Thermochemical experiments and modelling of the PO bleaching stage

The oxygen-pressurized peroxide bleaching of Finnish pine kraft pulp was st udied experimentally and with reaction kinetic and thermodynamic models. Ki netic experiments were performed at 5% consistency with fully bleached pulp , kappa 9.6 and kappa 12.9 pulp. Measurements were done in the range of 75- 120 degreesC and 0.1-1.2 MPa partial pressures of oxygen. pH, peroxide and alkali consumption were measured as a function of time. For each test the k appa number, pulp viscosity and brightness were measured. From the experime nts, an Arrhenius type of reaction kinetic model was further developed for kappa number reduction to describe the salient reaction process in PO bleac hing. In the thermodynamic model, the NaOH-H2O2-O-2-H2O system was used to describe the bleaching solution.