US 4,793,898 AGranted

Process for bleaching organic peroxyacid cooked material with an alkaline solution of hydrogen peroxide

AssigneeOy Keskuslaboratorio-Centrallaboratorium AB

InventorsLauri A. Laamanen, Jorma J. Sundquist, Ilkka Y. P. Wartiovaara, Seppo V. Kauliomaki, Kristiina J. Poppius

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Abstract

A lignocellulosic raw material is pulped with a cooking liquor containing organic peroxyacids, such as peroxyformic acid or peroxyacetic acid, and the defibered 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 if calculated as a percent of the dry weight of the material 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.

Claims21

Dependent claims

A sulfur free and chlorine free process for preparing bleached Chemically defibered pulp from lignocellulosic raw material, wherein said material is first treated with a cooking liquor containing an oxidizing component to form a pulp, whereinafter the pulp is bleached, which comprises:

(A) chemically defibering the lignocellulosic raw material by means of a cooking liquor comprising an active organic acid selected from the group consisting of peroxyformic acid and peroxyacetic acid to form a chemically defibered pulp having a Kappa number of 62.2 or less, and
(B) bleaching the chemically defibered pulp with an alkaline solution comprising hydrogen peroxide in an amount which when calculated as a percent of the dry weight of the material coming to the treatment, corresponds to from 0.20 to 0.80 times the kappa number of the chemically defibered pulp obtained from stage A of the process, at a pH of at least 10 in the initial stages of the bleaching, to form a bleached chemically defibered pulp having a brightness of at least 84.3%.

Dependencies are inferred from the claim text.