Low AOX Process for Bleaching High Kappa Pulps: 01 Delignification, 1994 Pulping Conference Proceedings

S. K. Mendiratta, D. W. Cawlfield, L. R. Ward, D. Breed

In order to meet the proposed EPA guidelines for pulp mill effluent, the formation of chlorinated phenols, organics and AOX must be minimized during pulp bleaching. AOX formation can be significantly reduced by lowering the unbleached pulp kappa number to a very low value and using 100% ClO2 for bleaching. Extensive delignification of pulp requires major equipment additions in the pulping line as well as an upgrade of the chemical recovery system. AOX and chloro-organics formation during ClO2 bleaching of high kappa pulps can be minimized by 1) minimizing the concentration of intermediates which prefer substitution reactions, and 2) maximizing ClO2 delignification efficiency. The formation of intermediates can be minimized by rapidly reaction with ClO2 lignin, reducing the diffusion resistance so that the ClO2 molecule can readily reach the lignin, and eliminating the free water in which intermediates can accumulate.