Abstract:

The thermo-gravimetric (TG) measurements of leaves in inert atmosphere was analysed by using a multi-component parallel reaction model in conjunction with a non-linear least-square fitting technique, which allowed for close observation on the contribution of individual chemical compositions to the pyrolysis process. The result showed that, with increasing temperature, the leaves experienced both physical and chemical processes, including dehydration, precipitation of volatile oil, successive pyrolysis of hemicellulose, cellulose and lignin, and the formation of chars (fixed carbon). The trend in the DTG curves over 150℃ was mainly a comprehensive result of the mass loss caused by thermal decomposition of hemicellulose, cellulose and lignin, which are similar to those appearing in the pyrolysis of the core compositions in wood. The hemicellulose primarily generated gases during pyrolysis, making little contribution to the formation of carbon, whereas the cellulosic compositions in leaves were slightly different. The lignin had predominated contribution to the formation of the carbon by pyrolysis. As a result, the amounts of hemicellulose and cellulose retained by a leaf mainly corresponded to the content of the volatile matter determined by the proximate analysis, while the content of fixed carbon very much relied on the portion of lignin stored in a leaf. A higher content of volatile matter in a leaf implies a relatively poorer thermal stability of the solid, and hence pointing to a higher flammability of the material; while for the content of fixed carbon is in the opposite. The established recognition would provide an important basis for evaluating the thermal stability of tree leaves and identifying fire-resistant tree species for fire prevention in forest areas.

Key words: tree leaves, pyrolysis mechanism, chemical kinetics, thermal stability, proximate analysis of solids