Improvement of Hydrogen Peroxide Bleaching of Kraft Pulp by Acid Pre-treatment

Abstract

The influence of manganese oxidation state on the decomposition of hydrogen peroxide was investigated, and a method to minimize the manganese induced hydrogen peroxide decomposition under an alkaline condition was developed. The inclusion of such a method for the production of fully bleached pulp was investigated.Upon the addition of DTPA (diethylenetriamine-N, N, N′, N″, N″-pentaacetic acid) to Mn (II) containing solution, the manganese induced hydrogen peroxide decomposition under a typical peroxide bleaching condition is minimized. On the other hand, manganese at a higher oxidation state, such as Mn (III, IV) exhibits a strong catalytic effect in decomposing hydrogen peroxide under the alkaline condition. Furthermore, it was confirmed that the higher valency manganese in pulp fibers can be reduced to lower valency form by carbohydrate in pulp fibers. This can be achieved under the conditions of pH2-2.5, 70t and 30-60 min.By applying such a concept to the bleaching of polysulphide-anthraquinone (PS-AQ) pulp from eucalyptus (Eucalyptus camaldulensis) wood in an Eop stage, i. e., acid pre-treatment (A), then the addition of DTPA, followed by an Eop stage, the performance of the Eop stage is improved. Following the AEOP HDP sequence produces a fully bleached pulp with a brightness of 88.8% ISO and a viscosity of 15.5cP.