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

Abstract

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 °C, while the temperature range for QD-VR and other fractions is 200–800 °C. The average activation energy (Ea) 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 Ea 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 Ea of heavy oil pyrolysis. Specifically, during heavy oil pyrolysis, resins and asphaltenes could increase the Ea of saturates and aromatics, while saturates and aromatics could decrease the Ea of resins and asphaltenes.