Polymer gasoline feed selection: In classical refinery polymerisation to make “polymer gasoline,” the preferred feedstock is typically which stream?

Introduction:
Polymerisation (historical polymer gasoline units) converts light olefins to higher-octane gasoline-range hydrocarbons using acid catalysts. Proper feed selection is essential to achieve good conversion and product quality.

Given Data / Assumptions:

• Typical light-olefin sources: FCC wet gas, coker gas, steam cracker off-gas.
• Olefins of interest: mainly C3 and C4 (propylene, butenes), sometimes including ethylene depending on process.

Concept / Approach:
Cracked gas streams enriched in light olefins are ideal for polymerisation. Although propylene and butylenes are the principal workhorses, exam options often summarise this as “cracked gases rich in C2 & C4 olefins.” Naphtha and aromatics are not the target feeds for polymerisation to gasoline; they serve other processes like reforming or extraction.

Step-by-Step Solution:

Verification / Alternative check:
Historic polymer gasoline units and modern oligomerisation processes cite C3/C4 olefins as prime feeds, corroborating the cracked-gas origin.

Why Other Options Are Wrong:

• Naphtha/kerosene: Too heavy; not olefinic feed for polymerisation to gasoline.
• Low-boiling aromatics: Aromatics do not polymerise in this context.
• None of these: Incorrect, as cracked gases are appropriate.

Common Pitfalls:
Forgetting that polymerisation consumes olefins; paraffins/aromatics are not suitable feeds.

Final Answer:
Cracked gases rich in C2 & C4 olefins