Refining chemistry – converting normal paraffins Which refinery process converts n-paraffins to i-paraffins, thereby improving octane number?

Introduction / Context:
Octane improvement can be achieved by altering hydrocarbon structure. Straight-chain paraffins have low octane; branching increases octane. Refineries use specific catalytic routes to rearrange molecules without major carbon number change.

Given Data / Assumptions:

• Feed contains normal paraffins (e.g., C4–C6).
• Goal: increase branching to raise octane while preserving carbon number.
• Low-temperature catalytic processes under hydrogen are available.

Concept / Approach:
Isomerisation catalytically rearranges straight-chain paraffins into isoparaffins. Over bifunctional catalysts (e.g., Pt on chlorided alumina or zeolites), skeletal rearrangement proceeds with minimal cracking, significantly boosting octane in light naphtha pools.

Step-by-Step Solution:

Verification / Alternative check:
Process flow diagrams for light naphtha isomerization units confirm production of isopentane/isomerized C6, improving pool octane.

Why Other Options Are Wrong:

• Alkylation: Combines isobutane with light olefins to form higher isoparaffins; not a simple n-paraffin → i-paraffin rearrangement.
• Polymerisation: Joins small olefins into larger molecules; different objective.
• None of these: Incorrect because isomerisation is the standard route.

Common Pitfalls:
Confusing isomerisation (rearrangement) with cracking (carbon number change). Operating severity must avoid excessive cracking to retain yield.

Final Answer:
Isomerisation