Pyrolytic behavior and kinetic of wood sawdust at isothermal and non-isothermal conditions

Pyrolytic behavior and kinetic of wood sawdust were studied at non-isothermal and isothermal conditions. The characteristic temperatures of ∼230 °C, ∼300 °C, ∼345 °C, ∼370 °C corresponded to degradation of pseudo hemicelluloses 1, hemicellulose 2, cellulose, lignin under non-isothermal condition, respectively. The release behaviors of gaseous products were closely related to the characteristic temperatures of weight loss. The tar generation could be characterized by CH₃ group that was mainly dominated the by decompositions of hemicelluloses and cellulose. Under isothermal condition, the weight of derived biochar was described by a function of w_char = 775.5–2.9T + 0.0037T²-1.6 × 10⁻⁶T³. A novel nth-order discrete distributed activation energy model was developed to study the non-isothermal kinetic. The characteristic weight fractions of woody sawdust pyrolysis were found at conversions of 0.29, 0.30, 0.65, 0.84, 0.88 and 0.95. Parallel reaction model could explain the non-isothermal kinetic well with similar reaction orders to discrete distributed activation energy model. The isothermal kinetic of pyrolysis could be described by three or four components parallel reaction with nth-order Avrami-Erofeev model.