WO1993014262A1 - Bleaching of chemical pulp - Google Patents

Bleaching of chemical pulp Download PDF

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Publication number
WO1993014262A1
WO1993014262A1 PCT/SE1993/000012 SE9300012W WO9314262A1 WO 1993014262 A1 WO1993014262 A1 WO 1993014262A1 SE 9300012 W SE9300012 W SE 9300012W WO 9314262 A1 WO9314262 A1 WO 9314262A1
Authority
WO
WIPO (PCT)
Prior art keywords
pulp
bleaching
complexing agent
consistency
peroxide
Prior art date
Application number
PCT/SE1993/000012
Other languages
French (fr)
Inventor
Lars-Åke LINDSTRÖM
Lars SJÖDIN
Solveig Norden
Mårten DAHL
Original Assignee
Sunds Defibrator Industries Aktiebolag
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Family has litigation
First worldwide family litigation filed litigation Critical https://patents.darts-ip.com/?family=20385065&utm_source=google_patent&utm_medium=platform_link&utm_campaign=public_patent_search&patent=WO1993014262(A1) "Global patent litigation dataset” by Darts-ip is licensed under a Creative Commons Attribution 4.0 International License.
Application filed by Sunds Defibrator Industries Aktiebolag filed Critical Sunds Defibrator Industries Aktiebolag
Priority to JP5512379A priority Critical patent/JPH07503042A/en
Priority to DE69309893T priority patent/DE69309893T2/en
Priority to EP93902618A priority patent/EP0621915B1/en
Priority to BR9305761A priority patent/BR9305761A/en
Priority to AU34125/93A priority patent/AU653467B2/en
Publication of WO1993014262A1 publication Critical patent/WO1993014262A1/en
Priority to FI943431A priority patent/FI943431A/en
Priority to NO942718A priority patent/NO942718L/en

Links

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
    • D21C9/147—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
    • D21C9/1057—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
    • 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

  • This invention relates to the bleaching of sulphate pulp without using bleaching agents containing chlorine.
  • the technique of bleaching chemical pulps is now developing rapidly, because the bleaching chemicals heretofore mainly used, CI 2 , ClO 2, and hypochl-orite, are feared to give rise to products being a risk for the environment and health.
  • Extended digestion with maintained pulp quality can be achieved by impregnating the chips with black liquor in the initial phase of the cook, as described in Finnish patent application 90 0663.
  • This method renders it possible to digest pulp down to a kappa number of about 10 and obtain strength properties equal to or better than with pulp digested to conventional level, kappa number 25-30. Combined with oxygen delignification, kappa numbers as low as 5-6 can be obtained for.further bleaching.
  • the present invention implies, that fully bleached pulp with a brightness above 83% ISO can be made without the use of chlorine-containing bleaching agents.
  • the pulp shall have a kappa number below 9.5. This can be achieved by conventional or extended digestion followed by O 2 -delignification, alternatively by conventional or extended digestion followed by O 2 - and O 3 -delignification.
  • the bleaching is initiated by a pretreatment step with complexing agent followed by treatment with hydroperoxide in alkaline environment in the presence of silicate or an organic complexing agent of the type phosphonic or carboxylic acid.
  • the pulp digested and delignified with oxygen and possibly ozone according to above shall have a kappa number below 9.5. This can be achieved by known methods of digestion and delignification.
  • the pulp shall thereafter be pretreated with complexing agent, for example EDTA or DTPA, at a pulp consistency of 1-15% for 1-60 minutes, preferably 5-30 minutes.
  • the temperature shall be 70-100°C, preferably 80-100°C, and the pH-value 5-7.
  • the pulp thus pretreated is washed and dewatered to a consistency of 18-4.0%, preferably 20-30%.
  • the pH-value is increased to alkaline level, and hydroperoxide is added together with silicate, for example sodium silicate, alternatively together with an organic complexing agent of the type phosphonic or carboxylic acid.
  • the dwell time of the pulp in this hydroperoxide step shall be 1/2 - 5 hours, preferably 1-4 hours, and the temperature 70-100°C, preferably 80-100°C.
  • the silicate charge shall be 2-30 kg/ton pulp, preferably 5-15 kg/ton pulp, expressed as SiO 2 .
  • the charge of the organic complexing agent shall be 0.5-5 kg/ton pulp.
  • Fig. 1 is a diagram, in which the brightness of the pulp is plotted as a function of the pulp consistency at the peroxide bleaching,partly at conventional peroxide bleaching and partly at bleaching according to the invention.
  • the starting pulp was oxygen-delignified coniferous wood sulphate pulp with kappa number 6.5 (10.5 after digestion).
  • Curve 1 showg. conventional peroxide bleaching, with a consumption of H 2 O 2 of 20 kg/ton pulp.
  • Curve 2 and, respectively, 3 refer to bleaching according to the invention with silicate addition and a consumption of H 2 O 2 of 20 and, respectively, 30 kg/ton pulp. It appears from the diagram how the brightness, after bleaching according to the invention and, respectively, after conventional bleaching, depends on the pulp consistency. At about 12% pulp consistency, the brightness obtained is" equal in both cases, but at increased pulp consistency in the peroxide step an increased brightness is obtained according to the invention, while conventional peroxide bleaching results in a deteriorated bright- ness.
  • a coniferous wood sulphate pulp with kappa number 13.3 (digested of Scandinavian fir/pine according to Finnish patent application 90 0663), oxygen delignified to kappa number 8.3 and ozone bleached in acid environment to kappa number 3.2, brightness 61% ISO, intrinsic viscosity 582 dm 3 /kg, was bleached according to the invention.

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

Abstract

A method of bleaching sulphate pulp without using chlorine-containing bleaching agents. The sulphate pulp is oxygen delignified and can possibly also be ozone delignified to a kappa number below 9.5. Thereafter a pretreatment with complexing agent is carried out for 1-60 minutes, at which the pulp consistency is 1-15 %, the temperature 70-110 °C and pH 5-7. The pulp thus pretreated is washed and dewatered to a consistency of 18-40 %. Thereafter peroxide bleaching in alkaline environment takes place in the presence of silicate or an organic complexing agent of the type phosphonic or carboxylic acid.

Description

Bleaching of chemical pulp
This invention relates to the bleaching of sulphate pulp without using bleaching agents containing chlorine. The technique of bleaching chemical pulps is now developing rapidly, because the bleaching chemicals heretofore mainly used, CI2, ClO2, and hypochl-orite, are feared to give rise to products being a risk for the environment and health.
Until now, the discussions have been concentrated on the emissions of chlorinated organic substance to the recipient. The majority of the countries in the world have now established limit values for these emissions, which normally are measured as AOX (Adsorbable organic halogens). As a new trend, the customers require to an ever increasing degree paper with a low content of chlorinated organic substance.
Conventional bleaching with Cl2 disappears now more and more, and CI2 is replaced primarily by ClO2. Bleaching with CIO2 causes substantially lower AOX-emissions to the recipient, but the amount of chlorinated substance in the pulp is affected only insignificantly.
In recent years, the use of hydroperoxide at the bleaching of chemical pulps has increased considerably. Hydroperoxide can replace part of the chlorine chemicals.
In patent application SE 89 02058-0, a method is described at which the pulp is pretreated with complexing agent under neutral conditions. By this process, coniferous sulphate pulp can be bleached with peroxide-containing bleaching agents to 70-75% ISO at about 10% pulp consistency. In order to achieve fully bleached pulp qualities., with higher ISO-brightness (above 83% ISO), this process can be combined with final bleaching with CIO2. As a result, th-is final bleaching then yields emission of AOX from the bleach plant and chlorinated organic susbstance in the bleached pulp. Other known methods of reducing emissions of chlorinated organic substance to the recipient are to extend the delignification further in the closed part of the mill, i.e. in the digester house and/or oxygen step.
Extended digestion with maintained pulp quality can be achieved by impregnating the chips with black liquor in the initial phase of the cook, as described in Finnish patent application 90 0663. This method renders it possible to digest pulp down to a kappa number of about 10 and obtain strength properties equal to or better than with pulp digested to conventional level, kappa number 25-30. Combined with oxygen delignification, kappa numbers as low as 5-6 can be obtained for.further bleaching.
By combining conventional digestion, oxygen delignificat- ion and ozone bleaching in acid environment, kappa numbers lower than 10 can be obtained.
It has, however, not been possible to produce fully bleached pulp qualities without final bleaching with ClO2.
The present invention implies, that fully bleached pulp with a brightness above 83% ISO can be made without the use of chlorine-containing bleaching agents.
At the start of the bleaching, the pulp shall have a kappa number below 9.5. This can be achieved by conventional or extended digestion followed by O2-delignification, alternatively by conventional or extended digestion followed by O2- and O3-delignification. The bleaching is initiated by a pretreatment step with complexing agent followed by treatment with hydroperoxide in alkaline environment in the presence of silicate or an organic complexing agent of the type phosphonic or carboxylic acid. The characterizing features of the invention are apparent from the attached claims.
The pulp digested and delignified with oxygen and possibly ozone according to above shall have a kappa number below 9.5. This can be achieved by known methods of digestion and delignification. The pulp shall thereafter be pretreated with complexing agent, for example EDTA or DTPA, at a pulp consistency of 1-15% for 1-60 minutes, preferably 5-30 minutes. The temperature shall be 70-100°C, preferably 80-100°C, and the pH-value 5-7.
The pulp thus pretreated is washed and dewatered to a consistency of 18-4.0%, preferably 20-30%. The pH-value is increased to alkaline level, and hydroperoxide is added together with silicate, for example sodium silicate, alternatively together with an organic complexing agent of the type phosphonic or carboxylic acid. The dwell time of the pulp in this hydroperoxide step shall be 1/2 - 5 hours, preferably 1-4 hours, and the temperature 70-100°C, preferably 80-100°C. The silicate charge shall be 2-30 kg/ton pulp, preferably 5-15 kg/ton pulp, expressed as SiO2.
Alternatively, the charge of the organic complexing agent shall be 0.5-5 kg/ton pulp.
Fig. 1 is a diagram, in which the brightness of the pulp is plotted as a function of the pulp consistency at the peroxide bleaching,partly at conventional peroxide bleaching and partly at bleaching according to the invention.
The starting pulp was oxygen-delignified coniferous wood sulphate pulp with kappa number 6.5 (10.5 after digestion). Curve 1 showg. conventional peroxide bleaching, with a consumption of H2O2 of 20 kg/ton pulp. Curve 2 and, respectively, 3 refer to bleaching according to the invention with silicate addition and a consumption of H2O2 of 20 and, respectively, 30 kg/ton pulp. It appears from the diagram how the brightness, after bleaching according to the invention and, respectively, after conventional bleaching, depends on the pulp consistency. At about 12% pulp consistency, the brightness obtained is" equal in both cases, but at increased pulp consistency in the peroxide step an increased brightness is obtained according to the invention, while conventional peroxide bleaching results in a deteriorated bright- ness.
The following examples have the object to additionally elucidate the invention and its advantages.
Example 1
An oxygen-delignified coniferous wood sulphate pulp
(Scandinavian fir/pine) with kappa number 6.4 (10.5 after digestion according to above Finnish patent application 90 0663), brightness 43% ISO, intrinsic viscosity 605 dur/kg, was pretreated with complexing agent and peroxide bleached according to the invention.
Pretreatment
Pulp consistency % 5
Time min 15
Temperature °C 90
EDTA kg/ton 2
Final pH 6.1
Peroxide step
Pulp consistency % 25
Time min 240
Temperature °C 90
SiO2 kg/ton 10
H2O2 consumption kg/ton 13.5 32.0
Final pH 10.2 10.3
Brightness % ISO 79.6 84.2
Intrinsic viscosity dm3/kg 520 447 Example 2
A coniferous wood sulphate pulp with kappa number 13.3 (digested of Scandinavian fir/pine according to Finnish patent application 90 0663), oxygen delignified to kappa number 8.3 and ozone bleached in acid environment to kappa number 3.2, brightness 61% ISO, intrinsic viscosity 582 dm3/kg, was bleached according to the invention.
Pretreatment as in Example 1
Peroxide bleaching
Pulp consistency % 25
Time min 24.0
Temperature °C 90
SiO2 kg/ton 10
H2O2 consumption kg/ton 7.3 14.2 30.1
Final pH 8.9 9.5 10.1
Brightness % ISO 85.3 88.4 90.4
Intrinsic viscosity dm3/kg 536 498 420
Example 3
An oxygen delignified coniferous wood sulphate pulp
(digested of Pinus taeda according to Finnish patent application 90 0663) with kappa number 9.9, ozone bleached to kappa number 4.8, brightness 54.5% ISO, intrinsic viscosity 607 dm3/kg was pretreated and bleached according to the invention.
Pretreatment as in Example 1
Peroxide bleaching
Pulp consistency % 25
Time min 240
Temperature °C 90
SiO2 kg/ton 10
H2O2 consumption kg/ton 7.9 14.6 29.6
Final pH 10.2 10.4 10.6 Brightness % ISO 81.3 85.3 87.8
Intrinsic viscosity dm3/kg 570 534 459
Example 4
An oxygen delignified birch sulphate pulp with kappa number 9.0, brightness 59.4% ISO and intrinsic viscosity 996 dm3/kg was bleached according to the invention.
Pretreatment as in Example 1
Peroxide bleaching
Pulp consistency % 25
Time min 240
Temperature °C 90
SiO2 kg/ton 10
H2O2 consumption kg/ton 8.5 17.5 35
Final pH 10.2 10.4 10.5
Brightness % ISO 82.2 85.5 86.5
Intrinsic viscosity dm3/kg 903 975 822
The invention is not restricted to the embodiments set forth above , but can be varied within the scope of the invention idea.

Claims

Claims
1. A method of bleaching sulphate pulp without using chlorine-containing bleaching agents, comprising oxygen delignification and possibly ozone delignification of the pulp to a kappa number below 9.5 and subsequent
peroxide bleaching, c h a r a c t e r i z e d i n
that the pulp directly after the delignification is
pretreated with complexing agent for 1-60 minutes,
the pulp consistency being 1-15%, the temperature 70-110°C and pH 5-7, and that the pulp thus pretreated is washed and dewatered to a consistency of 18-40% and thereafter peroxide bleached in alkaline environment in the presence of silicate or an organic. complexing agent of the type phosphonic or carboxylic acid.
2. A method as defined in claim 1, c h a r a c t e r i z e d i n that the peroxide bleaching is carried out for 1/2-5 hours at the temperature 70-110°C.
3. A method as defined in claim 1 or 2, c h a r a c te r i z e d i n that as complexing agent at the
pretreatment EDTA or DTPA is used.
4. A method as defined in any one of the preceding claims, c h a r a c t e r i z e d i n that at the peroxide bleaching silicate is added in an amount of
2-30 kg/ton pulp, expressed as SiO2.
5. A method as defined in any one of the claims 1-3, c h a r a c t e r i z e d i n that at the peroxide bleaching an organic complexing agent of the type phosphonic acid or carboxylic acid is added in an amount of
0.5-5 kg/ton pulp.
6. A method as defined in any one of the preceding claims, c h a r a c t e r i z e d i n that the
bleaching is carried out to a brightness exceeding 83% ISO.
PCT/SE1993/000012 1992-01-21 1993-01-12 Bleaching of chemical pulp WO1993014262A1 (en)

Priority Applications (7)

Application Number Priority Date Filing Date Title
JP5512379A JPH07503042A (en) 1992-01-21 1993-01-12 chemical pulp bleaching
DE69309893T DE69309893T2 (en) 1992-01-21 1993-01-12 BLEACHING OF CHEMICAL PULP
EP93902618A EP0621915B1 (en) 1992-01-21 1993-01-12 Bleaching of chemical pulp
BR9305761A BR9305761A (en) 1992-01-21 1993-01-12 Sulfate pulp bleaching process
AU34125/93A AU653467B2 (en) 1992-01-21 1993-01-12 Bleaching of sulphate pulp
FI943431A FI943431A (en) 1992-01-21 1994-07-20 Bleaching of chemical pulp
NO942718A NO942718L (en) 1992-01-21 1994-07-20 Bleaching of chemical pulp

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
SE9200152A SE469842C (en) 1992-01-21 1992-01-21 Bleaching of chemical pulp with peroxide
SE9200152-8 1992-01-21

Publications (1)

Publication Number Publication Date
WO1993014262A1 true WO1993014262A1 (en) 1993-07-22

Family

ID=20385065

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/SE1993/000012 WO1993014262A1 (en) 1992-01-21 1993-01-12 Bleaching of chemical pulp

Country Status (14)

Country Link
EP (1) EP0621915B1 (en)
JP (1) JPH07503042A (en)
AT (1) ATE151826T1 (en)
AU (1) AU653467B2 (en)
BR (1) BR9305761A (en)
CA (1) CA2124088A1 (en)
DE (1) DE69309893T2 (en)
ES (1) ES2102008T3 (en)
FI (1) FI943431A (en)
NO (1) NO942718L (en)
NZ (1) NZ246713A (en)
SE (1) SE469842C (en)
WO (1) WO1993014262A1 (en)
ZA (1) ZA93317B (en)

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1994029512A1 (en) * 1993-06-08 1994-12-22 Kvaerner Pulping Technologies Ab Method of bleaching pulp without using chlorine chemicals
WO1996006976A1 (en) * 1994-08-31 1996-03-07 Sunds Defibrator Industries Ab Pulp bleaching
EP0720676A1 (en) * 1993-09-02 1996-07-10 Union Camp Patent Holding, Inc. Improved method for bleaching lignocellulosic pulp
EP0578304B1 (en) * 1992-07-06 1996-09-18 SOLVAY INTEROX (Société Anonyme) Process for bleaching a chemical paper pulp
US5571377A (en) * 1993-06-08 1996-11-05 Kvaerner Pulping Technologies Ab Process for peroxide bleaching of chemical pulp in a pressurized bleach vessel
EP0759105B1 (en) * 1994-05-11 1998-12-02 Elf Atochem S.A. Method for preparing delignified and bleached chemical paper pulps
EP0728238B1 (en) * 1993-11-10 1999-01-13 SOLVAY INTEROX (Société Anonyme) Method of bleaching chemical paper pulp

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
BE1004674A3 (en) * 1991-03-11 1993-01-12 Interox Internat Sa Method of laundering of chemical pulp and application of the method of laundering pulp kraft.

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0262836A1 (en) * 1986-09-15 1988-04-06 The Dow Chemical Company Improved process for the bleaching of cellulosic pulps using hydrogen peroxide
US4938842A (en) * 1986-08-20 1990-07-03 Abitibi-Price Inc. High consistency peroxide bleaching
EP0402335A2 (en) * 1989-06-06 1990-12-12 Eka Nobel Ab Process for bleaching lignocellulose-containing pulps
WO1991012368A1 (en) * 1990-02-09 1991-08-22 Sunds Defibrator Rauma Oy Process for preparing kraft pulp

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4938842A (en) * 1986-08-20 1990-07-03 Abitibi-Price Inc. High consistency peroxide bleaching
EP0262836A1 (en) * 1986-09-15 1988-04-06 The Dow Chemical Company Improved process for the bleaching of cellulosic pulps using hydrogen peroxide
EP0402335A2 (en) * 1989-06-06 1990-12-12 Eka Nobel Ab Process for bleaching lignocellulose-containing pulps
WO1991012368A1 (en) * 1990-02-09 1991-08-22 Sunds Defibrator Rauma Oy Process for preparing kraft pulp

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
Journal of Wood Chemistry and Technology, Volume 2, No. 3, 1982, GOERAN GELLERSTEDT et al., "Chemical Aspects of Hydrogen Peroxide Bleaching", page 231 - page 250, esp. page 233, line 29 - line 33. *

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0578304B1 (en) * 1992-07-06 1996-09-18 SOLVAY INTEROX (Société Anonyme) Process for bleaching a chemical paper pulp
WO1994029512A1 (en) * 1993-06-08 1994-12-22 Kvaerner Pulping Technologies Ab Method of bleaching pulp without using chlorine chemicals
US5571377A (en) * 1993-06-08 1996-11-05 Kvaerner Pulping Technologies Ab Process for peroxide bleaching of chemical pulp in a pressurized bleach vessel
EP0720676A1 (en) * 1993-09-02 1996-07-10 Union Camp Patent Holding, Inc. Improved method for bleaching lignocellulosic pulp
EP0720676A4 (en) * 1993-09-02 1998-03-04 Union Camp Patent Holding Improved method for bleaching lignocellulosic pulp
EP0728238B1 (en) * 1993-11-10 1999-01-13 SOLVAY INTEROX (Société Anonyme) Method of bleaching chemical paper pulp
EP0759105B1 (en) * 1994-05-11 1998-12-02 Elf Atochem S.A. Method for preparing delignified and bleached chemical paper pulps
WO1996006976A1 (en) * 1994-08-31 1996-03-07 Sunds Defibrator Industries Ab Pulp bleaching
CN1065578C (en) * 1994-08-31 2001-05-09 瑞典商顺智公司 Pulp bleaching
US6540872B1 (en) 1994-08-31 2003-04-01 Velmet Fibertech Aktiebolag Process for chlorine dioxide bleaching using a chelating agent without an intermediate wash

Also Published As

Publication number Publication date
SE9200152D0 (en) 1992-01-21
NO942718D0 (en) 1994-07-20
BR9305761A (en) 1997-01-28
FI943431A0 (en) 1994-07-20
CA2124088A1 (en) 1993-07-22
DE69309893T2 (en) 1997-11-06
NZ246713A (en) 1995-04-27
ES2102008T3 (en) 1997-07-16
EP0621915B1 (en) 1997-04-16
AU653467B2 (en) 1994-09-29
AU3412593A (en) 1993-08-03
SE9200152L (en) 1993-07-22
NO942718L (en) 1994-07-20
DE69309893D1 (en) 1997-05-22
JPH07503042A (en) 1995-03-30
ZA93317B (en) 1993-08-19
SE469842C (en) 1996-01-15
FI943431A (en) 1994-07-20
EP0621915A1 (en) 1994-11-02
ATE151826T1 (en) 1997-05-15
SE469842B (en) 1993-09-27

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