Non-isothermal kinetics: best-fitting empirical models instead of model-free methods
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Non‑isothermal kinetics: best‑fitting empirical models instead of model‑free methods Gábor Várhegyi1 · Liang Wang2 · Øyvind Skreiberg2 Received: 30 August 2019 / Accepted: 5 December 2019 © The Author(s) 2019
Abstract The isoconversional (or model-free) methods cannot provide meaningful kinetic description for most samples in thermal analysis. Nevertheless, they can serve as empirical models. A usable empirical model should describe well the observed data and should be suitable for predictions, too. For this purpose, the functions in the isoconversional kinetic equation were parametrized, and the parameters were determined by the method of least squares. This procedure ensures that the data calculated from the model would be close to the experimental data. The present work supplemented a preceding work of Várhegyi (Energy and Fuels 33:2348–2358, 2019) by further considerations and by various evaluations on the TGA curves of a wood sample. The prediction capabilities of the models were also tested. It was found that an evaluation based on three experiments with constant heating rates could predict well two further experiments with stepwise temperature programs. Furthermore, a modification of the model was proposed and examined. The aim of this modification was to improve the fit quality without increasing the number of parameters in the least-squares procedure. Keywords Non-isothermal kinetics · Least-squares evaluation · Isoconversional methods · Model-free methods · Biomass · Wood · Spruce List of symbols α Reacted fraction [dimensionless] A/s−1 Pre-exponential factor Ã(α)/s−1 A(α) f(α)/(1 − α) at α
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