Distillation is a physical process of separating the component substances from a liquid mixture based on differences in the boiling point of the components of the mixture.

There are many types of distillation :

  • Simple distillation.
  • Fractional distillation.
  • Vacuum distillation.
  • Flash distillation.
  • Azeotropic distillation.

Simple distillation

Liquid is boiled and the vapours of the more volatile components are condensed and liquefied.

Fractional distillation

It is the same process of simple distillation but it has a fractionating column to achieve pure distillates.

Vacuum Distillation

It is used when the boiling point of the compound is too high to distil the compound without significant decomposition.

Flash distillation

the process of separating or purifying a substance by removing the solvent quickly. It is used to desalinate seawater.

Azeotropic distillation

It is based on adding a compound that forms an azeotrope with at least one of the components of a mixture which can be more readily separated.

What's the distillation main tool?

Distillation column is an essential item used in distillation of liquid mixtures, so as to separate the mixture into its component parts based on the differences in volatilities.
Distillation column has diameters ranging from about 65 centimetres to 6 meters and heights ranging from about 6 meters to 60 meters, or more.
There are many types of distillation column :

  • Plate Tower
  • Packed Tower

What's the difference between packed column and plate column?

Packed column :

It's used in many processes, such as removing contaminants from a gas stream (absorption), removing volatile components from a liquid stream by contacting it with an inert gas (stripping), and in distillation where the separation is difficult due to close boiling components.

Plate column :

It's used in many processes, such as distillation, absorption and extraction.
This column consists of trays used for increasing the contact time between the liquid and vapour to make a perfect distillation.
There are many types of trays (Bubble cap trays, Sieve trays, Valve trays)

Types of Trays that used inside the column

Bubble cap tray :

It has riser or chimney fitted over each hole, and a cap that covers the riser. The cap is mounted so that there is a space between riser and cap to allow the passage of vapour.

Sieve tray :

Simply, they are metal plates with holes in them. Vapour passes straight upward through the liquid on the plate. The arrangement, number and size of the holes are design parameters.

Valve tray :

in it, perforations are covered by liftable caps. Vapour flows lifts the caps, thus self-creating a flow area for the passage of vapour. The lifting cap directs the vapour to flow horizontally into the liquid, thus providing better mixing than is possible in sieve trays.

Temperature gradient in distillation column

In the distillation column, the temperature increases as you move down in the column. The feed enters the furnace -before entering the distillation column- to increase the temperature of the crude to nearly 400 °C at feed zone.

The products will appear at these temperatures :

  • Petroleum gas (below 30 °C)
  • Gasoline (30 °C to 150 °C)
  • kerosene ( 150 °C to 250 °C)
  • Diesel oil (250 °C to 350 °C)
  • Residue and lubricating oil (more than 400 °C)

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