Product

Vacuum Diesel is a deliberately created, stand-alone diesel product — not an overlap with LVGO. It exists because the atmospheric column is intentionally under-cut, and the Vacuum Distillation Unit (VDU) recovers the slipped diesel more sharply and more energy-efficiently. Its source is the uppermost side cut (or top pump-around draw) of the Vacuum Distillation Unit, in designs where the atmospheric column deliberately under-recovers diesel and slips it to the VDU.

Defining characteristics of vacuum diesel: true diesel boiling range, slightly heavier sulfur/cold-flow than atmospheric diesel, and a clear destination — the diesel hydrotreater, not the FCC. When modelling or configuring product slates, it should be represented as a separate product with its own assay-quality link to the crude's 300–400 °C fraction, not lumped into LVGO or atmospheric diesel.

Origin and Design Context

• In this design philosophy (common, e.g., in several Indian refinery configurations), the atmospheric column is not overstretched — its diesel endpoint is deliberately held back, typically allowing ~3–7% (often ~5%) of total diesel to slip into the atmospheric residue

• The VDU then recovers this slipped diesel as a distinct side cut above the LVGO draw, taking advantage of the sharper fractionation achievable under vacuum at lower temperatures (reduced thermal cracking risk)

• Benefits claimed for this integrated design: reduced atmospheric column height/trays, better diesel recovery, and improved overall energy efficiency

• The VD/LVGO split is typically clean, and LVGO quality (for FCC or hydrocracker feed) is not compromised

Typical Composition and Boiling Range

• TBP/ASTM D1160 range: approximately 300–380/400 °C (atmospheric equivalent), overlapping and extending the tail of the atmospheric diesel cut

• Composition: straight-run paraffins, naphthenes, and aromatics typical of virgin gasoil; fully saturated (no olefins)

• No C₄− light ends (stripped in the ADU)

Indicative Properties

• Density at 15 °C: ~0.83–0.86 g/cm³ (crude-dependent)

• Cetane index: ~45–55 (crude-dependent; paraffinic crudes higher)

• Sulfur: reflects crude and cut depth — typically 0.2–1.5 wt% (higher than atmospheric diesel from the same crude, as heavier, more refractory sulfur species concentrate in the tail)

• Nitrogen: low, but higher than atmospheric diesel

• Pour point / cold flow: somewhat poorer than atmospheric diesel (heavier paraffins)

• Metals, Conradson carbon: essentially nil — it is a true distillate cut, well clear of resid contamination

Downstream Fates

• Diesel hydrotreater (ULSD unit) feed , blended with atmospheric diesel/LCO — the primary and intended route

• Hydrocracker feed blending component where diesel hydrotreating capacity is constrained

• Occasionally heating oil / gasoil pool blending after desulfurization