Beyond the peak temperature: An experimental evaluation of conventional vs. effective thermodynamic models for biomass pyrolysis

Accurate interpretation of thermogravimetric data depends on the thermodynamic model used, yet experimental comparisons of standard methods are limited. This study critically evaluates the conventional (CA) and effective thermodynamic (ETA) approaches for analyzing the pyrolysis of Sotol bagasse (SB), an extractive-rich agro-industrial residue. Both models confirmed that SB pyrolysis is feasible and endothermic; however, they produced substantial differences in entropy (ΔS) and Gibbs free energy (ΔG) due to their theoretical foundations. The CA relies on a single peak temperature (Tp), which fails to represent the multi-stage nature of pyrolysis. In contrast, the ETA uses conversion-dependent temperatures (Tα), capturing reaction progression and biomass heterogeneity more accurately. Comparisons with other biomasses showed that CA consistently underestimates ΔS and overestimates ΔG below Tp, with the trend reversing above Tp, whereas ETA provided consistent and mechanistically meaningful trends. Although both models yielded similar enthalpy (ΔH), the ETA revealed a thermodynamic shift toward increased exothermicity and reduced spontaneity at higher conversions (α > 0.35), likely due to SB's high extractive content (≈23 %) and secondary charring reactions—information missed by CA. Overall, model selection strongly influences thermodynamic interpretation, and the ETA is validated as the superior approach for designing and optimizing pyrolysis of complex, extractive-rich, and non-extractive feedstocks.