Chemical kinetics of biomass pyrolysis

Biomass pyrolysis occurs during most of the processes related to biomass thermochemical conversion, such as production of liquid biofuels, synthesis gas, chemicals or charcoal, becoming a key factor in most applications. The characteristic parameters that control the kinetics of biomass pyrolysis are the activation energy and the frequency factor. Several models are available in the literature to describe biomass pyrolysis and, between them, the Distributed Activation Energy Model (DAEM) has been widely used due to its simplicity and accuracy in the determination of the characteristic parameters of the biomass pyrolysis process. DAEM has been proved to be valid to describe the pyrolysis of different fuels such as coal, charcoal, sewage sludge, microalgae and several types of lignocellulosic biomass.

Thermogravimetric measurements of biomass pyrolysis carried out at different heating rates can be employed to determine the activation energy and the frequency factor of the sample using the Distributed Activation Energy Model. In order to obtain accurate values of the activation energy and frequency factor of the samples, a certain number of TGA curves, obtained at different heating rates, is needed. Accurate values can be obtain applying directly DAEM based on nine TGA curves obtained at different heating rates, however the number of TGA curves can be reduced by considering the measurements uncertainties during the mathematical procedure needed to apply the model.

The Distributed Activation Energy Model can be also applied to describe the biomass pyrolysis process under parabolic and exponential temperature increases by a simple modification of the typical Arrhenius equation used for linear temperature increases.

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