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The performance of heavy oil visbreaking in supercritical cyclohexane (SCC6H12) was evaluated, followed by a comparison with its reaction in supercritical benzene (SCC6H6). The dealkylation-based viscosity reduction in the SCC6H12 was accelerated by improving the diffusivity, through which a product viscosity (80 °C) as low as 0.5 Pa.s was readily obtained by visbreaking at 380 °C for 5 min. A competition between dealkylation and condensation took place throughout the visbreaking process. As the reaction proceeded or the temperature increased, condensation played an increasingly dominant role in the visbreaking. Unlike the inert SCC6H6, the SCC6H12 participated in the visbreaking by saturating the alkyl carbon radicals essential for dealkylation and the aromatic carbon radicals essential for condensation. The viscosity reduction efficiency of the visbreaking in the SCC6H12 was initially suppressed by the H-donation of the solvent, but recovered rapidly due to the improved diffusion environment. Benefiting from the saturation of the aromatic carbon radicals, the asphaltene content of the product obtained in the SCC6H12 was lower than the corresponding value of the product obtained in the SCC6H6.

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