Kraft pulping of Eucalyptus globulus:: Kinetics of residual delignification

Kraft pulping of Eucalyptus globulus was studied in order to develop a kinetic model for residual delignification. Pulping runs were carried out in the temperature range of 150-180 degreesC and the hydroxide ion concentration range of 0.7-1.6 M. A mean value of 95.5% was found for lignin conversion at the transition between bulk and residual delignification. A dependence of the transition point on pulping conditions was observed. The influence of cooking temperature on the rate constant was expressed by an Arrhenius-type equation. A power-law function was employed to model hydroxide ion concentration influence. The activation energy obtained was 86 kJ/mol, whereas a value of 0.59 was calculated for the kinetic order of the hydroxide ion concentration.