METHOD OF EFFICIENTLY INCREASING WHITENESS DEGREE OF WOODPULP AND HARD PULP (VERSIONS) Russian patent published in 1997 - IPC

FIELD: pulp-and-paper industry. SUBSTANCE: method includes feeding woodpulp in amount providing its concentration 5-45% into silicate-free bleaching solution containing (based on oven-dried pulp) 0.2-0.6 wt % silicate substitute, 2-6 wt % hydrogen peroxide, and alkali; aging in bleaching solution at 35-85 C for 2-6 h; and separation of bleached pulp from a part of bleaching solution. According to invention, bleaching solution contains 2 to 6 wt % sodium carbonate. Two-step bleaching method is also provided, according to which, first-step bleaching solution contains 2 to 6 wt % sodium carbonate and second-step solution 3 to 4 wt % sodium carbonate. EFFECT: increased whiteness degree. 10 cl, 8 tbl