Journal of Thermal Analysis, Vol. 38 (1992) 729-738 THE DETERMINATION OF A COMPLEX KINETIC EXPRESSION OF OIL SHALE PYROLYSIS USING COMBINED NON-ISOTHERMAL AND ISOTHERMAL TG D. Skala* and M. Sokic FACULTY OF TECHNOLOGY AND METALLURGY, 11001 BEOGRAD, KARNEGIJEVA 4, P.O.BOX 494, YUGOSLAVIA The kinetic expression commonly used in the thermal analysis of oil shale pyrolysis was derived on the basis of a simple first order kinetic equation of kerogen decomposition. The activation energy, as well as the reaction rate constant of oil shale pyrolysis could be determined by using non-isothermal (NI) or isothermal (I) TG. However, the kinetic pa- rameters determined by using either NI or I did not enable the good prediction of the kero- gen conversion at other conditions. The comparative results of the NI and I-TG of different oil shales are discussed in the study, as well as the effects of the so-called combined non-isothermal and isothermal TG (NI/I). The obtained results indicate that a mechanism must be postulated based on a com- plex reaction scheme which involves more than one simple reaction. Keywords: kinetics, oil shale pyrolysis, TG Introduction A kinetic model of oil shale pyrolysis can be derived at different complexity levels, very often based on different thermal methods applied for detecting the effects of the thermal degradation of organic substances present in oil shale. The representation of the complex mechanism of the pyrolysis of oil shale by a sin- gle first-order reaction was commonly used, which has some advantages because only two parameters (the activation energy and frequency factor) and the stoi- chiometric equation of the simple reaction: K --->flP+fzR (1) * Author to whom all the correspondence should be addressed John Wiley & Sons, Limited, Chichester Akaddmiai Kiad6, Budapest