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The effect of oxygen in the ambient gas was studied at low sample masses (0.2 -0.4 mg) that excluded 2 the overheating due to the high reaction heat of the combustion process. The presence of oxygen affects the decomposition from ca. 220°C. Nevertheless, the extrapolated onset temperature of the hemicellulose decomposition is practically the same at 0, 5 and 21 V/V% oxygen. A group of 12 experiments, representing two grinding levels, three plant genera and four different heating programs were evaluated simultaneously by the method of least squares employing the model of independent pseudocomponents. All evaluated experiments were well described by the same set of kinetic parameters; only the parameters describing the peak area of the partial processes differed. A technique was recommended for the appropriate handling of the non-random errors in the simultaneous evaluation of experiment series.

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ABSTRACT. Charcoals produced by a modern, efficient method were studied in the kinetic regime, at oxygen partial pressures of 0.2 and 1 bar by thermogravimetric experiments and their reaction kinetic modeling. The charcoals were ground to an average particle size of 5 -13 µm. A partial removal of minerals from the feedstock (corncobs) by an acid-washing procedure resulted in ca. 6 times higher specific surface area in the charcoal. In spite of the increased surface area, this sample evidenced a much lower reactivity. A model based on three reactions gave an adequate description over a wide range of experimental conditions. 38 experiments on 4 charcoal samples were evaluated. The experiments differed in their temperature programs, in the ambient gas composition and in the grinding of the samples. Characteristics of the combustion process were determined, including activation energy values characteristic for the temperature dependence of the burn-off; formal reaction orders characterizing the dependence on the oxygen content of the ambient; and functions describing the conversion dependence of the partial processes.

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