Waxes in petroleum products – behavior and removal Which statement correctly describes the behavior of waxes naturally present in many petroleum products?

Introduction / Context:
Paraffinic waxes (n-alkanes of higher carbon number) naturally occur in many crude-derived products. Their low-temperature behavior critically affects pour point, filter plugging, and fuel operability in cold climates.

Given Data / Assumptions:

• Products considered: lube distillates, diesel/kerosene cuts, and wax-bearing fuels.
• We seek the statement that best reflects real behavior and standard refinery practice.
• Normal pressure simple distillation is assumed unless otherwise stated.

Concept / Approach:
Waxes are soluble at sufficiently high temperature but crystallise as temperature drops, forming networks that raise viscosity dramatically and can gel the fluid. Refineries remove wax primarily by solvent dewaxing (e.g., MEK/toluene) or catalytic dewaxing—not by simple distillation—because wax components overlap the boiling range of base oils and are difficult to separate by distillation alone.

Step-by-Step Solution:

Verification / Alternative check:
Cold-flow property tests (pour point, CFPP) and dewaxing process literature confirm wax crystallisation behavior.

Why Other Options Are Wrong:

• Separated by distillation: Not practical due to overlapping boiling ranges; dewaxing is used.
• Not soluble: They are soluble when hot; insolubility only appears as crystals at low temperature.
• Decrease viscosity: Opposite; wax raises viscosity and can gel the product.

Common Pitfalls:
Assuming wax is always solid regardless of temperature; solubility is temperature dependent.

Final Answer:
They crystallise out at low temperature.