Crude oil is separated through a process called fractional distillation.
What is Fractional Distillation?
Fractional distillation is a crucial process used to refine crude oil. Since crude oil is a complex mixture of hydrocarbons with varying boiling points, this method allows us to separate it into more useful components, called fractions.
The Fractional Distillation Process
The process generally involves these steps:
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Heating: Crude oil is heated to a high temperature (typically around 400°C or 750°F). This vaporizes most of the crude oil.
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Entering the Fractionating Column: The hot vapor is fed into the bottom of a fractionating column, which is a tall tower that is hotter at the bottom and cooler at the top.
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Rising and Cooling: As the vapor rises through the column, it cools.
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Condensation: Different hydrocarbons condense at different temperatures due to their varying boiling points. The larger molecules with higher boiling points condense at the bottom of the column, while smaller molecules with lower boiling points condense higher up where it's cooler.
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Collection: The condensed liquids, or fractions, are collected at different levels of the column.
Fractions and Their Uses
Here's a simplified table showing common fractions and their general uses:
| Fraction | Boiling Point (°C) | Uses |
|---|---|---|
| Refinery Gas | Below 40 | Fuel gas, bottled gas for heating and cooking |
| Gasoline (Petrol) | 40 - 75 | Fuel for cars |
| Naphtha | 70 - 190 | Making chemicals |
| Kerosene | 175 - 275 | Jet fuel, heating oil |
| Diesel Oil | 250 - 350 | Fuel for diesel engines |
| Fuel Oil | 300 - 400 | Fuel for ships and industrial heating |
| Bitumen/Asphalt | Above 350 | Road surfacing, roofing |
Atmospheric and Vacuum Distillation
The initial distillation is typically performed under atmospheric pressure, referred to as atmospheric distillation. The residue remaining after atmospheric distillation can be further processed using vacuum distillation. Reducing the pressure lowers the boiling points, allowing heavier fractions to be vaporized and separated without cracking (breaking down) at excessively high temperatures.
Fractional distillation leverages the different boiling points of the various hydrocarbon components in crude oil to separate it into valuable products.
