ED Sciences Physiques et de l'Ingénieur
Study of the chemical and kinetic mechanisms of biomass pyrolysis
by Joanna D'ANTONI (I2M - Institut de Mécanique et d'Ingénierie de Bordeaux)
The defense will take place at 14h00 - B6 Campus Bordes Bâtiment B6 RDC 33600 Pessac
in front of the jury composed of
- Wahbi JOMAA - Professeur des universités - Université de Bordeaux - Directeur de these
- Anthony DUFOUR - Directeur de recherche - CNRS - Rapporteur
- Thomas ROGAUME - Professeur des universités - Université de Poitiers - Rapporteur
- Jean LACHAUD - Professeur des universités - Université de Bordeaux - CoDirecteur de these
- Capucine DUPONT - Professeure associée - IHE Delft - Examinateur
- Manon CARRIER - Chargée de recherche - IMT Mines Albi - Examinateur
- Yann ROGAUME - Professeur des universités - Université de Lorraine - Examinateur
- Vincent DOUCET - Ingénieur - Novéa - Examinateur
This thesis investigates the chemical and kinetic mechanisms of lignocellulosic biomass pyrolysis, using maritime pine (Pinus pinaster) as the material of study. As the first stage of combustion, pyrolysis acts as the source term supplying combustible gases to the flame; understanding its kinetics is therefore essential for developing predictive models of fire risk. Beyond this aspect, pyrolysis plays a central role in thermochemical conversion processes for the production of bio-oils, char, and gases. It also offers significant potential for energy recovery and the production of green chemical feedstocks. A detailed understanding of this degradation therefore requires accurate prediction of mass loss, as well as of the nature and speciation of the products formed. This requires both advanced experimental tools and robust kinetic and physical models capable of describing the relevant phenomena from the particle scale to the reactor scale. An experimental characterization combining TGA/DSC, FTIR-ATR and GC/MS is carried out on cellulose, xylan, and lignin, as well as on maritime pine, at heating rates ranging from 5 to 100 K/min. These experiments provide insight into the different stages of thermal degradation and highlight the influence of heating rate on the distribution of volatile products. Comparison between the isolated constituents and the native wood also reveals matrix effects within the wood structure. These experimental results are then used to develop the multi-step kinetic mechanism proposed by Ranzi and Debiagi. The resulting mechanism, named CRECK-I2M, introduces in particular a renewed description of lignin degradation based on H-, G-, and S-type monolignol precursors. The kinetic and thermal parameters, together with the stoichiometric coefficients, are adjusted to reproduce the thermal behavior and the distribution of the main pyrolysis products observed experimentally at different heating rates. Finally, the CRECK-I2M mechanism is implemented in the open-source multiphysics solver PATO to illustrate its application at the scale of a maritime pine particle. Coupling the mechanism with heat and mass transfer and particle deformation makes it possible to investigate the evolution of temperature fields, pyrolysis fronts, internal pressure, and mechanical stresses during degradation. Overall, this work contributes to a better understanding of maritime pine pyrolysis and to the development of a kinetic and multiphysics model capable of describing its main degradation phenomena.