Question

In catalytic cracking

• A. Gasoline obtained has a very low octane number
• B. Pressure and temperature is very high
• C. Gasoline obtained has very high aromatic content
• D. Gasoline obtained has very high amount of gum forming compounds

Hint:

Catalytic Cracking vs. Thermal Cracking: Catalytic cracking uses acid catalysts to yield fuels rich in branched isoparaffins and aromatics, resulting in a much higher octane rating and fewer unstable gum-forming diolefins.

Answer 1

The Correct Option is C

Concept: Fluid Catalytic Cracking (FCC) is a vital conversion process in modern petroleum refining. It breaks down heavy, high-boiling petroleum fractions (like vacuum gas oil) into valuable lighter products such as gasoline and olefinic gases.

Step 1: Analyzing the composition of FCC gasoline.
Unlike thermal cracking, catalytic cracking utilizes acidic zeolitic catalysts. These catalysts promote carbonium ion intermediates, which favor specific secondary reaction pathways such as hydrogen transfer, isomerization, and cyclization.

Step 2: Justifying the high aromatic content.
The catalyst framework accelerates dehydrocyclization and olefin conversion pathways, producing a gasoline fraction with a very high aromatic and branched iso-paraffin hydrocarbon content. This high aromatic concentration provides FCC gasoline with a high octane rating (typically 80–90 RON), making it an excellent blending component for transport fuels. This matches option (3).

Step 3: Disproving alternative choices.

• Option (1) is incorrect: The product has a high octane number, not low.
• Option (2) is incorrect: FCC operates at high temperatures ($480^\circ\text{C}\text{--}540^\circ\text{C}$) but relatively low pressures ($100\text{ kPa}\text{--}300\text{ kPa}$). High pressures are avoided because they suppress the desired cracking reactions.
• Option (4) is incorrect: Catalytic pathways minimize the conjugated diolefins responsible for gum formation compared to purely thermal cracking processes.