Process for bleaching of lignocellulose-containing pulp using a chelating agent prior to a peroxide-ozone-peroxide sequence
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United States of America Patent
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Aug 19, 1997
Issued Date -
N/A
app pub date -
Sep 16, 1994
filing date -
Apr 30, 1991
priority date (Note) -
Expired
status (Latency Note)
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Abstract
A process for delignification and bleaching of chemically digested lignocellulose-containing pulp, where the pulp is treated with a complexing agent at a pH between 3.1 and 9.0, whereupon the pulp is bleached with ozone. The initial treatment with a complexing agent removes the ions of certain metals detrimental to the subsequent ozone bleaching, while retaining in the pulp the desirable ions, primarily of alkaline earth metals. Thereby, the selectivity in the delignification is increased and the strength of the pulp maintained. The pulp can be bleached with peroxide before the ozone step and/or after the treatment according to the invention, to obtain the desired final brightness and completely avoid formation and discharge of chlorinated organic compounds.
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