Thermal decomposition kinetics of sorghum straw via thermogravimetric analysis

The thermal decomposition of sorghum straw was investigated by non-isothermal thermogravimetric analysis, where the determination of kinetic triplet (activation energy, pre-exponential factor, and reaction model), was the key objective. The activation energy was determined using different isoconversional methods: Friedman, Flynn-Wall-Ozawa (FWO), Kissinger-Akahira-Sunose (KAS), Starink, Iterative method of Chai & Chen, Vyazovkin AIC method, and Li&Tang equation. The pre-exponential factor was calculated using Kissinger's equation; while the reaction model was predicted by comparison of z-master plot obtained from experimental values with the theoretical plots. The values of activation energy obtained from isoconversional methods were further used for evaluation of thermodynamic parameters, enthalpy, entropy and Gibbs free energy. Results showed three zones of pyrolysis having average activation energy values of 151.21 kJ/mol, 116.15 kJ/mol, and 136.65 kJ/mol respectively. The data was well fitting with two-dimension 'Valensi' model for conversion values from 0 to 0.4 with a coefficient of determination (R-2) value of 0.988, and with third order reaction model for values from 0.4 to 0.9 with an R-2 value of 0.843.