Reduction of organically bound chlorine formed in chlorine dioxide bleaching
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United States of America Patent
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N/A
Issued Date -
Mar 27, 2003
app pub date -
Aug 8, 2002
filing date -
Jun 6, 2001
priority date (Note) -
Abandoned
status (Latency Note)
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Abstract
The invention relates to an improvement in bleaching of kraft pulp. In ECF bleaching chlorine dioxide is most often a prefered bleaching chemical in certain process positions. The disadvantage is that residual amounts of organically bound chlorine in form of AOX, i.e organically bound chlorine in effluents, and/or OCl, i.e. chlorine organically bound in the produced pulp, is obtained. A normal approach has been to reduce charges of chlorine dioxide. According to the invention could substantial reductions in AOX levels be obtained if the process conditions in the chlorine dioxide stage elevated to above 91.degree. C. and extended to more than 90 minutes. A major reduction of AOX up to 50% have been shown without a corresponding increase in OCl. The chlorinated substances is degraded by the process conditions to harmless chloride ions, instead of being liberated into the effluent as AOX or bound to pulp as OCl.
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