Dynamic Modeling of Hydrogen Peroxide Decomposition in Pressurized Peroxide Bleaching, 1996 International Pulp Bleaching Conference Proceedings

Jeff A Stevens & Dr. Jeffery S. Hsieh

Georgia Institute of Technology

Previous efforts to describe hydrogen peroxide decomposition in kraft pulp bleaching have dealt with peroxide in an alkaline solution, typically at low temperatures. In order to fully describe the peroxide decomposition as it pertains to pulp bleaching decomposition in a fiber bed must be examined. Also, decomposition at bleaching temperatures must be examined to see if the rate is consistent with that at lower temperatures. This will better illustrate the actual nature of decomposition so that it may be better identified and controlled in an actual bleaching process. In this study the kinetics of hydrogen peroxide decomposition in a bed of fully bleached kraft pulp are examined. The effects of high temperature, consistency, alkali charge, peroxide charge, and stabilization by magnesium compounds on the rate of peroxide decomposition are examined. It is shown that the presence of pulp fibers actually inhibit the rate of decomposition of peroxide through a heterogeneous mechanism. Peroxide decomposition in fibers is compared at 0.2 and 10% consistency, and these rates are compared with decomposition in liquid solution. This effort shows that decomposition is slowed at higher pulp consistencies. The rates of decomposition are compared at 70, 90, and 110°C under both pressurized and unpressurized conditions, simulating decomposition in a pressurized peroxide bleaching tower. A semi-empirical decomposition model is developed to help predict the rate of decomposition of peroxide in a bleaching tower. A dynamic model for peroxide decomposition as it occurs in a heterogeneous fiber can be used to identify and control decomposition. In this way, a better overall model for peroxide bleaching of kraft pulp in ECF or TCF sequences may be developed.