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Lesson 2 - Fractional Distillation

Crude oil is separated into fractions using fractional distillation. Fractional distillation works by heating the crude oil so its components evaporate at different temperatures based on their varying boiling points. This allows the evaporated components to condense into fractions at different heights of the distillation tower based on their boiling points. Fractional distillation is used industrially to separate crude oil into useful fractions like liquid petroleum gas, gasoline, kerosene, diesel fuel, and fuel oil.

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Aditya Shyamsunder
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103 views5 pages

Lesson 2 - Fractional Distillation

Crude oil is separated into fractions using fractional distillation. Fractional distillation works by heating the crude oil so its components evaporate at different temperatures based on their varying boiling points. This allows the evaporated components to condense into fractions at different heights of the distillation tower based on their boiling points. Fractional distillation is used industrially to separate crude oil into useful fractions like liquid petroleum gas, gasoline, kerosene, diesel fuel, and fuel oil.

Uploaded by

Aditya Shyamsunder
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as PDF, TXT or read online on Scribd
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Crude oil is a mixture of many

different substances.
Most of these substances are hydrocarbons. Hydrocarbons are
compounds which contain only hydrogen and carbon combined together by strong
bonds inside the molecule.
H H H H H H H H H H
In fact, hydrocarbons with more carbon atoms
H C C C C C C C C C C H in their molecules tend to have a higher
boiling point.
H H H H H H H H H H

Each of these hydrocarbons has a different boiling temperature.


“Fractions” contain mixtures of hydrocarbons with similar boiling points.
How can we separate the complicated mixture in crude oil into fractions ?
The method uses the differences in their boiling points :
It is called : FRACTIONAL DISTILLATION.
How does it work ?
If you heat the oil and evaporate it, those hydrocarbons with the lowest boiling point (smallest
number of carbon atoms) will be the easiest to boil.
So, if we allow the oil vapour to condense at a number of different temperatures, we will collect a
different fraction at each temperature.
Fractional distillation.
Fractional distillation is carried out industrially on a very large
scale in oil refineries.

Oil refinery.
Fractional distillation
tower.
Fractional distillation.
Liquid petroleum gases
(LPG)

Petrol for car fuel


Naptha for chemicals.
Kerosene for jet fuel
The temperature falls as
Diesel for lorries/trains
we go higher up the
column.
Fuel oil for
industrial heating
We heat the crude oil Bitumen for road surfaces
so that it boils.

These are the fractions

The vapour rises up the distillation column and each fraction “exits” the column at a certain
height where the temperature allows it to condense.
Our crude oil has been separated into different fractions.
Uses of fractions.
Liquid petroleum gases (LPG)

Petrol for car fuel


Naptha for chemicals.
LPG : Kept as a liquid in cylinders but
comes out as a gas which burns very easily
Kerosene for jet fuel
when lit with a match.
Diesel for lorries/trains Uses :
Camping stoves & homes where “gas” has to
Fuel oil for be delivered into a tank.
industrial heating

Bitumen for road surfaces

Liquid fuels used for transport.


Sparks from the spark plugs set fire to petrol in a car engine.

We want jet fuel to produce less vapour and not catch fire so readily (safety reasons).

Diesel engines are designed for a thicker fuel which only burns at higher temperatures.
Topic test.
Check the Learning Objectives

What is fractional distillation used for & how does it work ?


The hydrocarbon mixture in crude oil is separated into a number of fractions.
It works because each fraction has a different boiling point and will condense at a different
temperature.
What is a ‘fraction’ ?
A fraction is a smaller mixture of hydrocarbons containing molecules with a narrow range of
sizes and similar boiling points.

Consider a number of hydrocarbon molecules with an increasing number of carbon


atoms. How do the following change as they get larger ? (a) ease of ignition
(b) boiling point. it gets less – higher temperature needed to start them burning.
increases – harder to boil & so condense at higher temperatures.

When a hydrocarbon burns, what are the products from both complete &
incomplete combustion ?
From complete combustion : carbon dioxide and water.
From incomplete combustion : carbon monoxide & carbon as well as water.

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