Catalysis and activation of oxygen and peroxide delignification of chemical pulps: a review

Environmental regulations coupled to market pressures have forced the pulp and paper industry to explore alternatives to chlorine based bleaching practices for the production of bleached kraft pulp.Various technologies and bleaching chemicals have been suggested as answers to kraft pulp bleaching concerns, from which oxygen, ozone and peroxides are the leading candidates for chlorine replacement. Unfortunately, these chemicals are not without drawbacks. Oxygen delignification is effective but its delignification effectiveness is limited to about 50% after which a severe loss of pulp strength occurs. Hydrogen peroxide under alkaline or acidic conditions is not an effective delignifying agent while ozone is considerably more effective but it promotes aggressive radical reactions which cause undesirable carbohydrate degradation. High brightness pulps appear to be difficult to produce only by applying suclowing classifications: