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US 8,262,856 B2Granted
Processes and systems for the bleaching of lignocellulosic pulps following cooking with soda and anthraquinone
AssigneeAndritz Inc.
InventorsPam O'Leary, Namhee Shin, C. Bertil Stromberg
Life of this patent
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Abstract
Process for bleaching of pulps following cooking of the lignocellulosic material with soda and anthraquinone. The process may produce a whiteness on par with the bleaching of kraft pulp when using a similar bleaching sequence. In some instances, the bleaching sequence may be O-A-Do-Eop-D, O-A-ZDo-Eop-D, A-Do, or A-ZDo.
Claims24
A process for a bleaching of lignocellulosic pulp comprising the steps of:
- cooking a lignocellulosic material with soda and anthraquinone to form a lignocellulosic pulp, wherein the soda comprises sodium hydroxide, sodium carbonate, or sodium hydroxide and sodium carbonate;
- wherein the cooking essentially excludes sulfides;
- feeding the lignocellulosic pulp to a first stage in which the lignocellulosic pulp contacts oxygen and a first alkali, wherein the first alkali comprises between 1 and 2 percent by weight of the lignocellulosic pulp;
- removing the lignocellulosic pulp from the first stage and feeding the lignocellulosic pulp to a second stage in which the lignocellulosic pulp contacts an acid wherein the acid comprises between 0.25 and 0.75 percent by weight of the pulp;
- removing the lignocellulosic pulp from the second stage and feeding the lignocellulosic pulp to a third stage in which the lignocellulosic pulp contacts a first chlorine dioxide, wherein the first chlorine dioxide comprises between 0.1 and 0.75 percent by weight of the lignocellulosic pulp;
- removing the lignocellulosic pulp from the third stage and feeding the lignocellulosic pulp to a fourth stage in which the lignocellulosic pulp contacts a second alkali and a hydrogen peroxide, wherein the second alkali comprises between 0.5 and 1.5 percent by weight of the lignocellulosic pulp, and wherein the hydrogen peroxide comprises between 0.25 and 0.75 percent by weight of the lignocellulosic pulp;
- removing the lignocellulosic pulp from the fourth stage and feeding the lignocellulosic pulp to a fifth stage of further bleaching in which the lignocellulosic pulp contacts a second chlorine dioxide and/or other bleaching chemicals in one or more stages to achieve a final brightness higher than 89 (% ISO) wherein the second chlorine dioxide comprises between 0.1 and 0.5 percent by weight of the lignocellulosic pulp;
- and
- removing the lignocellulosic pulp from the fifth stage.
6 more elements
A process for a bleaching of lignocellulosic pulp comprising the steps of:
- cooking a lignocellulosic material with soda and anthraquinone to form a lignocellulosic pulp;
- wherein the cooking essentially excludes sulfides;
- feeding the lignocellulosic pulp to a first stage in which the lignocellulosic pulp contacts oxygen and a first alkali, wherein the first alkali comprises between 1 and 2 percent by weight of the lignocellulosic pulp;
- removing the lignocellulosic pulp from the first stage and feeding the lignocellulosic pulp to a second stage in which the lignocellulosic pulp contacts an acid at a temperature greater than 105° C., wherein the acid comprises between 0.25 and 0.75 percent by weight of the pulp;
- removing the lignocellulosic pulp from the second stage and feeding the lignocellulosic pulp to a third stage in which the lignocellulosic pulp contacts a chlorine dioxide, wherein the chlorine dioxide comprises between 0.1 and 0.75 percent by weight of the lignocellulosic pulp;
- and
- removing the lignocellulosic pulp from the third stage.
4 more elements
Dependencies are inferred from the claim text.