Par définition la pyrolyse ménagée du bois est la décomposition physique et chimique de matières organiques sous l'action de la chaleur et en absence d'oxygène. Comprendre ce phénomène passe d'abord par l'identification des mécanismes réactionnels et la détermination des paramètres cinétiques mis en jeu lors de la dégradation thermique du bois et de ses constituants majeurs, c'est-à-dire cellulose, hémicelluloses et lignines. La richesse et la diversité des résultats issus de la littérature spécialisée rendent compte de la difficulté à expliquer ces cinétiques complexes. Cette étude se propose de contribuer de façon innovante au bois traité à haute température en proposant une approche théorique à l'échelle de la microparticule en vue d'une modélisation macroscopique des phénomènes couplés « thermiques, chimiques et physiques ». En restituant les résultats d'une étude bibliographique poussée, nous avons fait le choix de retenir une approche analytique cherchant à séparer les trois composés principaux du bois et à caractériser chacun d'entre eux séparément.Wood pyrolysis concerns the physical and chemical organic component decomposition under the action of heat in an inert atmosphere. To explain the phenomena involved in this process, the reaction mechanisms that take place during the thermal degradation of wood and its major components of cellulose, hemicellulose and lignin have to be identified. The number and the diversity of the results in the specialized literature illustrate the difficulty in explaining the complex kinetics involved during pyrolysis. This work proposes an innovative contribution to the modelling of wood treated at high temperature by proposing a theoretical approach at the micro-particle scale that allows a macroscopic modelling of the “thermal, chemical and physical” coupled phenomena to be realised. We will show how the cellulose, hemicellulose and lignin degradation models have evolved from a simplistic formulation towards complex reaction pathways which are at the origin of our model

The torrefaction (mild pyrolysis) process modifies biomass chemical and physical properties and is applied as a thermochemical route to upgrade solid fuel. In this work, the catalytic effect of thermo-acoustic on oxidizing woody torrefaction is assessed. The combined effect of two acoustic frequencies (1411, 2696 Hz) and three temperatures (230, 250, and 290 °C) was evaluated through weight loss and its deviation curves, calculated torrefaction severity index (TSI), as well as proximate, calorific, and compression strength analysis of Eucalyptus grandis. A new index to account for the catalytic effects on torrefaction (TCEI) was introduced, providing the quantitative analysis of acoustic frequencies influence. A two-step consecutive reaction numerical model allowed the thermo-acoustic experiment evaluation. For instance, the thermogravimetric profiles revealed that the acoustic field has a catalytic effect on wood torrefaction and enhances the biomass oxidation process for severe treatments. The kinetic simulation of the acoustic coupling resulted in faster conversion rates for the solid pseudo-components showing the boosting effect of acoustic frequencies in anticipating hemicellulose decomposition and enhancing second step oxidizing reaction.

New experimental techniques, as well as modern variants on known methods, have recently been employed to investigate the fundamental reactions underlying the oxidation of biochar. The purpose of this paper was to experimentally and statistically study how the relative humidity of air, mass, and particle size of four biochars influenced the adsorption of water and the increase in temperature. A random factorial design was employed using the intuitive statistical software Xlstat. A simple linear regression model and an analysis of variance with a pairwise comparison were performed. The experimental study was carried out on the wood of Quercus pubescens, Cyclobalanopsis glauca, Trigonostemon huangmosun, and Bambusa vulgaris, and involved five relative humidity conditions (22, 43, 75, 84, and 90%), two mass samples (0.1 and 1 g), and two particle sizes (powder and piece). Two response variables including water adsorption and temperature increase were analyzed and discussed. The temperature did not increase linearly with the adsorption of water. Temperature was modeled by nine explanatory variables, while water adsorption was modeled by eight. Five variables, including factors and their interactions, were found to be common to the two models. Sample mass and relative humidity influenced the two qualitative variables, while particle size and biochar type only influenced the temperature.