The kinetics of the kraft pulping of Acacia aulacocarpa heartwood

Delignification, or lignin removal, is a principal chemical process of pulping. Optimizing delignification kinetics is therefore essential for improving the pulping process. This study investigated the behavior of Acacia aulacocarpa wood from a plantation in Indonesia using the kraft (sulphate) delignification process. This study aims to evaluate the effect of heartwood and extractive removal on kraft pulping yields and delignification kinetics. The lignin content of the original and extracted heartwood was 29.68% and 29.79%, respectively. Kraft cooking of extracted heartwood results in a lower kappa number than the original heartwood. Pulping kinetics experiments were performed at 160, 170, and 180 °C for varying cooking times (5-150 minutes). Delignification kinetics can be modelled as a first-order process with two successive reactive phases—main and final phases—after an initial stage. Approximately 40% of the wood mass and 4-10% of the lignin content were dissolved in the initial phase. In the final phase at 180°C, 88.56% of lignin was removed from original heartwood and 87.84% from extracted heartwood. The activation energies for the original and extracted heartwood were 72.7 kJ/mol and 68.5 kJ/mol, respectively. Extractive removal could be optimized to further reduce activation energy.