Pyrolysis kinetics of lignocellulosic materials - three independent reactions model

The behaviour of biomass components (cellulose, xylan-representative of hem icelluloses-and lignin) was studied thermogravimetrically with linear tempe rature programming, under nitrogen and air. The results were compared and t he pyrolysis kinetics of cellulose determined, assuming a first-order kinet ic function. The thermal decomposition of xylan and lignin could not be mod elled with acceptable errors by means of simple reactions. Thermograms were determined for pine and eucalyptus woods and pine bark, under inert (nitro gen) or oxidizing (air) atmosphere. The pyrolysis of these lignocellulosic materials was modelled with good approximation by three first-order indepen dent reactions. One of these reactions is associated with the primary pyrol ysis of cellulose, its parameters being previously determined and fixed in the model. The model parameters are the activation energies and pre-exponen tial factors for the pyrolysis of the remaining two pseudo-components and t wo additional parameters related to the biomass composition. A method to de termine this composition was proposed. The results calculated in this way w ere compared with data from the literature and those determined thermogravi metrically in air, showing good agreement. (C) 1999 Elsevier Science Ltd. A ll rights reserved.