Sub-Product

Vacuum distillation residue is the remaining fraction of a crude oil or petroleum product after removing the fuel and oil fractions from petroleum by successive atmospheric and vacuum distillation. The yield of tar from various petroleum is 15–30 wt-%.

It is a black viscous substance and a a complex mixture of high-boiling-point components, including including:

• Heavy hydrocarbons: High-molecular-weight hydrocarbons, such as asphaltenes, resins, and waxes.
• Polycyclic aromatic hydrocarbons (PAHs): Complex aromatic molecules with multiple rings, which can be carcinogenic and toxic.
• Sulfur compounds: Organic sulfur-containing molecules, such as mercaptans and sulfides.
• Heavy metals: Metals like vanadium, nickel, and iron, which can be present in the residue.

The distillation residue is typically characterized by its:

• Boiling point: Higher than 400°C (752°F), often exceeding 500°C (932°F).
• Viscosity: Higher than 100 cSt (centistokes) at 100°C (212°F) or conventional viscosity of 18°-45°at 100° C. 
• Chemical composition: Complex mixture of hydrocarbons, sulfur compounds, and heavy metals.

The specific gravity of vacuum residuum varies depending on the crude oil source and the vacuum distillation conditions used to produce the residuum.
Some typical values are: 

• 0.87 for N'Kossa crude vacuum residuum

• 0.93 for Kuito crude vacuum residuum

• 1.0 for another type of vacuum residue

Distillation residue is often problematic due to its:

• Viscosity: High viscosity can lead to issues with pumping, transportation, and processing.
• Corrosivity: The presence of sulfur compounds and heavy metals can cause corrosion in equipment and pipelines.
• Toxicity: The presence of PAHs and other hazardous compounds can pose environmental and health risks.
• Recalcitrance: The residue’s complex composition and high boiling point make it challenging to refine or upgrade.

References

1. TheFreeDictionnary, Tar.
2. Brave search summarizer, Search term 'vacuum gasoil fuel oil' (accessed 15^th Dec 2024).