, for example, tartaric, citric, gluconic, ethylenediaminetetraacetic, diethylenetriaminepentaacetic, cyclohexanediaminetetraacetic and their salts, poly- ⁇ -hydroxyacrylic acid and its salts and a phosphonic acid such as ethylenediaminetetraonic acid ), diethylenetriaminepenta (methylenephosphonic), cyclohexanediaminetetra (methylenephosphonic) and their salts.
- an acid medium such as an inorganic phosphate or polyphosphate in an acid medium
- an acid medium such as, for example, a pyrophosphate or an alkali metal metaphosphate
- the Paa step is carried out in the presence of a metal ion sequestering agent.
- sequestering agents of metal ions such as iron and manganese are well suited.
- sequestering agents are the alkaline earth metal salts, in particular the soluble magnesium salts, the silicates, the phosphates and inorganic polyphosphates such as the alkali metal silicates, pyrophosphates and metaphosphates, the polycarboxylates and the aminopolycarboxylates organic such as tartaric, citric, gluconic, diethylenetriaminepentaacetic, cyclohexanediaminetetraacetic and their salts, poly- ⁇ -hydroxyacrylic acids and their salts and phosphonic acids such as ethylenediaminetetra (methylenephosphonic), diethylenetriaminepenta (methylenephosphonic) and their salts. It is also possible to combine several of these sequestering agents in a mixture.
- Step C A of treatment with peroxymonosulfuric acid (Caro acid) or one of its salts consists in treating the paste with H2SO5 or one of its alkali metal salts, alkaline earth or ammonium, or with a mixture of several of these salts or of H2SO5 with one or more of these salts.
- the peroxymonosulfuric acid or the salts used may, as a variant, have been prepared immediately before their use by reacting a concentrated aqueous solution of sulfuric acid or its salts with a concentrated aqueous solution of a peroxygen compound, by example, hydrogen peroxide.
- concentration solutions is intended to denote, respectively, solutions of H2SO5 with a concentration of at least about 10 moles per liter and of H2O2 with a concentration of at least about 20% by weight.
- step C A is also carried out in the presence of a metal ion sequestering agent.
- sequestering agents will advantageously be used as those which are suitable for the Paa stage and which have been described above. It is also possible to combine several of these sequestering agents in a mixture.
- step C A The initial pH of step C A will be adjusted so that, at the end of the reaction, the pH remains greater than or equal to 2 and, preferably, 2.5. Likewise, the pH at the end of the reaction should not exceed 7 and preferably not 6.
- step Ep it is generally preferred to insert, between step Ep and step P, washing the dough using an acidic aqueous solution.
- the term “acid” is intended to denote the anhydrides or inorganic acids such as sulfur dioxide and sulfuric, sulfurous, hydrochloric and nitric acids or their acid salts, as well as organic acids such as carboxylic or phosphonic acids or their acid salts.
- Sulfur dioxide or alkali or alkaline earth metal bisulfites are well suited.
- bisulfite is intended to denote the acid salts of sulfurous acid corresponding to the formula Me (HSO3) n, in which Me symbolizes a metal atom of valence n, n being an integer having the value 1 or 2.
- the amount of acid to be used in the washing step according to the invention depends on the type of wood and on the efficiency of the preceding steps. In general, we will implement the amount of acid required to set the pH of the dough to at least about 4 and preferably about at least 4.5. Likewise, the amount of acid will often be adjusted so that the pH does not exceed 7 and preferably not 6.5.
- the pulp is bleached using a treatment sequence free from chlorine reagent in at least 5 steps comprising the sequence OQPDP, OQP Paa P, OQPC A P and OQPZ P
- the symbols used to designate the processing steps have the same meaning as in the first embodiment of the invention with regard to the symbols O, Q, Paa and P.
- Z it is meant give it the following meaning: Z: ozone treatment.
- steps Q and Paa are carried out under conditions comparable to those described above for the first embodiment of the invention.
- the ozone treatment stage consists in bringing the paste into contact with a gaseous phase containing ozone.
- the gas phase contains a mixture of ozone and oxygen from an electric ozone generator which is supplied with dry gaseous oxygen.
- the treatment of the dough with ozone is preferably carried out in an acid medium.
- PH values of at least 0.5 and preferably 1.5 and not exceeding 5 and preferably 4 are suitable.
- the amount of hydrogen peroxide to be used in the final step is generally at least 0.5% by weight relative to the weight of dry pulp and, preferably, at least 0.8% of this weight. Likewise, the amount of hydrogen peroxide in this treatment step should not exceed 6% by weight relative to the weight of dry pulp and, preferably, not 5% of this weight.
- the temperature of the final step with hydrogen peroxide must be adjusted so as to remain at least equal to 50 ° C. and preferably to 70 ° C. It must also not exceed 140 ° C and, preferably do not exceed 130 ° C.
- the duration of the treatment with hydrogen peroxide in the final step must be sufficient for the bleaching reaction to be complete. In practice, it will be set to a value of at least 15 minutes and, preferably, 30 minutes. It should also most often not exceed 100 hours and, preferably, 50 hours. A combination of the temperature and time conditions of about 80 ° C and about 240 minutes has given good results.
- the pH of the final step with hydrogen peroxide is adjusted by means of the addition to the reaction mixture of an alkaline compound, for example sodium hydroxide, to an initial value of at least 10 and, preferably at least 11.
- an alkaline compound for example sodium hydroxide
- the initial pH of the final stage with hydrogen peroxide is generally adjusted to a value which does not exceed 13 and, preferably, not 12.
- the bleached pulp After the final step with hydrogen peroxide, it is possible and generally advantageous to wash the bleached pulp with an acidic aqueous solution in order to bring its pH to a value not exceeding 6.5 and, preferably, not 6.
- the inorganic acids such as sulfuric acid, sulfurous acid, hydrochloric acid or nitric acid are well suited.
- the sulfurous acid obtained by the absorption of gaseous sulfur dioxide in water is particularly suitable.
- the method according to the invention has the advantage of achieving a significant gain in whiteness.
- this gain can reach 20 to 25 ° ISO in the case of pulps whose whiteness before the final step with hydrogen peroxide is relatively low, for example kraft softwood or hardwood pulps of whiteness close to 65 to 70 ° ISO.
- the method according to the invention finds an application for the delignification and bleaching of chemical pastes of the kraft or sulfite type, or high-quality semi-chemical, especially those intended for food packaging. It is equally suitable for pasta from softwood or hardwood.
- a sample of softwood pulp having undergone kraft cooking (initial whiteness 26.3 ° ISO, kappa index 31.2 and degree of polymerization 1630) was bleached according to a sequence of 4 treatment steps starting with an oxygen step gaseous under pressure, followed by a step comprising chlorine and chlorine dioxide in an acid medium and applied as a mixture, a step of alkaline extraction in the presence of hydrogen peroxide and a final step with peroxide hydrogen in an alkaline medium (sequence symbolized by the acronyms OC / D Ep P).
- the operating conditions of the first three stages were as follows: 1st stage : oxygen stage (stage 0): pressure, bar: 6 NaOH content, g / 100 g of dry paste: 2.5 MgSO4.7H2O content, g / 100 g of dry paste: 0.5 temperature, degrees C: 125 duration, min: 40 consistency,% by weight of dry matter: 10 2nd stage : chlorine stage - chlorine dioxide (stage C / D): active chlorine content, g / 100 g of dry paste: 4.0 Cl2 / ClO2 ratio (expressed as active Cl): 60/40 temperature, degrees C: 50 duration, min: 45 consistency,% by weight of dry matter: 10 3rd stage : alkaline extraction stage (Ep stage): NaOH content, g / 100 g of dry paste: 3.2 H2O2 content, g / 100 g of dry paste: 0.5 DTMPNa7 content, g / 100 g of dry paste: 0.0 (Example 1R) DTMPNa7 content,
- the Mn content of the pulp after step Ep was 2.9 ppm by weight relative to the dry matter in Example 1R and 1.1 ppm in Example 2R.
- the whiteness gain achieved in the final step with hydrogen peroxide was 15.4 ° ISO for Example 1R and 16.4 ° ISO for Example 2R. At the end of the final step with peroxide of hydrogen, all of it had been consumed in each of Examples 1R and 2R.
- Example 2R was repeated, except that 2.0 g of Na silicate at 38 ° Bé and 0.6 g of MgSO4.7H2O per 100 g of dry paste were also introduced into step P.
- stage Ep the Mn content of the pulp was 1.1 ppm by weight relative to the dry matter and its kappa number of 1.9.
- the gain in whiteness achieved during the final stage P was 23.5 ° ISO.
- Example 3 was repeated, except that the final step with hydrogen peroxide was carried out at medium consistency (10% dry matter) and in the presence of 3 g of H2O2, 3.0 g of NaOH, 3, 0 g of Na silicate at 38 ° Bé and 1.0 g of MgSO4.7H2O per 100 g of dry paste.
- step Ep the Mn content of the pulp was 1.1 ppm by weight relative to the dry matter and its Kappa number of 1.9.
- Example 3 was reproduced by replacing, in the second step, chlorine with an equivalent amount of chlorine dioxide (expressed as active chlorine) so as to achieve an OD Ep P sequence.
- the temperature of step D was also brought to 70 ° C. and the amount of NaOH in the final stage P between 1.5 and 2.3 g / 100 g of dry paste.
- the Mn content determined before the final stage P was 9 ppm by weight relative to the dry litter and the kappa index of 3.0.
- the final step P was carried out with 2.0 g of H2O2 / 100 g of dry paste as in Examples 7R to 9R, in the presence of 1.6 g NaOH, of 3.0 g of Na silicate 38 ° Be and 1 g of MgSO4.7H2O / 100 g of dry paste.
- the Mn content after step Ep had dropped to 2.7 ppm by weight relative to the dry matter and the kappa number was 2.1.
- the whiteness gain achieved during the final stage P was 13.7 ° ISO.
- the kappa number of the dough after the Paa step was 4.3 and its Mn content was 0.2 ppm by weight relative to the dry matter.
- the whiteness gain achieved during the final stage P was 22.4 ° ISO.
- the mechanical properties of the bleached pulp were also determined after refining in a laboratory refiner.
- Example 10R The same softwood pulp sample as in Example 10R was bleached using a 5-step OQPDP elemental chlorine-free sequence under the following operating conditions: 1st stage : oxygen stage (O): pressure, bar: 6.0 NaOH content, g / 100 g of dry paste: 4.0 MgSO4.7H2O content, g / 100 g of dry paste: 0.5 temperature, degrees C: 120 duration, min: 60 consistency,% by weight of dry matter: 12 2nd stage : stage with a sequestering acid (Q): DTPA content, g / 100 g of dry paste: 0.5 H2SO4 for a pH of: 6 temperature, degrees C: 50 duration, min: 30 consistency,% by weight of dry matter: 4 3rd stage : stage at H2O2 (P): H2O2 content, g / 100 g of dry paste: 2.0 NaOH content, g / 100 g of dry paste: 2.0 MgSO4.7H2O content, g / 100 g of dry paste
- the Mn content of the pulp after step D was 0.7 ppm by weight relative to the dry matter.
- Degree of refinement ° SR Tear index mN.m2 / g Tensile strength index Nm / g 16 20.0 43.7 26 11.3 87.9 31 9.6 91.1 34 11.1 94.8 38 9.8 96.8
- the Mn content of the pulp after the Paa stage was 0.4 ppm by weight relative to the dry matter.
- Degree of refinement ° SR Tear index mN.m2 / g Tensile strength index Nm / g 16 20.7 38.2 24 11.4 80.9 33 10.4 92.3 38 10.1 100.4
- the Mn content of the pulp after step C A was 0.2 ppm by weight relative to the dry matter.
- Degree of refinement ° SR Tear index mN.m2 / g Tensile strength index Nm / g 16 20.4 40.8 24 11.5 81.6 33 11.2 90.0 39 10.5 98.6 47 9.9 101.2
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Abstract
Description
L'invention concerne un procédé pour le blanchiment de pâtes à papier cellulosiques appartenant à la catégorie des pâtes chimiques.The invention relates to a process for bleaching cellulosic paper pulps belonging to the chemical pulp category.
Il est connu de traiter les pâtes à papier chimiques écrues obtenues par cuisson de matières lignocellulosiques au moyen d'une séquence d'étapes de traitement délignifiant et/ou blanchissant impliquant la mise en oeuvre de produits chimiques oxydants. La première étape d'une séquence classique de blanchiment de pâte chimique a pour objectif de parfaire la délignification de la pâte écrue telle qu'elle se présente après l'opération de cuisson. Cette première étape délignifiante est traditionnellement réalisée en traitant la pâte écrue par du chlore en milieu acide ou par une association chlore - dioxyde de chlore, en mélange ou en séquence, de façon à réagir avec la lignine résiduelle de la pâte et donner naissance à des chlorolignines qui pourront être extraites de la pâte par solubilisation de ces chlorolignines en milieu alcalin dans une étape de traitement ultérieure.It is known to treat unbleached chemical paper pulps obtained by cooking lignocellulosic materials by means of a sequence of delignifying and / or bleaching treatment steps involving the use of oxidizing chemicals. The first step of a conventional chemical pulp bleaching sequence aims to complete the delignification of the unbleached pulp as it occurs after the cooking operation. This first significant step is traditionally carried out by treating the unbleached pulp with chlorine in an acid medium or by a chlorine-chlorine dioxide association, in mixture or in sequence, so as to react with the residual lignin of the pulp and give rise to chlorolignins which can be extracted from the pulp by dissolving these chlorolignins in an alkaline medium in a subsequent treatment step.
Pour des raisons diverses, il s'avère utile, dans certaines situations, de pouvoir remplacer cette première étape délignifiante par un traitement qui ne fasse plus appel à un réactif chloré ou qui mette en oeuvre une quantité réduite de réactifs chlorés.For various reasons, it proves useful, in certain situations, to be able to replace this first significant step with a treatment which no longer uses a chlorinated reagent or which uses a reduced amount of chlorinated reagents.
Depuis environ une dizaine d'années, on a proposé le remplacement, tout au moins partiel, de la première étape de traitement au moyen de chlore ou de l'association chlore - dioxyde de chlore par une étape à l'oxygène gazeux en milieu alcalin (KIRK-OTHMER Encyclopedia of Chemical Technology Third Edition Vol. 19, New-York 1982, page 415, 3e paragraphe et page 416, 1er et 2e paragraphes). Le taux de délignification que l'on obtient par ce traitement à l'oxygène n'est cependant pas suffisant si l'on vise à produire des pâtes chimiques de haute blancheur.For about ten years, it has been proposed to replace, at least partially, the first stage of treatment with chlorine or the chlorine-chlorine dioxide combination with a stage with gaseous oxygen in an alkaline medium. (KIRK-OTHMER Encyclopedia of Chemical Technology Third Edition Vol. 19, New York 1982, page 415, 3rd paragraph and page 416, 1st and 2nd paragraphs). The delignification rate obtained by this Oxygen treatment is however not enough if one aims to produce high whiteness chemical pulps.
Il a été proposé de blanchir des pâtes au sulfite ou au sulfate au moyen de peroxyde d'hydrogène à haute consistance en présence de silicate de sodium (J. KAPPEL, HC-Peroxidbleiche für Zellstoff, Wochenblatt für Papierfabrikation, 120, Mai 1992, n° 9, pages 328-334). Il est cependant difficile avec ce procédé d'obtenir une blancheur finale supérieure à 85 °ISO, même au prix de quantités importantes de peroxyde d'hydrogène supérieures à 3 g/100 g de pâte sèche.It has been proposed to whiten pulps with sulphite or sulphate using high consistency hydrogen peroxide in the presence of sodium silicate (J. KAPPEL, HC-Peroxidbleiche für Zellstoff, Wochenblatt für Papierfabrikation, 120, May 1992, n ° 9, pages 328-334). It is however difficult with this process to obtain a final whiteness greater than 85 ° ISO, even at the cost of large quantities of hydrogen peroxide greater than 3 g / 100 g of dry paste.
L'invention remédie à ces inconvénients des procédés connus, en fournissant un procédé nouveau de délignification et/ou de blanchiment de pâtes à papier chimiques qui permette d'atteindre des niveaux élevés de blancheur sans dégrader trop fortement la cellulose.The invention remedies these drawbacks of known methods by providing a new method for delignification and / or bleaching of chemical paper pulps which makes it possible to achieve high levels of whiteness without degrading the cellulose too much.
A cet effet, l'invention concerne un procédé pour le blanchiment d'une pâte à papier chimique permettant l'obtention de niveaux de blancheur élevés d'au moins 89 °ISO selon lequel on soumet la pâte à une séquence d'étapes de traitement comportant une étape finale au peroxyde d'hydrogène en milieu alcalin, l'étape finale au peroxyde d'hydrogène étant effectuée en présence d'au moins un agent stabilisant et à une consistance en pâte d'au moins 25 %, la pâte soumise à l'étape finale au peroxyde d'hydrogène ayant été épurée dans les étapes précédentes de manière telle que sa teneur en manganèse ne dépasse pas 3 ppm en poids par rapport à la matière sèche et ayant été délignifiée jusqu'à un indice kappa (mesuré selon la norme SCAN C1-59) ne dépassant pas 5.To this end, the invention relates to a process for bleaching a chemical paper pulp making it possible to obtain high whiteness levels of at least 89 ° ISO according to which the pulp is subjected to a sequence of treatment steps comprising a final step with hydrogen peroxide in an alkaline medium, the final step with hydrogen peroxide being carried out in the presence of at least one stabilizing agent and at a paste consistency of at least 25%, the paste subjected to the final step with hydrogen peroxide having been purified in the preceding steps so that its manganese content does not exceed 3 ppm by weight relative to the dry matter and having been delignified to a kappa number (measured according to SCAN C1-59) not exceeding 5.
Selon l'invention, par pâte à papier chimique, on entend désigner les pâtes ayant déjà subi un traitement délignifiant en présence de réactifs chimiques tels que le sulfure de sodium en milieu alcalin (cuisson kraft ou au sulfate), l'anhydride sulfureux ou un sel métallique de l'acide sulfureux en milieu acide (cuisson au sulfite ou au bisulfite). Selon l'invention, on entend également désigner par pâte à papier chimique, les pâtes appelées dans la littérature "pâtes semi-chimiques" telles que celles où la cuisson a été réalisée à l'aide d'un sel de l'acide sulfureux en milieu neutre (cuisson au sulfite neutre encore appelée cuisson NSSC), de même que les pâtes obtenues par des procédés utilisant des solvants, telles que les pâtes ORGANOSOLV, ALCELL®, ORGANOCELL® et ASAM décrites dans ULLMANN's Encyclopedia of Industrial Chemistry, 5th Edition, Vol. A18, 1991, pages 568 et 569.According to the invention, by chemical paper pulp is meant the pulp which has already undergone a delignifying treatment in the presence of chemical reagents such as sodium sulfide in alkaline medium (kraft or sulfate cooking), sulfur dioxide or a metallic salt of sulfurous acid in an acid medium (cooking with sulfite or bisulfite). According to the invention, it is also intended to denote by chemical paper pulp, the pulps called in the literature "semi-chemical pulps" such than those where cooking was carried out using a sulfurous acid salt in a neutral medium (cooking with neutral sulfite also called NSSC cooking), as well as pasta obtained by processes using solvents, such as ORGANOSOLV, ALCELL®, ORGANOCELL® and ASAM pastes described in ULLMANN's Encyclopedia of Industrial Chemistry, 5th Edition, Vol. A18, 1991, pages 568 and 569.
Celle-ci s'adresse particulièrement aux pâtes ayant subi une cuisson kraft. Tous les types de bois utilisés pour la production de pâtes chimiques conviennent pour la mise en oeuvre du procédé de l'invention et, en particulier ceux utilisés pour les pâtes kraft, à savoir les bois résineux comme, par exemple, les diverses espèces de pins et de sapins et les bois feuillus comme, par exemple, le hêtre, le chêne, l'eucalyptus et le charme.This is particularly intended for pasta that has undergone kraft cooking. All types of wood used for the production of chemical pulp are suitable for carrying out the process of the invention and, in particular those used for kraft pulp, namely softwoods such as, for example, the various species of pine and fir and hardwoods like, for example, beech, oak, eucalyptus and hornbeam.
Selon l'invention, le procédé de blanchiment comporte une étape finale de blanchiment au peroxyde d'hydrogène en milieu alcalin qui est réalisée à la fin de la séquence de blanchiment. De préférence, l'étape finale de blanchiment au peroxyde d'hydrogène termine cette séquence.According to the invention, the bleaching process comprises a final bleaching step with hydrogen peroxide in an alkaline medium which is carried out at the end of the bleaching sequence. Preferably, the final bleaching step with hydrogen peroxide ends this sequence.
Cette étape finale au peroxyde d'hydrogène est effectuée, conformément à l'invention, en présence d'au moins un agent stabilisant. Les agents stabilisants connus des produits peroxygénés conviennent bien. Des exemples de tels agents stabilisants sont les sels de métaux alcalino-terreux, en particulier les sels solubles de magnésium, les silicates, les phosphates et polyphosphates inorganiques tels que les silicates, les pyrophosphates et les métaphosphates de métaux alcalins, les polycarboxylates et les aminopolycarboxylates organiques tels que les acides tartrique, citrique, gluconique, éthylènediaminetétraacétique diéthylènetriaminepentaacétique, cyclohexanediaminetétraacétique et leurs sels, les acides poly-α-hydroxyacryliques et leurs sels et les acides phosphoniques tels que les acides éthylènediaminetétra(méthylènephosphonique), diéthylènetriaminepenta(méthylènephosphonique), cyclohexanediaminetétra(méthylènephosphonique) et leurs sels. Il est également possible d'associer plusieurs de ces agents stabilisants en mélange. En règle générale, les silicates, les polycarboxylates ou les acides phosphoniques conviennent bien, en particulier lorsqu'ils sont associés à au moins un sel de magnésium. Le silicate de sodium a donné de bons résultats.This final step with hydrogen peroxide is carried out, in accordance with the invention, in the presence of at least one stabilizing agent. The known stabilizing agents for peroxygenated products are very suitable. Examples of such stabilizing agents are the alkaline earth metal salts, in particular the soluble magnesium salts, the silicates, the phosphates and inorganic polyphosphates such as the alkali metal silicates, pyrophosphates and metaphosphates, the polycarboxylates and the aminopolycarboxylates. organic such as tartaric, citric, gluconic, ethylenediaminetetraacetic diethylenetriaminepentaacetic, cyclohexanediaminetetraacetic and their salts, poly-α-hydroxyacrylic acids and their salts and phosphonic acids such as ethylenediaminetetra (methylenephosphonic), diethylenethanephosphonic) ) and their salts. It is also possible to combine several of these stabilizing agents in a mixture. In general, silicates, polycarboxylates or phosphonic acids are very suitable, in particular when they are combined with at least one magnesium salt. Sodium silicate has given good results.
La quantité d'agent stabilisant à mettre en oeuvre dans l'étape finale au peroxyde d'hydrogène varie suivant le type de bois utilisé pour la fabrication de la pâte ainsi que des conditions opératoires de la cuisson ayant prévalu lors de la mise en pâte du type de bois utilisé et de l'efficacité des étapes de blanchiment qui ont précédé l'étape finale au peroxyde d'hydrogène. Dans certains cas, il est possible de ne mettre en oeuvre qu'une quantité réduite d'agent stabilisant. De préférence cependant, la quantité d'agent stabilisant sera au moins de 0,1 % en poids exprimé par rapport à la pâte sèche. Le plus souvent, elle ne dépassera pas 5 % et, de préférence pas 4 % du poids de la pâte sèche.The amount of stabilizing agent to be used in the final step with hydrogen peroxide varies according to the type of wood used for the manufacture of the paste as well as the operating conditions of the cooking which prevailed during the pulping of the type of wood used and the effectiveness of the bleaching stages which preceded the final stage with hydrogen peroxide. In some cases, it is possible to use only a reduced amount of stabilizing agent. Preferably, however, the amount of stabilizing agent will be at least 0.1% by weight expressed relative to the dry paste. Most often, it will not exceed 5% and preferably not 4% of the weight of the dry dough.
Conformément à l'invention, l'étape finale au peroxyde d'hydrogène s'effectue à une consistance en pâte d'au moins 25 % en matières sèches. Par consistance en pâte, on entend désigner le pourcentage pondéral des matières sèches par rapport au poids total des matières sèches et de la solution aqueuse de réactifs. De préférence, l'étape finale au peroxyde d'hydrogène sera effectuée à une consistance d'au moins 30 % en matières sèches.According to the invention, the final step with hydrogen peroxide is carried out at a paste consistency of at least 25% dry matter. By paste consistency is meant the percentage by weight of the dry matter relative to the total weight of the dry matter and the aqueous solution of reagents. Preferably, the final step with hydrogen peroxide will be carried out at a consistency of at least 30% in dry matter.
Généralement, la consistance de l'étape finale au peroxyde d'hydrogène ne dépasse pas 45 %. Une consistance de 30 % a donné de très bons résultats.Generally, the consistency of the final step with hydrogen peroxide does not exceed 45%. A consistency of 30% has given very good results.
Selon l'invention, la pâte soumise à l'étape finale au peroxyde d'hydrogène est sélectionnée parmi les pâtes ayant été délignifiées, dans les étapes qui ont précédé l'étape finale, jusqu'à un haut niveau de délignification correspondant à un indice kappa ne dépassant pas 5. De préférence, la pâte soumise à l'étape finale présentera un indice kappa ne dépassant pas 3. Généralement, la pâte soumise à l'étape finale a un indice kappa d'au moins 0,1. Toute séquence de traitement permettant de délignifier la pâte jusqu'à une telle valeur de l'indice kappa est conforme à l'invention. Des exemples de telles séquences comprennent des séquences faisant appel à des étapes mettant en oeuvre au moins un réactif chloré tel que le chlore en milieu acide, le dioxyde de chlore, l'association de chlore et de dioxyde de chlore en mélange ou en séquence, l'hypochlorite d'un métal alcalin ou alcalino-terreux ou encore, et de manière préférée, des séquences exemptes de réactifs chlorés comprenant au moins une étape à l'oxygène, à l'ozone, ou avec un peroxyacide inorganique tel que, par exemple, l'acide peroxymonosulfurique ou acide de Caro, ou encore avec un peroxyacide organique tel que l'acide peroxyformique, peroxyacétique, peroxypropionique ou peroxybutyrique.According to the invention, the dough subjected to the final step with hydrogen peroxide is selected from the doughs which have been delignified, in the steps which precede the final step, up to a high level of delignification corresponding to an index kappa not exceeding 5. Preferably, the dough subjected to the final step will have a kappa index not exceeding 3. Generally, the dough subjected to the final step has a kappa index of at least 0.1. Any treatment sequence which makes it possible to delignify the dough to such a value of the kappa index is according to the invention. Examples of such sequences include sequences using steps using at least one chlorinated reagent such as chlorine in an acid medium, chlorine dioxide, the combination of chlorine and chlorine dioxide in mixture or in sequence, hypochlorite of an alkali or alkaline-earth metal or alternatively, and preferably, sequences free from chlorinated reagents comprising at least one step with oxygen, with ozone, or with an inorganic peroxyacid such as, for example example, peroxymonosulfuric acid or Caro acid, or also with an organic peroxyacid such as peroxyformic, peroxyacetic, peroxypropionic or peroxybutyric acid.
Selon l'invention, la pâte soumise à l'étape finale au peroxyde d'hydrogène a été épurée dans les étapes précédentes de manière telle que sa teneur en manganèse ne dépasse pas 3 ppm en poids par rapport à la matière sèche. Toute séquence de traitement apte à épurer la pâte en manganèse est conforme à l'invention. Des exemples de telles séquences comprennent des séquences faisant appel à des étapes mettant en oeuvre au moins un réactif acide tel que l'acide sulfurique, l'acide sulfureux ou le chlore, ou un agent séquestrant en milieu acide à pH contrôlé. Ces différents réactifs peuvent également être mis en oeuvre en milieu acide à pH contrôlé au cours des lavages de la pâte qui sont effectués entre les étapes de délignification et/ou de blanchiment.According to the invention, the pulp subjected to the final step with hydrogen peroxide has been purified in the preceding steps so that its manganese content does not exceed 3 ppm by weight relative to the dry matter. Any treatment sequence capable of purifying the manganese paste is in accordance with the invention. Examples of such sequences include sequences using steps using at least one acid reagent such as sulfuric acid, sulfurous acid or chlorine, or a sequestering agent in acidic medium at controlled pH. These different reagents can also be used in an acidic medium at a controlled pH during the washing of the pulp which is carried out between the delignification and / or bleaching steps.
De préférence, la teneur en manganèse de la pâte soumise à l'étape finale au peroxyde d'hydrogène ne dépassera pas 2 ppm en poids par rapport à la matière sèche.Preferably, the manganese content of the pulp subjected to the final step with hydrogen peroxide will not exceed 2 ppm by weight relative to the dry matter.
Conformément à l'invention, toute séquence de traitement de la pâte précédant l'étape finale au peroxyde d'hydrogène, et capable de réduire l'indice kappa à 5 ou moins et la teneur en manganèse à 3 ppm ou moins, peut être mise en oeuvre pour préparer la pâte à l'opération de blanchiment par l'étape finale au peroxyde d'hydrogène. En particulier, on pourra utiliser des séquences faisant appel à des réactifs chlorés tels que le chlore en milieu acide, le dioxyde de chlore en milieu acide ou l'association de chlore et de dioxyde de chlore en milieu acide en mélange ou en séquence, ou encore les hypochlorites de métaux alcalins ou alcalino-terreux en milieu alcalin. De manière préférée, on s'adressera cependant à des séquences ne faisant pas appel à des réactifs chlorés ou, tout au moins, limitant la quantité de réactifs chlorés, telles que les séquences comprenant au moins une étape mettant en oeuvre de l'oxygène gazeux, de l'ozone, un réactif acide, un réactif alcalin ou un composé peroxygéné en milieu acide ou alcalin. Par composé peroxygéné, on entend désigner tout composé chimique inorganique ou organique comprenant le groupement -O-O- dans sa molécule. Des exemples de tels composés sont le peroxyde d'hydrogène, les peroxyacides inorganiques tels que l'acide peroxymonosulfurique ou acide de Caro et les persels inorganiques comme les perborates, les percarbonates et les perphosphates de métaux alcalins ou alcalino-terreux. D'autres exemples de tels composés peroxygénés sont les peroxyacides organiques carboxyliques comme les peracides formique, acétique et propionique ainsi que les hydroperoxydes organiques comme l'hydroperoxyde de tert-butyle. Les peroxyacides organiques carboxyliques sont préférés. Parmi ces derniers, l'acide peracétique a donné d'excellents résultats. Il est également possible de concevoir des séquences de traitement qui combinent des étapes mettant en oeuvre des réactifs chlorés avec des étapes exemptes de tels réactifs.According to the invention, any pulp treatment sequence preceding the final step with hydrogen peroxide, and capable of reducing the kappa index to 5 or less and the manganese content to 3 ppm or less, can be put used to prepare the dough for the bleaching operation by the final step with hydrogen peroxide. In particular, it is possible to use sequences using chlorine reagents such as chlorine in an acid medium, chlorine dioxide in an acid medium or the association of chlorine and chlorine dioxide in an acid medium in a mixture or in sequence, or alternatively the hypochlorites of alkali or alkaline earth metals in an alkaline medium. Preferably, however, we will address sequences which do not use chlorinated reagents or, at least, limiting the quantity of chlorinated reagents, such as the sequences comprising at least one step using gaseous oxygen. , ozone, an acid reagent, an alkaline reagent or a peroxygen compound in an acid or alkaline medium. By peroxygen compound is meant to denote any inorganic or organic chemical compound comprising the group -OO- in its molecule. Examples of such compounds are hydrogen peroxide, inorganic peroxyacids such as peroxymonosulfuric acid or Caro acid and inorganic persalts such as perborates, percarbonates and perphosphates of alkali or alkaline earth metals. Other examples of such peroxygen compounds are organic carboxylic peroxyacids such as formic, acetic and propionic peracids as well as organic hydroperoxides such as tert-butyl hydroperoxide. Organic carboxylic peroxyacids are preferred. Among these, peracetic acid has given excellent results. It is also possible to design treatment sequences which combine steps using chlorinated reagents with steps free of such reagents.
Selon un premier mode de réalisation de l'invention, on réalise le blanchiment de la pâte au moyen d'une séquence de traitement en au moins 4 étapes comprenant la séquence O C/D Ep P, O D Ep P, Q Paa Ep P et Q CA Ep P. Cette notation est conforme à celle de la littérature technique du domaine du blanchiment des pâtes à papier. Les symboles employés ont les significations suivantes :
- O :
- étape à l'oxygène gazeux sous pression,
- D :
- étape au dioxyde de chlore,
- C/D :
- étape au chlore et au dioxyde de chlore appliqués en mélange,
- Ep :
- étape d'extraction alcaline en présence de peroxyde d'hydrogène,
- P :
- étape au peroxyde d'hydrogène en milieu alcalin,
- CA :
- étape à l'acide peroxymonosulfurique (acide de Caro) ou l'un de ses sels,
- Paa :
- étape à l'acide peracétique,
- Q :
- étape de traitement par un acide ou un acide séquestrant.
- O:
- pressurized oxygen gas step,
- D:
- chlorine dioxide step,
- C / D:
- chlorine and chlorine dioxide step applied as a mixture,
- Ep:
- alkaline extraction step in the presence of peroxide hydrogen,
- P:
- step with hydrogen peroxide in an alkaline medium,
- C A :
- step with peroxymonosulfuric acid (Caro acid) or one of its salts,
- Paa:
- peracetic acid step,
- Q:
- step of treatment with an acid or a sequestering acid.
De manière préférée, ce premier mode de réalisation du procédé selon l'invention est effectué en réalisant l'étape Ep de la séquence de blanchiment en présence d'un agent séquestrant des ions métalliques. Tous les agents séquestrants des ions métalliques conviennent bien. Les agents séquestrants ayant une affinité particulière pour les ions fer et manganèse conviennent particulièrement bien. Des exemples de ces agents sont les silicates, les phosphates et polyphosphates inorganiques tels que les silicates, les pyrophosphates et les métaphosphates de métaux alcalins, les polycarboxylates et les aminopolycarboxylates organiques tels que les acides tartrique, citrique, gluconique, éthylènediaminetétraacétique, diéthylènetriaminepentaacétique, cyclohexanediaminetétraacétique et leurs sels, les acides poly-α-hydroxyacryliques et leurs sels et les acides phosphoniques tels que les acides éthylènediaminetétra(méthylènephosphonique), dié-thylènetriaminepenta(méthylènephosphonique), cyclohexanediaminetétra(méthylènephosphonique) et leurs sels.Preferably, this first embodiment of the method according to the invention is carried out by carrying out step Ep of the bleaching sequence in the presence of an agent sequestering metal ions. All metal ion sequestering agents are suitable. Sequestering agents having a particular affinity for iron and manganese ions are particularly suitable. Examples of such agents are silicates, inorganic phosphates and polyphosphates such as silicates, pyrophosphates and metaphosphates of alkali metals, polycarboxylates and organic aminopolycarboxylates such as tartaric, citric, gluconic, ethylenediaminetetraacetic, diethylenetriaminepentaacetic cyclohexanediaminetetraacetic and their salts, poly-α-hydroxyacrylic acids and their salts and phosphonic acids such as ethylenediaminetetra (methylenephosphonic), diethylenetriaminepenta (methylenephosphonic), cyclohexanediaminetetra (methylenephosphonic) acids and their salts.
Les acides phosphoniques et leurs sels ont donné les meilleurs résultats pour séquestrer les ions métalliques dans l'étape Ep.Phosphonic acids and their salts have given the best results for sequestering metal ions in the Ep step.
L'étape Q de traitement par un acide ou par un acide séquestrant comprend le traitement par les anhydrides ou les acides inorganiques tels que l'anhydride sulfureux et les acides sulfurique, sulfureux, chlorhydrique, et nitrique ou leurs sels acides, ainsi que les acides organiques tels que les acides carboxyliques ou phosphoniques ou leurs sels acides. L'anhydride sulfureux ou les bisulfites de métal alcalin ou alcalino-terreux conviennent bien. Par bisulfite on entend désigner les sels acides de l'acide sulfureux répondant à la formule Me(HSO₃)n, dans laquelle Me symbolise un atome de métal de valence n, n étant un nombre entier valant 1 ou 2. Il comprend aussi le traitement par au moins un agent séquestrant en milieu acide tel qu'un phosphate ou polyphosphate inorganique en milieu acide, comme, par exemple, un pyrophosphate ou un métaphosphate de métal alcalin, un polycarboxylate ou un aminopolycarboxylate organique comme, par exemple, l'acide tartrique, citrique, gluconique, éthylènediaminetétraacétique, diéthylènetriaminepentaacétique, cyclohexanediaminetétraacétique et leurs sels, l'acide poly-α-hydroxyacrylique et ses sels et un acide phosphonique comme l'acide éthylènediaminetétra(méthylènephosphonique), diéthylènetriaminepenta(méthylènephosphonique), cyclohexanediaminetétra(méthylènephosphonique) et leurs sels.Step Q of treatment with an acid or with a sequestering acid comprises treatment with anhydrides or inorganic acids such as sulfur dioxide and sulfuric, sulfurous, hydrochloric, and nitric acids or their acid salts, as well as the acids organic such as carboxylic or phosphonic acids or their acid salts. Sulfur dioxide or alkali or alkaline earth metal bisulfites are well suited. By bisulfite is intended to denote the acid salts of sulfurous acid corresponding to the formula Me (HSO₃) n, in which Me symbolizes a metal atom of valence n, n being an integer equal to 1 or 2. It also comprises the treatment with at least one sequestering agent in an acid medium such as an inorganic phosphate or polyphosphate in an acid medium, such as, for example, a pyrophosphate or an alkali metal metaphosphate, a polycarboxylate or an organic aminopolycarboxylate such as, for example, tartaric, citric, gluconic, ethylenediaminetetraacetic, diethylenetriaminepentaacetic, cyclohexanediaminetetraacetic and their salts, poly-α-hydroxyacrylic acid and its salts and a phosphonic acid such as ethylenediaminetetraonic acid ), diethylenetriaminepenta (methylenephosphonic), cyclohexanediaminetetra (methylenephosphonic) and their salts.
De manière préférée, l'étape Paa est effectuée en présence d'un agent séquestrant des ions métalliques. Les agents séquestrants connus des ions métalliques tels que le fer et le manganèse conviennent bien. Des exemples de tels agents séquestrants sont les sels de métaux alcalino-terreux, en particulier les sels solubles de magnésium, les silicates, les phosphates et polyphosphates inorganiques tels que les silicates, les pyrophosphates et les métaphosphates de métaux alcalins, les polycarboxylates et les aminopolycarboxylates organiques tels que les acides tartrique, citrique, gluconique, diéthylènetriaminepentaacétique, cyclohexanediaminetétraacétique et leurs sels, les acides poly-α-hydroxyacryliques et leurs sels et les acides phosphoniques tels que les acides éthylènediaminetétra(méthylènephosphonique), diéthylènetriaminepenta(méthylènephosphonique), cyclohexanediaminetétra(méthylènephosphonique) et leurs sels. Il est également possible d'associer plusieurs de ces agents séquestrants en mélange. En règle générale, les polycarboxylates ou les acides phosphoniques donnent de bons résultats, en particulier lorsqu'ils comprennent au moins un sel de magnésium. Les acides phosphoniques et leurs sels ont donné les meilleurs résultats.Preferably, the Paa step is carried out in the presence of a metal ion sequestering agent. Known sequestering agents of metal ions such as iron and manganese are well suited. Examples of such sequestering agents are the alkaline earth metal salts, in particular the soluble magnesium salts, the silicates, the phosphates and inorganic polyphosphates such as the alkali metal silicates, pyrophosphates and metaphosphates, the polycarboxylates and the aminopolycarboxylates organic such as tartaric, citric, gluconic, diethylenetriaminepentaacetic, cyclohexanediaminetetraacetic and their salts, poly-α-hydroxyacrylic acids and their salts and phosphonic acids such as ethylenediaminetetra (methylenephosphonic), diethylenetriaminepenta (methylenephosphonic) and their salts. It is also possible to combine several of these sequestering agents in a mixture. In general, polycarboxylates or phosphonic acids give good results, in particular when they comprise at least one magnesium salt. Phosphonic acids and their salts have given the best results.
L'étape CA de traitement par l'acide peroxymonosulfurique (acide de Caro) ou l'un de ses sels consiste à traiter la pâte avec H₂SO₅ ou l'un de ses sels de métaux alcalins, alcalinoterreux ou d'ammonium, ou encore avec un mélange de plusieurs de ces sels ou d'H₂SO₅ avec un ou plusieurs de ces sels.Step C A of treatment with peroxymonosulfuric acid (Caro acid) or one of its salts consists in treating the paste with H₂SO₅ or one of its alkali metal salts, alkaline earth or ammonium, or with a mixture of several of these salts or of H₂SO₅ with one or more of these salts.
L'acide peroxymonosulfurique ou les sels mis en oeuvre peuvent, en variante, avoir été préparés immédiatement avant leur emploi par réaction d'une solution aqueuse concentrée d'acide sulfurique ou de ses sels avec une solution aqueuse concentrée d'un composé peroxygéné, par exemple, le peroxyde de l'hydrogène. Par solutions concentrées, on entend désigner, respectivement, des solutions d'H₂SO₅ de concentration d'au moins environ 10 moles par litre et d'H₂O₂ de concentration d'au moins environ 20 % en poids.The peroxymonosulfuric acid or the salts used may, as a variant, have been prepared immediately before their use by reacting a concentrated aqueous solution of sulfuric acid or its salts with a concentrated aqueous solution of a peroxygen compound, by example, hydrogen peroxide. The term “concentrated solutions” is intended to denote, respectively, solutions of H₂SO₅ with a concentration of at least about 10 moles per liter and of H₂O₂ with a concentration of at least about 20% by weight.
De manière préférée, l'étape CA est aussi effectuée en présence d'un agent séquestrant des ions métalliques. On utilisera avantageusement les mêmes agents séquestrants que ceux qui sont adaptés pour l'étape Paa et qui ont été décrits plus haut. Il est également possible d'associer plusieurs de ces agents séquestrants en mélange.Preferably, step C A is also carried out in the presence of a metal ion sequestering agent. The same sequestering agents will advantageously be used as those which are suitable for the Paa stage and which have been described above. It is also possible to combine several of these sequestering agents in a mixture.
On ajustera le pH initial de l'étape CA de façon telle que, en fin de réaction, le pH reste supérieur ou égal à 2 et, de préférence, 2,5. De même, il conviendra que le pH en fin de réaction ne dépasse pas 7 et, de préférence, pas 6.The initial pH of step C A will be adjusted so that, at the end of the reaction, the pH remains greater than or equal to 2 and, preferably, 2.5. Likewise, the pH at the end of the reaction should not exceed 7 and preferably not 6.
Dans le cas de séquences en 4 étapes O C/D Ep P ou O D Ep P, on préfère généralement intercaler entre l'étape Ep et l'étape P un lavage de la pâte au moyen d'une solution aqueuse acide. Par acide on entend désigner les anhydrides ou les acides inorganiques tels que l'anhydride sulfureux et les acides sulfurique, sulfureux, chlorhydrique, et nitrique ou leurs sels acides, ainsi que les acides organiques tels que les acides carboxyliques ou phosphoniques ou leurs sels acides. L'anhydride sulfureux ou les bisulfites de métal alcalin ou alcalino-terreux conviennent bien. Par bisulfite on entend désigner les sels acides de l'acide sulfureux répondant à la formule Me(HSO₃)n, dans laquelle Me symbolise un atome de métal de valence n, n étant un nombre entier valant 1 ou 2.In the case of O C / D Ep P or O D Ep P 4-step sequences, it is generally preferred to insert, between step Ep and step P, washing the dough using an acidic aqueous solution. The term “acid” is intended to denote the anhydrides or inorganic acids such as sulfur dioxide and sulfuric, sulfurous, hydrochloric and nitric acids or their acid salts, as well as organic acids such as carboxylic or phosphonic acids or their acid salts. Sulfur dioxide or alkali or alkaline earth metal bisulfites are well suited. By bisulfite is intended to denote the acid salts of sulfurous acid corresponding to the formula Me (HSO₃) n, in which Me symbolizes a metal atom of valence n, n being an integer having the value 1 or 2.
La quantité d'acide à mettre en oeuvre dans l'étape de lavage selon l'invention dépend du type de bois et de l'efficacité des étapes qui ont précédé. En général, on mettra en oeuvre la quantité d'acide requise pour fixer le pH de la pâte à environ au moins 4 et, de préférence, environ au moins 4,5. De même, on ajustera souvent la quantité d'acide pour que le pH ne dépasse pas 7 et, de préférence, pas 6,5.The amount of acid to be used in the washing step according to the invention depends on the type of wood and on the efficiency of the preceding steps. In general, we will implement the amount of acid required to set the pH of the dough to at least about 4 and preferably about at least 4.5. Likewise, the amount of acid will often be adjusted so that the pH does not exceed 7 and preferably not 6.5.
Selon un deuxième mode de réalisation de l'invention, on réalise le blanchiment de la pâte au moyen d'une séquence de traitement exempte de réactif chloré en au moins 5 étapes comprenant la séquence O Q P D P, O Q P Paa P, O Q P CA P et O Q P Z P. Dans cette séquence, les symboles utilisés pour désigner les étapes de traitement ont la même signification que dans le premier mode de réalisation de l'invention en ce qui concerne les symboles O, Q, Paa et P. Pour le symbole Z, on entend lui donner la signification suivante : Z : traitement par l'ozone.According to a second embodiment of the invention, the pulp is bleached using a treatment sequence free from chlorine reagent in at least 5 steps comprising the sequence OQPDP, OQP Paa P, OQPC A P and OQPZ P In this sequence, the symbols used to designate the processing steps have the same meaning as in the first embodiment of the invention with regard to the symbols O, Q, Paa and P. For the symbol Z, it is meant give it the following meaning: Z: ozone treatment.
Selon ce deuxième mode de réalisation de l'invention, les étapes Q et Paa sont effectuées dans des conditions comparables à celles décrites plus haut pour le premier mode de réalisation de l'invention.According to this second embodiment of the invention, steps Q and Paa are carried out under conditions comparable to those described above for the first embodiment of the invention.
L'étape de traitement par l'ozone consiste à mettre la pâte en contact avec une phase gazeuse contenant de l'ozone.The ozone treatment stage consists in bringing the paste into contact with a gaseous phase containing ozone.
Le plus souvent, la phase gazeuse contient un mélange d'ozone et d'oxygène provenant d'un générateur électrique d'ozone que l'on alimente en oxygène gazeux sec.Most often, the gas phase contains a mixture of ozone and oxygen from an electric ozone generator which is supplied with dry gaseous oxygen.
Le traitement de la pâte par l'ozone se réalise de préférence en milieu acide. Des pH d'au moins 0,5 et de préférence 1,5 et ne dépassant pas 5 et, de préférence 4 conviennent bien.The treatment of the dough with ozone is preferably carried out in an acid medium. PH values of at least 0.5 and preferably 1.5 and not exceeding 5 and preferably 4 are suitable.
La quantité de peroxyde d'hydrogène à mettre en oeuvre dans l'étape finale est généralement d'au moins 0,5 % en poids par rapport au poids de pâte sèche et, de préférence, d'au moins 0,8 % de ce poids. De même, il conviendra que la quantité de peroxyde d'hydrogène dans cette étape de traitement ne dépasse pas 6 % en poids par rapport au poids de pâte sèche et, de préférence, pas 5 % de ce poids.The amount of hydrogen peroxide to be used in the final step is generally at least 0.5% by weight relative to the weight of dry pulp and, preferably, at least 0.8% of this weight. Likewise, the amount of hydrogen peroxide in this treatment step should not exceed 6% by weight relative to the weight of dry pulp and, preferably, not 5% of this weight.
La température de l'étape finale au peroxyde d'hydrogène doit être ajustée de façon à rester au moins égale à 50 °C et, de préférence à 70 °C. Elle doit aussi ne pas dépasser 140 °C et, de préférence, ne pas dépasser 130 °C.The temperature of the final step with hydrogen peroxide must be adjusted so as to remain at least equal to 50 ° C. and preferably to 70 ° C. It must also not exceed 140 ° C and, preferably do not exceed 130 ° C.
La durée du traitement par le peroxyde d'hydrogène dans l'étape finale doit être suffisante pour que la réaction de blanchiment soit complète. En pratique, elle sera fixée à une valeur d'au moins 15 minutes et, de préférence, 30 minutes. Elle devra aussi le plus souvent ne pas dépasser 100 heures et, de préférence, 50 heures. Une combinaison des conditions de température et de durée d'environ 80 °C et d'environ 240 minutes a donné de bons résultats.The duration of the treatment with hydrogen peroxide in the final step must be sufficient for the bleaching reaction to be complete. In practice, it will be set to a value of at least 15 minutes and, preferably, 30 minutes. It should also most often not exceed 100 hours and, preferably, 50 hours. A combination of the temperature and time conditions of about 80 ° C and about 240 minutes has given good results.
Le pH de l'étape finale au peroxyde d'hydrogène est réglé au moyen de l'addition au mélange réactionnel d'un composé alcalin, par exemple de l'hydroxyde de sodium, à une valeur initiale d'au moins 10 et, de préférence, d'au moins 11. De même, le pH initial de l'étape finale au peroxyde d'hydrogène est généralement réglé à une valeur qui ne dépasse pas 13 et, de préférence, pas 12.The pH of the final step with hydrogen peroxide is adjusted by means of the addition to the reaction mixture of an alkaline compound, for example sodium hydroxide, to an initial value of at least 10 and, preferably at least 11. Likewise, the initial pH of the final stage with hydrogen peroxide is generally adjusted to a value which does not exceed 13 and, preferably, not 12.
Après l'étape finale au peroxyde d'hydrogène, il est possible et généralement avantageux de laver la pâte blanchie avec une solution aqueuse acide afin de ramener son pH à une valeur ne dépassant pas 6,5 et, de préférence, pas 6. Les acides inorganiques tels que l'acide sulfurique, l'acide sulfureux, l'acide chlorhydrique ou l'acide nitrique conviennent bien. L'acide sulfureux obtenu par l'absorption d'anhydride sulfureux gazeux dans l'eau convient particulièrement bien.After the final step with hydrogen peroxide, it is possible and generally advantageous to wash the bleached pulp with an acidic aqueous solution in order to bring its pH to a value not exceeding 6.5 and, preferably, not 6. The inorganic acids such as sulfuric acid, sulfurous acid, hydrochloric acid or nitric acid are well suited. The sulfurous acid obtained by the absorption of gaseous sulfur dioxide in water is particularly suitable.
Le procédé selon l'invention présente l'avantage de réaliser un gain de blancheur important. En particulier, ce gain peut atteindre 20 à 25 °ISO dans le cas de pâtes dont la blancheur avant l'étape finale au peroxyde d'hydrogène est relativement basse, par exemple les pâtes kraft de résineux ou de feuillus de blancheur voisine de 65 à 70 °ISO.The method according to the invention has the advantage of achieving a significant gain in whiteness. In particular, this gain can reach 20 to 25 ° ISO in the case of pulps whose whiteness before the final step with hydrogen peroxide is relatively low, for example kraft softwood or hardwood pulps of whiteness close to 65 to 70 ° ISO.
Le procédé selon l'invention trouve une application pour la délignification et le blanchiment de pâtes chimiques de type kraft ou au sulfite, ou semi-chimiques de haute qualité, notamment celles qui sont destinées aux emballages alimentaires. Il convient indifféremment pour les pâtes provenant de bois résineux ou de bois feuillus.The method according to the invention finds an application for the delignification and bleaching of chemical pastes of the kraft or sulfite type, or high-quality semi-chemical, especially those intended for food packaging. It is equally suitable for pasta from softwood or hardwood.
Les exemples suivants sont donnés pour illustrer l'invention, sans pour autant en limiter la portée. Les exemples 1R, 2R, 4R à 7R, 10R, 14R à 17R et 22R ne sont pas conformes à l'invention et ont été donnés à titre de référence. Les exemples 3, 8, 9, 11 à 13, 18 à 21 et 23 sont conformes à l'invention.The following examples are given to illustrate the invention, without however limiting its scope. Examples 1R, 2R, 4R to 7R, 10R, 14R to 17R and 22R are not in accordance with the invention and have been given by way of reference. Examples 3, 8, 9, 11 to 13, 18 to 21 and 23 are in accordance with the invention.
Dans tous les exemples, on a utilisé les normes qui suivent pour les déterminations expérimentales :
- blancheur : norme ISO 2470,
- indice kappa : norme SCAN C1-59,
- degré de polymérisation : norme SCAN C15-62,
- indice de déchirement : norme SCAN P11-64,
- indice de résistance à la traction : norme SCAN P38-80,
- degré de raffinage : norme SCAN C21-65.
- whiteness: ISO 2470 standard,
- kappa index: SCAN C1-59 standard,
- degree of polymerization: standard SCAN C15-62,
- tear index: SCAN P11-64 standard,
- tensile strength index: SCAN P38-80 standard,
- degree of refinement: SCAN C21-65 standard.
Un échantillon de pâte de résineux ayant subi une cuisson kraft (blancheur initiale 26,3 °ISO, indice kappa 31,2 et degré de polymérisation 1630) a été blanchi suivant une séquence de 4 étapes de traitement commençant par une étape à l'oxygène gazeux sous pression, suivie d'une étape comportant du chlore et du dioxyde de chlore en milieu acide et appliqués en mélange, d'une étape d'extraction alcaline en présence de peroxyde d'hydrogène et d'une étape finale au peroxyde d'hydrogène en milieu alcalin (séquence symbolisée par les sigles O C/D Ep P).A sample of softwood pulp having undergone kraft cooking (initial whiteness 26.3 ° ISO, kappa index 31.2 and degree of polymerization 1630) was bleached according to a sequence of 4 treatment steps starting with an oxygen step gaseous under pressure, followed by a step comprising chlorine and chlorine dioxide in an acid medium and applied as a mixture, a step of alkaline extraction in the presence of hydrogen peroxide and a final step with peroxide hydrogen in an alkaline medium (sequence symbolized by the acronyms OC / D Ep P).
Après blanchiment, on a effectué sur la pâte traitée les déterminations de blancheur, d'indice kappa et de degré de polymérisation.After bleaching, the whiteness, kappa number and degree of polymerization were determined on the treated pulp.
Les conditions opératoires des trois premières étapes ont été les suivantes :
Avant de soumettre la pâte a l'étape finale au peroxyde d'hydrogène, on a procédé à son lavage au moyen d'une solution aqueuse contenant 1 g d'H₂SO₄ / 100 g de pâte sèche (ce qui a amené la pâte à un pH de 5) à 20 °C pendant 10 minutes et à 2,5 % de consistance.Before subjecting the dough to the final step with hydrogen peroxide, it was washed with an aqueous solution containing 1 g of H₂SO₄ / 100 g of dry dough (which brought the dough to a 5) pH at 20 ° C for 10 minutes and at 2.5% consistency.
La teneur en Mn de la pâte après l'étape Ep était de 2,9 ppm en poids par rapport à la matière sèche dans l'exemple 1R et de 1,1 ppm dans l'exemple 2R.The Mn content of the pulp after step Ep was 2.9 ppm by weight relative to the dry matter in Example 1R and 1.1 ppm in Example 2R.
L'étape finale au peroxyde d'hydrogène a ensuite été réalisée en l'absence de stabilisants à 80 °C, à 30 % de consistance et pendant 240 minutes en mettant en oeuvre 2,0 g de peroxyde d'hydrogène et 2,0 g de NaOH pour 100 g de pâte sèche. Les résultats obtenus sont donnés au tableau qui suit :
Le gain de blancheur réalisé à l'étape finale au peroxyde d'hydrogène a été de 15,4 °ISO pour l'exemple 1R et de 16,4 °ISO pour l'exemple 2R. A l'issue de l'étape finale au peroxyde d'hydrogène, la totalité de celui-ci avait été consommé dans chacun des exemples 1R et 2R.The whiteness gain achieved in the final step with hydrogen peroxide was 15.4 ° ISO for Example 1R and 16.4 ° ISO for Example 2R. At the end of the final step with peroxide of hydrogen, all of it had been consumed in each of Examples 1R and 2R.
On a reproduit l'exemple 2R, excepté que l'on a en outre introduit dans l'étape P 2,0 g de silicate de Na à 38 °Bé et 0,6 g de MgSO₄.7H₂O pour 100 g de pâte sèche.Example 2R was repeated, except that 2.0 g of Na silicate at 38 ° Bé and 0.6 g of MgSO₄.7H₂O per 100 g of dry paste were also introduced into step P.
Après l'étape Ep, la teneur en Mn de la pâte était de 1,1 ppm en poids par rapport à la matière sèche et son indice kappa de 1,9.After stage Ep, the Mn content of the pulp was 1.1 ppm by weight relative to the dry matter and its kappa number of 1.9.
Les résultats obtenus ont été :
Le gain de blancheur réalisé au cours de l'étape P finale a été de 23,5 °ISO.The gain in whiteness achieved during the final stage P was 23.5 ° ISO.
On a reproduit l'exemple 3, excepté que l'étape finale au peroxyde d'hydrogène a été effectuée à moyenne consistance (10 % de matières sèches) et en présence de 3 g de H₂O₂, 3,0 g de NaOH, 3,0 g de silicate de Na 38 °Bé et 1,0 g de MgSO₄.7H₂O pour 100 g de pâte sèche.Example 3 was repeated, except that the final step with hydrogen peroxide was carried out at medium consistency (10% dry matter) and in the presence of 3 g of H₂O₂, 3.0 g of NaOH, 3, 0 g of Na silicate at 38 ° Bé and 1.0 g of MgSO₄.7H₂O per 100 g of dry paste.
Après l'étape Ep, la teneur en Mn de la pâte était de 1,1 ppm en poids par rapport à la matière sèche et son indice Kappa de 1,9.After step Ep, the Mn content of the pulp was 1.1 ppm by weight relative to the dry matter and its Kappa number of 1.9.
Les résultats ont été les suivants :
On a reproduit l'exemple 3 en remplaçant, dans la deuxième étape, le chlore par une quantité équivalente de dioxyde de chlore (exprimée en chlore actif) de façon à réaliser une séquence O D Ep P. On a par ailleurs porté la température de l'étape D à 70 °C et fait varier la quantité de NaOH dans l'étape P finale entre 1,5 et 2,3 g/100 g de pâte sèche.Example 3 was reproduced by replacing, in the second step, chlorine with an equivalent amount of chlorine dioxide (expressed as active chlorine) so as to achieve an OD Ep P sequence. The temperature of step D was also brought to 70 ° C. and the amount of NaOH in the final stage P between 1.5 and 2.3 g / 100 g of dry paste.
La teneur en Mn déterminée avant l'étape P finale a été de 9 ppm en poids par rapport à la litière sèche et l'indice kappa de 3,0.The Mn content determined before the final stage P was 9 ppm by weight relative to the dry litter and the kappa index of 3.0.
Les résultats obtenus ont été les suivants :
On a tenté d'abaisser la teneur en manganèse de la pâte obtenue après l'étape Ep d'une séquence de blanchiment O D Ep P effectuée code aux exemples 5R à 7R en intercalant entre les étapes O et D d'une part et entre les étapes D et Ep d'autre part un traitement de lavage de la pâte au moyen d'une solution d'agent séquestrant. Le lavage effectué entre l'étape O et D a consisté en un lavage en présence de 0,12 % d'acide diéthylènetriaminepentaacétique (DTPA) et de 2,0 % d'acide sulfurique, celui effectué entre l'étape D et l'étape Ep en un lavage en présence de 0,2 % du sel heptasodique de l'acide diéthylènetriaminepenta(méthylènephosphonique) (DTMPNa₇). L'étape P finale a été réalisée avec 2,0 g d'H₂O₂ / 100 g de pâte sèche comme dans les exemples 7R à 9R, en présence de 1,6 g NaOH, de 3,0 g de silicate de Na 38 °Bé et de 1 g de MgSO₄.7H₂O / 100 g de pâte sèche.An attempt was made to lower the manganese content of the pulp obtained after step Ep of an OD Ep P bleaching sequence carried out code in Examples 5R to 7R by intercalating between steps O and D on the one hand and between the steps D and Ep, on the other hand, a treatment for washing the dough using a solution of sequestering agent. The washing carried out between stage O and D consisted of a washing in the presence of 0.12% of diethylenetriaminepentaacetic acid (DTPA) and of 2.0% of sulfuric acid, that carried out between stage D and the Ep step in a wash in the presence of 0.2% of the heptasodium salt of diethylenetriaminepenta acid (methylenephosphonic acid) (DTMPNa₇). The final step P was carried out with 2.0 g of H₂O₂ / 100 g of dry paste as in Examples 7R to 9R, in the presence of 1.6 g NaOH, of 3.0 g of Na silicate 38 ° Be and 1 g of MgSO₄.7H₂O / 100 g of dry paste.
La teneur en Mn après l'étape Ep était descendue à 2,7 ppm en poids par rapport à la matière sèche et l'indice kappa était de 2,1.The Mn content after step Ep had dropped to 2.7 ppm by weight relative to the dry matter and the kappa number was 2.1.
Les résultats obtenus ont été les suivants :
Le gain de blancheur réalisé au cours de l'étape P finale a été de 13,7 °ISO.The whiteness gain achieved during the final stage P was 13.7 ° ISO.
Un autre échantillon de pâte de résineux ayant subi une cuisson kraft (blancheur initiale 29,4 °ISO, indice kappa 26,0 et degré de polymérisation 1500) a été blanchie au moyen d'une séquence totalement exempte de réactifs chlorés en 5 étapes O Q P Paa P dans les conditions opératoires suivantes :
L'indice kappa de la pâte après l'étape Paa était de 4,3 et sa teneur en Mn de 0,2 ppm en poids par rapport à la matière sèche.The kappa number of the dough after the Paa step was 4.3 and its Mn content was 0.2 ppm by weight relative to the dry matter.
Les résultats obtenus ont été les suivants :
Le gain de blancheur réalisé au cours de l'étape P finale a été de 22,4 °ISO.The whiteness gain achieved during the final stage P was 22.4 ° ISO.
Un échantillon d'une pâte d'un mélange de bois résineux provenant de Finlande et ayant subi une cuisson kraft (blancheur initiale 27,9 °ISO, indice kappa 26,7 et degré de polymérisation 1680) a été blanchi au moyen d'une séquence classique en 6 étapes O C/D E D E D dans les conditions opératoires suivantes :
Les résultats obtenus ont été les suivants :
On a aussi déterminé les propriétés mécaniques de la pâte blanchie (indice de déchirement et indice de résistance à la traction) après raffinage dans un raffineur de laboratoire.The mechanical properties of the bleached pulp (tear index and tensile strength index) were also determined after refining in a laboratory refiner.
Les résultats ont été les suivants :
Le même échantillon de pâte de résineux qu'à l'exemple 10R a été blanchi au moyen d'une séquence exempte de chlore élémentaire en 5 étapes O Q P D P dans les conditions opératoires suivantes :
Les résultats obtenus ont été les suivants :
La teneur en Mn de la pâte après l'étape D était de 0,7 ppm en poids par rapport à la matière sèche.
Le même échantillon de pâte de résineux qu'aux exemples 10R et 11 a été blanchi au moyen d'une séquence totalement exempte de chlore en 5 étapes O Q P Paa P dans les conditions opératoires suivantes :
Les résultats obtenus ont été les suivants :
La teneur en Mn de la pâte après l'étape Paa était de 0,4 ppm en poids par rapport à la matière sèche.
Le même échantillon de pâte de résineux qu'aux exemples 10R, 11 et 12 a été blanchi au moyen d'une séquence totalement exempte de chlore en 5 étapes O Q P CA P dans les conditions opératoires suivantes :
Les résultats obtenus ont été les suivants :
La teneur en Mn de la pâte après l'étape CA était de 0,2 ppm en poids par rapport à la matière sèche.
Un autre échantillon d'une pâte d'un mélange de bois résineux provenant de Finlande et ayant subi une cuisson kraft (blancheur initiale 30,5 °ISO, indice kappa 26,7 et degré de polymérisation 1510) a été blanchi au moyen d'une séquence totalement exempte de réactifs chlorés en 4 étapes Q Paa Ep P dans les conditions opératoires suivantes :
Les résultats obtenus sont donnés au tableau qui suit :
Le même échantillon de pâte de résineux qu'aux exemples 14R à 17R a été blanchi à l'aide de la même séquence de blanchiment en 4 étapes Q Paa Ep P dans les conditions suivantes :
Ces conditions opératoires sont identiques à celles des exemples 14R à 17R excepté la consistance de l'étape P finale qui a été portée à 30 % de matière sèche.These operating conditions are identical to those of Examples 14R to 17R except the consistency of the final stage P which was brought to 30% of dry matter.
Les résultats obtenus sont donnés au tableau qui suit :
Le même échantillon de pâte kraft de résineux (blancheur initiale 30,5 °ISO, indice kappa 26,7 et degré de polymérisation 1510) que celui utilisé aux exemples 14R à 17R et 18 à 21 a été blanchi au moyen d'une séquence totalement exempte de réactifs chlorés en 5 étapes O Q P Z P dans les conditions opératoires suivantes :
Les résultats obtenus ont été les suivants :
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BE9200626A BE1006056A3 (en) | 1992-07-06 | 1992-07-06 | Method of laundering of chemical pulp. |
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WO1995009945A1 (en) * | 1993-10-01 | 1995-04-13 | Kvaerner Pulping Technologies Ab | Method of treating chemical paper pulp without using chlorine-containing chemicals |
WO1995013420A1 (en) * | 1993-11-10 | 1995-05-18 | Solvay Interox (Société Anonyme) | Method of bleaching chemical paper pulp |
FR2719853A1 (en) * | 1994-05-11 | 1995-11-17 | Atochem Elf Sa | Process for delignification and bleaching of a chemical paper pulp. |
FR2719854A1 (en) * | 1994-05-11 | 1995-11-17 | Atochem Elf Sa | Process for preparing delignified and bleached chemical paper pulps |
WO1996001921A1 (en) * | 1994-07-11 | 1996-01-25 | Beloit Technologies, Inc. | High efficiency vessels for bleaching lignocellulosic, cellulosic and synthetic polymeric fibrous materials |
WO1996001920A1 (en) * | 1994-07-11 | 1996-01-25 | Beloit Technologies Inc. | Peroxide bleaching process for cellulosic and lignocellulosic material |
EP2082991A1 (en) | 2008-01-22 | 2009-07-29 | Thermphos Trading GmbH | Method of Water Treatment |
US9376650B2 (en) | 2008-01-22 | 2016-06-28 | Italmatch Chemicals Spa | Method of water treatment |
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SE500616C2 (en) * | 1993-06-08 | 1994-07-25 | Kvaerner Pulping Tech | Bleaching of chemical pulp with peroxide at overpressure |
US7001484B2 (en) | 2000-05-04 | 2006-02-21 | University Of New Brunswick | Peroxide bleaching of wood pulp using stabilizers and sodium hydrosulfide reducing agent |
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WO2008101952A1 (en) * | 2007-02-21 | 2008-08-28 | Solvay (Societe Anonyme) | Process for the bleaching of paper pulp |
CN101903591A (en) * | 2007-12-20 | 2010-12-01 | 三菱瓦斯化学株式会社 | Process for production of bleached pulp |
SE532370C2 (en) * | 2008-02-28 | 2009-12-29 | Metso Paper Inc | Method of bleaching a pulp |
EP2128331A1 (en) | 2008-05-26 | 2009-12-02 | SOLVAY (Société Anonyme) | Process for the bleaching of paper pulp |
US8034759B2 (en) * | 2008-10-31 | 2011-10-11 | Ecolab Usa Inc. | Enhanced stability peracid compositions |
US8845860B2 (en) | 2010-09-16 | 2014-09-30 | Georgia-Pacific Consumer Products Lp | High brightness pulps from lignin rich waste papers |
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US11937626B2 (en) | 2020-09-04 | 2024-03-26 | Nicoventures Trading Limited | Method for whitening tobacco |
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- 1993-06-29 ES ES93201886T patent/ES2094465T3/en not_active Expired - Lifetime
- 1993-06-29 EP EP93201886A patent/EP0578304B1/en not_active Expired - Lifetime
- 1993-06-29 DE DE69304822T patent/DE69304822T2/en not_active Expired - Fee Related
- 1993-06-29 US US08/083,183 patent/US6221209B1/en not_active Expired - Fee Related
- 1993-06-30 NZ NZ248029A patent/NZ248029A/en unknown
- 1993-07-02 SK SK702-93A patent/SK70293A3/en unknown
- 1993-07-02 AU AU41705/93A patent/AU654623B2/en not_active Ceased
- 1993-07-05 BR BR9302764A patent/BR9302764A/en not_active Application Discontinuation
- 1993-07-05 AR AR93325341A patent/AR247258A1/en active
- 1993-07-05 CA CA002099827A patent/CA2099827A1/en not_active Abandoned
- 1993-07-06 JP JP5167132A patent/JPH06166981A/en active Pending
- 1993-07-06 SI SI9300362A patent/SI9300362A/en unknown
- 1993-07-06 FI FI933103A patent/FI111170B/en active
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EP0415149A2 (en) * | 1989-08-18 | 1991-03-06 | Degussa Aktiengesellschaft | Process for bleaching and delignification of lignocellulosic materials |
WO1992012289A1 (en) * | 1991-01-03 | 1992-07-23 | Union Camp Patent Holding, Inc. | Chlorine-free process for bleaching lignocellulosic pulp |
Cited By (14)
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WO1995009945A1 (en) * | 1993-10-01 | 1995-04-13 | Kvaerner Pulping Technologies Ab | Method of treating chemical paper pulp without using chlorine-containing chemicals |
US6605181B1 (en) | 1993-10-01 | 2003-08-12 | Kvaerner Pulping Aktiebolag | Peroxide bleach sequence including an acidic bleach stage and including a wash stage |
WO1995013420A1 (en) * | 1993-11-10 | 1995-05-18 | Solvay Interox (Société Anonyme) | Method of bleaching chemical paper pulp |
BE1007757A3 (en) * | 1993-11-10 | 1995-10-17 | Solvay Interox | Method of laundering of chemical pulp. |
WO1995031598A1 (en) * | 1994-05-11 | 1995-11-23 | Elf Atochem S.A. | Delignification and bleaching method for chemical paper pulp |
WO1995031599A1 (en) * | 1994-05-11 | 1995-11-23 | Elf Atochem S.A. | Method for preparing delignified and bleached chemical paper pulps |
FR2719854A1 (en) * | 1994-05-11 | 1995-11-17 | Atochem Elf Sa | Process for preparing delignified and bleached chemical paper pulps |
CN1065304C (en) * | 1994-05-11 | 2001-05-02 | 埃尔夫阿托化学有限公司 | Method for preparing delignified and bleached chemical paper pulps |
FR2719853A1 (en) * | 1994-05-11 | 1995-11-17 | Atochem Elf Sa | Process for delignification and bleaching of a chemical paper pulp. |
WO1996001921A1 (en) * | 1994-07-11 | 1996-01-25 | Beloit Technologies, Inc. | High efficiency vessels for bleaching lignocellulosic, cellulosic and synthetic polymeric fibrous materials |
WO1996001920A1 (en) * | 1994-07-11 | 1996-01-25 | Beloit Technologies Inc. | Peroxide bleaching process for cellulosic and lignocellulosic material |
EP0919661A1 (en) * | 1994-07-11 | 1999-06-02 | Beloit Technologies, Inc. | Peroxide bleaching process for cellulosic and lignocellulosic material |
EP2082991A1 (en) | 2008-01-22 | 2009-07-29 | Thermphos Trading GmbH | Method of Water Treatment |
US9376650B2 (en) | 2008-01-22 | 2016-06-28 | Italmatch Chemicals Spa | Method of water treatment |
Also Published As
Publication number | Publication date |
---|---|
DE69304822T2 (en) | 1997-04-10 |
BE1006056A3 (en) | 1994-05-03 |
SI9300362A (en) | 1994-03-31 |
ATE143074T1 (en) | 1996-10-15 |
SK70293A3 (en) | 1994-04-06 |
AU654623B2 (en) | 1994-11-10 |
FI933103A (en) | 1994-01-07 |
FI111170B (en) | 2003-06-13 |
AR247258A1 (en) | 1994-11-30 |
BR9302764A (en) | 1994-02-08 |
JPH06166981A (en) | 1994-06-14 |
DE69304822D1 (en) | 1996-10-24 |
FI933103A0 (en) | 1993-07-06 |
NZ248029A (en) | 1995-10-26 |
AU4170593A (en) | 1994-01-13 |
US6221209B1 (en) | 2001-04-24 |
ES2094465T3 (en) | 1997-01-16 |
EP0578304B1 (en) | 1996-09-18 |
CA2099827A1 (en) | 1994-01-07 |
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