In modern refineries, the catalytic cracking of heavier petroleum fractions (e.g., vacuum gas oil) is primarily carried out to maximize which valuable product stream?

Introduction:
Catalytic cracking, especially in fluid catalytic cracking (FCC) units, upgrades heavy gas oils into lighter, higher-value products. The core economic driver is the conversion of heavy feed into the gasoline pool along with LPG/propylene co-products.

Given Data / Assumptions:

• Feed: vacuum gas oil/heavy gas oils.
• Process: catalytic cracking using acidic zeolite catalysts.
• Key KPI: gasoline yield and octane.

Concept / Approach:
FCC catalysts and operating conditions are tuned to maximize gasoline-range molecules with adequate octane, while also producing LPG/propylene and some light cycle oil. Heavy resid is minimized or processed upstream (e.g., hydrocracking) depending on configuration.

Step-by-Step Solution:
1) Identify target products of FCC.2) Recognize refinery economics favor gasoline production in many markets.3) Select gasoline as the primary objective.

Verification / Alternative check:
Typical FCC yield profiles show gasoline as the largest single product cut by volume, with LPG as a significant secondary product; diesel is not the primary target for FCC (hydrocracking is preferred for distillate mode).

Why Other Options Are Wrong:
Asphalt/tar: Not the purpose of catalytic cracking; those are heavy residues.Diesel: FCC does make some LCO, but not as the main objective.Sulfur: A contaminant to be removed, not a product.

Common Pitfalls:
Confusing FCC with hydrocracking (distillate mode) or visbreaking/coking which handle resid with different product slates.

Final Answer:
Gasoline (petrol)