D - Textiles – Paper – 21 – C
Patent
D - Textiles, Paper
21
C
D21C 1/00 (2006.01) D21C 1/04 (2006.01) D21C 3/00 (2006.01) D21C 3/02 (2006.01) D21C 3/22 (2006.01)
Patent
CA 2330409
The amount of metals that can be removed from comminuted cellulosic fibrous material (such as wood chips) in the production of chemical pulp, prior to bleaching, is enhanced by extracting metals during an early stage of digestion, and prior to the addition of a chelating agent. After the material is steamed and slurried it is impregnated with cooking liquor at a temperature of 90°C or more, and during or after impregnation metals are removed by an extraction (e.g. in a continuous digester), which typically removes about 30% or more of the Mn. Prior to this extraction it is not necessary to introduce chelating agents, and undesirable to do so since they may compete or interfere with the natural removal of metals. After the extraction, such as during the first part of cooking, about 0.05-10 kg/dry ton of material of chelant (such as EDTA) is added, and the chelant combines with released metal ions in the slurry to produce metal complexes. The metal complexes are substantially removed before bleaching. In this way more than 93% of Mn (and other undesirable metal ions) may be removed prior to bleaching with a minimal amount of chelating agent used.
Henricson Kaj O.
Jiang Jian Er
Andritz Inc.
Andritz-Ahlstrom Inc.
Bereskin & Parr
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