Effects of Changes in Asphaltenes on Viscosity Reduction of Heavy Oil after Thermal Visbreaking

Changes in asphaltene content in heavy oils after thermal visbreaking at different cracking temperatures and reaction times were studied by various techniques, including elemental analysis, X-ray diffraction, Fourier transform infrared spectroscopy and nuclear magnetic resonance spectroscopy. The yield of asphaltene decreased at the beginning of thermal visbreaking, but further increased with deep thermal visbreaking. The aromaticity of asphaltene increased with higher cracking severity. In addition, the effect of asphaltene on viscosity was investigated before and after thermal visbreaking. There was a close relationship between asphaltene content and viscosity, and the viscosity increased dramatically with higher asphaltene content. The viscosities were also different at the same asphaltene content due to the differences in chemical composition and macrostructure of the asphaltene molecules. Therefore, both the contents and structures of asphaltene had significant influences on the viscosity of heavy oils. However, the changes in the content and structure of asphaltene were not major causes for the decrease in viscosity after thermal visbreaking.