Process for bleaching a lignocellulosic pulp
OwnerKrister Sjoblom, Malena Rennelinventors
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Abstract
The invention relates to improvements in the bleaching of a lignocellulosic pulp by adding carbon dioxide to provide a beneficial pH profile in the chlorine dioxide bleaching or delignification. The resulting bleached pulp is used in the production of paper or pulp. The invention also relates to the use of carbon dioxide for providing a desired pH profile in a chlorine dioxide bleaching stage.
Claims16
A process for bleaching a lignocellulosic pulp with chlorine dioxide in an aqueous suspension at different pH values, said process comprising the following stages:
- providing an aqueous lignocellulosic pulp suspension in a chlorine dioxide bleaching stage after cooking,
- adding carbon dioxide to said lignocellulosic pulp,
- subsequently adding a chlorine dioxide bleaching agent to said lignocellulosic pulp suspension,
- said carbon dioxide being added in an amount sufficient for providing in said suspension a buffering system causing an initial chlorine dioxide bleaching period at a pH≧4.5 and after said initial period a subsequent chlorine dioxide bleaching period at a pH below 4.5,
- and continuing said chlorine dioxide bleaching at a pH below 4.5 and thereby achieving an increased brightness of the bleached pulp compared to a similar bleach without carbon dioxide.
Use of carbon dioxide in the chlorine dioxide bleaching of an aqueous lignocellulosic pulp suspension for providing in said suspension a buffering system causing, after an addition of chlorine dioxide to said suspension, an initial chlorine dioxide bleaching period at a pH≧4.5 and after said initial period a subsequent chlorine dioxide bleaching period at a pH below 4.5.
Dependencies are inferred from the claim text.