Asphaltic matter in crude oils: With reference to refinery practice, which statement correctly characterizes “asphalts” present in or derived from crude oils?

Introduction / Context:
“Asphalts” (asphaltenes and resinous bodies) are heavy, high-boiling constituents concentrated in vacuum residues and asphaltic crudes. Their behavior affects fouling, stability, and product quality in downstream units.

Given Data / Assumptions:

• Focus on qualitative properties used in refinery exams.
• Asphalts are associated with residue streams, not light distillates.
• Coke formation tendency is generally undesirable in cracking units.

Concept / Approach:
Asphalts are high molecular weight, high boiling, polyaromatic/polar species. They oxidize readily and can form carbonaceous sludge and sediments. They are not low molecular weight/light boiling (so option a is false). They are also not “desirable” in catalytic cracking; excessive asphaltenes increase coke, deactivating catalyst and reducing liquid yields (so option b is false). Therefore, the correct characterization is their oxidisability and sludge-forming tendency (option c).

Step-by-Step Solution:

Verification / Alternative check:
Refinery operations literature highlights sludge/asphalt stability issues (e.g., storage, blending) and catalyst fouling when asphaltic feeds are excessive.

Why Other Options Are Wrong:

Common Pitfalls:
Misreading “produce coke” as beneficial; in FCC, coke forms on catalyst and must be burned off, limiting yields.

Final Answer:
readily oxidisable and prone to carbonaceous sludge formation