WOOD-PULP BLEACHING PROCESS Russian patent published in 2000 - IPC

FIELD: paper-and-pulp industry. SUBSTANCE: thermomechanical or chemico-thermomechanical-origin aqueous suspension of pulp is treated with bleaching reagent, preferably hydrogen peroxide or sodium hydrosulphite, and complexation agent: mixture of sodium salts of diethylenediamine-tetramethylenephosphonic acid, diethylenetriamine-pentamethylenephosphonic acid, and triethyleneteramine-hexamethylenephosphonic acid at their ratio (0.8- 1.2): (0.8-1.2): (0.8-1.2). Treatment is carried out in presence of supplementary complexation agent, namely sodium tripolyphosphate at weight ratio of salt mixture to the latter from 5:1 to 10:1 and total consumption of complexation agents 0.1-0.2% based on the weight of absolutely dry fibers. Treatment temperature is 40-80 C and treatment time 60-120 min. Treatment can be carried out either in single stage or in two stages. In the latter case, salt mixture in presence of sodium tripolyphosphate is first used (40-60 min) and then bleaching reagent is added and treatment is continued for further 40-60 min. EFFECT: intensified process, reduced consumption of reagents, and improved whiteness of fibers. 4 cl, 1 tbl, 7 ex