Non-isothermal pyrolysis of torrefied stump - A comparative kinetic evaluation

The pyrolysis of native and torrefied stump materials was studied in the kinetic regime by means of a thermogravimetric analyzer operated in the non-isothermal fashion. Three different kinetic models applicable to biomass pyrolysis were evaluated for the collected data, which include a single-reaction model, two three pseudo-components models, and a distributed activation energy model (DAEM). It was shown that the single-reaction model was not suitable to simulating stump biomass pyrolysis. The other models including the three pseudo-components model with n = 1 and n ≠ 1, and the DAEM demonstrated very good fits between simulated and experimental curves. However, the three pseudo-components model with n ≠ 1 is recommended as the most suitable for simulation and prediction of kinetic behaviour of slow pyrolysis for both untreated and torrefied stump, considering that it offers the best fits to the experimental data and that the generated reaction orders are realistic, being slightly higher than unity. It appears that the torrefied stump has higher activation energy than its native material. The activation energy predicted for the native stump pyrolysis is in the range of 105.2-108.9 kJ/mol, 183.5-183.6 kJ/mol, and 40.3-48.01 kJ/mol for hemicelluloses, celluloses, and lignin, respectively. That for pyrolysis of the stump torrefied at 200 °C is 105.13-111.19 kJ/mol, 183.68-185.79 kJ/mol, and 40.49-50.70 kJ/mol, respectively.