METHOD OF BLEACHING SULFATE CELLULOSE Russian patent published in 2001 - IPC

FIELD: cellulose derivatives. SUBSTANCE: cellulose is treated with oxygen in reactor in presence of alkali. Non-washed cellulose is additionally treated with oxygen or hydrogen peroxide, or their mixture, or a peroxide compound in alkali medium in mixer at pH 9.5- 12.1 followed by keeping treated cellulose in storage tank at atmospheric pressure during 20 to 120 min. Peroxide compound utilized can be peroxomonosulfuric acid or peroxodisulfuric acid or sodium salt of one of indicated acids in amounts 0.001-1.50% of the weight of absolutely dry cellulose. First chlorine dioxide treatment stage is performed in presence of sulfuric acid at pH 3-5. Then follow oxygen treatment in presence of alkali, hydrogen peroxide, and magnesium sulfate (protector) in bleaching tower with ascending cellulose flow. After that, cellulose undergoes second chlorine dioxide treatment and can further be subjected to additional alkali treatment followed by chlorine dioxide treatment. The second chlorine dioxide treatment can be carried out in presence of sulfuric acid at pH 4-6. EFFECT: reduced consumption of chlorine dioxide leading to better environmental condition and reduced process expenses; improved strength characteristics of cellulose due to increased selectivity of oxygen delignification. 4 cl, 2 tbl, 10 ex