Enhancing High Temperature Peroxide Bleaching of Mixed Office Waste (MOW) Using Formulated Bleach Stabilizers, 1998 Pulping Conference Proceedings

Recent process improvements in peroxide bleaching, such as pressurization and higher reaction temperatures (e.g.,PHT-stage), have extended the versatility of peroxide for bleaching MOW pulps to high brightness. A key factor for the successful implementation of PHT bleaching is the control of wasteful peroxide decomposition reactions caused from transition metal ions. In this paper, we examine several different low-silicate methods for minimizing peroxide decomposition and maximizing peroxide brightening reactions. DTMPA and several organophosphate-based bleach stabilizers enhanced post-PHT and post-PHTY brightness better than DTPA and aminocarboxylate-based stabilizers under low-silicate PHT conditions. Pretreating the MOW stock with a Q-stage afforded similar bleaching results as adding DTPA directly to a low-silicate PHT stage. Additional analyses indicated that the Q-stage was ineffective at removing the iron that was strongly attached to the fibers. The results from this work suggest that some formulated bleach stabilizers can be used to partially replace sodium silicate for augmenting or maintaining PHT bleaching effi-ciency.