Pyrolysis kinetics of almond shells and olive stones considering their organic fractions

The kinetics of thermal decomposition of two lignocellulosic materials (olive stones and almond shells) were studied using dynamic TG at heating rates between 2 and 25 K min(-1) at atmospheric pressure. Different kinetic models were tested, that consider that the thermal decomposition of lignocellulosic materials can be grouped in two or three overall processes (each one being the result of a great number of reactions) corresponding to the hemicellulose, cellulose and lignin decompositions. The best results were obtained with a model that considers that the biomass decomposes via three independent reactions. There is a qualitative agreement between the decomposition of hemicellulose, cellulose and lignin with the peaks observed in the TG-DTG diagram, but the simple addition of the kinetics of isolated compounds cannot satisfactorily reproduce the kinetic behaviour of any raw material, and consequently some interactions must exist between the fractions considered. (C) 1997 Elsevier Science B.V.