Processing of TGA data: Analysis of isoconversional and model fitting methods

Thermogravimetric analysis (TGA) is routinely used to characterize coal. Apart from proximate analysis, TGA data is also used to characterize kinetics of devolatilization and char combustion. Various methods have been proposed to process the TGA data [isoconversional or model free methods such as Friedman method, Kissinger method, Flynn-Wall-Ozawa method (FWO), Kissinger-Akahira-Sunose method (KAS) or single or multi-reaction models (SRMs/MRMs) and distributed activation energy models (DAEMs)]. In this work, we have critically examined various models for processing TGA data obtained with typical Indian coal. A generalized equation has been proposed to encompass different models as special cases. We have also considered a model based on a possibility of distribution of frequency factor along with constant or distribution of activation energies. The results of TGA data described by different models were critically analyzed. The presented results and methodology will be useful for selecting appropriate strategy for processing TGA data.