METHOD FOR BLEACHING BISULPHITE CELLULOSE Russian patent published in 2021 - IPC D21C9/10 

FIELD: pulp and paper industry.

SUBSTANCE: invention relates to the pulp and paper industry and can be used to obtain from unbleached bisulfite cellulose soluble bleached and refined cellulose intended for chemical processing, in particular for nitration. According to the method, hard unbleached bisulfite cellulose of increased yield with a high mass fraction of lignin of more than 6% is subjected to bleaching, cellulose is delignified with hydrogen peroxide in the presence of a sodium molybdate catalyst at a mass concentration of 10%, followed by the continuation of delignification in an alkaline medium, then cellulose is bleached with sodium chlorite in two stages with intermediate alkalization. Delignification is carried out in two stages: at the first stage in an acidic medium at a temperature of 70-75 °С for 120-150 minutes, a H₂O₂ consumption of 4.5-5.0%, H₂SO₄ 0.5-0.6%, Na₂MoO₄ 0, 15-0.35% by weight of absolutely dry cellulose; at the second stage in an alkaline medium at a temperature of 80-85°С for 90-120 min, H₂O₂ consumption 1.5-2.0%, NaOH 1.5-2.0%, Na₂SiO₃ 2.5-3.0% from the mass of absolutely dry cellulose; after all stages of delignification, a two-stage bleaching of cellulose with sodium chlorite in an acidic medium is carried out, at both stages at a mass concentration of 10%, a consumption of hydrochloric acid to sodium chlorite of 0.6-0.8% of the mass of absolutely dry cellulose; moreover, the first stage of bleaching (Xт₁) is carried out at a consumption of sodium chlorite of 1.5-2.0% of the mass of absolutely dry cellulose, at a temperature of 70-75°C for 120-150 minutes, the second stage of bleaching (Хт₂) - at a sodium chlorite consumption of 0.8-2.3% of the mass of absolutely dry cellulose, a temperature of 80-100°C for 100-180 minutes, and hot alkaline refining is carried out between the stages of bleaching at a consumption of NaOH 13 -15% of the mass of absolutely dry cellulose, at a temperature of 95-100°С for 150-180 minutes.

EFFECT: invention allows the use of bleached refined cellulose for chemical processing, in particular for nitration.

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