Crude assay methods: the True Boiling Point (TBP) distillation apparatus is primarily used for which refinery/lab purpose?

Introduction:
Crude assay provides the foundational data for refinery planning. The True Boiling Point (TBP) distillation curve is one of the most informative characterizations, guiding cut points for naphtha, kerosene, gas oil, and residue and informing yields and qualities for downstream units.

Given Data / Assumptions:

• TBP distillation is a laboratory method with high reflux and equilibrium-like conditions.
• Used on crude oils and wide boiling-range fractions.
• Output: temperature vs. volume percent distilled curve.

Concept / Approach:
TBP distillation gives a near-equilibrium boiling curve, unlike simple or ASTM D86 methods. Refiners use the TBP curve for cut planning, unit feed predictions, and property correlations. It is not intended for direct true vapour pressure measurement, and characterization factor (K) is computed from density and boiling relationships, not solely from the TBP apparatus itself.

Step-by-Step Solution:
Define TBP purpose: detailed distillation profile for evaluation of stocks.Connect to refinery planning: select cut points and estimate yields/qualities.Conclude: the apparatus is for evaluation of oil stocks.

Verification / Alternative check:
Assay reports list TBP curves and derived PNA (paraffin-naphthene-aromatic) and property correlations used in LP planning models and blend optimizations.

Why Other Options Are Wrong:

• Characterization factor: a derived index (e.g., Watson K), not a direct TBP apparatus output.
• True vapour pressure: measured by separate RVP/TVP methods.
• None of these: incorrect, as TBP is indeed for stock evaluation.

Common Pitfalls:
Confusing ASTM D86/D1160 with TBP; TBP aims to approximate equilibrium distillation more closely with higher theoretical plates.

Final Answer:
Evaluation of oil stocks via detailed distillation curve (cut planning)