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
  • D21C9/1026—Other features in bleaching processes
  • D21C9/1042—Use of chelating agents
• • 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
• • 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

• This invention relates to chlorine free bleaching of pulp from lignocellulosic material.
• the method comprises treat ⁇ ment of the pulp with chelating agent and subsequent bleach ⁇ ing in at least one step with chlorine free bleaching agents .
• the bleaching sequence usually includes only the chemicals oxygen and hydrogen peroxide.
• Hydrogen peroxide is a highly effective bleaching chemical when the bleaching conditions are the right ones.
• brightness levels pf substantially full brightness, i.e. almost 90% ISO have been achieved on mill scale. This presupposes, however, very special con ⁇ ditions, such as that the papermaking pulp is subjected
• a low metal content in the pulp prior to the hydrogen peroxide step is obtained by treating the pulp with a chelating agent, for example EDTA or DTPA , and there ⁇ after to wash the pulp in order to eliminate the released metal ions before the hydrogen peroxide step.
• a chelating agent for example EDTA or DTPA
• This method is described in the patent SE 467 006 (EKA Nobel).
• the treatment with chelating agent shall be carried out between 10-100°C f° r a period of up to 6 hours at a pH between 3.1 and 9.
• EKA Nobel has at a later date, a.o.
• the pulpmaking industry of today manufactures paper ⁇ making pulp mostly by digesting and oxygen bleaching the pulp to a far-reaching degree, whereafter the blea ⁇ ching proper is carried out by using all towers and tanks in the existing plants, so that a very long stay- time in the chelating agent step, and especially in the hydrogen peroxide step, is obtained.
• the pulp is also washed very accurately between the different bleaching steps. Such washing, however, requires large amounts of water, and therefore it cannot be used if and when the bleach plants must be closed at their effluent, which in most pulp mills will be required in order to meet various environmental obligations.
• the present invention has the object to solve the aforesaid problems. It implies, that papermaking pulp can be bleached with chlorine free chemicals in an effectively closed system without forming disturbing in- crustrations .
• the invention is described in greater detail in the following by way of some embodiments thereof.
• the invention is directed to chlorine free bleaching pf pulp, where pH is held above 9, suitably between 9 and 11.5, during the entire delignification and bleaching process.
• the chelating agent step (Q-step) is carried out at a considerably higher than normal pH prior to a subsequent peroxide bleaching (P-step).
• P-step peroxide bleaching
• chelating agents which are active at a con ⁇ siderably higher pH value than that which normally is used at bleaching according to SE-patent 467 006 (see above).
• the chelating agent EDTA normally used is a poor chelating agent at alkaline conditions and can . be replaced, for example, by DTPA, which is active evwn at higher pH.
• Incrustrat- ions normally become a problem difficult solve when the bleach plant is closed, because the concentrations of a.o. calcium, barium, oxalate, carbonate and sul ⁇ phate can increase above the solubility maximum, which results in precipitations to begin to form.
• some type of initiation of the precipitation process is also required, for example via a pH or temperature change, in order to cause the precipitation to start, but in that case the precipitation can proceed very rapidly.
• Another advantage is, that the metals and a.o.
• the transistion metals dangerous for the process i.e. especially manganese, further can be oxidized by adding an oxidation agent, so that their capacity of degrading peroxide is reduced, alter ⁇ natively entirely eliminated.
• the oxidation of these metals is carried out preferably with oxygen gas and/or hydrogen peroxide at a temperature of above 75 C prior to the bleaching with chlorine free bleaching agents, such as hydrogen peroxide.
• a suggested suitable sequence comprises: digestion - Q-step - 02 ⁇ delignification - Q-step - P-step.
• An initiating chelating agent step and an oxygen step thus, can be carried out directly after the digestion. Thereafter the treatment proper with chelating agent is carried out prior to the hydrogen peroxide bleach ⁇ ing.
• the pH value shall be held above 9, suitably at 9-11, preferably at 9-11.5, through the entire sequence.
• Both Q-steps can advantageously be carried out in the presence of oxidation agent, preferably oxygen and/or hydrogen peroxide for the oxidation of metals present. The metals become thereby less disturbing for the bleaching.
• bleachings can be carried out where oxygen and/or peracids can be used.
• the bleach ⁇ ing preferably is carried out in at least two oxidiz ⁇ ing steps, where hydrogen peroxide and oxygen can be used in the same bleaching step.
• the charge should be 1-10 kg (100%-product) per ton pulp, preferably 2-5 kg per ton pulp.
• the invention also implies that an effluent-free pro ⁇ cess can be obtained.
• the process is preferably closed in such a way, that washing steps are carried out after every treatment step (Q-step and, respectively, bleaching step), and the filtrate from every washing step is recycled as washing liquid in preceding washing steps.
• a high and uniform pH level being maintained during the entire process, no precipitations of in- crustrations occur, in spite of the closing of the bleaching process.

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• Life Sciences & Earth Sciences (AREA)
• Engineering & Computer Science (AREA)
• Wood Science & Technology (AREA)
• Paper (AREA)

Priority Applications (3)

Applications Claiming Priority (2)

Publications (1)

Family

ID=20398166

Family Applications (1)

Country Status (6)

Cited By (3)

Citations (2)

• 1995
  • 1995-05-02 SE SE9501623A patent/SE9501623L/ not_active Application Discontinuation
• 1996
  • 1996-03-27 CA CA002219767A patent/CA2219767A1/en not_active Abandoned
  • 1996-03-27 JP JP8533220A patent/JPH11504399A/ja active Pending
  • 1996-03-27 WO PCT/SE1996/000405 patent/WO1996035015A1/en active Application Filing
• 1997
  • 1997-10-31 NO NO975038A patent/NO975038D0/no unknown
  • 1997-11-03 FI FI974115A patent/FI974115A0/fi unknown

Patent Citations (2)

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