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
  • D21C9/16—Bleaching ; Apparatus therefor with per compounds
  • D21C9/163—Bleaching ; Apparatus therefor with per compounds with peroxides
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H17/00—Non-fibrous material added to the pulp, characterised by its constitution; Paper-impregnating material characterised by its constitution
  • D21H17/02—Material of vegetable origin

Definitions

• the present invention relates to a process for bleaching a plant material, in the form of a micronized powder, with hydrogen peroxide in the presence of a base.
• all plant sources are suitable, in particular the softwood species such as fir, pine, spruce, hardwoods such as birch, beech, hornbeam, chestnut, and others.
• the vegetable source comes from vegetable waste and in particular wood waste.
• Wood waste can, for example, come from forestry, the primary or secondary wood processing industry, the sawing, planing, veneer industry. Wood waste can also come from the industries of the use or transformation of wooden products, in particular light or heavy wooden packaging. Wood waste can also come from chemical pulp production facilities.
• the vegetable source can also come from vegetable waste from the harvest of cereals such as in particular corn cobs.
• This micronized vegetable filler can be subjected to a conventional bleaching treatment in the stationery field in order to obtain a whiteness between 60 and 90 degree of white (measured according to French standard Q03039), said degree of white being expressed in percentage compared to a control having a value of 100%.
• This whiteness is obtained by bleaching with 4% hydrogen peroxide, 2% soda, 3% silicate and 0.25% DTPA (diethylenetriamine sodium pentaacetate). This bleaching is therefore carried out using a single aqueous solution comprising a dilute mixture of hydrogen peroxide, soda, silicate and DTPA and involves washing the vegetable load with water.
• DTPA diethylenetriamine sodium pentaacetate
• These vegetable fillers can be used in the manufacture of pulp, paper, cardboard and nonwovens on the one hand, and on the other hand, in the manufacture of plastics, composites, paint, coatings and building materials .
• patent EP 0419385 B1 discloses a process for the manufacture of bleached and dry vegetable pulps in which the bleaching is carried out using hydrogen peroxide and the drying by vaporization of the water of the pulp by means of a dry gas atmosphere circulating in contact with the pulp, the bleaching being carried out simultaneously with drying.
• This process uses a single bleaching solution or liquor containing hydrogen peroxide and optionally products such as alkaline agents, complexing agents and stabilizing products of hydrogen peroxide.
• This liquor is mixed with the vegetable pulp so that the initial consistency of the mixture thus obtained is at least 10% and preferably between about 20% and 35%, the consistency of the pulp being its dry matter content. expressed in percent by weight relative to its total weight.
• the vegetable pulps used in this process are characterized by a high content of dietary fiber. They are chosen from beet, citrus, fruit, oilseed, cereal, vegetable pulps, after the product normally recoverable from each of them, such as sugar, fruit juice, pectin, oil, starch, flour, if applicable grain, has been extracted or separated from it.
• the production of sugar beet pulp is described, for example, in the document "Sucrerie facie” October 1985, 439-454.
• the dry matter of these pulps is not in the micronized state of a few hundred micrometers.
• this type of bleaching which is carried out at average consistencies of 10 to 20% in general and up to 30% for extreme cases, is followed by neutralization with an acid and washing with water. 'water.
• These treatments are intended to remove the excess of alkaline agent before drying, and thus to avoid irreversible color reversion canceling the benefit of bleaching.
• aqueous effluents are large in volume and heavily loaded with organic matter. These effluents entail high costs of purification treatment before discharge.
• the object of the present invention is to find a method for bleaching a micronized plant material which does not have the drawbacks of the conventional bleaching mentioned above.
• the plant material in the micronized powder state can come from the same sources as those of patent EP 0433413 B1 mentioned above.
• the beet pulp after sugar extraction can also be the source of a micronized powder.
• micronized powder a powder having a particle size d 95 of less than 300 ⁇ m (micrometers) and preferably less than 200 ⁇ m.
• the plant material before being micronized may advantageously have undergone a complexing treatment of known metals to catalyze the decomposition of the hydrogen peroxide. This treatment with a complexing agent followed by washing with water, known per se, is carried out using complexing agents chosen from DTPA (diethylene triamine sodium pentaacetate), EDTA (Sodium ethylenediamine tetraacetate). ), poly- ⁇ -hydroxyacrylic acid salts, and salts of phosphonic acids.
• DTPA diethylene triamine sodium pentaacetate
• EDTA Sodium ethylenediamine tetraacetate
• poly- ⁇ -hydroxyacrylic acid salts and salts of phosphonic acids.
• step a) the humidity of the micronized powder is preferably that of the plant material at the end of the micronization operation.
• the initial humidity of the micronized powder before being brought to the temperature t a of step a) is between 4 and 15% of water by weight relative to its total weight.
• the temperature t a of step a) is from 20 to 40 ° C., that is to say the temperature of the micronized powder obtained during its preparation after grinding and sieving operations.
• a temperature t a of the order of 90-100 ° C. is advantageous when the micronized plant material contains catalase. This enzyme is secreted by microorganisms that can develop on finely divided plant materials. This enzyme that breaks down hydrogen peroxide can be inactivated by heating.
• step b) the powder is impregnated on the one hand, with an aqueous solution A containing hydrogen peroxide and on the other hand, with an aqueous solution B containing an alkaline agent and optionally a stabilizing agent for peroxide hydrogen and / or a metal complexing agent of metal salts.
• the impregnation with A preferably precedes the impregnation with B, although the impregnation with B may, in a variant, precede the impregnation with A.
• a and B are applied simultaneously to the powder.
• the powder is impregnated by spraying solution A and by spraying solution B.
• spraying solution A and by spraying solution B the fine droplets of A and B only meet on or near the grains of the powder.
• solutions A and B highly concentrated respectively in hydrogen peroxide on the one hand, and on the other hand, in alkaline agent and / or stabilizing agent or complexing agent.
• a single solution C or A and B would have been mixed beforehand with the same contents of active products would be unstable, the hydrogen peroxide being decomposed and the stabilizing agent in particular the sodium silicate precipitating by gel formation.
• the volume ratio of the B / A solutions ranges from 0.5 to 2 and even better is approximately 1.
• the amount of H 2 0 2 (calculated in the pure state, therefore expressed in 100%) used for the impregnation is from 1 to 10% by weight relative to the weight of the powder obtained at the end of step a).
• solution A containing from 100 to 350 g of H 2 0 2 counted in the pure state per liter, that is to say a solution A having a content of 10 to 35% by weight of H 2 0 2 by volume.
• Solutions A having a concentration greater than 35% are more difficult to implement due to the reaction exothermic reaction which they cause and the risk of fire under normal atmosphere. These risks can be partially controlled by practicing steps b), c) and drying under an inert atmosphere, in particular under a nitrogen atmosphere.
• the temperature t b of the powder during the impregnations of step b) is between 60 and 90 ° C.
• step b) is advantageously from 5 minutes to 2 hours and preferably from 10 to 30 minutes.
• the alkaline agent of solution B is advantageously chosen from NaOH, KOH, Na 2 CO 3 , K 2 CO 3 , sodium silicate, DTPA or any other reagent making it possible to obtain a pH greater than 7 for solution B
• the amount of alkaline agent used by weight relative to the weight of the powder to be impregnated varies according to the amount of H 2 O 2 used and the nature of the plant material. This quantity is chosen so that the final pH of the powder at the end of step c) is from 6.5 to 8.5.
• an amount of 0.5 to 5% by weight of NaOH, based on the weight of the vegetable powder to be impregnated, is suitable.
• the amount of water used to constitute solution B is chosen so that the active constituent (s) of this solution are completely dissolved.
• the total amount of the two solutions A and B is calculated as a function of the moisture content of the powder at the end of step a) to obtain, after the impregnation of step b), a water content of 30 to 40% by weight relative to the weight relative to the total weight of the powder.
• the stabilizing agent for hydrogen peroxide is chosen from sodium silicate, magnesium salts, sodium phosphate, sodium polyphosphates, sodium pyrophosphate and phosphonates.
• sodium silicate is used and even better sodium silicate in aqueous solution of density 1.33.
• the amount of stabilizing agent (s) ranges from 1 to 10% by weight relative to the weight of powder to be impregnated in step b), expressed in the dry state. The preferred amount ranges from 4 to 8%.
• the complexing agent is chosen from DTPA (diethylene triamine sodium pentaacetate), EDTA (sodium ethylenediamine tetraacetate), the salts of poly- ⁇ -hydroxyacrylic acids, and the salts of phosphonic acids.
• the preferred agent for reasons of cost and efficiency is DTPA in 40% solution.
• the amount used is advantageously from 0.1 to 1% by weight of DTPA 40% relative to the weight of the plant material before impregnation.
• solution B also contains an optical brightener to improve the shade of the final white.
• This brightener can be chosen from those usually used in the manufacture of paper.
• the amount of added brightener is advantageously between 0.01 and 0.5% by weight relative to the weight of the powder expressed in the dry state and reacted in step b).
• Stage c the so-called latency stage, constitutes the completion of the laundering.
• the impregnated micronized vegetable powder is stirred for a period d c and at a temperature t c .
• the preferred temperature t c is 60 ° to 90 ° C.
• the duration d c depends on the nature of the plant material and the temperature t c . In general, this duration is from 5 to 120 min. and preferably between 15 and 60 minutes.
• drying is then carried out after step c).
• This drying is carried out according to conventional techniques used in the wood and vegetable matter industry, taking into account the particular risks of ignition and / or explosion in an oxidizing atmosphere. To avoid this risk, this drying can be carried out under an atmosphere of inert gas or very poor in oxygen.
• Sodium silicate if present in solution B, plays a flame-retardant role by its presence in the final powder because no washing is necessary from step a).
• the powder obtained at the end of step c) is dried to a water content of 5 to 20% by weight relative to its total weight.
• the process can be carried out discontinuously (called “batch”) or continuously.
• micronized vegetable powder is loaded into a powder mixer preheated to about 40 ° C., then the 35% H 2 O 2 solution is sprayed simultaneously with the alkaline solution on the one hand, and the alkaline solution on the other hand .
• the 35% H 2 0 2 solution and the alkaline solution have a volume ratio close to 1.
• the temperature t b of the powder rises to around 80 ° C. Stirring is continued, after the end of the addition of the solutions, for a further 30 to 60 min., At a powder temperature of 70 ° C., then the powder is discharged, optionally dried and then packaged in containers.
• the materials used for the mixer must be compatible and resistant to the use of H 2 0 2 and, for example, chosen from stainless steel, steel enamelled or coated with resistant paints, plastics.
• This embodiment is preferred for high capacity industrial production and allows better control of the exotherm of the bleaching reaction.
• micronized plant material is introduced continuously by a dosing screw into a continuous mixer into which the H 2 O 2 solution is injected continuously , on the one hand, and the basic solution, on the other hand.
• the residence time in the mixer is of the order of 1 to 5 seconds and can range up to 1 to 3 minutes.
• the micronized powder continuously passes through a residence tank, the retention time of which is sufficient to ensure the consumption, and therefore the disappearance, of at least 75% of the H 2 O 2 introduced.
• the optimum bleaching temperature t b is 70 to 80 ° C. This temperature is preferably obtained by the exotherm of the oxidation reaction with H 2 0 2 .
• the maximum temperature t b reached depends on the amount of H 2 0 2 introduced, the humidity of the plant material after mixing the reactants, the initial temperature of the plant material and the temperature of each solution A, B , injected into the mixer.
• the plant material is then heated before or during the addition of the reagents.
• the heating must be uniform and must not create local overheating.
• the preferred heating means are the circulation of hot water in a double jacket around the mixer and / or the retention tank or else the injection of water vapor into the mixer.
• Heating the basic solution B is also a convenient way to add calories to the reaction medium.
• the basic solution B is brought to a temperature of 40 to 90 ° C.
• Preheating of the micronized plant material before its introduction into the continuous mixer can be done in the dosing screw or in the feed tank of this dosing screw, by steam injection or by circulation of hot water in a double jacket around the dosing screw and / or the screw feed tank.
• step b the impregnation (step b) and the residence time (step c) can be carried out in the same device.
• micronized woods were used:
• micronized woods with a particle size d 95 of less than 150 ⁇ m come from the elaborate Parisienne des Sciures.
• the measurement of the degree of white is carried out with a Hunterlab spectrophotometer according to the "ISO Brightness" standard used by the paper industry at the wavelength of 457 nm for the measurement of the whiteness of the paper.
• a double jacketed glass reactor with a capacity of 1 liter, is heated by circulation of hot water in the double jacketed and is equipped, for stirring the contents, with a rapid central propeller and two scraping blades slow.
• the spraying of solution A (H 2 0 2 at 35%) is carried out by pumping the solution using a high pressure pump of the HPLC type, then by spraying it using a nozzle above of the reactor.
• the means for spraying the basic solution B are a replica of the above means.
• the whiteness, the pH and the H 2 0 2 consumed are then measured.
• the amounts of hydrogen peroxide and NaOH are expressed as a percentage by weight of pure product relative to the weight of micronized plant material in the dry state.
• the amounts of DTPA are expressed as a percentage by weight of commercial solution (approximately 40%) relative to the weight of plant material micronized in the dry state.
• the amounts of sodium silicate are expressed as a percentage by weight of aqueous sodium silicate solution with a density equal to 1.33 relative to the weight of plant material in the dry state.
• a pretreatment with DTPA is carried out with 0.5% of DTPA, at a consistency of 10%, a temperature of 90 ° C. and for a duration of 15 minutes.
• the micronized plant material is filtered, washed with water, then dried to the initial humidity level indicated.
• Example 3 The procedure is as for Example 3, with another micronized spruce wood, with an initial white of 44.7% ISO, 94% consistency and initial pH of 5.
• the whiteness is 62.5% ISO.
• the temperature t b reaches 78 ° C. and the final water content of the impregnated micronized wood is 40%.
• Example 16 This example is identical to Example 16, except that the amount of NaOH is lower: 105 g instead of 126 g (or 1.6% instead of 1.8% compared to dry wood).
• the maximum temperature reached during the two simultaneous sprays is 70 ° C. After 45 min. stirring at 70 ° C, the pH is 8.5, the amount of residual H 2 0 2 is 1.25% and the whiteness of 62.3% ISO.
• micronized materials were used.
• micronized powders have a particle size d 95 of 180 ⁇ m.
• a 35% H 2 O 2 solution is sprayed on the one hand, and an alkaline solution is sprayed on the other hand, simultaneously in the mixer. It is left to react until consumption of at least 75% of the hydrogen peroxide reacted, then it is dried under vacuum.
• Tables III and IV show Examples 18 to 20 and their results.

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• 1995
  • 1995-01-06 FR FR9500093A patent/FR2729096A1/fr active Granted
  • 1995-12-07 EP EP95402756A patent/EP0722010A1/fr not_active Ceased
  • 1995-12-28 CA CA002166242A patent/CA2166242C/fr not_active Expired - Fee Related
• 1996
  • 1996-01-03 SK SK11-96A patent/SK1196A3/sk unknown
  • 1996-01-04 PL PL96312152A patent/PL181230B1/pl unknown
  • 1996-01-04 NO NO960023A patent/NO960023L/no not_active Application Discontinuation
  • 1996-01-05 CN CN96100617A patent/CN1075144C/zh not_active Expired - Fee Related
  • 1996-01-05 JP JP8000217A patent/JPH08232184A/ja active Pending
  • 1996-01-05 FI FI960065A patent/FI960065A/fi unknown
  • 1996-01-08 CZ CZ9662A patent/CZ284990B6/cs not_active IP Right Cessation

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