METHOD OF BLEACHING SULPHITE PULP Russian patent published in 2021 - IPC D21C9/16 

FIELD: pulp and paper industry.

SUBSTANCE: invention relates to pulp and paper industry and can be used in production of sulphite refined cellulose intended for nitration, i.e. obtaining nitrate esters of cellulose. Unbleached unferized sulphite cellulose of medium hardness with increased lignin content of 1.7-2.0% is bleached. According to the method delignification of cellulose mass is carried out in three stages alternating acidic and alkaline stages. At that, at the first and third stages - hydrogen peroxide treatment in acidic medium in presence of Na₂MoO₄ catalyst at temperature of 70-75°C for 120-150 minutes and with weight concentration of 10%, wherein at first step at flow rate H₂O₂ 2.0-3.5%, H₂SO₄ 0.30-0.35%, Na₂MoO₄ 0.01-0.2%, at third stage at flow rate H₂O₂ 1.3-1.8%, H₂SO₄ 0.20-0.25%, Na₂MoO₄ 0.05-0.10% of weight of absolutely dry cellulose. Between the first and third steps, alkaline delignification is carried out using hydrogen peroxide, NaOH and Na₂SiO 3 at flow rate H₂O₂ 1.5-2.0%, NaOH 1.5-2.0%, Na₂SiO₃ 2.5-3.0% of weight of absolutely dry cellulose, temperature 80-85°C for 90-120 minutes. After all delignification steps, hot alkaline refining is carried out at NaOH consumption of 9.0-10.5% of the weight of absolutely dry cellulose at temperature of 90-100°C for 150-180 min and acid treatment of the mass.

EFFECT: higher efficiency of the process of producing cellulose for chemical processing owing to reduced consumption of spruce wood while maintaining operational properties of sulphite cellulose intended for nitration.

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