Devolatilization and Combustion Kinetics of Quercus cerris Bark

Thermogravimetric curves in air of bark from Quercus cerris, a common oak extensively diffused in Southern Europe and Asia Minor, and related char have been measured for heating rates between 5-20 K/min and interpreted by multistep reaction mechanisms. As in the case of wood char, a model consisting of two parallel reactions provides good agreement between predictions and measurements of char oxidation. However, the most important combustion reaction, accounting for about 80% of volatile mass produced, is associated with a lower activation energy (169 versus 182 kJ/mol). This result testifies a reduced reactivity caused, as indicated by scanning electron microscopy (SEM) images, by a less porous structure where high amounts of calcium and a glaze of polymerized products hinder the access of the oxygen toward the active material. In addition to the two char combustion reactions, three parallel reactions are needed to describe the thermogravimetric behavior of bark. These require relatively low activation energies (70-100 kJ/mol) and represent the release of volatiles from the major components of bark, that is, extractives (51%) and lignin (35%), and the small content of holocellulose (14%).