Storage Stability of the Visbreaking Product from Venezuela Heavy Oil

The relationship between the structure and stability of the visbreaking product of Venezuela extra heavy oil has been studied. The number of resin layers adsorbed to asphaltene is proposed to describe the colloidal stability of Venezuela heavy oil and its visbreaking product. The results show that the colloidal stability of the visbreaking product is inferior to Venezuela heavy oil. The factors influencing the storage stability of the visbreaking product have been studied by analyzing the changes of kinematic viscosity, total acid number (TAN), weight loss, ratio of resins/asphaltenes, as well as free-radical content of visbreaking samples sealed and exposed to air or nitrogen for 90 days. It is found that the storage stability of the visbreaking product is influenced by oxidative condensation, evaporation, and non-oxygen condensation, among which oxidative condensation is the most significant factor. The free-radical reactions do not terminate after the thermal reaction, and the content of free radicals is reduced to different degrees for the storage cases. Antioxidants 2,6-di-tert-butyl-4-methylphenol and p,p-di-iso-octyl-diphenylamine were added to visbreaking products by 1 wt % to prevent oxidative condensation. When the TAN and content of free radicals of visbreaking samples with and without antioxidant are compared, it is demonstrated that the antioxidants play the role of generating stable free radicals, which favors the retention of stability.