Comparative pyrolysis behaviors and reaction mechanisms of hardwood and softwood

•Thermal degradation of both hardwood and softwood was studied by TG.•A model-fitting method was combined with a model-free method.•Reaction mechanism was predicted by the Coats-Redfern method.•Two pyrolysis regions were divided by Ea with the same temperature.•Reaction mechanism was verified as diffusion followed by reaction order model. Comparative pyrolysis behaviors of typical hardwood (Fagus sylvatica) and softwood (Cunninghamia lanceolata) were investigated based on thermogravimetric analysis over a wide heating rate range from 5K/min to 60K/min. The Flynn-Wall-Ozawa model-free method was applied to estimate the various activation energy values at different conversion rates, and the Coats-Redfern model-fitting method was used to predict the possible reaction mechanism. Two pyrolysis regions were established by the trend of activation energy, divided by the threshold of conversion rate (0.4 for hardwood and 0.2 for softwood) but with the same distinguished temperature at about 580K. For the region under the conversion rate threshold, the activation energy of hardwood increased gradually while softwood decreased. Furthermore, the activation energy remained the same for both hardwood and softwood in the region over the conversion rate threshold. However, softwood behaved greater activation energy than hardwood during the whole pyrolysis process. The pyrolysis differences of hardwood and softwood could be attributed to the chemical component, molecular structure, component proportion and various extractives. The same reaction mechanism of hardwood and softwood was verified by applying the Coats-Redfern approach. By checking activation energies obtained according to different models with those obtained through the Flynn-Wall-Ozawa method, the best model was based on diffusion mechanism when the conversion rate was less than its threshold, otherwise based on reaction order (2nd to 3rd).