Ozone Activation of Oxygen Bleaching and TCF Bleaching Sequences, 1993 Pulping Conference Proceedings

The potential of using ozone treatment as an activating stage between two oxygen bleaching stages was studied. The ozone charge was varied from .2 to 1%. The OZO kappa decreases as a function of the ozone charge. The difference in the kappa number between the OZ and the OZO stage was about 5 units. This kappa reduction was independent of the ozone charge. However, the percent delignification in the second 0 stage of an OZO sequence increased with the ozone charge. The selectivity of the OZO pulps is also better than the 00 baseline pulps. Consequently, the activation potential of an intermediate ozone stage is dependent on the definition of activation, The effect of pH and temperature was also studied for low ozone charges. The efficiency of ozone decreases as the pH and temperature are increased. At low charges (2 kg/ton), temperatures of 50 degrees C and pH of 4-5 can be used without affecting the selectivity. Various extraction/oxygen bleaching strategies after an OZ sequence showed that E, (EOP) and 0 stages provided the best incremental reduction in kappa number. The following TCF sequences were evaluated with respect to brightness and strength: 0 Z E Z PP, 0 Z (EOP) Z P P, 0 Z 0 Z P P,O O Z P Z P,O O Z(EOP)Z P. The O O Z P Z P,O O Z (EOP) Z P had the highest brightness. This indicates that it may not be necessary to activate between two oxygen bleaching stages to achieve the best brightness. The strengths of the TCF pulps are significantly lower than the conventional (CD)EDED sequence. No significant differences in strength were found between the TCF sequences studied.