Oxidative self-heating modeling of iron sulfides during the processing of high sulfur oil

Scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) were used to analyze the surface micromorphology and components of the iron oxide sulfide powders respectively. Differential scanning calorimetry (DSC) and thermogravimetry (TG) were used to investigate the self-heating properties. It was observed that temperature had a significant effect on the microscopic morphology and composition of the sulfide products. The product powders were homogeneously distributed in small particles and the composition of the products were converted from non-stationary FeS to FeS₂ with the sulfidation temperature increased. The apparent activation energy at a sulfidation temperature of 300 °C was 66.5 % of that at a sulfidation temperature of 150 °C. The apparent activation energies were 114.65 kJ/mol, 95.41 kJ/mol, 89.5 kJ/mol and 76.27 kJ/mol respectively at 150 °C, 200 °C, 250 °C and 300 °C during the self-heating reaction phase. There was only one main weight loss phase for the 100 °C, 150 °C and 200 °C products, while the 250 °C and 300 °C products had an additional weight loss phase before the main weight loss phase. The apparent activation energies of the main weight loss phase of the five temperature products were 318.1–333.7 kJ/mol, 266.2–293.2 kJ/mol, 212.7–234.0 kJ/mol, 174.7–193.1 kJ/mol and 168.7–188.7 kJ/mol, respectively. The apparent activation energies of the first weight loss phase of the 250 °C and 300 °C products were 217.4–243.2 kJ/mol and 198.2–214.6 kJ/mol respectively. The mechanism function for the thermal oxidation of elemental sulfur in the first weight loss phase was determined to follow the spherical contraction phase boundary reaction model, i.e. g(α)= [1-(1-α)^1/3]^m. In the main weight loss phase, the mechanism function for the thermal oxidation of iron sulfate followed the random nucleation followed by subsequent growth model, i.e. g(α)= [ln(1-α)]^m.