METHOD OF BLEACHING HARDWOOD SULPHATE CELLULOSE Russian patent published in 2017 - IPC D21C9/10 D06L4/70 

FIELD: chemistry.

SUBSTANCE: method includes the steps of delignification with hydrogen peroxide followed by alkaline treatment and final bleaching by using hydrogen peroxide. Delignification of cellulose is carried out in two stages, at the first stage with hydrogen peroxide in an acidic medium in the presence of a sodium molybdate catalyst at the flow rate of H₂O₂ 2.5-4.0%, H₂SO₄ 0.5-1.5%, Na₂MoO₄ 0.05-0.5 wt % of absolutely dry cellulose at 65-85°C for 2-2.5 hours and a mass concentration of 10% followed by the alkaline treatment of NaOH at the flow rate of 2.0 wt % of absolutely dry cellulose at the temperature of 60-70°C for 1.5-2 hours in the presence of hydrogen peroxide at the flow rate of 0.5 wt % of absolutely dry cellulose. The second stage of delignification is carried out with hydrogen peroxide in an alkaline medium at the flow rate of H₂O₂ 1.5-2.5%, NaOH 2.0%, Na₂SiO₃ 3.0 wt % of absolutely dry cellulose at the temperature of 85-90°C for 2-3 hours. After the stages of delignification, the weight is treated with a chelating agent, which uses an aqueous solution of polyaminomethylene phosphonates, at the flow rate of 0.2-0.4 wt %, HCl 1.0 wt % of absolutely dry cellulose for 50-80 min at the temperature of 60-70°C. Then, final bleaching is carried out by hydrogen peroxide at the flow rate of H₂O₂ 1.2-2.0%, NaOH 0.7%, Na₂SiO₃ 1.7 wt % of absolutely dry cellulose at the temperature of 75-85°C for 2-3 hours.

EFFECT: increasing the ecological efficiency of the bleaching process of hardwood sulphate cellulose while maintaining its physicochemical and mechanical properties.

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