Gasoline lead response: Among the listed gasoline streams, which typically shows the highest susceptibility to tetraethyl lead (TEL) octane improvement?
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AStraight-run gasoline
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BPlatinum-reformed gasoline (reformate)
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CCatalytically cracked gasoline (FCC gasoline)
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DPolymer gasoline
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ENatural gasoline (casing-head)
Answer
Correct Answer: Catalytically cracked gasoline (FCC gasoline)
Explanation
Introduction:“Lead susceptibility” refers to the increase in octane number achievable by adding an organo-lead antiknock such as TEL. Different gasoline streams respond differently depending on composition (paraffins, olefins, aromatics).
Given Data / Assumptions:
- Streams considered: straight-run, reformate, FCC (catalytically cracked), polymer gasoline, natural gasoline.
- Legacy context where TEL usage was allowed (historical/technical).
Concept / Approach:Lead response tends to be higher for olefinic and isoparaffinic streams and lower for highly aromatic reformates that already have high intrinsic octane.
Step-by-Step Solution:
Step 1: FCC gasoline is olefinic and responds strongly to TEL.Step 2: Reformate has high aromatics and high base octane, leaving less headroom for lead response.Step 3: Straight-run and natural gasoline show moderate to low susceptibility; polymer gasoline varies but is typically less than FCC in response.Verification / Alternative check:Textbook lead response curves show FCC gasoline with the steepest octane gain per millilitre of TEL.
Why Other Options Are Wrong:
- Straight-run: Lower olefin content, moderate response.
- Reformate: Already high octane from aromatics; limited incremental response.
- Polymer gasoline: Less response than FCC on average.
- Natural gasoline: Often low octane and variable response.
Common Pitfalls:Confusing “highest octane” with “highest lead susceptibility” — they are not the same.
Final Answer:Catalytically cracked gasoline (FCC gasoline)