Application of an Experimental Design to Modeling of Ozone Bleaching Stage in TCF Processes

Abstract

ABSTRACT An oxygen delignified eucalyptus Kraft pulp was bleached in a totally chlorine-free (TCF) sequence using an ozone stage (Z) followed by a hydrogen peroxide stage (P). Ozone treatments were carried out at a laboratory scale with new automated equipment. The Z stage was modeled using a four-variable sequential statistical plan over the following ranges: 10–20 g o.d.p. mass pulp, 20–50 mg/L ozone inlet concentration, 80–220 LN h ozone flow, and 0.25–0.65% o.d.p. ozone dose. The influence of these variables on several pulp properties after the Z and P stages of the XZP sequence was examined. The models defined from the results obtained predicted, in the Z stage, variations in ISO brightness, viscosity, and kappa number of 74.6–85.6%, 496–876 mL/g, and 0.44–2.27, respectively. For the P stage, the models predicted variations in ISO brightness and viscosity of 84.2–92.7% and 568–857 mL/g respectively. It is possible to obtain bleached eucalyptus pulp of brightness over 89% ISO and viscosities over 800 mL/g. The variable most strongly influencing the pulp properties was found to be the ozone dose.