A summative model for the pyrolysis reaction heats of beech wood

Kinetic models of beech wood decomposition, based on the three main pseudo-components, hemicellulose (one or two steps), cellulose (one step) and lignin (one or two steps), are applied for the first time to predict differential thermogravimetric (DTG) and differential scanning calorimeter (DSC) curves available from the literature. For the conditions that minimize the activity of secondary reactions, it is found that while the DTG curves are already well predicted by the extensively used three-step model, at least an additional step is required for the pseudo-lignin decomposition for a good prediction of the DSC data. The pseudo-cellulose decomposition is a globally endothermic process with the corresponding heat varying from about 601-528 J/g (of volatile evolved), as the number of reaction steps is increased from three to five. Pseudo-hemicellulose decomposition also takes place endothermally with reaction heats of 245 J/g (one step) or 321 and 226 J/g (two steps). Instead pseudo-lignin decomposition occurs with remarkable exothermicity corresponding to -923 J/g (one step) or -728 and -635 J/g (two steps).