Kinetic and thermodynamic parameters of petroleum pitch pyrolysis using thermogravimetric analysis (TGA): Part I

Knowledge of the kinetics of petroleum pitch pyrolysis is crucial to improve and optimize the design of pyrolysis reactors, gasification reactors, and circulating fluidized bed combustors (CFBC) to use as feedstock. Thermogravimetric analysis (TGA) was performed to understand the kinetic aspects of the pitch pyrolysis. The isoconversional Friedman, Kissinger-Akahira-Sunose (KAS), Flynn-Wall-Ozawa (FWO), and Starink methods were used to calculate the divergence of activation energy and mechanistic understanding of the complex nature of pitch pyrolysis. The mean activation energies were 176.46, 178.79, 176.79, and 189.90 kJ mol-1 for the KAS, FWO, Starink, and Friedman methods. The three-dimensional diffusion model, followed by the pyrolysis process, was determined using model-based Coats-Redfern and Criado methods. The linear relationship of the pre-exponential factor and the activation energy was obtained through the kinetic compensation effect (KCE) relationship. The positive values of enthalpy and Gibbs Free energy confirmed the endothermic nature of the pitch pyrolysis. The positive to negative variation of entropy was observed because of the complicated nature of the pitch pyrolysis process. During pyrolysis, the residue's surface morphology detected pores, cracks, and mesophase formation in scanning electron microscope (SEM) analysis, and sulfur, vanadium, and nickel were present in energy-dispersive spectrometer (EDS) analysis of the residue. Fourier transform infrared spectroscopy (FTIR) analysis of the sample and residue showed an intermediate cross-link reaction, which led to the formation of a mesophase coke structure in the pyrolysis process.