Classifications

• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
  • D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
  • D21C9/10—Bleaching ; Apparatus therefor
  • D21C9/1057—Multistage, with compounds cited in more than one sub-group D21C9/10, D21C9/12, D21C9/16
• • 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.
• EP-A-O 402 335 describes a process for bleaching a chemical pulp according to which the pulp is subjected to a treatment for removing metals before a step with peroxide. A whiteness degree of at least 89 ° ISO is reached by a subsequent step with chlorine and chlorine dioxide.
• 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 purification of the manganese paste and 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 minus 25%, the pulp 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 up to '' to a kappa index (measured according to the SCAN C1-59 standard) 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 up 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, the hypochlorite of an alkali or alkaline-earth metal or alternatively, and preferably, sequences free of 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, the hypochlorite of an alkali or alkaline-earth metal or alternatively, and preferably, sequences free of chlorinated reagents comprising at least one step with oxygen, with ozone, or with an inorganic peroxyacid such as
• 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.
• Stage 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 (HSO 3 ) n, in which Me symbolizes a metal atom of valence n, n being an integer equal to 1 or 2.
• 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
• a polycarboxylate or an organic aminopolycarboxylate
• 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 H 2 SO 5 or one of its alkali metal salts, alkaline earth or ammonium, or with a mixture of several of these salts or of H 2 SO 5 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 H 2 SO 5 with a concentration of at least about 10 moles per liter and of H 2 O 2 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 In the case of sequences in 4 steps OC / D Ep P or OD Ep P, it is generally preferable to interpose, 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 (HSO 3 ) 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 sulphite type, or high-quality semi-chemical, especially those which are 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 0 C / 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 MgSO 4 .7H 2 O 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 Cl 2 / ClO 2 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 H 2 O 2 content , g / 100 g of dry paste: 0.5 DTMPNa 7 content, g / 100 g of dry paste: 0.0 (Example 1R) DTMPNa 7 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 final step with hydrogen peroxide was then carried out in the absence of stabilizers at 80 ° C, 30% consistency and for 240 minutes using 2.0 g of hydrogen peroxide and 2.0 g of NaOH per 100 g of dry paste.
• 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 reproduced, except that 2.0 g of Na silicate at 38 ° Bé and 0.6 g of MgSO 4 .7H 2 O per 100 g of dry dough.
• 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 H 2 O 2 , 3.0 g of NaOH , 3.0 g of 38 ° Bé Na silicate and 1.0 g of MgSO 4 .7H 2 O 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 P stage was carried out with 2.0 g of H 2 O 2/100 g of dry pulp as in Examples 5R to 7R in the presence of 1.6 g NaOH, 3.0 g of silicate Na 38 ° Bé and 1 g of MgSO 4 .7H 2 O / 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.
• 2nd stage chlorine stage - chlorine dioxide (stage C / D): active chlorine content, g / 100 g of dry paste: 2.0 Cl 2 / ClO 2 ratio (expressed as active Cl): 50/50 temperature, degrees C: 50 duration, min: 30 consistency,% by weight of dry matter: 4 3rd stage: alkaline extraction stage (stage E): NaOH content, g / 100 g of dry paste: 2.0 temperature, degrees C: 90 duration, min: 120 consistency,% by weight of dry matter: 10 4th stage: chlorine dioxide stage (stage D): active chlorine content, g / 100 g of dry paste: 2.0 temperature, degrees C: 70 duration, min: 120 consistency,% by weight of dry matter: 10 5th stage: alkaline extraction stage (stage E): NaOH content, g / 100 g of dry paste: 1.0 temperature, degrees C: 70 duration, min: 90 consistency,% by weight of dry matter: 10 6th stage: chlorine dioxide stage (stage D): active chlorine content, g / 100 g of dry paste:
• the mechanical properties of the bleached pulp were also determined after refining in a laboratory refiner.
• Example 10R The same sample of coniferous pulp as in Example 10R was bleached using a 5-step sequence of elementary chlorine O Q P D P under the following operating conditions:
• 1st stage oxygen stage (O): pressure, bar: 6.0 NaOH content, g / 100 g of dry paste: 4.0 MgSO 4 .7H 2 O 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 H 2 SO 4 for a pH of: 6 temperature, degrees C: 50 duration, min: 30 consistency,% by weight of dry matter: 4
• stage D chlorine dioxide stage
• stage D active chlorine content
• g / 100 g of dry paste 1.5 temperature
• degrees C 70 duration
• min 120 consistency
• % by weight of dry matter 10
• 5th stage final stage with hydrogen peroxide (P): H 2 O 2 content
• g / 100 g of dry paste 2.0 NaOH content
• g / 100 g of dry paste 1.6 content of Na silicate 38 ° Be
• g / 100 g of dry paste 3.0 MgSO 4 .7H 2 O content
• g / 100 g of dry paste 1.0 temperature
• degrees C 90 duration
• min 240 consistency
• % by weight of dry matter 30
• 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.m 2 / 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
• 1st stage oxygen stage (O): pressure, bar: 6.0 NaOH content, g / 100 g of dry paste: 4.0 MgSO 4 .7H 2 O 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: 0.2 SO 2 for a pH of: 6 temperature, degrees C: 90 duration, min: 60 consistency,% by weight of dry matter: 4
• 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.m 2 / 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
• 1st stage oxygen stage (O): pressure, bar: 6.0 NaOH content, g / 100 g of dry paste: 4.0 MgSO 4 .7H 2 O 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: 0.2 SO 2 for a pH of: 6 temperature, degrees C: 90 duration, min: 60 consistency,% by weight of dry matter: 4 3rd stage: H 2 O 2 stage (P): H 2 O 2 content , g / 100 g of dry paste: 2.0 NaOH content, g / 100 g of dry paste: 2.0 MgSO 4 .7H 2 O content, g / 100 g of dry paste: 0.2 DTMPNa 7 content, g / 100 g of dry paste: 0.1 temperature, degrees C: 90 duration, min: 120 consistency,% by weight
• 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.m 2 / 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
• 2nd stage peracetic acid (Paa) stage: Paa content, g / 100 g of dry dough: 9.0 DTMPNa 7 content, g / 100 g of dry paste: 0.25 temperature, degrees C: 90 duration, min: 240 consistency,% by weight of dry matter 10
• 3rd stage alkaline extraction stage (Ep stage): NaOH content, g / 100 g of dry paste: 3.0 H 2 O 2 content , g / 100 g of dry paste: 0.5 DTMPNa 7 content, g / 100 g of dry paste: 0.1 temperature, degrees C: 70 duration, min: 60 consistency,% by weight of dry matter: 10
• 1st stage stage with a sequestering acid (Q): DTPA content, g / 100 g of dry paste: 0.16 H 2 SO 4 content , g / 100 g of dry paste: 0.5 temperature, degrees C: 55 duration, min: 30 consistency,% by weight of dry matter: 3 2nd stage: peracetic acid (Paa) stage: Paa content, g / 100 g of dry dough: 9.0 DTMPNa 7 content, g / 100 g of dry paste: 0.25 temperature, degrees C: 90 duration, min: 240 consistency,% by weight of dry matter: 10 3rd stage: alkaline extraction stage (Ep stage): NaOH content, g / 100 g of dry paste: 3.0 H 2 O 2 content , g / 100 g of dry paste: 0.5 DTMPNa 7 content, g / 100 g of dry paste: 0.1 temperature, degrees C: 70 duration, min: 60 consistency,% by weight of dry matter: 10
• Q sequestering acid
• 1st stage oxygen stage (O): pressure, bar: 5.5 NaOH content, g / 100 g of dry paste: 4.0 MgSO 4 .7H 2 O content, g / 100 g of dry paste: 0.5 temperature, degrees C: 120 duration, min: 60 consistency,% by weight of dry matter: 14 2nd stage: stage with a sequestering acid (Q): DTPA content, g / 100 g of dry paste: 0.2 SO 2 content, g / 100 g of dry paste: 0.5 temperature, degrees C: 25 duration, min: 30 consistency,% by weight of dry matter: 4

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