EP0669999A1 - Method of bleaching pulp - Google Patents

Method of bleaching pulp

Info

Publication number
EP0669999A1
EP0669999A1 EP93919365A EP93919365A EP0669999A1 EP 0669999 A1 EP0669999 A1 EP 0669999A1 EP 93919365 A EP93919365 A EP 93919365A EP 93919365 A EP93919365 A EP 93919365A EP 0669999 A1 EP0669999 A1 EP 0669999A1
Authority
EP
European Patent Office
Prior art keywords
stage
accordance
pulp
bleaching
peroxide
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.)
Withdrawn
Application number
EP93919365A
Other languages
German (de)
French (fr)
Inventor
Hakan Finne
Kaj Henricson
Uno Lundgren
Ingvar Ollandt
Kenneth Winberg
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Ahlstrom Corp
Original Assignee
Ahlstrom Corp
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
Application filed by Ahlstrom Corp filed Critical Ahlstrom Corp
Publication of EP0669999A1 publication Critical patent/EP0669999A1/en
Withdrawn legal-status Critical Current

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
    • D21C9/1057—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.

Landscapes

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

Abstract

The present invention relates to a method for bleaching pulp and especially to novel types of pro-environmental bleaching processes used in the wood-processing industry, in which methods the chlorine chemicals have been replaced by other bleaching chemicals involving discharges less harmful to the environment. It is a characteristic feature of the invention that bleaching comprises at least two peroxide stages between which stages the fibers are subjected to an activating treatment, for example, acidation or hot alkali extraction.

Description

METHOD OF BLEACHING PULP
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. 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. Partially for the above mentioned reasons 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. By using the processes in accordance with the present invention it is possible to intensify peroxide and oxygen bleaching in such a way that no or hardly any difference may be seen in the quality of the final product, at least any negative, compared with chlorine bleaching.
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.
Following abbreviations are used of the bleaching stages in the enclosed text:
0 = oxygen stage P = peroxide stage
CONFIRMATION COFY E = alkali extraction stage
HAE = hot alkali extraction
Z = ozone stage
A = acidation stage
It is possible to use additional chemicals in different stages, and the following abbreviations are used to refer to them:
e = entzyme
Q = complex former The above symbols are used in such a way that, for example, AQ refers to acid stage, in which a complex former, such as EDTA, is used for removing metal ions. Respectively AeQ 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.
HAE, i.e. hot alkali extraction stage is an alkali stage, in which the temperature is above 90°C, preferably above 100°C. In said hot alkali stage 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.
It is a characterizing feature of the present bleaching method that in multistage bleaching in at least two points of the sequence the fibers are subjected to a treatment, which improves the bleachability thereof. The invention will be described more in detail below with reference to the examples.
Example 1
It is known that by using bleaching sequence 0-AQ-P-P and 0-Ae-P-P it is possible to bleach pulp to the kappa number 12 - 8 when the brightness is with birch about 75 - 80 and with pine 65 - 75.
The experiments have surprisingly shown that the addition of entzymes prior to the first bleaching stage when bleaching birch pulp affects the bleaching result only very little, but instead when used between two peroxide stages the entzymes significantly intensify the bleaching process. Thus the sequence 0-AQ-P-Ae-P results in high brightness and low consumption of peroxide. It became apparent in research that a two-stage peroxide treatment with birch pulp including entzyme activation between the two P-stages, produces with the same peroxide consumption approximately 5 % higher brightness in the final product. Respectively, the same final brightness is achieved by about 10 kg H202/adt lower peroxide dosing.
The phenomenon illustrated in the above example 1 may be utilized in many ways. In the peroxide bleaching 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-AQ-( Z )-P-Ae-(Z )-P-(Z ) .
It is seldom useful to us such a long sequence, and therefore applicable sequences are, for example: 0-AΛ-P-A Z-P or 0-AQ-Z -P-Ae-P or 0-AQ-P-Ae-P-Z .
The combination AeZ 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.
The possibility to use a 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 Ae-stage. The temperature of the HAE-stage might be, for example, 120°C. A suitable bleaching sequence would therefore be, for example,
0-AQ-Z-P-HAE-P or 0-AQ-P-HAE-P-Z.
An alternative to replace the second P-stage is to add peroxide to the HAE-stage (HAEp), whereby the sequence is simplified considerably. The sequence might then be 0-AQ- P-HAEp-Z or 0-AQ-HAEp-P-Z, although the ozone stage may, if required, also be positioned subsequent to the AQ-stage either to replace the ozone stage in the above described sequence or to add a second ozone stage to the sequence.
Example 2
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-AeQ-EPO-Ae-P. EPO means peroxide stage, in which also oxygen is used.
In the test runs the final product obtained was pulp, the brightness of which was almost 80 and the kappa number at the end of the test run 6. The consumption of peroxide was only 30 kg H202. By adding an ozone stage to the sequence the brightness might readily be raised above 85 and respectively the kappa number to about 2 - 4.
As may be seen from the examples and a number of different bleaching sequences described therewith, it is possible to obtain quality pulps with very high brightness and very low kappa number. The above given examples as well as the sequences described therewith must be considered only examples of the innumerous variations, which the process arrangement in accordance with the present invention enables. Therefore, the above examples and example sequences are by no means given to limit the invention from what is described in the attached claims which alone define the scope of invention. For example, although both in the description and in the claims a sequence seems to end at the ozone stage, it has no significance, since it is obvious that, if desired, it is possible to extend the sequence by adding a treatment stage, which, however, has no specific meaning in view of the present invention.

Claims

1. Method of bleaching pulp by chlorine-free chemicals, such as, for example, oxygen, peroxide or ozone in a multistage bleaching sequence, in which fibers are treated in at least one of the following treatments: acidation, metal stripping, entzyme treatment and hot alkali stage, at least at two points of the sequence to be such that the bleachability thereof improves, characterized in that a) pulp is treated in an acid stage, b) pulp is bleached in an alkali stage with peroxide, to which stage oxygen is added and the temperature of which stage is raised above 90°C, and c) pulp is further bleached with ozone.
2. Method in accordance with claim 1, characterized in that complex formers, entzyme and/or ozone is/are used as additional chemicals in stage a) .
3. Method in accordance with claim 1, characterized in that the temperature in stage b) is above 100°C.
4. Method in accordance with claim 1, characterized in that acid treatment is combined to the ozone bleaching of stage c) .
5. Method in accordance with one of claims 1 - 4, characterized in that there is yet another peroxide stage subsequent to the stage c).
6. Method in accordance with claims 1-4, characterized in that pulp is washed and/or pressed subsequent to stages a) , b) and c) .
7. Method in accordance with claim 5 or 6, characterized in that pulp is washed and/or pressed subsequent to the peroxide stage following stage c).
8. Method in accordance with claims 1-7, characterized in that the temperature in stage b) is 120°C.
9. Method in accordance with claims 4 - 8, characterized in that one ozone stage is used in the sequence to increase the final brightness above 85 (ISO).
10. Method in accordance with claim 8, characterized in that the kappa number of pulp is subsequent to bleaching 2 - 4.
11. Method in accordance with one of claims 1 - 10, characterized in that the consumption of peroxide is less than 30 kg H202/adt.
12. Method of bleaching pulp by chlorine-free chemicals, such as, for example, oxygen, peroxide or ozone in a multistage bleaching sequence, in which fibers are treated in at least one of the following treatments: acidation, metal stripping, entzyme treatment and hot alkali stage, at least at two points of the sequence to be such that the bleachability thereof improves, characterized in that a) pulp is treated in an acid stage, b) pulp is bleached at an EPO stage.
13. Method in accordance with claim 12, characterized in that pulp is bleached with oxygen prior to stage a) .
AMENDED CLAIMS
[received by the International Bureau on 12 April 1994 ( 12.04.94 ) ; original claims 12 and 13 deleted ; original claim 1 amended ; new claim 11 added; original claim 11 renumbered as claim
12 ; remaining claims unchanged ( 2 pages) ]
1. Method of bleaching pulp with chlorine-free chemicals , such as , for example, oxygen, hydrogen peroxide or ozone in a multistage bleaching sequence, in at least at two points of which fibers are treated in at least one of the following treatments : acidification, metal stripping, entzyme treatment and hot alkali stage, in order to improve the bleachability thereof , said sequence being characterized in that a) pulp is treated in an acid stage, b) pulp is bleached in a hot alkali stage with peroxide, to which stage oxygen is added and the temperature of which stage is raised above 90 °C, and c) pulp is further bleached with ozone.
2. Method in accordance with claim 1, characterized in that complex formers, entzyme and/or ozone is/are used as additional chemicals in stage a).
3. Method in accordance with claim 1, characterized in that the temperature in stage b) is above 100°C.
4. Method in accordance with claim 1, characterized in that acid treatment is combined to the ozone bleaching of stage c) .
5. Method in accordance with one of claims 1 - 4, characterized in that there is yet another peroxide stage subsequent to the stage c) .
6. Method in accordance with claims 1-4, characterized in that pulp is washed and/or pressed subsequent to stages a), b) and c).
7. Method in accordance with claim 5 or 6, characterized in that pulp is washed and/or pressed subsequent to the 8. Method in accordance with claims 1-7, characterized in that the temperature in stage b) is 120°C.
9. Method in accordance with claims 4 - 8, characterized in that one ozone stage is used in the sequence to increase the final brightness above 85 (ISO).
10. Method in accordance with claim 8, characterized in that the kappa number of pulp is subsequent to bleaching 2 - 4.
11. Method in accordance with claim 5, characterized in that the peroxide stage is performed at a temperature of 90 - 120 °C.
12. Method in accordance with one of claims 1 - 11, characterized in that the consumption of peroxide is less than 30 kg H202/adt.
EP93919365A 1992-11-13 1993-09-14 Method of bleaching pulp Withdrawn EP0669999A1 (en)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
FI925159A FI925159A0 (en) 1992-11-13 1992-11-13 FOERFARANDE FOER BLEKNING AV MASSA
FI925159 1992-11-13
PCT/FI1993/000362 WO1994011568A1 (en) 1992-11-13 1993-09-14 Method of bleaching pulp

Publications (1)

Publication Number Publication Date
EP0669999A1 true EP0669999A1 (en) 1995-09-06

Family

ID=8536209

Family Applications (1)

Application Number Title Priority Date Filing Date
EP93919365A Withdrawn EP0669999A1 (en) 1992-11-13 1993-09-14 Method of bleaching pulp

Country Status (6)

Country Link
EP (1) EP0669999A1 (en)
JP (1) JPH08503267A (en)
BR (1) BR9307443A (en)
CA (1) CA2149332A1 (en)
FI (1) FI925159A0 (en)
WO (1) WO1994011568A1 (en)

Families Citing this family (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FI89516B (en) 1989-05-10 1993-06-30 Ahlstroem Oy Foerfarande Foer blekning av cellulosamassa med Otson
SE9301960L (en) * 1993-06-08 1994-07-25 Kvaerner Pulping Tech Bleaching of chemical pulp with peroxide at overpressure
WO1995008021A1 (en) * 1993-09-15 1995-03-23 Kamyr, Inc. Eop stage for chlorine free bleaching
JP2002266272A (en) * 2001-03-12 2002-09-18 Nippon Paper Industries Co Ltd Method for bleaching cellulosic fibrous material pulp
RU2634586C1 (en) * 2016-08-01 2017-10-31 федеральное государственное бюджетное образовательное учреждение высшего образования "Пермский национальный исследовательский политехнический университет" Method of bleaching hardwood sulphate cellulose

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3207157C1 (en) * 1982-02-27 1983-06-09 Degussa Ag, 6000 Frankfurt Process for the production of semi-bleached cellulose
CA2023916A1 (en) * 1989-11-11 1991-05-12 Augustine I Dalton Delignification of lignocellulose-containing fiber
FR2655668B1 (en) * 1989-12-11 1995-06-09 Du Pin Cellulose PROCESS FOR BLEACHING CHEMICAL CELLULOSIC PASTA.
SE468355B (en) * 1991-04-30 1992-12-21 Eka Nobel Ab CHEMISTRY OF CHEMICAL MASS THROUGH TREATMENT WITH COMPLEX PICTURES AND OZONE

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO9411568A1 *

Also Published As

Publication number Publication date
JPH08503267A (en) 1996-04-09
FI925159A0 (en) 1992-11-13
WO1994011568A1 (en) 1994-05-26
BR9307443A (en) 1999-06-01
CA2149332A1 (en) 1994-05-26

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