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
  • 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
  • D21C9/101—Bleaching ; Apparatus therefor in solvent medium
• • 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
  • D21C9/1026—Other features in bleaching processes
  • D21C9/1036—Use of compounds accelerating or improving the efficiency of the processes

Definitions

• the present invention relates to the bleaching of high-yield paper pulps with hydrogen peroxide.
• wood chips are subjected to separate or associated actions of mechanical, chemical or thermal origin.
• Chemical pulps are obtained by chemical defibration of wood. Their yield is generally less than 50%.
• yield is meant the weight of the pulp in the dry state relative to the weight of the starting lignocellulosic material in the dry state, for example wood chips in the dry state.
• Mechanical type pulps are produced by mechanical defibration of wood chips, for example in a grinding wheel shredder or a disc shredder or refiner.
• the yield is generally equal to or greater than 85%.
• the mechanical characteristics of these pastes in particular the resistance to rupture, to tearing and to bursting, are poor.
• thermomechanical pasta TMP
• TMP thermomechanical pasta
• the wood chips were also treated with a sodium sulfite solution at acidic or basic pH depending on the nature of the wood.
• the pulps obtained also called chemical-mechanical pulps (CMP), have good mechanical characteristics.
• This latter treatment consists in cooking the lignocellulosic material, carried out at a temperature equal to or greater than 100 ° C., under saturated steam pressure, in the presence of sodium sulfite or sodium bisulfite.
• CTMP pastes have mechanical resistance is improved, the yield remaining equal to or greater than 85% and more often than not, at least equal to approximately 90% and therefore similar to that of purely mechanical origins.
• a high-yield paper pulp is defined as being a pulp obtained by defibering the wood and various treatments with a yield equal to or greater than 85%.
• the consistency (weight of dry matter relative to the total weight of the pulp) of the bleaching medium must be relatively high from 15 to 20% and even 30% to obtain effective bleaching.
• the bleaching temperature should generally be between 60 ° C and 80 ° C.
• WO-A-93 19245 describes a process for bleaching a high-yield paper pulp with an aqueous solution containing hydrogen peroxide, sodium carbonate and chelating agents.
• JP-A-4,065,592 discloses a process for deinking paper according to which the paper to be recycled or the paper pulp is subjected to a treatment with an alcohol-alkaline solution containing hydrogen peroxide. After removing the ink, the paste is bleached with a hydrosulfite solution.
• the present invention makes it possible to avoid the drawbacks set out below or at least some of them.
• said ratio is from 0.01 to 0.1.
• the use of such a reaction medium makes it possible to carry out bleaching without sodium silicate.
• bleaching can be carried out without complexing metals such as DTPA.
• the residual bleaching liquid recoverable by filtration of the pulp can be purified by distillation and the residue from this distillation can be easily incinerated. This treatment of the residual liquid avoids the rejection of aqueous bleaching effluent.
• the ratio by weight of the alcohol to the weight of the pulp considered in the dry state is from 1 to approximately 50.
• the consistency can vary between very large limits ranging from 50% to approximately 2%.
• the alcohol is chosen from methanol and ethanol. These two alcohols are available industrially in large quantities and easily evaporated or distilled for their recovery.
• an activator of hydrogen peroxide capable of being oxidized in the medium into a peroxidant is added to the reaction medium, during its formation or during the reaction.
• This activator can be a nitrile of general formula R-CN in which R is an alkyl or aryl group. It is assumed that this nitrile leads to an iminoperacid of general formula:
• the alkyl group is preferably a lower alkyl chosen from methyl, ethyl and propyl.
• the aryl group is preferably phenyl.
• the activator can also be a mineral or organic acid or one of its salts, capable of being oxidized in the medium to a peracid or one of its salts.
• the acid is preferably chosen from acetic acid, boric acid and boric anhydride (B 2 O 3 ).
• the reaction medium also contains an alkaline agent.
• bleaching is more effective in the presence of such an agent.
• this agent is chosen from sodium hydroxide, sodium carbonate, potassium carbonate.
• the reaction medium is maintained at a temperature of 20 ° C. to 80 ° C.
• the most preferred temperature range is 50 to 60 ° C.
• the reaction medium formed is filtered to obtain a solid and a filtrate, then the solid thus collected is washed with water to give a wet paste. whitened.
• the high-yield paper pulp is washed beforehand with alcohol to reduce or even eliminate a large part of its water content before using this pulp thus washed to form the bleaching reaction medium.
• the hydrogen peroxide used is a solution of pure H 2 O 2 in water at a content ranging from 10 to 70% by weight.
• the sodium hydroxide solution in water can contain from 40 g to 700 g of pure NaOH per liter.
• the activator is generally used in an amount of 1 to 50%.
• the soda can be added all at once with the other reagents or else added little by little during the bleaching so as to keep the pH constant.
• the apparent pH is measured with a CHEMTRIX pH meter fitted with an INGOLD ref glass electrode. 9823.
• the dough is filtered and washed with water.
• the filtrates are combined and the residual hydrogen peroxide is assayed to determine the amount by weight relative to the amount by weight of initial pulp considered in the dry state: 1.4%.
• the washed dough is neutralized with sulfur dioxide at a pH equal to 5.5 and the whiteness of the dough is measured according to ISO standard, ie 75 ° ISO.

Landscapes

• Life Sciences & Earth Sciences (AREA)
• Engineering & Computer Science (AREA)
• Wood Science & Technology (AREA)
• Paper (AREA)
• Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)

Applications Claiming Priority (3)

Publications (2)

Family

ID=9452745

Family Applications (1)

Country Status (9)

Families Citing this family (5)

Family Cites Families (2)

• 1993
  • 1993-11-10 FR FR9313446A patent/FR2712313B1/fr not_active Expired - Fee Related
• 1994
  • 1994-11-07 WO PCT/FR1994/001286 patent/WO1995013421A1/fr active IP Right Grant
  • 1994-11-07 JP JP7513627A patent/JPH09504841A/ja active Pending
  • 1994-11-07 AT AT95900797T patent/ATE156877T1/de active
  • 1994-11-07 DE DE69405006T patent/DE69405006T2/de not_active Expired - Fee Related
  • 1994-11-07 AU AU81473/94A patent/AU8147394A/en not_active Abandoned
  • 1994-11-07 CN CN94194659.2A patent/CN1139466A/zh active Pending
  • 1994-11-07 CA CA002176030A patent/CA2176030A1/fr not_active Abandoned
  • 1994-11-07 EP EP95900797A patent/EP0728239B1/fr not_active Expired - Lifetime

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