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
  • D21C9/1005—Pretreatment of the pulp, e.g. degassing the pulp

Definitions

• the present invention relates to bleaching using hydrogen peroxide from mechanical, thermomechanical, chemo-mechanical, chemo-thermal pulp in the pulp and related fields.
• the dry matter yield of such an operation is always very high and can reach and even exceed 90%.
• acceptable bleaching cannot be obtained at a temperature between 100 ° C. and 150 ° C. in a water vapor atmosphere by means of hydrogen peroxide in the presence of an alkaline agent. only if the action of hydrogen peroxide is exerted on the material to be bleached together with an action of disintegration of the fibers by mechanical defibering or refining for a duration of the order of only a fraction of a second.
• the method of the present invention provides effective bleaching although it includes known conditions to oppose the achievement of such a result.
• the complexing or sequestering agent In the treatment with the complexing or sequestering agent, the latter is used in an amount of approximately 0.1% to 1% by weight of the weight of dry pulp. Unless specified or obvious, the quantities of products in all that follow are also expressed in percent by weight of the weight of dry dough.
• the complexing or sequestering agent is most often chosen from sodium tripolyphosphate, sodium tetrapyrophosphate, sodium salts of citric acids, nitrilotriacetic, ethylenediaminetetraacetic, diethylenetriaminepentaacetic.
• the treatment with the complexing or sequestering agent is most generally carried out at a pH value of between 4 and 8, the result of the invention then not depending on such a value.
• the consistency, percentage by weight of dough in the dry state in the treatment medium can, in the present treatment using a complexing or sequestering agent, vary within fairly wide limits, approximately 5% to 30% . It is most often between about 10% and 15% to best reconcile economy and efficiency of subsequent washing.
• the duration of treatment with a complexing or sequestering agent depends on the other parameters. It is generally between approximately 5 minutes and 2 hours.
• washing is meant the operation which consists in eliminating more or less completely and here effectively the liquid present in the dough. This elimination is carried out for example by pressing the dough on a filter or by means of a dilution-pressing sequence of the dough, repeated or not, in which the dilution is very generally ensured by water.
• the washing which follows the treatment by means of a complexing or sequestering agent is most often carried out at a temperature generally between approximately 20 ° C. and 90 ° C., often between 20 ° C. and 60 ° C. for essentially economic reasons.
• efficiency is meant, expressed in percent, the degree of elimination of the liquid phase present before washing in the dough.
• the action of hydrogen peroxide is exerted in the process of the invention preferably at a temperature above 120 °. C, for example 140 ° C and above.
• the amount of hydrogen peroxide used is that commonly accepted in the traditional bleaching of mechanical pulps and is therefore between approximately 0.5% and 10%, most often not less than approximately 2%.
• the alkaline agent present with the hydrogen peroxide which is very suitable for carrying out the invention is sodium hydroxide used most often at a rate of approximately 0.25% to 5% with a weight ratio of sodium hydroxide / hydrogen peroxide preferably between 0.2 and 1.
• the invention allows a duration of action of hydrogen peroxide both long enough to allow this product to fully develop its effectiveness, and advantageously reduced compared to that of traditional bleaching. It usually does not exceed 15 minutes and often even around 5 minutes.
• hydrogen peroxide exerts its action in a medium at a pressure practically equal to the pressure of saturated steam at the chosen temperature. This pressure is most often between 2 bar absolute and 40 bar absolute.
• the consistency of the paste as placed in the presence of hydrogen peroxide is preferably chosen to be as high as possible, remaining compatible with the production of a mixture of satisfactory homogeneity of the paste with the other products present.
• This quality of the mixture means that the consistency is generally limited to a value of not more than about 30%, or even 25%. However, it is rarely less than preferably around 10%.
• the present invention leads to high results in bleaching pulps of mechanical origin without the presence of compounds having a stabilizing effect for hydrogen peroxide being essential to the effectiveness of its action. This can however be improved by the presence of such compounds such as for example, the sodium silicate used most often at a rate of approximately 2% to 6%, the magnesium salts such as the magnesium sulfate used in a quantity generally included between 0.05% and 0.5%, derivatives of poly ( ⁇ -hydroxyacrylic acid) used in an amount of approximately 0.05% to 2%, such as Claresse® products.
• the process of the invention can be carried out batchwise or continuously in any installation mainly comprising mixing equipment, generally of the mixer type, in which the treatment can be carried out using the complexing or sequestering agent and the mixing of the initial paste. or washed with hydrogen peroxide and the alkaline agent, washing equipment such as, for example, filters, presses, finally, for the stage of action of hydrogen peroxide, pressure-resistant equipment and impervious to water vapor, such as a tubular reactor equipped for example with a screw type dough progression system or an autoclave.
• mixing equipment generally of the mixer type, in which the treatment can be carried out using the complexing or sequestering agent and the mixing of the initial paste. or washed with hydrogen peroxide and the alkaline agent, washing equipment such as, for example, filters, presses, finally, for the stage of action of hydrogen peroxide, pressure-resistant equipment and impervious to water vapor, such as a tubular reactor equipped for example with a screw type dough progression system or an autoclave.
• the treatment of the dough is carried out in a kneader using 0.5% of DTPA, for 15 minutes, at 60 ° C. in the case of examples 1 to 11, at 90 ° C. in the case of examples 12 to 14, at a pH of between 4 and 8 each time and which is the same in a given example and in the example provided for comparison, with a consistency equal to 10%.
• the following washing, each greater than 95% effective, is carried out at 60 ° C.
• the initial paste or the paste washed after treatment with DTPA is mixed with hydrogen peroxide, sodium hydroxide NaOH, the quantity of water sufficient to ensure the desired consistency here equal to 20%, and if necessary the silicate or Clarene® by kneading for less than 5 minutes at 20-25 ° C before being subjected to the action of hydrogen peroxide in a reactor of the pressure-resistant autoclave type, equipped with an airlock introduction of the paste, and impermeable to saturated steam which ensures the pressure at the temperature T chosen, -
• the degree of white of the paste collected after decompression of the autoclave and rapid cooling is measured (457 nm) in% using a CARL ZEISS spectrophotometer of the ELREPHO type.
• Each of the examples relates to the bleaching of 100 g of softwood millstone pulp with a degree of white equal to 53.7% and a dry weight equal to 38.2 g.
• This improvement is accompanied by a significant reduction in the consumption of hydrogen peroxide or, at the very least, practically does not increase it.
• a given degree of white is achieved with a substantial saving of hydrogen peroxide.
• Each of the examples relates to the bleaching of 100 g of chemothermal-mechanical pulp with sulphite with a white degree equal to 59.6% and a dry weight equal to 40 g.

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• Life Sciences & Earth Sciences (AREA)
• Engineering & Computer Science (AREA)
• Wood Science & Technology (AREA)
• Paper (AREA)
• Detergent Compositions (AREA)
• Treatment Of Fiber Materials (AREA)
• Dental Preparations (AREA)
• Seasonings (AREA)
• Transition And Organic Metals Composition Catalysts For Addition Polymerization (AREA)
• Glass Compositions (AREA)
• Noodles (AREA)

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• 1987
  • 1987-04-02 FR FR8704844A patent/FR2613388B1/fr not_active Expired - Lifetime
• 1988
  • 1988-03-29 EP EP88420102A patent/EP0285530B1/de not_active Expired - Lifetime
  • 1988-03-29 NO NO881404A patent/NO173886C/no unknown
  • 1988-03-29 DE DE8888420102T patent/DE3877403T2/de not_active Expired - Fee Related
  • 1988-03-29 ES ES198888420102T patent/ES2004846T3/es not_active Expired - Lifetime
  • 1988-03-29 AT AT88420102T patent/ATE84581T1/de active
  • 1988-03-29 DE DE198888420102T patent/DE285530T1/de active Pending
  • 1988-03-31 FI FI881544A patent/FI93749C/fi not_active IP Right Cessation
  • 1988-03-31 CA CA000563118A patent/CA1310797C/fr not_active Expired - Lifetime
  • 1988-03-31 AU AU14067/88A patent/AU606930B2/en not_active Ceased
  • 1988-04-02 JP JP63082116A patent/JPS63256786A/ja active Granted
  • 1988-04-06 NZ NZ224144A patent/NZ224144A/xx unknown

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