Measurement of Cracking Kinetics of Pure Model Compounds by Thermogravimetric Analysis

Determination of cracking kinetics by thermogravimetric analysis (TGA) is attractive but requires careful experimental design to ensure consistent results. Here, we examine three methods for determining kinetic parameters by TGA: differential analysis at a constant heating rate (differential), temperature for constant conversion at multiple heating rates (isoconversional), and maximum rate at multiple heating rates (peak temperature). The test compounds used in this study are based on pyrene, with boiling points high enough that mass loss was dominated by the reaction rather than evaporation. The methods using multiple heating rates gave comparable results to each other but were very different from the results from the differential method. The results of the differential method were insensitive to the heating rate and consistent with kinetics of cracking reported in the literature for similar structures. The differential analysis method for cracking of model compounds was the best approach, because the methods of multiple heating rates consumed more sample and were reported in the literature to be very sensitive to minor experimental errors. The conversion in a microreactor experiment was accurately predicted using the kinetics from the differential TGA method, suggesting a consistent reaction rate in these two different reactions. Hence, the differential approach was concluded to be much more accurate when compared to isoconversional and peak temperature methods.