EP0621915B1 - Bleaching of chemical pulp - Google Patents
Bleaching of chemical pulp Download PDFInfo
- Publication number
- EP0621915B1 EP0621915B1 EP93902618A EP93902618A EP0621915B1 EP 0621915 B1 EP0621915 B1 EP 0621915B1 EP 93902618 A EP93902618 A EP 93902618A EP 93902618 A EP93902618 A EP 93902618A EP 0621915 B1 EP0621915 B1 EP 0621915B1
- Authority
- EP
- European Patent Office
- Prior art keywords
- pulp
- bleaching
- complexing agent
- peroxide
- consistency
- Prior art date
- Legal status (The legal status 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 status listed.)
- Expired - Lifetime
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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 a method of delignifying and bleaching of sulphate pulp without using bleaching agents containing chlorine.
- the method comprises oxygen delignification and possibly ozone delignification of the pulp and subsequent peroxide bleaching.
- EP-A-402 335 a method is described at which the pulp is pretreated with complexing agent under neutral conditions.
- coniferous sulphate pulp can be bleached with peroxide-containing bleaching agents to 70-75% ISO at about 10% pulp consistency.
- this process can be combined with final bleaching with Cl0 2 .
- this final bleaching then yields emission of AOX from the bleach plant and chlorinated organic substance in the bleached pulp.
- 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 WO-A- 91/12368.
- 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 sulphate pulp with a brightness above 83% ISO can be made without the use of chlorine-containing bleaching agents.
- the pulp shall have a low kappa number. 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 for 1-60 minutes, the pulp consistency being 1-15%, the temperature 70-110°C and pH 5-7, followed by treatment with hydrogen peroxide.
- 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 18-40%, preferably 20-30%.
- the pH-value is increased to alkaline level, and peroxide 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 peroxide step shall be 1/2-5 hours, preferably 1-4 hours, and the temperature 70-110°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 shows 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, respetively, 30 kg/ton pulp.
- Pulp consistency % 25 Time min. 240 Temperature °C 90 SiO 2 kg/ton 10 H 2 O 2 consumption kg/ton 13.5 32.0 Final pH 10.2 10.3 Brightness % ISO 79.6 84.2 Intrinsic viscosity dm 3 /kg 520 447
- a coniferous wood sulphate pulp with kappa number 13.3 (digested of Scandinavian fir/pine according to WO-A- 91/12368), 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 pretreated and bleached according to the invention.
- Pulp consisstency % 25 Time min. 240 Temperature °C 90 SiO 2 kg/ton 10 H 2 O 2 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 dm 3 /kg 570 534 459
- Pulp consistency % 25 Time min 240 Temperature °C 90 SiO 2 kg/ton 10 H 2 O 2 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 dm 3 /kg 903 975 822
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- Life Sciences & Earth Sciences (AREA)
- Engineering & Computer Science (AREA)
- Wood Science & Technology (AREA)
- Paper (AREA)
- Detergent Compositions (AREA)
Abstract
Description
- This invention relates to a method of delignifying and bleaching of sulphate pulp without using bleaching agents containing chlorine. The method comprises oxygen delignification and possibly ozone delignification of the pulp and subsequent peroxide bleaching.
- The technique of bleaching chemical pulps is now developing rapidly, because the bleaching chemicals heretofore mainly used, Cl2, C102, and hypochlorite, 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 Cl2 is replaced primarily by Cl02. Bleaching with Cl02 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 hydrogen peroxide at the bleaching of chemical pulps has increased considerably. Hydrogen peroxide can replace part of the chlorine chemicals.
- In EP-A-402 335 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 Cl02. As a result, this final bleaching then yields emission of AOX from the bleach plant and chlorinated organic substance 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 WO-A- 91/12368. 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 delignification 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 Cl02
- In bleaching of mechanical pulp with hydrogen peroxide, silicate has been supplied in the peroxide step as disclosed in EP-A-262 836 and US-A-4 938 842. However, there are important differences between bleaching of chemical and mechanical pulps, primarily due to the lignin content. Thus, in chemical pulp bleaching the intention is to remove the lignin content completely. In mechanical bleaching the intention is to reduce colored (chromophore) groups in the lignin, while the lignin content is substantially maintained. Therefore, problems and their solutions are quite different in bleaching chemical and mechanical pulp, so that bleaching methods and bleaching results cannot be transferred from one type of pulp to the other.
- The present invention implies, that fully bleached sulphate 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 low kappa number. 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 for 1-60 minutes, the pulp consistency being 1-15%, the temperature 70-110°C and pH 5-7, followed by treatment with hydrogen peroxide.
- 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 18-40%, preferably 20-30%. The pH-value is increased to alkaline level, and peroxide 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 peroxide step shall be 1/2-5 hours, preferably 1-4 hours, and the temperature 70-110°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 shows 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, respetively, 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 brightness.
- The following exemples have the object to additionally elucidate the invention and its advantages.
- An oxygen-delignified coniferous wood sulphate pulp (Scandinavian fir/pine) with kappa number 6.4 (10.5 after digestion according to above WO-A- 91/12368), brightness 43% ISO, intrinsic viscosity 605 dm3/kg, was pretreated with complexing agent and peroxide bleached according to the invention.
-
Pulp consistency % 5 Time min. 15 Temperature °C 90 EDTA kg/ ton 2 Final pH 6.1 -
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 - A coniferous wood sulphate pulp with kappa number 13.3 (digested of Scandinavian fir/pine according to WO-A- 91/12368), 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 pretreated and bleached according to the invention.
-
Pulp consistency % 25 Time min. 240 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 - An oxygen delignified coniferous wood sulphate pulp (digested of Pinus taeda according to WO-A- 91/12368) 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.
-
Pulp consisstency % 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 - 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.
-
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 claims.
Claims (6)
- A method of delignifying and bleaching sulphate pulp without using chlorine-containing bleaching agents, comprising oxygen delignification and possibly ozone delignification of the pulp and subsequent peroxide bleaching wherein 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 the pulp thus pretreated is washed,
characterized in that the delignification is made to a kappa number below 9.5 and that the pulp after the washing is 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. - A method as defined in claim 1,
characterized in that the peroxide bleaching is carried out for 1/2-5 hours at the temperature 70-110°C. - A method as defined in claim 1 or 2,
characterized in that as complexing agent at the pretreatment EDTA or DTPA is used. - A method as defined in any one of the preceding claims, characterized in that at the peroxide bleaching silicate is added in an amount of 2-30 kg/ton pulp, expressed as SiO2.
- A method as defined in any on of the claims 1-3, characterized in 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
- A method as defined in any one of the preceding claims, characterized in that the bleaching is carried out to a brightness exceeding 83% ISO.
Applications Claiming Priority (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
SE9200152 | 1992-01-21 | ||
SE9200152A SE469842C (en) | 1992-01-21 | 1992-01-21 | Bleaching of chemical pulp with peroxide |
PCT/SE1993/000012 WO1993014262A1 (en) | 1992-01-21 | 1993-01-12 | Bleaching of chemical pulp |
Publications (2)
Publication Number | Publication Date |
---|---|
EP0621915A1 EP0621915A1 (en) | 1994-11-02 |
EP0621915B1 true EP0621915B1 (en) | 1997-04-16 |
Family
ID=20385065
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP93902618A Expired - Lifetime EP0621915B1 (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) | FI943431A0 (en) |
NO (1) | NO942718L (en) |
NZ (1) | NZ246713A (en) |
SE (1) | SE469842C (en) |
WO (1) | WO1993014262A1 (en) |
ZA (1) | ZA93317B (en) |
Families Citing this family (8)
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. |
BE1006056A3 (en) * | 1992-07-06 | 1994-05-03 | Solvay Interox | Method of laundering of chemical pulp. |
SE501253E8 (en) * | 1993-06-08 | 1994-12-19 | Chlorine-free bleaching of chemical pulp | |
SE9301960L (en) * | 1993-06-08 | 1994-07-25 | Kvaerner Pulping Tech | Bleaching of chemical pulp with peroxide at overpressure |
JPH09502229A (en) * | 1993-09-02 | 1997-03-04 | ユニオン キャンプ パテント ホールディング インコーポレイテッド | Improved bleaching method for lignocellulosic pulp |
BE1007757A3 (en) * | 1993-11-10 | 1995-10-17 | Solvay Interox | Method of laundering of chemical pulp. |
FR2719854B1 (en) * | 1994-05-11 | 1996-06-21 | Atochem Elf Sa | Process for the preparation of delignified and bleached chemical paper pulps. |
SE514697C2 (en) * | 1994-08-31 | 2001-04-02 | Valmet Fibertech Ab | Elimination of metal ions in pulp bleaching |
Family Cites Families (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
GB8620222D0 (en) * | 1986-08-20 | 1986-10-01 | Abitibi Price Inc | Peroxide bleaching |
US4732650A (en) * | 1986-09-15 | 1988-03-22 | The Dow Chemical Company | Bleaching of cellulosic pulps using hydrogen peroxide |
DE69004492T3 (en) * | 1989-06-06 | 2001-11-15 | Eka Nobel Ab | Process for bleaching pulps containing lignocellulose. |
FI93866B (en) * | 1990-02-09 | 1995-02-28 | Sunds Defibrator Rauma Oy | Method for preparing sulphate pulp |
-
1992
- 1992-01-21 SE SE9200152A patent/SE469842C/en unknown
-
1993
- 1993-01-12 DE DE69309893T patent/DE69309893T2/en not_active Expired - Fee Related
- 1993-01-12 BR BR9305761A patent/BR9305761A/en not_active Application Discontinuation
- 1993-01-12 WO PCT/SE1993/000012 patent/WO1993014262A1/en active IP Right Grant
- 1993-01-12 AT AT93902618T patent/ATE151826T1/en not_active IP Right Cessation
- 1993-01-12 JP JP5512379A patent/JPH07503042A/en active Pending
- 1993-01-12 CA CA002124088A patent/CA2124088A1/en not_active Abandoned
- 1993-01-12 AU AU34125/93A patent/AU653467B2/en not_active Ceased
- 1993-01-12 EP EP93902618A patent/EP0621915B1/en not_active Expired - Lifetime
- 1993-01-12 ES ES93902618T patent/ES2102008T3/en not_active Expired - Lifetime
- 1993-01-12 NZ NZ246713A patent/NZ246713A/en unknown
- 1993-01-18 ZA ZA93317A patent/ZA93317B/en unknown
-
1994
- 1994-07-20 NO NO942718A patent/NO942718L/en unknown
- 1994-07-20 FI FI943431A patent/FI943431A0/en unknown
Also Published As
Publication number | Publication date |
---|---|
AU3412593A (en) | 1993-08-03 |
ZA93317B (en) | 1993-08-19 |
SE469842C (en) | 1996-01-15 |
WO1993014262A1 (en) | 1993-07-22 |
DE69309893D1 (en) | 1997-05-22 |
NO942718D0 (en) | 1994-07-20 |
FI943431A (en) | 1994-07-20 |
DE69309893T2 (en) | 1997-11-06 |
SE9200152D0 (en) | 1992-01-21 |
SE9200152L (en) | 1993-07-22 |
CA2124088A1 (en) | 1993-07-22 |
NZ246713A (en) | 1995-04-27 |
BR9305761A (en) | 1997-01-28 |
ATE151826T1 (en) | 1997-05-15 |
ES2102008T3 (en) | 1997-07-16 |
FI943431A0 (en) | 1994-07-20 |
EP0621915A1 (en) | 1994-11-02 |
NO942718L (en) | 1994-07-20 |
AU653467B2 (en) | 1994-09-29 |
JPH07503042A (en) | 1995-03-30 |
SE469842B (en) | 1993-09-27 |
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