Optimizing Pressurized Peroxide Bleaching of a Hardwood Sulfite Pulp, 1997 Pulping Conference Proceedings

Laboratory bleaching was undertaken on a washed, mill-cooked mixed hardwood sulfite pulp having an 11.5 ermanganate number. The bleaching utilized oxygen to pressurize a temperature controlled reactor and involved pre-mixing of bleach chemicals with pulp. Independent variables studied included temperature, pressure, peroxide charge, alkali charge and organic stabilizer addition. Dependent variables measured included micro-Kappa and Permanganate numbers, brightness, heat-reverted brightness, residual peroxide, final pH and TAPPI dirt count.

The primary objective of this work was to determine whether brightness gain could be predicted by better understanding the relationship of the key operating variables. In conclusion, a linear regression analysis undertaken on the raw data obtained gave an equation as follows: Brightness = 59.59 + 0.08*temperature + 0.03*pressure + 2.72*H2O2% + 1.78*NaOH%. The R-square value for this equation was very acceptable at 0.96. Further analysis demonstrated that reverted brightness and Permanganate number could also be well-predicted by fitting the experimental results into linear regression equations.

This data would be useful at a sulfite mill using a pressurized peroxide stage to brighten pulp and interested in: a) lowering operating costs (e.g. increasing temperature to decrease peroxide charge) or b) improving product quality (e.g. increasing final brightness at the lowest incremental operating cost). The conclusions reached regarding impact of variables such as temperature and alkali charge can also bring about reduced variance in bleached pulp quality if included in an operating mill control strategy.