Comparative pyrolysis kinetics of heavy oil and its SARA fractions using distributed activation energy model

The pyrolysis behaviors of Qingdao vacuum residue (QD-VR) and its SARA (saturates, aromatics, reins, and asphaltenes) fractions were evaluated by thermo-gravimetric with mass spectrometer (TG-MS). The pyrolysis kinetics were determined by Friedman, one-parallel and four-parallel distributed activation energy model (DAEM), respectively. The results indicated that the pyrolysis behavior of QD-VR was similar to that of aromatics. For saturates, the release of H₂, CH₄, CO, and CO₂ occurred in 80–400 ℃, while the temperature range for QD-VR and other fractions is 200–800 ℃. The average activation energy (E_a) via Friedman method was 179.72 kJ/mol and increased with the conversion ratio. One-parallel Gaussian DAEM was more suitable to describe the pyrolysis process of the single SARA fractions, while four-parallel Gaussian DAEM was more suitable to describe the pyrolysis process of heavy oil. Furthermore, comparing the weighted E_a from one-parallel (227.64 kJ/mol) and four-parallel Gaussian DAEM (204.63 kJ/mol), the results suggested that during pyrolysis process of heavy oil, there was an interaction between the SARA fractions, which could reduce the E_a of heavy oil pyrolysis. Specifically, during heavy oil pyrolysis, resins and asphaltenes could increase the E_a of saturates and aromatics, while saturates and aromatics could decrease the E_a of resins and asphaltenes.