Feature articleEffective vacuum residue upgrading using sacrificial nickel(II) dimethylglyoxime complex in supercritical methanol

- Upgrading of vacuum residue was examined using sacrificial Ni-DMG.
- High distillable fraction (72 wt.%) obtained with Ni-DMG in supercritical methanol.
- Use of low H2 increased distillable fraction to 92 wt.% by suppressing coke formation.
- Highly denitrogenated, desulphurized and demetallized upgraded oil was obtained.

The petroleum refining industry has become more profitable in recent years owing to the extraordinary value-adding processes of petroleum and petroleum-based products that generate a minimal amount of leftover. However, effectively utilizing vacuum residue (VR) to meet the rising demand for middle distillates in the near future remains a great challenge. The high-cost and low-surplus of hydrogen source in refineries complicate the application of existing slurry hydrocracking technologies at a practical scale. As such, supercritical methanol can serve as an effective and economically viable alternative to conventional VR upgrading techniques. Herein, an effective catalytic upgrading of VR using sacrificial nickel(II) dimethylglyoxime (Ni-DMG) complex in supercritical methanol is reported. The sacrificial Ni-DMG complex prevents low-temperature poisoning, which is typically caused by the heteroatoms present in asphaltenes, as well as catalyst coking. Under an optimized reaction condition of 400 °C, 30.5-31.2 MPa in supercritical methanol at a reaction time of 1 h, a high amount of directly distillable fraction (72.2 wt.%) was obtained using Ni-DMG in supercritical methanol. In the presence of low H2 pressure (initial pressure: 1 MPa), the distillable fraction increased significantly to 92.2 wt.% with an extremely low coke content (6.2 wt.%). In addition, the upgraded oil was completely denitrogenated with noticeable desulfurization and significant demetallization activities (60.4%, 51.2%, and 85.7% reduction of nickel, iron, and vanadium, respectively).

188