METHOD FOR PRODUCTION OF MAGNESIUM-BASED BLEACHED SULFITE CELLULOSE Russian patent published in 2001 - IPC

FIELD: paper-and-pulp industry. SUBSTANCE: method for production of magnesium-based bleached sulfite cellulose for manufacturing paper with elevated requirements for whiteness includes preliminary two-step treatment of cellulose suspension, the first step involving treatment with acid and the second one, after intermediate washing, treatment with magnesium- containing compound followed by second washing. Bleaching is accomplished by treating cellulose suspension with chlorine-free hydrogen peroxide-based bleaching reagent (optionally containing oxygen ) in presence of magnesium hydroxide suspension. Preliminary acid treatment involves magnesium-based sulfite cooking lye with SO₂ level 0.5-1.5%. Above-mentioned magnesium- containing compound is magnesium hydroxide present in amounts 0.5 to 2.0% (MgO equivalent) based on the weight of absolutely dry cellulose. Bleaching is further repeated with only hydrogen peroxide solution at pH 10.5-12.0 and temperature 75-85 C for 180-240 min, concentration of pulp being 7 to 29%. Distinguishing feature of invention is also subjecting washed cellulose suspension after first-step treatment to chelation procedure, in which chelation agent (Trylon B) is consumed in amounts 0.1- 0.3% based on the weight of pulp. EFFECT: enhanced process efficiency. 4 cl, 1 tbl, 7 ex