Organic Chemistry Of Fluid catalytic cracking and reforming

 

WAEC Chemistry Practice Quiz: Fluid Catalytic Cracking & Reforming

Test your knowledge with these 5 WAEC-style objective questions on refinery operations. Click "Show Answer" to view the correct option and solution.

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1. The primary purpose of fluid catalytic cracking (FCC) in a petroleum refinery is to ________.

A. separate crude oil into its various boiling point fractions B. break down heavy, high-molecular-weight hydrocarbons into lighter fractions like petrol C. convert branched alkanes into straight-chain alkanes to decrease volatility D. remove sulfur impurities from straight-run naphtha

Correct Answer: B

Explanation: Fluid Catalytic Cracking is a destructive process that takes heavy, long-chain fractions (like gas oils) that have low commercial demand and breaks them down into lighter, high-demand molecules within the gasoline ($\text{C}_5$ to $\text{C}_{12}$) range.

2. Which of the following catalysts is typically used in the Fluid Catalytic Cracking unit?

A. Finely divided iron B. Synthetic zeolite aluminosilicate C. Platinum-Rhenium on alumina D. Concentrated tetraoxosulfate(VI) acid

Correct Answer: B

Explanation: Modern FCC units use synthetic zeolites (crystalline aluminosilicates) because they have highly uniform pore structures and provide excellent catalytic activity and selectivity for producing gasoline-range fractions.

3. In refinery operations, low-octane straight-chain alkanes are converted to high-octane aromatic and branched hydrocarbons without changing their carbon numbers by ________.

A. thermal cracking B. catalytic reforming C. polymerization D. steam distillation

Correct Answer: B

Explanation: Catalytic reforming rearranges (reforms) the structures of naphtha molecules via isomerization and aromatization. It focuses on changing the molecular shape to improve the quality/octane rating rather than splitting the molecules apart.

4. Which of the following gaseous byproducts is heavily produced during catalytic reforming and reused for hydrotreating inside the refinery?

A. Carbon(II) oxide ($\text{CO}$) B. Hydrogen gas ($\text{H}_2$) C. Ethene gas ($\text{C}_2\text{H}_4$) D. Hydrogen sulfide ($\text{H}_2\text{S}$)

Correct Answer: B

Explanation: A major chemical reaction during catalytic reforming is dehydrogenation (removing hydrogen from saturated rings to form aromatic compounds like benzene). This process produces massive quantities of highly valuable hydrogen gas ($\text{H}_2$).

5. What is the fundamental operational difference between cracking and reforming?

A. Cracking changes physical states; reforming changes chemical formulas. B. Cracking involves precious metals; reforming uses non-metal powders. C. Cracking decreases fuel yield; reforming dramatically increases total yield. D. Cracking reduces molecular size to increase fuel quantity; reforming rearranges molecular structures to improve fuel quality.

Correct Answer: D

Explanation: Cracking targets *quantity* by breaking down larger, unusable fractions into smaller petroleum molecules. Reforming targets *quality* by upgrading small, straight-chain molecules into branched/aromatic molecules with much higher octane ratings.