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
  • D21C9/166—Bleaching ; Apparatus therefor with per compounds with peracids
• • 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 invention relates to a method for delignifying a chemical pulp. It particularly relates to a method for improving the selectivity of such a delignification operation.
• the invention aims to remedy the drawbacks of known methods by providing a method which achieves effective delignification of the unbleached chemical pulp with a high selectivity which makes it possible to obtain pulps having high intrinsic qualities.
• the invention relates to a process for improving the selectivity of the delignification of a chemical paper pulp by means of an organic peroxyacid according to which the unbleached pulp from the cooking operation is treated with a aqueous solution of this organic peroxyacid at a temperature between 2 and 47 ° C.
• chemical paper pulp the pulp having 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 salt metal of sulfurous acid in an acid medium (cooking with sulfite).
• chemical reagents such as sodium sulfide in alkaline medium (kraft or sulfate cooking), sulfur dioxide or a salt metal of sulfurous acid in an acid medium (cooking with sulfite).
• Semi-chemical pastes 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) or even those obtained by treatment with caustic soda cold followed by mechanical defibration can also be bleached and / or delignified by the process according to the invention.
• the organic peroxyacid is selected from aliphatic carboxylic peroxyacids comprising a single percarboxylic group and a saturated linear or branched alkyl chain of less than 11 carbon atoms.
• Aliphatic carboxylic peroxyacids with a linear saturated alkyl chain having less than 6 carbon atoms are preferred. Examples of such peroxyacids are performic acid, peracetic acid, perpropanoic acid, n-perbutanoic acid and n-perpentanoic acid.
• Peracetic acid is particularly preferred because of its effectiveness and its good biodegradable properties.
• the organic peroxyacid is selected from diperoxyacarboxylic acids comprising a linear or branched alkyl chain of less than 16 carbon atoms and two percarboxylic groups substituted on carbon atoms situated in the alpha-omega l position 'one over the other.
• diperoxyacarboxylic acids comprising a linear or branched alkyl chain of less than 16 carbon atoms and two percarboxylic groups substituted on carbon atoms situated in the alpha-omega l position 'one over the other.
• Examples of such peroxyacids are 1,6-diperoxyhexanedioic acid, 1,8-diperoxyoctanedioic acid and 1,10-diperoxydecanedioic acid, and 1,12-diperoxydodecanedioic acid.
• the organic peroxyacid is selected from aromatic peroxyacids comprising at least one percarboxylic group per benzene nucleus.
• aromatic peroxyacids which have only one percarboxylic group per benzene nucleus will be chosen.
• An example of such an acid is peroxybenzoic acid.
• Another variant of the process according to the invention consists in choosing an organic peroxyacid substituted with one or more halogen atoms or by any other organic functional substituent.
• organic functional substituent is meant a functional group such as the carbonyl group (ketone, aldehyde or carboxylic acid), the alcohol group, the groups containing nitrogen such as the nitrile, nitro, amine and amide groups, groups containing sulfur such as the sulfo and mercapto groups.
• the peroxyacid can equally be used in the form of an aqueous solution of peroxyacid or alternatively in the form of an ammonium, alkali metal or alkaline earth metal salt of this peroxyacid.
• the treatment with organic peroxyacid is carried out at a temperature between 35 and 45 ° C.
• the treatment is carried out with organic peroxyacid at atmospheric pressure.
• the duration of this treatment depends on the temperature and the essence of the wood used to prepare the dough, as well as the efficiency of the preceding cooking. Times of about 120 minutes to about 240 minutes are fine, and it is even possible to exceed this limit by about 100% without risking substantial degradation of the mechanical strength properties of the dough.
• the temperature of the treatment is high, that is to say above 45 ° C., it is possible to use shorter times ranging between approximately 45 minutes to approximately 120 minutes.
• the treatment according to the invention can be carried out in any type of apparatus suitable for the treatment of paper pulp by means of acid reagents.
• the retention tank for unbleached pulp present in all bleaching installations and acting as a buffer tank between the wood cooking unit and the pulp bleaching unit is particularly suitable for carrying out the process according to the invention.
• the dough can thus be treated there during its storage without requiring the investment of an expensive specific device.
• the ability to safely exceed the normal duration of treatment is particularly well suited to the role of storage buffer for the retention tank.
• the consistency of the treatment step with organic peroxyacid will generally be chosen between 2 and 40% of dry matter and, more often, between 10 and 40%. High consistencies are preferred, for example those between 20 and 40%.
• the amount of organic peroxyacid used is chosen as a function of the level of residual lignin in the pulp as well as the average duration of the treatment. Generally, amounts of between 0.5 and 4% by weight of peroxyacid relative to the dry pulp are very suitable. Most often, an amount of peroxyacid will not be used which does not exceed 3% by weight relative to the dry paste and greater than 1% of this weight.
• a decontaminating pretreatment step using an acidic aqueous solution.
• the purpose of this step is to extract from the pulp the impurities present in the form of metal ions which are detrimental to the proper conduct of the bleaching and / or delignification operations.
• All the inorganic or organic acids used in aqueous solution, alone or as a mixture are suitable. Strong inorganic acids such as, for example, sulfuric acid or hydrochloric acid are well suited.
• the acid decontaminating pretreatment is also carried out in the presence of an agent complexing metal ions.
• mixtures of the strong inorganic acids mentioned above with organic acids from the class of aminopolycarboxylic or aminopolyphosphonic acids or their alkali metal salts are particularly suitable.
• suitable aminopolycarboxylic acids are diethylenetriaminepentaacetic acid, ethylenediaminetetraacetic acid, cyclohexanediaminetetraacetic acid and nitrilotriacetic acid.
• Diethylenetriaminepentaacetic acid (DTPA) is preferred.
• aminopolyphosphonic acids are diethylenetriaminepentamethylene phosphonic acid (DTMPA), ethylenediaminetetra acid (methylenephosphonic), cyclohexanediamine-tetramethylenephosphonic acid (CDTMPA) and nitrilotri acid (methylenephosphonic acid). DTMPA is preferred.
• the operating conditions for the acid decontaminant pretreatment are not critical. They must be determined in each particular case according to the type of paper pulp and the equipment in which the treatment is carried out. In general, the choice of acid and the quantity used should be fixed to impose on the medium a pH of less than 7, for example between approximately 1 and approximately 6.5. Especially advantageous pHs are those between about 2.0 and about 5.0. Temperature and pressure are not critical, with room temperature and atmospheric pressure generally suitable. The duration of the pretreatment can vary within wide limits depending on the type of equipment used, the choice of acid, the temperature and the pressure, for example from about 15 minutes to several hours.
• the latter are chosen from the same complexing agents as those described above for the decontaminating kneading step.
• Example 1 R unlike the other three examples, did not include washing the dough with water between the step of treatment with peracetic acid and the step of alkaline extraction.
• the hydrogen peroxide present in the alkaline extraction step of Example 1 R also comes from the residual hydrogen peroxide of the step with peracetic acid which preceded.
• the step with peracetic acid was preceded by an acid pretreatment using diethylenetriaminepentaacetic acid or DTPA (step Q).
• peracetic acid aqueous solution of commercial quality and contained hydrogen peroxide in equilibrium with peracetic acid (2.6 b of H 2 O 2 per 100 a of dry paste).

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• 1992
  • 1992-09-25 EP EP97122629A patent/EP0844328A3/de not_active Withdrawn
  • 1992-09-25 DE DE69226143T patent/DE69226143T2/de not_active Expired - Fee Related
  • 1992-09-25 ES ES92202952T patent/ES2120984T3/es not_active Expired - Lifetime
  • 1992-09-25 EP EP92202952A patent/EP0535741B1/de not_active Revoked
  • 1992-09-25 AT AT92202952T patent/ATE168149T1/de not_active IP Right Cessation
  • 1992-09-28 AU AU25382/92A patent/AU660326B2/en not_active Ceased
  • 1992-10-01 PL PL92296122A patent/PL171990B1/pl unknown
  • 1992-10-02 FI FI924448A patent/FI924448A/fi not_active Application Discontinuation
  • 1992-10-02 NZ NZ244592A patent/NZ244592A/en unknown
  • 1992-10-05 JP JP4266321A patent/JPH05195467A/ja active Pending

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