Claims
- 1. A single stage bleaching process for bleaching wood pulp which comprises, in combination, the steps of adding to the wood pulp a bleach liquor having an effective amount of hydrogen or sodium peroxide bleaching agent and 0.5 to 65% sodium hydroxide, 0 to 5% sodium silicate, 0 to 1% magnesium sulphate, and a chelating agent in an amount sufficient to sequester heavy metal ions, to produce a pulp consistency of 1 to 16% at a temperature in the range of the bleach liquor freezing point to 25.degree. C., uniformly mixing the bleach liquor with the wood pulp, passing said wood pulp and bleach liquor directly to a thickening stage and thickening the wood pulp and bleach liquor to a consistency in the range of 20 to 70%, and bleaching the thickened wood pulp.
- 2. A process as claimed in claim 1 in which said wood pulp is subjected to a preliminary treatment by the addition of a chelating agent in an amount sufficient to sequester chelatable heavy metals including manganese at a pulp consistency of 1 to 10%, and dewatering said pulp to a consistency of 20 to 70% to remove the sequestered manganese to less than 10 ppm.
- 3. A process as claimed in claim 2 in which said hydrogen peroxide is present in an amount of from about 1 to 5% by weight and said sodium peroxide is present in an amount of from about 2 to 10% by weight of the diluted wood.
- 4. A process as claimed in claim 3 in which said magnesium sulphate is added in an amount of 0.02 to 0.05% by weight of the diluted wood pulp.
- 5. A process as claimed in claim 3 in which said chelating agent is added in an amount up to 0.5% by weight of the diluted wood pulp.
- 6. A process as claimed in claim 3 in which chelating agent is selected from the group consisting of DTPA, EDTA, DTMPA, and the chemical equivalent.
- 7. A process as claimed in claim 1 in which the liquor produced by thickening of the diluted wood pulp is cooled and recycled for addition to fresh wood pulp.
- 8. A process as claimed in claim 3 in which the thickened wood pulp is bleached at a temperature in the range of 10.degree. C. to 95.degree. C. for a time sufficient to achieve the desired brightness.
- 9. A process as claimed in claim 3 in which the thickened wood pulp is bleached at a temperature in the range of about 50.degree. to 80.degree. C. for a time in the range of 4 to 1 hours.
- 10. A process as claimed in claim 3 in which the liquor produced by thickening of the diluted wood pulp is re-fortified with chemicals in the addition sequence of chelating agent, sodium silicate, magnesium sulphate, sodium hydroxide and hydrogen peroxide, and cooled to a temperature in the range of the freezing point of the liquor to 25.degree. C.
- 11. A process as claimed in claim 3 in which the liquor produced by thickening of the diluted wood pulp is re-fortified with a chelating agent in an amount sufficient to stabilize the hydrogen peroxide and cooled to a temperature near the freezing point of the liquor.
Priority Claims (1)
Number |
Date |
Country |
Kind |
8620222 |
Aug 1986 |
GBX |
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Parent Case Info
This application is a continuation of application Ser. No. 087,488 filed Aug. 20, 1987 (now abandoned).
US Referenced Citations (2)
Number |
Name |
Date |
Kind |
4294653 |
Lindahl et al. |
Oct 1981 |
|
4599138 |
Lindahl |
Jul 1986 |
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Continuations (1)
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Number |
Date |
Country |
Parent |
87488 |
Aug 1987 |
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