Ultrasound Irradiation for Upgrading Vacuum Residue: A Comprehensive Study on Its Effects on Rheological, Structural, Thermal Behavior, and Catalytic Hydrocracking Performance

Upgrading vacuum residue (VR) is essential for efficient utilization of conventional oil, and poor quality VR can cause catalyst deactivation, which is the primary problem that needs to be solved. In this study, ultrasound irradiation was introduced to treat VR, and the original and ultrasonicated samples were investigated using viscosity measurement, group-fraction separation, Fourier transform infrared (FT-IR), and thermogravimetric analysis/differential thermal analysis (TGA/DTA). Furthermore, catalytic hydrocracking was conducted on the original VR and VR treated with ultrasound. The SARA and FT-IR results showed that acoustic cavitation caused the evaporation of light aliphatic components (resulting in a decrease of about 7% in saturate fraction), the breaking of alkyl side chains on aromatic rings or aliphatic chains, and the relaxation or disaggregation of macroaromatic cores (resulting in an increase in aromatic rings and CH3 vibration intensity). Significantly, the TGA carbon residue of the US-120s sample was reduced by 5.7% compared to the original VR. More importantly, catalytic hydrocracking revealed that ultrasound irradiation was able to increase light fraction productivity by 4.962 and 3.880% at the simulation distillation temperature of 420 and 460 °C, respectively. These results directly prove that ultrasonication is beneficial for VR catalytic hydrocracking. Based on these experimental results, this study demonstrates that ultrasound is an effective method for upgrading the vacuum residue.