BLEACHING PROCESS OF HARDWOOD SULPHATE PULP Russian patent published in 2014 - IPC D21C9/10 

FIELD: textiles, paper.

SUBSTANCE: method comprises the steps of delignification followed by alkaline treatment and final bleaching with sodium chlorite followed by alkaline extraction with use of hydrogen peroxide. Delignification is carried out with hydrogen peroxide in an acidic medium in the presence of catalyst sodium molybdate at a rate of H₂O₂ 1.0-3.0%, H₂SO₄ 0.5-1.5%, Na₂MoO₄ 0.05-0.5% by weight of absolutely dry pulp at a temperature 60-90°C for 90-180 min and the mass concentration of 10%. The alkaline treatment is carried out at a rate of NaOH 1.5% by weight of absolutely dry pulp at a temperature of 60-70°C for 60-90 min. Then, final bleaching is carried out with sodium chlorite at its rate of 0.5-1.5% and the rate of hydrochloric acid of 0.5-1.5% by weight of absolutely dry pulp at a temperature of 60-90°C for 100-180 min. Alkaline bleaching with hydrogen peroxide is carried out in two stages in the presence of stabiliser sodium silicate and complexing agent trilon C. The first stage of bleaching with hydrogen peroxide is carried out at a rate of H₂O₂ 1.0-1.5%, NaOH 1.0-1.5%, Na₂SiO₃ 3.0%, trilon C 0.1-0.5% by weight of absolutely dry pulp at the temperature of 60-80°C for 150-180 min. The second stage - at a rate of H₂O₂ 0.9-1.2%, NaOH 0.9-1.2%, Na₂SiO₃ 3.0%, trilon C 0.1-0.3% by weight of absolutely dry pulp at the same temperature for 100-150 minutes.

EFFECT: increase in pulp whiteness while maintaining its mechanical properties, environmental friendliness, efficiency of the bleaching process.

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