CA2083319A1 - Process for improving the degree of whiteness obtained by peroxide bleaching of wood pulp by the addition of cyanates - Google Patents
Process for improving the degree of whiteness obtained by peroxide bleaching of wood pulp by the addition of cyanatesInfo
- Publication number
- CA2083319A1 CA2083319A1 CA 2083319 CA2083319A CA2083319A1 CA 2083319 A1 CA2083319 A1 CA 2083319A1 CA 2083319 CA2083319 CA 2083319 CA 2083319 A CA2083319 A CA 2083319A CA 2083319 A1 CA2083319 A1 CA 2083319A1
- Authority
- CA
- Canada
- Prior art keywords
- pulp
- whiteness
- degree
- hydrogen peroxide
- wood pulp
- 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.)
- Abandoned
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
- D21C9/16—Bleaching ; Apparatus therefor with per compounds
- D21C9/163—Bleaching ; Apparatus therefor with per compounds with peroxides
-
- 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
Abstract
ABSTRACT OF THE DISCLOSURE
The invention relates to a process for improving the degree of whiteness of chlorine-free prebleached woodpulp, in which an alkali metal cyanate is used with hydrogen peroxide in a further bleaching step.
The invention relates to a process for improving the degree of whiteness of chlorine-free prebleached woodpulp, in which an alkali metal cyanate is used with hydrogen peroxide in a further bleaching step.
Description
The invention relates to a process for improving the degree of whiteness obtained by peroxide bleaching of wood pulp by the addition of cyanates. Stopping the use of chlorine-containing bleaches has led to an altered level of whiteness during the bleaching of wood pulps. Previously, the degree of whiteness was 88 to 90% ISO, but now, when bleaching exclusively with oxygen and hydrogen peroxide, normally only 83 to 85~ ISO is achieved with softwood pulps or 85 to 87%
with hardwood pulps. These lower degrees of whiteness may some~imes be acceptable because wood pulp bleached with hydrogen peroxide has a much lower tendency to turn yellow during thermal ageing. Basically, however, it would still be desirable to achieve the same degree of whiteness using chlorine-~ree bleaching processes as with chlorine bleaching.
However, the thresholds mentioned above represent economically reasonable final levels with the exclusive use of oxygen and hydrogen peroxide for delignifying and bleaching. Higher degrees of whiteness cannot be reached reliably even with the use of extremely high amounts of hydrogen peroxide. only the use of supplementary bleaches, such as for example ozone, allows the production of higher final levels of whiteness. This additional investment, for example in an EOP-Z-P bleaching sequence, may be avoided if another way to improve the results of peroxide bleaching could be found.
This invention is a process to improve the degree of whiteness of wood pulp which has been predelignified and prebleached using oxygen, peroxide (hydrogen peroxide) and/or ozone, characterised in that an alkali metal cyanate is added with hydrogen peroxide in a further bleaching step.
Pre-bleached and pre-delignified means that the wood pulp has previously passed through generally well-known bleaching sequences and extraction steps using oxygen, peroxide and/or ozone or combinations thereof. The kappa value of the wood pulp to be bleached is between 2 and 15, particularly 2 and lO, and its degree of whiteness is generally between 60 and 75% IS0 (for beech wood pulp) and 40.. to 50% IS0 (for spruce wood pulp and kraft pulp).
The process conditions for the peroxide bleaching step accordinq to the invention correspond with the known conditionæ per se for bleaching steps of this type: the pH
is generally between 10 and 12, the pulp density has a value between, 5 and 30% by weight, preferably 10 to 25% by weight.
The bleaching temperature is between 40C and 90C, preferably 50C and 80C, depending on the type of wood pulp to be bleached.
The amount of alkali metal cyanate used, especially sodium cyanate, is S to 50% by weight, preferably 15 to 40% by weight, of the amount o~ hydrogen peroxide used, of which 0.5 to 5~0% by weight is used, especially 1.5 to 3.0~ by weight, relative to oven-dry wood pulp.
It was found that it was possible to greatly improve the results of bleaching with hydrogen peroxide if cyanates are added during bleaching. An addit.ional in¢rease in the degree of whiteness of 1 to 2 points is possible. The stability of the higher degree of whiteness achieved in this way is equivalent to the stability of the degree of whiteness without an additive.
The process is suitable for wood pulps made from softwoods and hardwoods and one-year old plants, prepared by the kraft pulp process, or the acid or alkaline sulphite process, optionally in the presence of alcohols (methanol, ethanol).
Examples Table 1 Bleaching a beech sulphite wood pulp, pre-delignified to kappa 5.5 with 2 and H22~ after extraction with oxygen and peroxide, at 25% pulp density and 75C using hydrogen peroxide in the presence of cyanate. Constant additive, 2%
waterglass.
Test ~22 NaOH ~aOCN Whiteness ISO
% ~ ~ content ~ aged* after bleaching 1 1 0.25 - 85.3 82.8 2 1 0.25 0.15 86.6 83.1 0 3 1 0.20 0.25 87.1 84.1 ____________________~____________________________________ ~ 1.5 0.25 - 86.5 84.4 5 1.5 0.25 Q.15 87.4 85.8 6 1.5 0.20 0.25 88.6 86.0 7 1.5 0.20 0.35 88.8 86.1 _______________________ ___ ______________________________ * Heat-ageing according to Tappi Standard.
Table 2 Bleaching a spruc~ sulphite wood pulp, pre-delignified to kappa 6.5 and whiteness 75.1~, after extraction with oxygen and peroxide, using H202at 12~ pulp density and 60C with the addition of cyanate.
2~83319 Test H202 NaOH NaOCN Whiteness content ~ ~ ~ ISO
1 1.0 1.0 - 81.2 2 1.0 1.0 0.20 82.8 S ----________ 3 2.0 1.2 - 84.3 4 2.0 1.2 0.~ 85.8 5 2.0 1.0 0.4 86.5 Bleaching kraft pulp (spruce) delignified to kappa 7.5 and 44.8% ISO whiteness using oxygen and ozone, with hydrogen peroxide at 25% pulp density and 75C with soda/waterglass buffering and the addition of cyanate.
Teqt H202 NaO~ Na2CO3 Water NaOCN Whitene~s content % ~ ~ glass % ~ ~ISO
12.0 0.6 0.5 1.0 - 72~7 22.0 0.6 0.5 1.0 0.2 74.9 33.0 0.8 0.6 1.0 - . 74.8 43.0 0.7 0.6 1.0 0.4 79.1
with hardwood pulps. These lower degrees of whiteness may some~imes be acceptable because wood pulp bleached with hydrogen peroxide has a much lower tendency to turn yellow during thermal ageing. Basically, however, it would still be desirable to achieve the same degree of whiteness using chlorine-~ree bleaching processes as with chlorine bleaching.
However, the thresholds mentioned above represent economically reasonable final levels with the exclusive use of oxygen and hydrogen peroxide for delignifying and bleaching. Higher degrees of whiteness cannot be reached reliably even with the use of extremely high amounts of hydrogen peroxide. only the use of supplementary bleaches, such as for example ozone, allows the production of higher final levels of whiteness. This additional investment, for example in an EOP-Z-P bleaching sequence, may be avoided if another way to improve the results of peroxide bleaching could be found.
This invention is a process to improve the degree of whiteness of wood pulp which has been predelignified and prebleached using oxygen, peroxide (hydrogen peroxide) and/or ozone, characterised in that an alkali metal cyanate is added with hydrogen peroxide in a further bleaching step.
Pre-bleached and pre-delignified means that the wood pulp has previously passed through generally well-known bleaching sequences and extraction steps using oxygen, peroxide and/or ozone or combinations thereof. The kappa value of the wood pulp to be bleached is between 2 and 15, particularly 2 and lO, and its degree of whiteness is generally between 60 and 75% IS0 (for beech wood pulp) and 40.. to 50% IS0 (for spruce wood pulp and kraft pulp).
The process conditions for the peroxide bleaching step accordinq to the invention correspond with the known conditionæ per se for bleaching steps of this type: the pH
is generally between 10 and 12, the pulp density has a value between, 5 and 30% by weight, preferably 10 to 25% by weight.
The bleaching temperature is between 40C and 90C, preferably 50C and 80C, depending on the type of wood pulp to be bleached.
The amount of alkali metal cyanate used, especially sodium cyanate, is S to 50% by weight, preferably 15 to 40% by weight, of the amount o~ hydrogen peroxide used, of which 0.5 to 5~0% by weight is used, especially 1.5 to 3.0~ by weight, relative to oven-dry wood pulp.
It was found that it was possible to greatly improve the results of bleaching with hydrogen peroxide if cyanates are added during bleaching. An addit.ional in¢rease in the degree of whiteness of 1 to 2 points is possible. The stability of the higher degree of whiteness achieved in this way is equivalent to the stability of the degree of whiteness without an additive.
The process is suitable for wood pulps made from softwoods and hardwoods and one-year old plants, prepared by the kraft pulp process, or the acid or alkaline sulphite process, optionally in the presence of alcohols (methanol, ethanol).
Examples Table 1 Bleaching a beech sulphite wood pulp, pre-delignified to kappa 5.5 with 2 and H22~ after extraction with oxygen and peroxide, at 25% pulp density and 75C using hydrogen peroxide in the presence of cyanate. Constant additive, 2%
waterglass.
Test ~22 NaOH ~aOCN Whiteness ISO
% ~ ~ content ~ aged* after bleaching 1 1 0.25 - 85.3 82.8 2 1 0.25 0.15 86.6 83.1 0 3 1 0.20 0.25 87.1 84.1 ____________________~____________________________________ ~ 1.5 0.25 - 86.5 84.4 5 1.5 0.25 Q.15 87.4 85.8 6 1.5 0.20 0.25 88.6 86.0 7 1.5 0.20 0.35 88.8 86.1 _______________________ ___ ______________________________ * Heat-ageing according to Tappi Standard.
Table 2 Bleaching a spruc~ sulphite wood pulp, pre-delignified to kappa 6.5 and whiteness 75.1~, after extraction with oxygen and peroxide, using H202at 12~ pulp density and 60C with the addition of cyanate.
2~83319 Test H202 NaOH NaOCN Whiteness content ~ ~ ~ ISO
1 1.0 1.0 - 81.2 2 1.0 1.0 0.20 82.8 S ----________ 3 2.0 1.2 - 84.3 4 2.0 1.2 0.~ 85.8 5 2.0 1.0 0.4 86.5 Bleaching kraft pulp (spruce) delignified to kappa 7.5 and 44.8% ISO whiteness using oxygen and ozone, with hydrogen peroxide at 25% pulp density and 75C with soda/waterglass buffering and the addition of cyanate.
Teqt H202 NaO~ Na2CO3 Water NaOCN Whitene~s content % ~ ~ glass % ~ ~ISO
12.0 0.6 0.5 1.0 - 72~7 22.0 0.6 0.5 1.0 0.2 74.9 33.0 0.8 0.6 1.0 - . 74.8 43.0 0.7 0.6 1.0 0.4 79.1
Claims (17)
1. A process for improving the degree of whiteness of wood pulp which has been pre-delignified and pre-bleached using a bleaching agent selected from oxygen, peroxide, ozone and a mixture thereof, comprising a further bleaching step using an alkali metal cyanate and hydrogen peroxide.
2. The process of claim 1, wherein the hydrogen peroxide comprises 0.5 to 5.0 weight percent relative to oven-dry wood pulp.
3. The process of claim 2, wherein the hydrogen peroxide comprises 1.5 to 3.0 weight percent.
4. The process of claim 2, wherein the alkali metal cyanate comprises 5 to 50 weight percent of the hydrogen peroxide.
5. The process of claim 4, wherein the alkali metal cyanate comprises 15 to 40 weight percent.
6. The process of claim 4, wherein the alkali metal cyanate is sodium cyanate.
7. The process of any one of claims 1 to 6, effected at 40 to 90°C.
8. The process of claim 7, effected at 50 to 80°C.
9. The process of claim 7, effected at a pH of 10 to 12.
10. The process of claim 9, wherein the pulp density is 5 to 30 weight percent.
11. The process of claim 10, wherein the pulp density is 10 to 25 weight percent.
12. The process of claim 10, wherein the kappa value of the pulp to be bleached is 2 to 15.
13. The process of claim 12, wherein the kappa value is 2 to 10 .
14. The process of claim 12, wherein the degree of whiteness of the pulp is 60 to 75 percent ISO for beech wood pulp and 40 to 50 percent ISO for spruce wood or kraft pulp.
15. The process of any one of claims 1 to 6 or 8 to 14, wherein the pulp is kraft pulp.
16. The process of any one of claims 1 to 6 or 8 to 14, wherein the pulp is prepared by the acid or alkaline sulphite process.
17. The process of any one of claim 1 to 6 or 8 to 14, wherein the improvement in the degree of whiteness is 1 to 2 points.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DEP4138006.1 | 1991-11-19 | ||
| DE19914138006 DE4138006A1 (en) | 1991-11-19 | 1991-11-19 | METHOD FOR IMPROVING THE WHITE CONTENT IN THE PEROXIDE BLEACHING OF CELLULAS BY THE ADDITION OF CYANATES |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2083319A1 true CA2083319A1 (en) | 1993-05-20 |
Family
ID=6445118
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2083319 Abandoned CA2083319A1 (en) | 1991-11-19 | 1992-11-19 | Process for improving the degree of whiteness obtained by peroxide bleaching of wood pulp by the addition of cyanates |
Country Status (4)
| Country | Link |
|---|---|
| EP (1) | EP0543175A1 (en) |
| CA (1) | CA2083319A1 (en) |
| DE (1) | DE4138006A1 (en) |
| FI (1) | FI925146A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US7159333B2 (en) | 2000-08-18 | 2007-01-09 | The University Of Leeds | Use of percarbamic acids and diacyl percarbamates and precursors therefor |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2175621B (en) * | 1985-05-28 | 1989-07-05 | Lion Corp | Bleaching compositions |
| DE4004364A1 (en) * | 1990-02-13 | 1991-08-14 | Sueddeutsche Kalkstickstoff | Bleaching and delignifying pre-balanced cellulose - in two stages with peroxide activated with cyanamide or cyanamide salt, avoiding agents contg. chlorine |
-
1991
- 1991-11-19 DE DE19914138006 patent/DE4138006A1/en not_active Withdrawn
-
1992
- 1992-10-23 EP EP92118163A patent/EP0543175A1/en not_active Withdrawn
- 1992-11-12 FI FI925146A patent/FI925146A/en unknown
- 1992-11-19 CA CA 2083319 patent/CA2083319A1/en not_active Abandoned
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US7159333B2 (en) | 2000-08-18 | 2007-01-09 | The University Of Leeds | Use of percarbamic acids and diacyl percarbamates and precursors therefor |
Also Published As
| Publication number | Publication date |
|---|---|
| FI925146A0 (en) | 1992-11-12 |
| DE4138006A1 (en) | 1993-05-27 |
| EP0543175A1 (en) | 1993-05-26 |
| FI925146A (en) | 1993-05-20 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| FZDE | Dead |