| 摘要 |
A bleaching process for chemical paper pulp comprises successive steps of ozone treatment, alkali metal borohydride treatment and a complementary bleaching treatment. Pref. the complementary treatment is carried out with H202 and/or oxygen and may be preceded by an alkaline treatment such as alkaline extn. The pulp has a consistency of 3-40% and may be bleached with 02 and/or H202 prior to the 03 treatment, the pulp may be treated, esp. with a sequester extn such as EDTA, to eliminate or sequester metal cations prior to the 03 treatment and/or after the borohydride treatment. The 03 treatment is carried out using an 03 concn. of 0.1-3% by wt. of pulp at 15-50 deg. C. The borohydride treatment is carried out using sodium or potassium borohydride at a concn. of 0.01-3 (pref. 0.01-1%) by wt. of pulp and at 50-100 deg. C for 10 mins. to 2 hrs. the treatment being carried out in alkaline medium at pH 7.5-12, esp. 8-11. The complementary bleaching treatment is carried out with H202 at 0.1-3% concn. by wt. of pulp and at 50-100 deg.C. for 0.5-3 hrs. ADVANTAGE - The process is chlorine free, and has high bleaching power and avoids cellulose degradation even though the ozone treatment is followed by a complementary alkaline treatment.
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