Ozone effluent bleaching

Details Ozone effluent bleaching Ozone effluent bleaching

D - Textiles, Paper

21

C

8/82

D21C 9/10 (2006.01)

Patent

CA 1137257

OZONE EFFLUENT BLEACHING ABSTRACT The bleaching of fluff cellulosic pulp with a gaseous ozone bleaching agent at an acidic pH is often followed by an alkaline treatment, usually an alkaline extraction or an alkaline hydrogen peroxide bleaching treatment, at a much higher water content than the gaseous ozone treatrnent of the fluff pulp. Such a bleaching sequence of gaseous ozone bleaching followed by an alkaline treatment is improved by the present invention based upon two discoveries, first, the discovery of peroxygen bleaching values irt the water associated with the fluff pulp leaving the ozone hleaching treatment, and second, the peroxygen values are destroyed at the alkaline pH used for the alkaline treatment that follows the gaseous ozone bleaching treatment. In accordance with the discoveries, a Low Consistency Acidic Retention Treatment is Jnterposed between the gaseous ozone bleaching treatment and the alkaline treatment. The retention treatment comprises retaining the ozone bleached pulp in contact with the watPr associatèd with the fluff pulp during gaseous ozone bleaching along with additional water and at an acidic pH for at least ten minutes during which tTrne the peroxygen values contained in the water react with the pulp to bleach the pulp. Thereafter, sufficient al!<ali is added lbo raTse the ptl above 7 in preparation for the subsequent alkaline treatment.

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