Patent ID: 8262856

Claim:
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.