Kerosene composition – most undesirable component for clean burning Which class of hydrocarbons is considered most undesirable in kerosene due to soot formation and low smoke point?

Introduction / Context:
Kerosene quality for illumination and combustion hinges on clean burning with minimal smoke. Hydrocarbon classes influence flame chemistry, soot precursors, and ultimately the smoke point. Understanding which constituents are most detrimental guides refining and hydrotreating strategies.

Given Data / Assumptions:

• Typical kerosene contains paraffins (normal and iso-), naphthenes (cycloalkanes), and aromatics.
• Objective: identify the fraction linked to higher soot formation.
• Smoke point is a proxy for clean burning; higher is better.

Concept / Approach:
Aromatics have ring structures that favor soot formation via polycyclic aromatic hydrocarbon growth. They depress smoke point and lead to luminous, smoky flames. In contrast, paraffins and naphthenes generally burn cleaner, with normal paraffins usually giving the highest smoke points among the listed classes.

Step-by-Step Solution:

Verification / Alternative check:
Refinery practices (hydrotreating and selective hydrocracking) aim to reduce aromatics in kerosene pool to meet smoke point specifications, confirming their undesirability for illumination use.

Why Other Options Are Wrong:

• i-paraffins / n-paraffins: Generally high smoke points; desirable for clean combustion.
• Naphthenes: Intermediate behavior; less problematic than aromatics.

Common Pitfalls:
Equating density with poor burning; density alone is not determinant—aromatic ring structures dominate soot chemistry.

Final Answer:
Aromatics