54. Crude Oil and Fractional Distillation

1. What is Crude Oil?

  • Definition: A fossil fuel found deep underground that consists of a mixture of many different compounds.

  • Chemical Composition: Nearly all the compounds in crude oil are hydrocarbons (specifically alkanes), meaning they contain only hydrogen and carbon atoms.

  • Formation: It formed naturally over millions of years from the remains of dead plants and animals, particularly plankton, that were buried in mud. High temperatures and pressures underground turned this organic biomass into oil.

  • Non-Renewable: Crude oil is a finite resource. Because it takes millions of years to form, it is considered non-renewable; if we continue to use it at current rates, it will eventually run out.

2. The Process: Fractional Distillation

Because the different hydrocarbons in crude oil have different boiling points, they can be separated using a process called fractional distillation.

  • Step 1: Evaporation: The crude oil is heated in a chamber until most of it has turned into a gas.

  • Step 2: The Column: The hot gases rise up a fractionating column, which is hot at the bottom and becomes cooler toward the top.

  • Step 3: Condensation: As the gases rise, they condense into liquids when they reach a level that is cooler than their specific boiling point.

    • Long-chain hydrocarbons: Have high boiling points. They condense back into liquids and drain out near the bottom of the column early on.

    • Short-chain hydrocarbons: Have lower boiling points. They stay as gases for longer and rise much higher up the column before condensing.

    • Very short chains: Some are so short that they stay as gases the entire time and leave from the very top of the column.

3. Fractions and Their Uses

The separated groups of hydrocarbons are called "fractions." They are used as fuels or as feedstock (raw materials) for the petrochemical industry.

  • LPG (Liquefied Petroleum Gas): Contains very short chains like propane and butane; used as a gas.

  • Petrol and Diesel: Used as fuel for cars and road vehicles.

  • Kerosene: Used as fuel for jet engines.

  • Heavy Fuel Oil: Used for heating oil or lubricating oil.

  • Bitumen: The longest chains with the highest boiling points; used to surface roads.

4. Trends in the Column

  • Top of the column: Shorter chains, lower boiling points, and higher flammability (making them the best fuels).

  • Bottom of the column: Longer chains, higher boiling points, and lower flammability.