Catalytic cracking operating trends Which statement set correctly captures typical effects in catalytic cracking units regarding pressure, temperature, and catalyst-to-oil (C/O) ratio?

Introduction / Context:
Fluid catalytic cracking (FCC) and related catalytic cracking processes convert heavy feeds to lighter products. Operating variables such as pressure, temperature, and catalyst-to-oil ratio (C/O) strongly influence conversion, selectivity, and product quality. This question checks whether you understand common qualitative trends used in troubleshooting and optimization.

Given Data / Assumptions:

• Conventional catalytic cracking of gas oils (not hydrocracking).
• Comparison is qualitative and exam-style, using widely taught rules of thumb.
• Octane refers to gasoline pool octane from the cracker.

Concept / Approach:
(a) Higher reactor pressure promotes hydrogen transfer reactions, which saturate olefins and increase paraffinicity. This reduces gasoline octane, because olefins and aromatics usually carry higher octane than paraffins.
(b) At higher temperature, selectivity shifts toward lighter gases and LPG; for a set overall conversion target, the incremental gasoline yield can decline due to increased cracking severity, even as gasoline octane tends to rise.
(c) Raising C/O generally increases conversion since more active sites contact the feed per unit time, improving cracking extent up to hydrodynamic and diffusion limits.

Step-by-Step Solution:

Verification / Alternative check:
FCC operating guides show octane falling with pressure due to hydrogen transfer, and yield curves shifting with temperature and C/O as described.

Why Other Options Are Wrong:

• Any single-statement option omits other true effects; the comprehensive answer is the combined one.

Common Pitfalls:
Assuming higher pressure always improves quality; in cracking, it can decrease gasoline octane. Also, conflating total conversion increase with gasoline yield increase—selectivity matters.

Final Answer:
All of (a), (b) and (c)