PROCESS OF CHLORINE-FREE BLEACHING OF SULFATE CELLULOSE Russian patent published in 2004 - IPC

FIELD: paper-and-pulp industry.

SUBSTANCE: process comprises tow-stage treatment of kraft pulp by alternation of acid and alkali treatments. In the first step, 5-20% kraft pulp is treated with solution of ammonium persulfate in 40-50% sulfuric acid at ratio of ammonium persulfate 0.5-2 weight parts to 1 weight part of absolutely dry cellulose at about 22-24^оС for 1-4 h. Resulting 5-10% pulp is then treated for 1 h with 3-4% sodium or potassium hydroxide solution at temperature close to boiling point of water.

EFFECT: excluded use of explosive and expensive hydrogen peroxide, reduced number of stages so reducing consumption of power and materials, and minimized destruction of cellulose fibers so increasing yield of bleached pulp.

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