If you mix salt and water, you can easily separate them by boiling the water away. But what happens if you accidentally mix two liquids together, like Alcohol and Water? Because both are liquids, simple boiling won't work perfectly.
To separate a complex mixture of two or more completely mixed liquids (miscible liquids), chemists use an advanced technique called Fractional Distillation.
Principle: Separating a liquid mixture based strictly on the different boiling points of its components.
Requirement: Used when the difference in boiling points is very small (less than 25 Kelvin).
Key Equipment: A Fractionating Column packed with glass beads to create multiple condensation cycles.
Primary Industrial Use: Refining crude petroleum oil into petrol, diesel, and kerosene.
Air Separation: It is also used to cool down and separate atmospheric air into pure liquid Oxygen and pure liquid Nitrogen.
Fractional distillation relies entirely on one massive physical property: Different liquids have different Boiling Points. For example, pure Alcohol boils at a very low 78°C, while Water boils at a much higher 100°C. If you heat the mixture to exactly 80°C, the alcohol will aggressively boil and turn into a gas, while the water will simply sit there as a hot liquid. You can then catch the alcohol gas, cool it down, and you have successfully separated the two.
Simple distillation only works if the boiling points of the two liquids are very far apart (a difference of more than 25°C). However, if the boiling points are very close (like 78°C and 100°C), simple distillation fails because both liquids will start evaporating together. Fractional distillation fixes this by using a tall, glass Fractionating Column packed with glass beads. This column forces the hot vapors to repeatedly condense and boil over and over again on the beads, ensuring that only the liquid with the lowest boiling point makes it to the very top to be collected.
This is one of the most important industrial processes on Earth. When we drill thick, black Crude Oil out of the ground, it is totally useless. Crude oil is a messy mixture of hundreds of different hydrocarbons. Oil Refineries use giant fractional distillation towers to separate it. As they heat the crude oil, the lighter liquids with low boiling points (like Petrol / Gasoline) boil off and are collected at the top of the tower, while the heavy, thick liquids with high boiling points (like Diesel and Asphalt) fall to the bottom.
It is a laboratory and industrial process used to precisely separate a mixture of miscible liquids that have very close boiling points.
The entire process relies completely on the fact that different chemicals evaporate and boil at different specific temperatures (Boiling Points).
Crude oil is heated in a massive fractional distillation tower. Petrol boils at a lower temperature and rises to the top as a gas, while heavy diesel boils at a higher temperature and is collected lower down.
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