Fuel sulphur across refinery cuts: Among common petroleum products used in transport and heating (petrol/gasoline, kerosene/ATF-range, diesel/gasoil, and heavy fuel oil), which fraction typically contains the highest sulphur content before deep desulphurisation?

Introduction / Context:
Sulphur in petroleum fuels originates from organosulphur compounds present in crude. The distribution of sulphur among product cuts depends on boiling range: heavier fractions concentrate higher-boiling sulphur species, whereas lighter products contain less and are often further hydrotreated. Understanding which product generally has the highest sulphur helps in environmental compliance and unit selection for hydrotreating.

Given Data / Assumptions:

• Relative comparison of untreated product cuts from the same crude slate.
• Modern ultra-low-sulphur specifications exist, but the question targets inherent tendencies before deep desulphurisation.
• Products considered: petrol (gasoline), kerosene/ATF range, diesel/gasoil, and heavy fuel oil (residual).

Concept / Approach:
Sulphur compounds are more prevalent and higher boiling in heavier streams. During distillation, these concentrate in gasoils and especially in atmospheric/vacuum residues blended into heavy fuel oils. Lighter cuts—gasoline and kerosene—contain fewer sulphur compounds intrinsically and are routinely hydrotreated to very low levels. Therefore, heavy fuel oil typically exhibits the greatest sulphur content among listed products.

Step-by-Step Solution:

Verification / Alternative check:
Crude assays show higher sulphur numbers in bottoms/resid streams. Regulatory mandates then drive HDT/HDS severity; nonetheless, without treatment, residual fuels contain the most sulphur.

Why Other Options Are Wrong:

Common Pitfalls:
Assuming modern “on-spec” retail fuels reflect inherent tendencies; regulations lower sulphur across the board but do not reverse the underlying distribution without processing.

Final Answer:
Fuel oil (heavy oil)