The use of the IKP method for evaluating the kinetic parameters and the conversion function of the thermal dehydrochlorination of PVC from non-isothermal data

Abstract

The isoconversional methods (Friedman and Flynn–Wall–Ozawa) as well as the invariant kinetic parameters method (IKP) were used to discriminate the kinetic models and to determine the kinetic parameters for the thermal degradation of PVC from the simultaneous analysis of a set of TG data obtained at different heating rates ranging from 2 to 10 K min −1 . The activation energy ( E ) value obtained by the IKP method is in good agreement with the values obtained by isoconversional methods. It was also shown that the values of the pre-exponential factor ( A ) and the conversion function ( f ( α ), where α is the conversion) calculated by means of the IKP method depend on the set of kinetic models considered. The ratio of the values of f ( α ), corresponding to two sets of kinetic model, does not depend on the conversion. This proportionality and the differences between f ( α ) values calculated for a certain set of kinetic models and the real values of f ( α ) can be explained by inherent errors in the evaluation of the invariant pre-exponential factor. The kinetic triplet obtained for the investigated process is: E=104.1 kJ mol −1 ; A=1.06×10 8 s −1 and f ( α )= α 0.63 (1− α ) 1.55 ≅(1− α ) 1.81 [−ln(1− α )] 0.62 .