Extensive thermogravimetric and thermo-kinetic study of waste motor oil based on iso-conversional methods

Abstract The pyrolytic kinetics of waste motor oil (WMO) based on various differential and integral based model-free methods is studied utilizing the data obtained from TGA. For the different heating rates, i.e., 5 °C/min, 10 °C/min, and 40 °C/min the overall volatile conversion was found to be > 90%. The calculation of activation energy is performed using four different models (a) Friedman (b) Kissinger-Akahira-Sunnose (c) Flynn-Wall-Ozawa and (d) Starink methods. The mean activation energy was found to be 139.863 kJ/mol, which has been later used for the determination of z(α) master plots. Moreover, the prediction of the reaction model has been made by analyzing the different theoretical and experimental z(α) master plots. Further, the unknown parameters of the Sestak & Berggrens’s model are obtained using the model fitting methods in MATLAB. The obtained reaction model is f α = d α dt = 3.21 x 10 10 β e - 139863 RT ( 1 - α ) 3.049 α - 6.994 - ln 1 - α 5.626 which followed the autocatalytic (sigmoidal) mechanism. Furthermore, the thermodynamic stability of the system had been determined by calculating the change in entropy, enthalpy and Gibbs free energy. The kinetic parameters along with the thermodynamic results recommend a highly reactive system feasible for waste to energy generation using pyrolysis.