Efficient Use of Hydrogen Peroxide as a Chemical Pulp Delignification Agent: The Macrox SM Process, 1992 Pulping Conference Proceedings

Kraft pulps can be delignified by greater than 50% with alkaline hydrogen peroxide. Best results for pulp brightness-and; more importantly, physical properties require the careful control of the transition metal ion residuals in the pulp. Careful control of the conditions of the treatment gives the additional benefit of reducing the hydrogen peroxide consumption necessary to achieve a certain brightness target.

The control of the transition metal residuals is achieved by a combination of a pretreatment and peroxide stage stabilisation. The pretreatment should preferably be with an aminocarboxylate sequestrant coupled with sulphur dioxide. The sulphur dioxide is added not only to ensure that the treatment is carried out close to the pH optimum at 6, but also for its ability to enhance subsequent delignification. This combination is particularly good at removing manganese from pulps. The iron and copper present in the pulps are more tightly bound; the iron and copper are only liberated as delignification occurs and would catalytically decompose the hydrogen peroxide if no sequestrant is present. A phosphonate sequestrant is most effective at tieing up these metals and preventing them from interfering with the delignification.