Isomerisation chemistry: The isomerisation process primarily converts which hydrocarbon family into iso-paraffins to improve octane?

Introduction / Context:
Isomerisation is a key octane-boosting process used to improve light naphtha quality by rearranging the carbon skeleton of hydrocarbons without changing their carbon number.

Given Data / Assumptions:

• Target products are high-octane iso-paraffins (e.g., isopentane, isohexane).
• Typical feeds contain normal paraffins in C5–C6 range.
• Process conditions: low temperature, chlorinated alumina or zeolitic catalysts, hydrogen present to suppress coking.

Concept / Approach:
Normal paraffins have lower octane numbers than their branched isomers. Isomerisation increases branching (skeletal isomerization), turning n-paraffins into iso-paraffins, thereby raising octane without changing boiling range.

Step-by-Step Solution:

Verification / Alternative check:
Refinery flow schemes show C5/C6 isomerization units feeding into gasoline blending pools to increase Research Octane Number (RON).

Why Other Options Are Wrong:

• Olefins: Double-bond isomerization exists but is not the primary refinery isomerisation objective for octane in light naphtha.
• Naphthenes: Can equilibrate among ring isomers, but octane uplift focus is on n-paraffins.
• None of these: Incorrect because paraffins are correct.

Common Pitfalls:
Confusing isomerisation with reforming (which also increases octane but via dehydrogenation/cyclization/aromatization).

Final Answer:
Paraffins (normal paraffins to iso-paraffins)