Watson (UOP) characterization factor: The characterization factor for crude petroleum oil (Kw = (Tb)^1/3 / SG at 60°F) typically lies around which value, indicative of an intermediate paraffinic-naphthenic nature?

Introduction / Context:
The Watson characterization factor (also called UOP K-factor) is a widely used empirical index to describe the general nature of a petroleum fraction or crude using average boiling point and specific gravity. It helps infer whether a crude is more paraffinic (higher Kw) or more naphthenic/aromatic (lower Kw).

Given Data / Assumptions:

• Kw = (Tb in Rankine)^1/3 / SG (60°F) for the stream.
• Typical crude values cluster roughly between 10 and 13.
• Higher Kw → paraffinic; lower Kw → naphthenic.

Concept / Approach:
Most world crudes have Kw near 11–12; values near 12.5 denote strongly paraffinic; near 10–10.5 denote naphthenic/asphaltic. Extremely low or high numbers (e.g., 3 or 28) are nonphysical for crude characterization under this definition and unit basis.

Step-by-Step Solution:

Verification / Alternative check:
Crude assay summaries commonly list Kw in the stated band, with paraffinic crudes > 12 and naphthenic crudes < 11.

Why Other Options Are Wrong:

Common Pitfalls:
Forgetting the temperature unit for Tb in the formula and miscomputing Kw magnitude; the cube-root form compresses variation.

Final Answer:
11