Changes in chemical structure and solvation of heavy oil components during thermal upgrading of a vacuum residue

The Venezuelan vacuum residue was used as a feedstock for thermal upgrading experiments to investigate the changes in chemical structure and composition and the solvation interaction of heavy oil components in a micro-batch reactor at 410℃ with an initial pressure of nitrogen 2.0MPa. The ¹H-nuclear magnetic resonance measurement was applied to analyze the reaction pathway of hydrogen atoms with different chemical shift of the heavy oil components. The average molecular structural parameters of asphaltenes and heavy resins in the oil produced by thermal upgrading of the feedstock were calculated and analyzed by the modified Brown-Lander methods. The vapor pressure osmometry was used to determine the average molecular weights of supramolecular structures formed by asphaltenes and heavy resins in toluene. The results show that both H/C atomic ratio and hydrogen donating ability of asphaltenes and heavy resins decrease with reaction time, and the conjugate degree of aromatic ring system and f_A become greater clearly after 45min. The aggregation of asphaltenes rises slowly and increases sharply after 15 min, while there is a slight change of aggregation for the heavy resins during the whole reaction time, and the differences in aggregation correlation values between asphaltenes and heavy resins are increased by 1.5% at 15min, 50.8% at 25min, and 142.3% at 45min, respectively. The solvation interaction of heavy resins with asphaltenes weakens with time, and the solvation parameters decrease from 32.9% at the beginning to 29.5% at 15min, 14.1% at 25min, and 9.6% at 45min, respectively. The changes may contribute to the dropping of thermal colloidal stability of resins and the increasing of spot ratings.