Hydrogen Peroxide Use in 100% Chlorine Dioxide Bleaching Sequences, 1991 Pulping Conference Proceedings

Hydrogen peroxide use was examined in the EO-, E2- stages, density storage and high of softwood and hardwood 100% chlorine dioxide bleaching sequences, D(EO)DED. The objective was to determine the impact of H202 on effluent quality and bleach plant chemical costs while maintaining brightness, 90% ISO+.

Results on softwood pulps showed that EOP- or E2P- stages could produce 90%+ IS0 brightness at 0.22 Kappa factor compared to 0.28 kappa factor without peroxide. AOX and color in bleach plant effluent for pulps reinforced with peroxide were about 10% lower, 1.8kg AOX/ADt and 94kg PCU/ADt, compared to pulps with only chlorine dioxide. While chlorinated phenols were 40% lower, 5gm/t. Laboratory studies on hardwood showed similar results producing 0.4 and 22kg/t of AOX and color, respectively and chlorinated phenols of 4gm/t.

The capability of hydrogen peroxide to decrease chlorine dioxide requirements for softwood varied from 2.3 kg of Cl02 per kg of H202 for an EOP-stage to 5.8 kg per kg of H202 for an density storage. E2P-stage or high For hardwood the savings were only 0.8 kg ClO2/kg H202 for an EOP-stage. Bleach plant chemical savings of $3 to $5/t could be achieved with hydrogen peroxide use in softwood bleaching sequences, while bleaching costs increased $2/t for hardwoods.