Cause of gum formation in stored gasoline

Introduction / Context:
Gum formation during storage degrades gasoline quality, fouls injectors/carburetors, and increases engine deposits. Understanding the mechanism informs additive selection and handling practices.

Given Data / Assumptions:

• Stored gasoline contains trace oxygen exposure and possibly metals that catalyze reactions.

Concept / Approach:
Unsaturated hydrocarbons (olefins) autoxidize to peroxides, then polymerize into higher-molecular-weight species (gums). Antioxidants and metal deactivators are added to inhibit these pathways. Sulphur presence is undesirable for other reasons but is not the primary cause of gum. Aromatics tend to be oxidation-stable relative to olefins; paraffins are even more stable.

Step-by-Step Solution:

Verification / Alternative check:
Induction period and existent gum tests correlate high-olefin blends with faster gum formation unless inhibited.

Why Other Options Are Wrong:

• Alkylation is a refinery process, not a storage degradation route.
• Sulphur affects corrosion and emissions but is not the gum initiator.
• Aromatics and paraffins are relatively oxidation-resistant.

Common Pitfalls:
Confusing “gum” with soot; soot is a combustion phenomenon, not a storage polymerization issue.

Final Answer:
Oxidation and polymerisation of unsaturates