D - Textiles – Paper – 21 – C
Patent
D - Textiles, Paper
21
C
D21C 9/16 (2006.01) D21C 9/10 (2006.01)
Patent
CA 2229893
A method at the bleaching of pulp, comprising bleaching with peracetic acid where the pH value during the bleaching reaction is held within 5-7. In the final phase of the bleaching with peracetic acid, metals released in the pulp are rebound to the fibers in the pulp by increasing the pH value to at least 9, whereafter the pulp is washed. The pH value is increased preferably 1-10 minutes before the washing. It is thereby possible to close the bleaching process in counterflow without risk of accumulation of the metals in the process.
L'invention concerne un procédé pour blanchir la pâte à papier, consistant à effectuer ce blanchiment à l'acide peracétique, la valeur du pH durant la réaction de blanchiment étant maintenue à 5-7. Dans la phase finale du blanchiment à l'acide peracétique, les métaux libérés dans la pâte sont fixés à nouveau aux fibres de la pâte, par une augmentation de la valeur du pH à au moins 9. La pâte est ensuite lavée. La valeur de pH est augmentée de préférence 1-10 minutes avant le lavage. Il est ainsi possible de mettre le processus de blanchiment à contre-courant en circuit fermé, sans risque d'accumulation des métaux dans ce processus.
Germgard Ulf
Lindquist Jonas
Fetherstonhaugh & Co.
Sunds Defibrator Industries Ab
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