Aniline point test: The aniline point of an oil qualitatively indicates which type of hydrocarbon content in that oil?

Introduction / Context:
The aniline point is the lowest temperature at which equal volumes of aniline and a hydrocarbon mixture are completely miscible. It is widely used as an empirical indicator in fuels and lube testing to infer hydrocarbon type distribution qualitatively.

Given Data / Assumptions:

• Aniline point is measured per standard test methods.
• We need to identify which hydrocarbon family correlates with the value.
• General trends suffice; exact numerical correlation is not required.

Concept / Approach:
Aromatics tend to mix more readily with aniline than paraffins. Therefore, the higher the aromatic content, the lower the aniline point; conversely, paraffinic materials have higher aniline points. Hence, the aniline point serves as a qualitative indicator of aromaticity in petroleum products.

Step-by-Step Solution:

Verification / Alternative check:
Fuel specification guides note that kerosene/jet fuels with lower aromatics typically have higher aniline points, aligning with smoke point and combustion quality trends.

Why Other Options Are Wrong:

• Paraffin: High paraffin → high aniline point; not directly indicated as increasing with the test.
• Olefin: Olefinic content is not what aniline point primarily tracks.
• Naphthene: Cycloparaffins influence exists but the key qualitative indicator is aromaticity.

Common Pitfalls:
Assuming the aniline point rises with aromatics; it actually decreases with more aromatics.

Final Answer:
Aromatic