Near neutral chlorine dioxide bleaching of pulp
AssigneeFPInnovations
InventorsZhi-Hua Jiang, Richard McKinnon Berry
Life of this patent
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Abstract
Final chlorine dioxide bleaching of lignocellulosic materials is most effective at a near-neutral pH but present industrial practice typically targets a final pH of between 3.5 and 4.0 because of the difficulty in achieving and maintaining near-neutral pH cost effectively. The in situ formation of bicarbonate before the addition of chlorine dioxide provides a way of maintaining the required near-neutral pH. Near-neutral final chlorine dioxide bleaching also produces a bleached pulp that is in a state that responds more effectively to fluorescent whitening or optical brightening agents.
Claims20
In a process for delignification of a lignocellulosic pulp in an aqueous suspension in which delignification is carried out with chlorine dioxide at least in a final bleaching stage, the improvement wherein said final bleaching stage is carried out at a buffered pH of 4.5 to 7, the buffered pH being established by in situ generation of bicarbonate in said pulp suspension from an alkaline agent and carbon dioxide in the suspension;
- wherein the penultimate stage is an alkaline stage or a neutralization (n) stage.
A process for delignification of a lignocellulosic pulp in an aqueous suspension comprising the steps of:
- a) bleaching the pulp in said suspension, in which a final bleaching is carried out with chlorine dioxide at a buffered pH of 4.5 to 7, wherein the buffered pH is established by in situ generation of bicarbonate in said pulp suspension, from an alkaline agent and carbon dioxide in the suspension;
- wherein the penultimate stage is an alkaline stage or a neutralization (n) stage, and
- b) brightening the bleached pulp from step a) with a fluorescent whitening agent or a brightening agent.
Dependencies are inferred from the claim text.