Examinations of chemical properties and pyrolysis behaviors of torrefied woody biomass prepared at the same torrefaction mass yields

•Torrefaction of leucaena at the same mass yield was conducted.•The chemical properties of the torrefied leucaena were examined in detail.•The pyrolysis behaviors of the torrefied leucaena were examined in detail.•The difference of the pyrolysis behavior was observed for the mass yield of 60 wt%.

The torrefaction of leucaena at the same torrefaction mass yield, but different torrefaction temperatures and holding times was conducted. Three values of torrefaction mass yields were selected; 60 wt%, 70 wt%, and 80 wt%. For each torrefaction mass yield, three to four torrefaction temperatures and holding times were varied. It was found that the elemental compositions of the torrefied leucaena at the torrefaction mass yield of 80 wt% were not affected by the torrefaction condition. On the other hand, at the torrefaction mass yield of 60 wt% the carbon content of the torrefied leucaena increased, while the oxygen content of the torrefied leucaena decreased with the increase in torrefaction temperature. From the TGA analysis during the pyrolysis, it was found that the weight decreasing profiles were almost the same and they did not depend on the torrefaction conditions for the torrefaction mass yield of 70 wt% and 80 wt%. On the other hand, the significant difference of the pyrolysis behaviors was observed for the torrefied leucaena prepared at the torrefaction mass yield of 60 wt%. The char yield at 800 °C for the torrefied leucaena prepared at 320 °C and 6 min holding time was as high as 27.0%, while it was around 24.0% for the torrefied leucaena prepared at other conditions. Through the results from the gas formation during the pyrolysis of cellulose and the XRD analysis, it may be concluded that the torrefaction of 320 °C and 6 min holding time led to the significant modification of cellulose in the leucaena structure resulting in the different chemical properties when compared to those other torrefaction conditions.