Prediction of biomass composition by autocatalytic modelling of biomass thermogravimetric analysis

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Figure 1: Fitting for the hemicellulose decomposition with a heating rate of 20 ºC/min. W: water, HC: hemicellulose, XHC: hemicellulose char, TOTAL: simulated behaviour and EXP: experimental data

Biomass is a renewable substance formed by three solid components (hemicellulose, cellulose and lignin) in which water and oil can be also present. Kinetics use an auto-catalytic model because it has been used successfully by other authors to reproduce the characteristic degradation in cellulosic materials.

 The reaction pathway follows the Waterloo’s mechanism completed by the vaporization of water and oil. So, all solid compounds break into volatiles and charcoal, which can produce volatiles by a slow reaction too. In order to analyse the main factors that can affect thermal degradation, pure (cellulose, hemicellulose and lignin) and complex samples are studied and fitted. In addition, the effect of using and isothermal or no isothermal process is assessed too, concluding that the structure of biomass and the interactions between its compounds have a strong effect in its thermal degradation. The obtained model is suitable to adjust the experimental data with absolute deviations lower than 7% (Figure 1). The model is able to reproduce the behavior of the individual components present in biomass (Figure 2) and the effect of the heating rate too. The latter is done by a non-Arrhenius’ dependence with temperature. Furthermore, the model is able to predict the initial composition of the studied biomass with deviations lower than 7% for lignin and cellulose.

Figure 2: Simulated differential thermography of the hemicellulose TGA. W: water, HC: hemicellulose, XHC: hemicellulose char and TOTAL: simulated behaviour
Figure 2: Simulated differential thermography of the hemicellulose TGA. W: water, HC: hemicellulose, XHC: hemicellulose char and TOTAL: simulated behaviour

Álvaro Cabeza – Project FRACBIOFUEL – ENE2012-33613

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