Reaction kinetics analysis of heavy oil visbreaking with reduced diffusion limitation

•Reaction kinetics analysis of heavy oil visbreaking in SCbenzene was applied.•SCF visbreaking features low reaction temperature and shortened reaction time.•Competition between dealkylation and condensation exists throughout visbreaking.•Dealkylation-based visbreaking is accelerated by reducing diffusion limitation.•Condensation-based lumped reactions respond sensitively to temperature variation. To understand the reaction behavior of heavy oil visbreaking with reduced diffusion limitation, the visbreaking of an atmospheric residual oil in the solvent of supercritical benzene (SCbenzene) was applied, followed by a reaction kinetics analysis based on a hybrid lumping with combination of boiling point distribution and group composition of oil components. The visbreaking under SCbenzene environment was found to be much faster than that under nitrogen environment, proceeding effectively even at a temperature lower to 350 °C. Although the dealkylation-based lumped reactions responsible for light component production and viscosity reduction are supposed to dominate the visbreaking, a competition between dealkylation and condensation exists throughout the visbreaking. Because of the reduced diffusion limitation to reaction kinetics, the condensation-based lumped reactions with a higher activation energy up to 306 kJ.mol−1 respond more sensitively to the variation of reaction temperature, greatly shortening the reaction time window for the visbreaking at high temperatures.