Upper secondary · 15 min

Refining crude oil: distillation and cracking

Separate crude oil into fractions by boiling range, then crack heavy molecules into useful light fuels.

Goal

Distinguish physical separation (distillation by boiling point) from chemical transformation (cracking of long alkanes).

Apparatus and reagents

Virtual refinery train: crude feed, furnace, fractionating column, catalytic cracker.

Procedure

Follow the crude oil through the furnace (~400 °C) into the column: which fractions leave at the top, which at the bottom?
Order the fractions — gases, gasoline, kerosene, diesel, fuel oil, bitumen — by boiling range and chain length.
Track the heavy fraction into the cracker: long alkanes break into shorter alkanes plus alkenes.
Write a generic cracking equation like $\ce{C16H34 -> C8H18 + C8H16}$ and explain why alkenes are valuable.

What to observe

Low-boiling small molecules rise and exit high in the column; heavy long chains collect near the bottom.
Cracking increases the yield of gasoline-range molecules and produces alkenes — raw material for polymers.

Explanation

Fractional distillation is physical: components separate because they condense at different temperatures. Cracking is chemical: C–C bonds of long alkanes are broken over zeolite catalysts or by heat, doubling value by matching supply to the demand for light fuels and petrochemical feedstocks.