Determination of the kinetic parameters of the multi-stage thermal decomposition of solids under non-isothermal conditions by the non-linear estimation approach

Abstract

The activation energy of decomposition of alurniniurn hydroxide vs. weight loss was estimated from thermogravirnetric data collected over a wide range of heating rates, without resorting to the model of the reaction mechanism.These activation energy values were subsequently used to distinguish individual dehydration stages and to determine the best models of the reaction kinetics for these stages.Finally, the overall decomposition model was formulated, and its parameters were determined by the non-linear estimation approach.Owing to the development of numerical, computer-based identification method, derivation of a model for the multi-stage thermal decomposition of a solid has become a greatly simplified task [1 ]. However, a suitable procedure for processing of experimental data to obtain the most information possible on the individual decomposition stages remains of significance. Such a procedure should help to establish a preliminary model structure and determine the activation energy values for the individual stages.Here, a method is advanced for determining the activation energy and the model structure for the individual thermal decomposition stages, and for develoifing a kinetic model of overall decomposition that would most accurately account for the, experimental data over a wide range of experimental conditions. TheoreticalIn the multi-stage thermal decomposition of a solid under increasing temperature it often happens that the successive stages of the process overlap rather than proceed separately.Depending on the decomposition mechanism involved, the chemical reactions corresponding to the individual stages can occur either consecutively or simultaneously.