METHOD FOR BLEACHING OF HARDWOOD SULPHATE PULP Russian patent published in 2009 - IPC D21C9/14 D21C9/10 D21C9/12 

FIELD: textile fabrics, paper.

SUBSTANCE: method is related to bleaching of hardwood sulphate pulp and may be used in pulp and paper industry for production of fibrous semi-finished products for production of printing types of paper. Suggested method is realised in the following manner. Unbleached hardwood sulphate pulp is disintegrated in water, then squeezed, placed into bleaching bath and delignificated by sodium hypochlorite with its consumption of 3% (in units of active chlorine) from mass of absolutely dry fiber. Then cellulose mass is flushed by water. Then double-stage bleaching of cellulose is carried out by sodium chlorite in acid medium with intermediate alkaline extraction. At the first stage of bleaching sodium chlorite consumption makes 1.5-2.5% (in units of active chlorine), and at the second stage of bleaching it makes 0.4-0.5% (in units of active chlorine) from mass of absolutely dry cellulose. After the first stage of bleaching by sodium chlorite mass is flushed by water and exposed either to oxidising alkaline treatment in the presence of hydrogen peroxide at its expenditure of 0.5%, expenditure of sodium hydroxide of 2.0% from mass of absolutely dry fiber, or alkaline treatment with hydrogen peroxide at its expenditure of 1.0%, expenditure of sodium hydroxide of 0.5%, sodium silicate - 3.0% from mass of absolutely dry fiber. After alkaline extraction cellulose is flushed, and the second stage of bleaching by sodium chlorite is carried out. Afterwards mass is flushed with water, and its acid treatment is carried out with hydrochloric acid.

EFFECT: improved quality of bleached cellulose, enhanced efficiency of process and ecological safety.

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