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 of delignification of a chemical paper pulp. It particularly concerns a process for improving the selectivity of such an operation delignification.
• the first step in a sequence conventional chemical pulp bleaching aims to perfect the delignification of the unbleached dough as it is present after the cooking operation.
• This first step delignifying is traditionally carried out by treating the dough unbleached by chlorine in an acid medium or by a chlorine association - chlorine dioxide, in mixture or in sequence, so as to react with the residual lignin from the pulp and give rise to chlorolignins which can be extracted from the pulp by solubilization of these chlorolignins in an alkaline medium in a step further processing.
• FR-A-1 014 536 a chemical wood pulp is first treated with hypochlorite and then with a peracid at low temperatures.
• FR-A-1 014 536 can possibly be carried out in a single step with peracid.
• JP-A-57 21591 discloses a bleaching process in which we perform a Paa step, and we add to the medium from this sodium hydroxide step to activate the residual peroxide, without washing between the Paa and Ep stages.
• the invention aims to remedy the drawbacks of the methods known by providing a process which achieves delignification efficiency of unbleached chemical pulp with selectivity which allows the production of pasta with high intrinsic qualities.
• the invention relates to a method for improving the selectivity of the delignification of a dough chemical paper using an organic peroxyacid that treating the unbleached dough from the cooking operation by an aqueous solution of this organic peroxyacid at a temperature between 2 and 47 ° C.
• chemical paper pulp designate pasta that has undergone a minor treatment by presence of chemical reagents such as sodium sulfide in alkaline medium (kraft or sulphate cooking), anhydride sulfurous or a metallic salt of sulfurous acid in the middle acid (sulphite cooking).
• chemical reagents such as sodium sulfide in alkaline medium (kraft or sulphate cooking), anhydride sulfurous or a metallic salt of sulfurous acid in the middle acid (sulphite cooking).
• Semi-chemical pastes such as those where cooking was carried out using an acid salt sulfurous in neutral medium (cooking with neutral sulfite again called NSSC cooking) or those obtained by cold caustic soda followed by mechanical defibration can also be bleached and / or delignified by the process according to the invention.
• the organic peroxyacid is selected among the aliphatic carboxylic peroxyacids comprising a only percarboxylic group and a saturated alkyl chain linear or branched with less than 11 carbon atoms.
• the aliphatic carboxylic peroxyacids with saturated alkyl chain linear with less than 6 carbon atoms are preferred. Examples of such peroxyacids are performic acid, peracetic acid, perpropanoic acid, acid n-perbutanoic and n-perpentanoic acid.
• Peracetic acid is particularly preferred because of its effectiveness and its good biodegradable properties.
• the peroxyacid organic is selected from diperoxyacids carboxylic comprising a linear or branched alkyl chain of less than 16 carbon atoms and two percarboxylic groups substituted on carbon atoms located in position alpha-omega relative to each other.
• Examples of such peroxyacids are 1,6-diperoxyhexanedioic acid, acid 1,8-diperoxyoctanedioic acid and 1,10-diperoxydecanedioic acid, and 1,12-diperoxydodecanedioic acid.
• the organic peroxyacid is selected from peroxyacids aromatics comprising at least one percarboxylic group by benzene nucleus.
• peroxyacids aromatics which have only one percarboxylic group by benzene nucleus.
• An example of such an acid is peroxybenzoic acid.
• Another variant of the process according to the invention consists in choose an organic peroxyacid substituted by one or more halogen atoms or any other functional substituent organic.
• any other organic functional substituent intends to designate a functional group such as the group carbonyl (ketone, aldehyde or carboxylic acid), the group alcohol, nitrogen-containing groups such as nitrile, nitro, amine and amide groups, the groups containing sulfur such as the sulfo and mercapto groups.
• the peroxyacid can indifferently be used at the state of an aqueous solution of peroxyacid or in the form an ammonium, alkali metal, or alkaline earth metal salt of this peroxyacid.
• treatment with organic peroxyacid takes place at a temperature between 35 and 45 ° C.
• the treatment is carried out with peroxyacid organic at atmospheric pressure.
• the duration of this treatment depends on the temperature and the type of wood used prepare the dough, as well as the efficiency of the baking which has preceded. Duration of approximately 120 minutes to approximately 240 minutes agree well, and it is even possible to exceed this limit of about 100% without risk of substantial degradation mechanical strength properties of the dough.
• the treatment temperature is high, i.e. above 45 ° C, it is possible to use shorter durations from about 45 minutes to about 120 minutes.
• the treatment according to the invention can be done in any type of suitable equipment for the treatment of paper pulp using acid reagents.
• the retention tank for the unbleached dough present in all bleaching and playing facilities the role of buffer tank between the wood cooking unit and the dough bleaching unit is particularly suitable for carrying out the method according to the invention.
• the dough can thus be treated there during its storage without requiring the investment of an expensive specific device.
• the faculty of be able 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 peroxyacid treatment step organic will generally be chosen between 2 and 40% of materials dry and, most often, between 10 and 40%. We prefer high consistencies, for example those between 20 and 40%.
• the amount of peroxyacid organic used is chosen according to the rate of residual lignin in the dough as well as the average duration of the treatment. Generally, amounts between 0.5 and 4% by weight of peroxyacid relative to the dry paste agree well. Most often, a quantity of peroxyacid not exceeding 3% by weight with respect to the paste dry and greater than 1% of this weight.
• a step of decontaminating pretreatment with an aqueous solution acid is to extract the dough from the impurities present in the form of metal ions which are harmful to the proper conduct of laundering operations and / or of delignification.
• All inorganic or organic acids used in aqueous solution, alone or as a mixture are suitable. Strong inorganic acids such as, for example, acid sulfuric or hydrochloric acid are suitable.
• the acid decontaminating pretreatment is also carried out in the presence of an ion complexing agent metallic.
• an ion complexing agent metallic metallic.
• mixtures of strong acids inorganic mentioned above with organic acids of the class of aminopolycarboxylic or aminopolyphosphonic acids or their alkali metal salts are suitable particularly well.
• aminopolycarboxylic acids suitable are diethylenetriaminepentaacetic acid, ethylenediaminetetraacetic acid, cyclohexanediaminetetraacetic acid and nitrilotriacetic acid.
• Diethylenetriaminepentaacetic acid (DTPA) is preferred.
• aminopolyphosphonic acids are diethylenetriaminepentamethylenephosphonic acid (DTMPA), ethylenediaminetetra (methylenephosphonic acid), cyclohexanediaminetetramethylenephosphonic acid (CDTMPA) and nitrilotri acid (methylenephosphonic). DTMPA is preferred.
• the operating conditions of the decontaminating pretreatment acid are not critical. They must be determined in each particular case depending on the type of pulp and the apparatus in which the treatment is carried out. Of a in general, the choice of acid and the quantity used to impose on the medium a pH below 7, for example between approximately 1 and approximately 6.5. PH especially advantageous are those between about 2.0 and about 5.0. Temperature and pressure are not critical, ambient temperature and atmospheric pressure generally well suited. The duration of the pretreatment can vary widely depending on the type of equipment used, the choice of acid, temperature and pressure, by example from about 15 minutes to several hours.
• the latter are chosen from the same agents complexing agents than those described above for the decontaminating treatment.
• Example 1R unlike the other three examples, did not involve washing the dough with water between the peracetic acid treatment and extraction step alkaline.
• the hydrogen peroxide present in the step alkaline extraction of Example 1R also comes from residual hydrogen peroxide from the peracetic acid stage which preceded.
• Example 4 according to the invention, we have made precede the peracetic acid step with 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 g of H 2 O 2 per 100 g of dry paste).

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• Life Sciences & Earth Sciences (AREA)
• Engineering & Computer Science (AREA)
• Wood Science & Technology (AREA)
• Paper (AREA)
• Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
• External Artificial Organs (AREA)
• Preliminary Treatment Of Fibers (AREA)

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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 EP EP92202952A patent/EP0535741B1/de not_active Revoked
  • 1992-09-25 AT AT92202952T patent/ATE168149T1/de not_active IP Right Cessation
  • 1992-09-25 ES ES92202952T patent/ES2120984T3/es not_active Expired - Lifetime
  • 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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