Pick out the single incorrect statement regarding visbreaking, thermal cracking, catalytic cracking, and related severity/conditions in petroleum conversion processes.
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AHigher temperature is employed in visbreaking than in thermal cracking.
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BPyrolysis (steam cracking) is a severe form of thermal cracking carried out at very high temperature.
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CLead susceptibility of catalytically produced petrol generally exceeds that of thermally cracked petrol.
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DThermal cracking typically operates at higher temperature/pressure than catalytic cracking.
Answer
Correct Answer: Higher temperature is employed in visbreaking than in thermal cracking.
Explanation
Introduction:This question checks conceptual understanding of conversion process severity in refining: visbreaking (mild thermal), thermal cracking (severe), catalytic cracking (lower pressure/temperature than thermal), and pyrolysis/steam cracking (very severe).Given Data / Assumptions:
- We compare typical operating severities (T, P) and gasoline qualities.
- Only one statement must be incorrect after recovery.
Concept / Approach:Visbreaking is designed to mildly reduce viscosity and produce limited conversion; it operates at lower severity than conventional thermal cracking. Catalytic cracking reduces required pressure (and often temperature) relative to purely thermal routes. Pyrolysis (steam cracking) is an extreme case with very high temperatures for olefin production.Step-by-Step Solution:
1) Statement (a) claims visbreaking uses higher temperature than thermal cracking. This contradicts fundamentals; visbreaking is milder.2) Statement (b) is true: pyrolysis/steam cracking is a severe thermal process at very high T.3) Statement (c) is true: catalytic gasoline exhibits higher octane and good lead response historically.4) Statement (d) is true: thermal cracking is generally more severe in T/P than catalytic routes.Verification / Alternative check:Standard refining texts list visbreaking temperatures lower than severe thermal/steam cracking and describe FCC as lower-pressure than thermal cracking.Why Other Options Are Wrong (i.e., not the incorrect one):
(b) Correct: pyrolysis is severe, not mild.(c) Correct: catalytic gasolines have high octane and higher lead susceptibility historically.(d) Correct: thermal cracking typically needs higher T/P than catalytic routes.Common Pitfalls:Thinking “cracking” is uniformly severe; visbreaking is deliberately mild. Also, confusing pyrolysis severity with mild thermal steps.Final Answer:Higher temperature is employed in visbreaking than in thermal cracking.