Method of pretreating pulp with yield or strength-enhancing additive
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United States of America Patent
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Jun 10, 2003
Grant Date -
N/A
app pub date -
Sep 12, 2000
filing date -
Sep 13, 1999
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Abstract
Chemical pulp is produced from a slurry of comminuted cellulosic fibrous material using a beneficial additive such as AQ, or polysulfide. In the first treatment zone the effective alkali concentration and temperature conditions are such so that substantially no alkali degradation of the cellulose occurs, but so that the material is effectively impregnated with the additive. Then the material is treated with an alkaline cooking liquor, at cooking temperature, to produce a chemical cellulose pulp with higher yield or strength than if the low temperature, low alkali, additive pretreatment was not practiced. Typical alkali and temperature conditions in the first zone are less than 10 g/l expressed as NaOH, and between about 80-130.degree. C., e.g. about 80-110.degree. C. The first zone is preferably a feed system (which may include a separate impregnation vessel) for a continuous digester, while cooking is in a continuous digester.
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