Kinetics of thermal degradation of wood biomass

Abstract

Pyrolysis kinetics of a hardwood representative, beech (Fagus sylvatica), was investigated by two different kinetic approaches: model-free isoconversional method and model-fitting method. The model-free isoconversional method was used for the determination of apparent kinetic parameters, i.e. the activation energy and pre-exponential factor. The model fitting method was used for the optimization of kinetic parameters of the reaction pathways of three selected reaction mechanisms: one-step, two-step, and three-step one. In both approaches, thermo-gravimetric data were used at five heating rates: 2°C min−1, 5°C min−1, 10°C min−1, 15°C min−1 and 20°C min−1. As the most suitable mechanism, the three-step mechanism containing the intermediate degradation step was chosen. This selection was supported by experimental results from the 13C NMR analysis of solid residues prepared at the key temperatures within the range of 230–500°C. The progress of mass fraction values of each component in this mechanism was simulated. Conclusions from the simulation were confronted with experimental results from the 13C NMR.

Kinetic Study of the Thermochemical Degradation of Lignocellulosic Materials Based on TG-FTIR, Py-GC/MS and 13 C NMR Experiments

“…This mechanism was selected as the simplest one for use in the initial stages 14 of modelling 3,37,38 . Mechanisms B are two-step and three-step mechanisms describing wood 15 transformation via parallel and competitive parallel steps. For example, the competing 16 mechanism B1 has been considered by many authors as much more relevant than the one-step 17 mechanism 1,22,39,40 .…”

“…To identify structural changes of solid materials, scanning electron mi-croscopy (SEM) and nuclear magnetic resonance (NMR) are often used. 13 C NMR has been often used and cited in the literature as a promising method that provides important results regarding biomass transformation into char [13][14][15][16] . Based on analytical results, many authors have reported either speculative reaction mechanisms including exact chemical reactions, or simplified forms of reaction mechanisms including reaction pathways.…”

“…Thus, it can be concluded that the presence 14 intermediate is connected to the presence of the lignin structure. In the temperature interv 15 300 °C, changes mainly connected with the release of volatiles V1 were observed (Figs 16 Considering the release of volatiles only, this temperature interval is characterized 17 cleavage of hemicellulose acetyl groups and by lignin demethoxylation. At 320 °C, 18 remaining residues of hemicellulose and cellulose can be found, and volatiles V2 are…”