Modeling of sapwood and heartwood delignification kinetics of Eucalyptus globulus using consecutive and simultaneous approaches

Eucalyptus globulus sapwood and heartwood were delignified at 130A degrees, 150A degrees, or 170A degrees C by kraft pulping. Pulp yields of heartwood were lower than those of sapwood (46.5% vs. 50.4% at 170A degrees C). Delignification was modeled using consecutive and simultaneous kinetic models. The modeling was similar for heartwood and sapwood, and either approach could be used, with both yielding good correlations between experimental and model data. The consecutive model identified two delignification phases with similar reaction rates and activation energies for heartwood and sapwood at 150A degrees and 170A degrees C. At 130A degrees C only one phase was identified. Three reactive types of lignin fractions were identified using the simultaneous model, without differences between heartwood and sapwood. Their reaction rates were 0.152, 0.138, and 0.003 min(-1) at 170A degrees C, and the activation energies were 132, 119, and 102 kJ.mol(-1). The presence of heartwood did not influence the kinetic development of delignification. The negative impact of heartwood in pulping is related to the higher content of extractives (9.8% vs. 3.9% in heartwood and sapwood) and to their influence on the process, namely in the heating-totemperature phase when a substantial mass loss occurs (30% vs. 20% for heartwood and sapwood).