METHOD FOR BLEACHING SULFITE PULP Russian patent published in 2022 - IPC D21C9/10 D21C9/16 D21C3/00 

FIELD: pulp and paper industry.

SUBSTANCE: invention relates to the pulp and paper industry and can be used to obtain soluble bleached and refined pulp intended for chemical processing, for example, to obtain viscose. Bleaching is subjected to unbleached sulfite pulp of medium hardness with a high lignin content of 1.7-2.0%. According to the method, pulp delignification is carried out with hydrogen peroxide in an acidic medium in the presence of sodium molybdate catalyst Na₂MoO₄ in two stages at a mass concentration of 10%, followed by alkaline treatment after each stage of treatment with hydrogen peroxide. Delignification with hydrogen peroxide at the first stage is carried out at a temperature of 80-85°C for 120-150 min, consumption of H₂O₂ 2.0-3.0%, H₂SO₄ 0.30-0.35%, Na₂MoO₄ 0.05-0.10 % by weight of absolutely dry pulp. Delignification with hydrogen peroxide at the second stage is carried out at a temperature of 70-75°C for 120-150 min, consumption of H₂O₂ 1.5-2.0%, H₂SO₄ 0.20-0.25%, Na₂MoO₄ 0.05-0.10 % by weight of absolutely dry pulp. Alkaline treatment after the first stage of delignification is carried out at a temperature of 65-75°C for 90-150 min, NaOH consumption is 2.0-3.0% by weight of absolutely dry cellulose. After the second stage of delignification, alkali treatment is combined with hot refining, which is carried out at a temperature of 95-100°C for 150-180 min, NaOH consumption is 10-15% by weight of absolutely dry cellulose. After hot refining, whitening is carried out in two stages: at the first stage - with sodium chlorite at a consumption of sodium chlorite 1.5-2.0%, hydrochloric acid 0.6-0.8% by weight of absolutely dry cellulose, temperature 70-75°C in for 120-150 min, the second - with sodium hypochlorite at a consumption of sodium hypochlorite 1.5-2.0%, NaOH 0.5-1.0% by weight of absolutely dry cellulose, temperature 40-45°C for 120-150 min.

EFFECT: invention makes it possible to impart qualitative characteristics to cellulose, allowing the use of soluble bleached refined cellulose for chemical processing, in particular for obtaining viscose.

1 cl, 4 ex, 2 tbl