TG-DSC and TG-FTIR analysis of heavy fuel oil and vacuum residual oil pyrolysis and combustion: characterization, kinetics, and evolved gas analysis

Residual oils, high viscosity and large sulfur content petroleum products from the refining process of crude oil, are receiving increasing interest in pre-combustion carbon capture applications. Gasification is a promising technology to convert such complicated hydrocarbons into syngas. Pyrolysis and combustion are very important stages in the gasification process, and therefore a better understanding of these processes leads to higher efficiency and better development of such applications. In this work, pyrolysis and combustion of heavy fuel oil (HFO) and vacuum residual oil (VRO) were studied in a thermogravimetric analyzer (TGA). The HFO studied in this work is a blend of VRO and diesel, which provides insight into the performance of residual oils/diesel blends. The TGA experiments were conducted using nitrogen and mixtures of oxygen and nitrogen for pyrolysis and combustion studies, respectively, at different heating rates (5–20 °C min⁻¹). The oxygen concentration was varied from 0 to 71.4%_vol. to replicate oxygen concentration in applications ranging from pyrolysis (0% O₂) to combustion (21% O₂) and gasification (high O₂%). The TGA experiments covered a temperature range from ambient to 1200 °C. The results show that pyrolysis is slightly slower than combustion at low temperatures for both oils. However, pyrolysis is significantly faster at high temperatures. The combustion of both oils resulted in minimal residue, while the residue remaining in the pyrolysis is 10–19%. The TGA was coupled with Fourier transform infrared spectroscopy (FTIR) to monitor the evolved volatiles from the pyrolysis and combustion processes. The results show more aromatics evolved from VRO than HFO. Apparent kinetic parameters were calculated using three model-free methods and a model-based method (Coats and Redfern).