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
  • D21C9/1057—Multistage, with compounds cited in more than one sub-group D21C9/10, D21C9/12, D21C9/16
• • 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
  • D21C9/147—Bleaching ; Apparatus therefor with oxygen or its allotropic modifications
  • D21C9/153—Bleaching ; Apparatus therefor with oxygen or its allotropic modifications with ozone
• • 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

Definitions

• the present invention relates to a method of bleaching pulp. It relates especially to novel pro-environmental bleaching process types used in the wood-processing in ⁇ dustry, in which methods the chlorine chemicals are replaced by other bleaching chemicals involving dis ⁇ charges less harmful to the environment.
• Cellulose pulp is traditionally bleached with chlorine- containing chemicals, such as chlorine gas and chlorine dioxide.
• chlorine- containing chemicals such as chlorine gas and chlorine dioxide.
• the chlorine compounds generating in bleaching processes are unpleasent because they are malodorous and also because they cause problems in the purification of the effluents.
• the environmental requirements on the cellulose industry have become more strict, and therefore there is a tendency to use more and more chlorine-free/non-chlorine bleaching chemicals, such as peroxide and ozone.
• Peroxide and ozone bleaching are both known bleaching processes. However, replacing chlorine chemicals with peroxide or ozone has not always led to final products of sufficient quality.
• the present invention relates to a method of bleaching pulp in such a way that peroxide and ozone bleaching is intensified with metal stripping, acidation and enzyme treatment.
• a Q refers to acid stage, in which a complex former, such as EDTA, is used for removing metal ions.
• a complex former such as EDTA
• a eQ refers to acidation stage, in both the complex former and entzymes are used.
• Complex formers are substances, which are used for removing metal ions from the pulp stock because the metal ions decompose peroxide and ozone and thus decrease the bleaching efficiency.
• Entzymes are used for treating the fibers in such a way that the bleaching chemicals may more readily affect the lignin. Entzymes partly cause the fiber walls to swell and partly open pores.
• hot alkali extraction stage is an alkali stage, in which the temperature is above 90°C, preferably above 100°C.
• the pores of the fiber swell in such a way that the bleaching chemical is better able to react and also the residual lignin may be more readily extracted from the fiber walls.
• the phenomenon illustrated in the above example 1 may be utilized in many ways.
• the brightness may further be increased by using ozone.
• An ozone stage is preferably added to follow the acid stage, because ozone requires acid conditions to act.
• Appropriate points for ozone bleaching are pointed out in the following sequence with (Z). Normally it is reasonable to add one or two ozone stages at most in a bleaching sequence.
• the sequences using ozone as an additional chemical for peroxide bleaching, are thus: 0-A Q -( Z )-P-A e -(Z )-P-(Z ) .
• the combination A e Z means that there is no washing between the A- and Z- stages.
• the dash “-" means that there is either a washing or pressing stage between the stages.
• HAE-stage between the peroxide stages has not yet been tested more accurately in the laboratory. Since the peroxide stages are hot, it might be possible to position a HAE-stage between the P-stages.
• the purpose of the HAE-stage would correspond to that of A e -stage.
• the temperature of the HAE-stage might be, for example, 120°C.
• a suitable bleaching sequence would therefore be, for example,
• HAE-stage HAE-stage
• HAE p peroxide to the HAE-stage
• the sequence might then be 0-A Q - P-HAE p -Z or 0-A Q -HAE p -P-Z, although the ozone stage may, if required, also be positioned subsequent to the A Q -stage either to replace the ozone stage in the above described sequence or to add a second ozone stage to the sequence.
• the pulp was digested to a kappa number 20-25 prior to the oxygen bleaching, in which the kappa number decreased to 12 - 16.
• the bleaching sequence subsequent to the digestion was 0-A eQ -EPO-A e -P.
• EPO means peroxide stage, in which also oxygen is used.

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

Applications Claiming Priority (3)

Publications (1)

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ID=8536209

Family Applications (1)

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Family Cites Families (4)

• 1992
  • 1992-11-13 FI FI925159A patent/FI925159A0/fi not_active Application Discontinuation
• 1993
  • 1993-09-14 EP EP93919365A patent/EP0669999A1/de not_active Withdrawn
  • 1993-09-14 CA CA 2149332 patent/CA2149332A1/en not_active Abandoned
  • 1993-09-14 WO PCT/FI1993/000362 patent/WO1994011568A1/en not_active Application Discontinuation
  • 1993-09-14 JP JP6511734A patent/JPH08503267A/ja active Pending
  • 1993-09-14 BR BR9307443A patent/BR9307443A/pt not_active Application Discontinuation

Non-Patent Citations (1)

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