Pyrolysis Characteristics and Determination of Kinetic and Thermodynamic Parameters of Raw and Torrefied Chinese Fir

Torrefaction influences the structural and physicochemical properties of biomass, thus further altering its thermal degradation behavior. In this study, the pyrolysis characteristics, reaction kinetics, and thermodynamic parameters of raw and torrefied Chinese fir (CF) were investigated. The torrefaction was conducted at 220 °C (mild) and 280 °C (severe), the pyrolysis was performed from ambient temperature to 600 °C, and four different heating rates (i.e., 5, 15, 25, and 35 °C/min) were adopted. The activation energy for pyrolysis was estimated by adopting three isoconversional methods. The master-plot method was employed to analyze the reaction mechanism. Furthermore, thermodynamic parameters, i.e., the enthalpy change (ΔH), Gibbs free energy change (ΔG), and entropy change (ΔS), were calculated. The average activation energy increased with the torrefaction temperature, whose values estimated by using different methods ranged from 88.57 to 97.70, from 121.04 to 126.35, and from 167.51 to 179.74 kJ/mol for raw, mildly, and severely torrefied CF samples, respectively. A compensation effect between the activation energy and pre-exponential factor was observed for all samples. The degradation process was characterized as endothermic, involving the formation of activated complexes and requiring extra energy for torrefied samples.