Vacuum Distillation Process and Working principle

In this post, we are going to learn what is vacuum distillation process and what are the use of VDU in industries.

VDU full form is a vacuum distillation unit. In the chemical industry, various types of separation techniques are used and among the Distillation process is one of them. Distillation is a unit operation and in the previous article, we discussed what is the distillation process and types of distillation.

Vacuum Distillation Working Principle

Among the distillation types, the vacuum distillation process is the one that we are going to discuss in detail. Before we jump into the tutorial, we would like to tell you that we had posted a detailed article on Azeotropic Distillation Process so do read it out. Now let us continue with the topic. It has vast applications i.e separate liquids from nonvolatile solids, solvent recovery, removal of impurities, petrol refining process, and many more. Let us start with the definition, what is vacuum distillation.

Vacuum distillation definition

A distillation operation that is performed at a pressure below atmospheric pressure is called vacuum distillation. In other words, distillation under reduced pressure is known as Vacuum distillation. This is performed by lowering the pressures in the column or the reactor.

Vacuum distillation working principle

When you have a solution that you need to separate using distillation, you need to heat the mixture above the boiling point of one component so that it can be converted into vapor form and then condensed to cover again in liquid form.

If the boiling point of the component is very high (generally boiling point of more than 150 is considered high) it is difficult to achieve as it requires a utility that can evaporate it which can be costly. So the pressure of the column is reduced, as pressure decrease, the boiling point of the compound also decrease. This decrease in the boiling point of the compound can be achieved with cost-effective utilities also and can achieve easily.

How is the vacuum developed in a vacuum distillation equipment | Vacuum Distillation Setup

Vacuum Distillation column

To create a vacuum is a distillation column, a steam ejector is used. The steam ejector is used to generate a vacuum which is connected to a vacuum trap where vacuum is stored. The distillation column receiver is then connected through-line with the vacuum to get the vacuum in the column receiver. Through the column receiver, we can get the vacuum in the distillation column. This was the procedure where the column is used for the distillation operation.

Vacuum in Reactor

Vacuum Distillation In Reactor
vacuum distillation in reactor

You can see the diagram which explains to you how vacuum is lined up to reactor in the chemical industry.

In pharmaceutical industries, dyes, color and pigment plants, or a batch plant where multiple products are being manufactured, or where the product is not fixed, distillation column in not used as not every manufacturing process requires it. To perform distillation in such plants, reactors are used. As you can see, In these plants, a water steam jet ejector, oil ring vacuum pump, or other is used to generate vacuum. The vacuum is developed in a vacuum trap.

The reactor, vapor column is mounter which is connected with the condenser. The condenser outlet is connected to the reflux pot, Reflux pot is then connected to the receiver where the distillate is collected. This receiver is in lineup with the vacuum trap where the vacuum is stored. In this way, vacuum in the reactor is developed using vacuum pump a and vacuum distillation in the reactor is performed.

When is vacuum distillation used?

There is a number of reasons for selecting vacuum distillation which is also known as selection criteria. We had covered this topic in detail along with examples of the selection criteria of Vacuum Distillation.

Advantage of VDU

  1. It allows you to heat the material at a lower temperature
  2. It prevents other side reactions that can occur at high temperature
  3. It prevents material to get decomposed which it can be at high temperatures.

How to break vacuum in distillation column – Release vacuum in column

In a distillation column, a nitrogen line is provided. similarly, in reactors, also a provision of nitrogen supply is there. After completion is the distillation process. Nitrogen is purged to break the vacuum as nitrogen is a neutral gas and it won’t react with the material. Air vents of columns and reactors are not used to release vacuum as oxygen from the atmosphere will enter into the system and can oxidize the material and foreign material from the surrounding can also enter along with the air that enters while breaking of vacuum.

Crude oil distillation

To separate petroleum products from Crude oil, the distillation of crude oil is performed and it is atmospheric distillation. After atmospheric distillation which is considered as a primary process, leftover heavy oils are feed to a vacuum distillation unit where the separation of compounds is done in a vacuum. Hence is crude oil distillation also, VDU is used.
Read more about the petroleum refining process at

FAQ (Vacuum distillation process)

1. What is vacuum distillation method?

Vacuum distillation is a type of distillation in which the distillation process is carried out at a pressure lower than atmospheric pressure. As we lower the operating pressure, the boiling point of solvents is reduced hence energy consumption to boil the component reduces.

2. What is the difference between atmospheric and vacuum distillation?

As the name suggests, difference between atmospheric and vacuum distillation is the operating pressure. Atmospheric distillation is being carried out at atmospheric pressure i.e. equal to 1 atm, while vacuum distillation is carried out at pressure less than atmospheric pressure or negative pressure.

3. Why is a vacuum distillation unit needed?

If the boiling point of the material in the binary solution is high, we can use vacuum distillation which will lower the boiling point, and hence, we can carry out the distillation process with the supply of less energy.

Wrapping up

This was detailed information about the vacuum distillation process and the vacuum distillation principle. If you have any problems regarding the topic then feel free to use the comment section. Also, suggest the topic that you want us to cover. If you are interested in reading chemical engineering articles and chemical engineering concepts then do check our blog and articles like pnid symbols.

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Me - Founder of Chemical Tweak - A Chemical Engineer by profession and a part-time self-trained technology blogger.

3 thoughts on “Vacuum Distillation Process and Working principle”

  1. Great work, well detailed!

    Which of the distillation type (atmospheric and VDU)has more efficiency ?


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