Detailed speciation of biomass pyrolysis products with a novel TGA-based methodology: the case-study of cellulose

Pyrolysis of waste biomass represents a key route for the circular economy and a promising solution for the generation of valuable chemicals and liquid biofuels. The complex multi-component and multi-phase nature of the process, however, poses a challenge in acquiring comprehensive experimental data on biomass devolatilization. These data are essential for refining kinetic schemes and optimizing technology. This work presents a novel experimental methodology suitable for the collection of kinetically relevant data on biomass devolatilization combined with a complete characterization of the product slate. This methodology consists of a thermogravimetric analyser employed to carry out pyrolysis experiments, useful for the accurate monitoring of mass loss dependencies at varying heating rate, for the control of reaction temperatures and for the suppression of secondary gas-phase reactions as well as of transfer limitations. Multiple analytical methodologies and sampling protocols were combined for product speciation – downstream online MS for gases and H2O, sorbing traps for integral offline GC/FID-MS measurement of heavy oxygenates, point vapour collection for instant GC/FID-MS analysis of light oxygenates – and allowed to independently determine the integral mass yield of each pyrolysis product, closing mass balances with very high accuracy. Experiments of cellulose pyrolysis at varying heating rate were carried out to tune and validate the methodology. Speciation protocols allowed to identify and individually quantify 31 species among pyrolysis products, including gases, condensable oxygenates, H2O and char. The comparison of experimental findings with predictions from a state-of-art lumped model has highlighted the significance of the present methodology in unravelling the kinetics governing both devolatilization and product distribution.