Tobacco pyrolysis. Kinetic evaluation of thermogravimetric–mass spectrometric experiments

Abstract

The thermal decomposition of two tobacco blends was studied by thermogravimetry -mass spectrometry (TGA-MS) at slow heating programs under well defined conditions. The kinetic evaluation was based on a distributed activation energy model (DAEM) which is a suitable tool for complex materials of plant origin. Linear and non-linear (stepwise) heating programs were employed to obtain information for reliable kinetic modeling. Series of experiments were evaluated simultaneously by the method of least squares. Efforts were made to identify and describe kinetically the similarities between two, highly different tobacco samples as well as between the various mass spectrometric intensity curves.This was achieved by evaluating large series of experimental results and assuming several kinetic parameters to be common for both samples and/or a group of mass spectrometric intensities. (4) and (5)) cnormed,j cj coefficients normalized so that their sum equals to one (see Eq. (8)) E0,j mean activation energy in a distributed activation energy model (kJ mol -1 )FWHM full width at half maximum (°C) fitN a measure of the fit quality that expresses the difference between a group of N experimental curves and their simulated counterparts (%) (See Eqs. (5) and (6)

Thermal Decomposition Kinetics of Woods with an Emphasis on Torrefaction

“…The employed numerical methods have been described in details earlier. 27 The kinetic evaluation was based on the least squares evaluation of the -dm obs /dt curves, where m obs is the sample mass normalized by the initial dry sample mass. The method used for the determination of -dm obs /dt does not introduce considerable systematic errors into the least squares kinetic evaluation of experimental results.…”

“…The minimization of the least squares sum was carried out by a direct search method, as described earlier. 27 Such values were searched for the unknown model parameters that minimized the following objective function (of):…”

“…Two stepwise temperature programs were employed which also served to increase the amount of experimental information for the kinetic evaluation. 22,[26][27][28][29] Figure 2 shows a test on the employed sample masses. The comparison of experiments with 3 and 10 mg initial sample masses (solid and dashed curves) indicates that the enthalpy change of the decomposition does not result in a considerable thermal lag at the higher sample mass.…”

“…[22][23][24][25][26][27][28][29] According to this model the sample is regarded as a sum of M pseudocomponents, where M is usually between 2 and 4. Here a pseudocomponent is the totality of those decomposing species which can be described by the same reaction kinetic parameters in the given model.…”

“…[22][23][24][25] The increased number of unknown model parameters required the least squares evaluation of larger series of experiments with linear and non-linear temperature programs. 22,[26][27][28][29] The model parameters obtained in this way allowed accurate prediction outside the domain of the experimental conditions of the given kinetic evaluations. 22,26,28,29 The prediction tests helped to confirm the reliability of the model.…”