Principle in fractional distillation of crude oil

I will explain to you what are the principles,construction and working of the fractional distillation of crude and what are its products after its distillation?

The petroleum carried out from the surface of earth is not in pure form and is fractioned in the distillation column to get it into purest form. As the petroleum taken from the Earth is carries a lot of impurities in it which is not suitable for the exact use in industries and factories. Therefore it should be fractionally distilled in the fractional distillation column.

What is fractional distillation?

It is the process of separation of a mixture of various components such as chemical compounds by using their boiling points by heating them to a temperature where they will easily evaporate and forms different fractions. It also requires standard atmospheric pressure for carried out this operation.

Principle of fractional distillation?

The fractional distillation process is based on the difference of boiling points between the mixtures of two substances which is being used for the distillation. As the substances have different boiling points. So, with the passage of heat different impurities show different boiling point and separated easily with the help of outlet pipe.

How is it different from simple distillation?

In simple distillation boiling points among the two or more liquids is greater than 25 degree Celsius but in fractional distillation it is near between 1 degree to 25 degrees.
Moreover simple distillation is basically used for two or three substances whereas in fractional distillation, we have a lot of liquids which a boiling point very close to each other.

Tools used in Distillation carried out in Laboratory

The simple distillation is easy to carry doesn't require too much complex work to do and even don't require too much area for its operation. It can also took place in the laboratory. The instrument required are glass ware and other apparatus which includes Burner, round flask, conical flask, condenser, thermometer and fractional column.

Principle in fractional distillation of crude oil

Construction of laboratory distillation

Take the mixture in the round flask such that burner is providing below the flask to provide heat and fractional column is fitted at the top of the flask to separate the mixture with the help of fractional readings.

The thermometer an also attach at the tip of fractional column to measure temperature inside it. The fractional point is also attached to the condenser for converting the vapors back into water and finally collected in the conical flask.

Working of laboratory distillation

A Bunsen burner is used which is used to provide heat to the round bottom flask which acts as a distilling flask in which we have taken the mixture to which we have to distill.

With the passage of heat liquid start getting evaporates and then the impurity with less boiling point goes on the upper side. As in the above figure water is having lower boiling point so it will evaporates and then condensed in the condenser and finally collected in the conical flask..

The Impurities with the higher boiling point remain separated with in the fractional distillation column and then carried out separately according to their sorted order.

The thermometer is also used to check the temperature maintained with in the flask. It should be up to a certain limit otherwise it will going to have more temperature which leads to the favorable conditions for a blast.

For Example – we have to distill the mixture of water and alcohol. As Alcohol is having boiling point of 79 degrees Celsius while the boiling point of water is 100 degree Celsius. When we provide the heat from Bunsen burner then the most volatile and lighter impurities will go the upper side of fractional column and leaving behind the water.

In which Plants Fractional distillation are carried out?

It is the method of separating a mixture of crude oil which is taken out from the earth surface and the whole fractional process is carried out either in petroleum refineries, petrochemicals and natural gas plants. Some extra substance is always added to the fractional column to remove the impurities. The extra substance which is added is chosen in such a way that when it is added immediately react with the impurities in the form volatile matter which is being lighter rises at the top of Column.

Construction of fractional distillation

Principle in fractional distillation of crude oil

Fractional distillation is also known as Industrial distillation and performed in the very large and vertical columns or towers with the diameter of around 8 meters and the height of fractional between 10 to 70 meters, mainly depend upon the requirement of crude oil we have taken in the column. The fractional columns are consists of different fractions for liquids with different boiling points and also provided with the outlets pipes to take respective liquid from the respective column reading as boiling point of the liquids vary from one another.

The mixture of substances used in the column is directly proportional with the temperature such that low boiling point liquids are on the top side of the column and extracted from the top and the liquids with high boiling point remain in the lower side of the column and extracted from the bottom side of the distillation column.

Working of fractional distillation

It is the distillation process used for distillation of mainly crude oil as it contains so many impurities which is difficult to separate using ordinary laboratory method. The area required for its operation is large as compare to the area required during simple distillation.

The crude oil mixture is taken within the fractional distillation vertical tower and heated at the temperature more than 500 degrees and operation is mainly performed in the oil refineries to get useful substances having different hydrocarbons with the different boiling points. The lighter substances rises in the column have less carbon atoms as there carbon chain is not too much long with less molecular mass and less viscosity and having low ignition temperature. Therefore the lighter substances are always kept in the liquid where providing oxidation is not possible. whereas the heavy substances that left behind in the column have heavy molecular mass and less inflammable as compare to the substances rises at the top of fractional distillation column. It is used for the producing separate substances at the large scale production level.

Principle in fractional distillation of crude oil

Various substances obtained from the distillation are following –

Petroleum gas

At the lower temperature of around 20 degrees liquefied petroleum gas gets vaporized and taken outside with the help of outlet pipe and fed into another plant for it's further purification and after further purification used in households and other domestic purposes for cooking foods and heating water as filled in the cylinders.

Naphtha Chemical

At around 40 degrees Celsius the chemicals used in industries for carrying various operations are used and taken with the help separate outlet pipe and send for further processing.


At around 70 degrees Celsius petrol is taken from its respective fractional column and kept in the large vertical container to provide from the supply of oxygen. As, it is highly inflammable substance and used in two wheelers and four wheelers vehicles for running them for transportation and other purposes. The petrol which is taken out is in form of gasoline which is separated from the by using metallurgical operations.

Kerosene oil and jet fuel

The temperature of around 130 degrees the kerosene oil and the paraffin oil is taken out from the middle way pipe. As it lies in middle of fractional column and used for domestic heating purposes and in jet engine for the running the jets and airplanes.

Diesel fuel

At around 200 degree temperature the diesel is carried out from the pipe which is also used in motor vehicles and other industrial purposes for reducing frictions which in machinery parts.

Lubricating oil

It is the dark viscous semi-liquid substance which is having large number of carbon chains and having higher molecular mass. At around 280 degree Celsius the lubricating oil is taken out from the lower member pipe and used for providing metals from corrosion and other polishing purposes.

Fuel oil

At around temperature of 400 degree Celsius fuel is taken out from the lower pipe which act as a fuel for the ship yards, factories and other motor vehicles. It is highly molecular mass with high ignition temperature.


At around 500 degree Celsius the other residues like wax, grease and other lubricating substances are taken from the pipe adjust at lower of fractional column which is again used in making u of roads as it is an sticky substance.
The various substances obtained from the various distillations are sometimes condensed and taken it with the help of pipe and the process is known as condensation and with less operating cost and high throughput.

All the activities which are carried out in our day to day life are based on the fuel through which we even cannot travel from one city to city. Neither any industry or nor any factory works without the petrol. Therefore, we should fully depend on the fractional distillation for our day to day life.

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Guest Author: ibrahim31 May 2014

Can you please put the advantages and disadvantages of fractional distillation?

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