Journal of Thermal Analysis, Vol. 47 (1996)535-542 Kinetics APPLICATION OF COMPLEX REACTION KINETIC MODELS IN THERMAL ANALYSIS The least squares evaluation of series of experiments G. Vdrhegyi 1, M. J. Antal, Jr. 2 Piroska Szab61, Emma Jakab 1 and F. Till 1 1Hungarian Academy of Sciences, Research Laboratory for Inonganie Chemistry, P.O.Box 132, Budapest 1518, Hungary 2Hawaii Natural Energy Institute and the Department of Mechanical Engineering, University of Hawaii at Manoa, Honolulu, HI 96822, USA Abstract The complexity of the phenomena which arise during the heating of the various substances seldom can be described by a single reaction kinetic equation. As a consequence, sophisticated models with several unknown parameters have to be developed. The determination of the un- known parameters and the validation of the models requires the simultaneous evaluation of whole series of experiments. We can accept a model and its parameters if, and only if we get a reason- able fit to several experiments carried out at different experimental conditions. In the field of the thermal analysis the method of least squares alone seldom can select a best model or a best set of parameter values. Nevertheless, the careful evaluation of the experiments may help in the dis- eerning between various chemical or physical assumptions by the quality of the corresponding fit between the experimental and the simulated date. The problem is illustrated by the thermal de- composition of eeUulose under various experimental conditions. Keywords: cellulose, kinetics, thermogravimetry Introduction The mathematical modelling of the chemical processes is a crucial problem of the thermal analysis. Without a proper model we cannot answer even a ques- tion like "Do the same reactions occur in an isothermal and a non-isothermal experiment?". A single kinetic equation of type 0368-4466/96/$ 5. O0 9 1996 Akad~miai Kiadr, Budapest John Wiley & Sons, Limited Chichester