Least squares criteria for the kinetic evaluation of thermoanalytical experiments. Examples from a char reactivity study

The mathematical modeling of the chemical processes is a crucial problem of the thermal analysis. Simple models with few parameters seldom can describ e the real complexity of the phenomena arising during the heating of the va rious substances. In the case of more complex models the determination of t he parameters and the validation of the model require the evaluation of car efully designed experimental series. The one-by-one evaluation of the exper iments is a mathematically ill-defined problem at a larger number of unknow n parameters. The non-statistical experimental errors of the thermal analys is hinder the determination of a single parameter set by the simultaneous l east squares evaluation of the experiments. This paper discusses several ev aluation techniques for the handling of the non-statistical errors during t he least squares evaluation of experimental series. The methods are illustr ated by the evaluation of oxidative thermogravimetric experiments of a lign ite and a coal char. (C) 2001 Elsevier Science B.V. All rights reserved.