Crude distillation trends — heteroatom distribution In atmospheric crude distillation, how does sulphur content typically vary from lighter fractions to heavier fractions?

Introduction / Context:
Understanding how heteroatoms distribute across crude fractions is essential for refinery processing and environmental compliance. Sulphur content affects hydrotreating severity and product pool quality.

Given Data / Assumptions:

• Typical crude oil behavior (exceptions exist).
• Fractions considered range from light naphtha to heavy gas oil and residue.

Concept / Approach:
Sulphur compounds tend to concentrate in higher-boiling fractions because they are often larger, more complex molecules with higher boiling points (e.g., dibenzothiophenes). Thus, as you go heavier, sulphur content usually rises.

Step-by-Step Solution:
Compare light vs. heavy cuts: light naphtha has lower sulphur; heavy gas oils/resid have higher.Therefore, sulphur increases from lighter to heavier fractions.

Verification / Alternative check:
Hydrotreaters are staged by cut because heavier feeds require higher severity to remove sulphur, confirming the trend.

Why Other Options Are Wrong:

• “Sulphur decreases” is opposite of typical crude behavior.
• “Nitrogen decreases” addresses another heteroatom and is not asked; nitrogen also tends to increase in heavier fractions.
• “None of these” is incorrect because a clear trend exists.

Common Pitfalls:

• Assuming all crudes behave identically; however, the general refinery design basis follows this trend.

Final Answer:
sulphur increases