Towards a meaningful non-isothermal kinetics for biomass materials and other complex organic samples
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The literature of the kinetics in thermal analysis deals mainly with models that consist of a single reaction equation. However, most samples with practical importance are too complex for such an oversimplified description. There is no universal way to overcome the difficulties, though there are well-established models that can express the complexity of the studied reactions for several important types of samples. The assumption of more than one reaction increases the number of unknown parameters. Their reliable estimation requests the evaluation of a series of experiments. The various linearization techniques cannot be employed in such cases, while the method of least squares can be carried out at any complexity of the models by proper numerical methods. It is advantageous to evaluate simultaneously experiments with linear and nonlinear temperature programs because a set of constant heating rate experiments is frequently not sufficient to distinguish between different models or model variants. It is well worth including modulated and constant reaction rate temperature programs into the evaluated series whenever they are obtainable. Sometimes different samples share some common features. In such cases one can try to describe their reactions by assuming parts of the kinetic parameters to be common for the samples. One should base the obtained models and parameter values on a sufficiently large amount of experimental information, in a reliable way. This article is based on the authors’ experience in the indicated directions from 1979 till the present. Though the examples shown are taken from biomass research, the models and methods shown in the article are also hoped to be relevant for other materials that have complicated structure or exhibit complicated thermal reactions, or both.
KeywordsNon-isothermal reaction kinetics Thermal analysis Complex kinetic models Method of least squares Modulated experiments Biomass Charcoal
The authors acknowledge the financial support by the Research Council of Norway and a number of industrial partners through the project BioCarb + (“Enabling the Biocarbon Value Chain for Energy”).
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