Mechanistic Understanding of Petroleum Pitch Combustion via TGA and SEM-EDS: A Dual Approach Using Model-Free and Model-Based Kinetics

With the exponential rise in global energy demand, waste-to-energy conversion has attracted significant scientific interest. In this context, the present study investigates the combustion characteristics, kinetics, and thermodynamics of petroleum pitch, an underutilized refinery byproduct, using thermogravimetric analysis (TGA) and SEM-EDS. This is the first comprehensive kinetic and thermodynamic study focused solely on petroleum pitch combustion, establishing foundational data essential for its integration into industrial combustion systems. TGA experiments were conducted at 1.5, 1.75, 2.4, and 2.5 °C/min to evaluate combustion kinetics. The mechanistic understanding of petroleum pitch combustion was captured using model-free (Starink, KAS, FWO, Friedman) and model-based (Coats-Redfern, Criado) kinetic methodologies. The Starink, KAS, and FWO methods showed a variation in activation energies (Eaα) of 74.6–173.2,74.1–172.8, and 82.7–175.5 kJ/mol, with an average of 101.4, 94.0, and 94.5 kJ/mol. The Friedman method showed the variation in activation energy (Eaα) of 13.6–196.3 kJ/mol with an average of 94.3 kJ/mol. The petroleum pitch combustion followed an order-based chemical reaction model, f(α) = 3/2(1-α)1/3, as obtained from model-based Coats-Redfern (C-R), Ciado’s methods, and comparison of activation energy with model-free methods. Thermodynamic parameters (ΔHα, ΔGα, ΔSα) indicated a non-spontaneous but energetically feasible reaction, with well-ordered product formation. Surface morphology and elemental analysis of residues further confirmed intermediate processes such as dehydrogenation, cross-linking, and coke formation. The findings support the feasibility of petroleum pitch as a viable alternative fuel, contributing to energy recovery and sustainable waste management in petroleum refining.