Kinetic study of the thermal decompositions of biopolymers extracted from various plants

A knowledge of the kinetics of decomposition of biopolymers on heating is i mportant mainly in two domains: forest fires and the incineration of biomas s for the production of electric energy. For the study by thermogravimetry of biopolymers (cellulose, holocellulose and lignin), samples of several Me diterranean plants were used. The cellulose decomposition fits well with apparent first-order kinetics. T he activation energy in an air flow is about 185 kJ mol(-1). It ranges betw een 149 and 200 kJ mol(-1) for holocellulose (cellulose+hemicellulose) in a n air flow. Under nitrogen, the values are higher. Differences in the chemi cal structures of the hemicelluloses (pentosan and hexosan) may explain the se variations. The lignins also display various chemical structures. We obs erved large differences in the thermal decompositions of the various sample s. The decomposition rate is increased in a nitrogen flow containing 6% oxy gen. We observed a correlation between the maximum decomposition rate and t he heating rate. This variation presents a particular form (linear with two slopes). Only the second part seems to be interesting.