PROCESS FOR PREPARING BLEACHED PULP OUT OF LIGNOCELLULOSIC RAW MATERIAL

摘要

Lignocellulosic raw material is pulped with a cooking liquor containing organic peroxyacids, such as peroxyformic acid or peroxyacetic acid, and the defibred pulp is bleached with an alkaline solution containing hydrogen peroxide, the pH of which is at least 10 in the beginning of the treatment, and which is provided by adding to a sodium hydroxide solution hydrogen peroxide in an amount which calculated as per cents of the dry weight of the matter coming to the treatment corresponds to from 0.20 to 0.80, preferably from 0.25 to 0.70 and most preferably from 0.45 to 0.65 times the kappa number of the pulp obtained from the previous stage of the process.