The fractal nature of kraft pulping kinetics applied to thin Eucalyptus nitens chips

A kinetic model is developed, based on the power law of growth and Avrami's concepts in nuclei growth, to characterise the heterogeneous nature of kraft pulping kinetics, taking into account the effects of effective alkali concentration, sulphidity, and temperature.The final form of the model applied to kraft pulping of thin chips of Eucalyptus nitens in isothermal flow-through reactors can be represented by a first order rate equation with a time-dependent rate constant:−dLdt=8.55×109×[OH−]0.31×[HS−]0.43×exp(−97.3RT)n×t1−n×LThe exponential n varies within 0.62–1.36. This variation reflexes the non-homogeneous nature of the wood samples. The average value of n for all the samples is close to 1, suggesting that the classic first-order rate equations can be also used to approximate the delignification kinetics of large samples of E. nitens chips.