New Efficient Selective TCF Pulp Bleaching, 1998 Pulping Conference Proceedings

A new TCF bleaching technology is described in which hydrogen peroxide is activated catalytically to rapidly bleach softwood kraft wood pulp under mild conditions in basic water. The process is based upon easily prepared iron catalysts comprised of nontoxic elements that, by virtue of the ligand design strategy employed to produce them, are long-lived under operating conditions. Bleaching proceeds rapidly at micromolar catalyst concentrations from ambient temperature to 90 °C to deliver high selectivity for lignin over cellulose oxidation. Peroxide is used efficiently. For example, at 90 °C with a charge of 4% H 2 O 2 on oven-dried pulp and 80 ppm of activator 2a, significant delignification (kappa number 21.5 to 7.8) is achieved in a 60 minute bleaching cycle; the viscosity change is 37.4 to 25.3 mPa.s. Early results on the use of the activators for peroxide bleaching of colored effluent and for oxidative decomposition of AOX are also presented. These and other factors indicate that the new technology, labeled “P Fe ” to denote that it is a peroxide bleaching process activated by iron catalysts, promises to be a useful tool for papermaking.