Steam Distillation – Process, Principle and Diagram – Full Details

Steam distillation is a separation process in which we separate a mixture of immiscible components by introducing steam and subsequently condensing the vapours. In this blog, I will walk you through steam distillation and its principles. First, let us understand the instances in which we opt for Steam distillation over other separation processes.

  1. What is Steam Distillation?
  2. Steam Distillation Principle
  3. Steam Distillation Process
  4. Steam Distillation Advantages
  5. Conclusion

What is Steam Distillation?

In the typical distillation process, we usually have a mixture of components that are miscible with one another. The vapour pressure that the combination exerts on heating depends on the components that make up the mixture.

steam distillation diagram

To start boiling, the vapour pressure of the mixture should become equal to the atmospheric pressure or the pressure to which it is subjected to. Hence we must heat the system of the liquid mixture to a temperature where the system can create enough vapour to equalise the operating pressure or the atmospheric pressure.

The temperature that must be attained depends on the operating pressure; if it is less than one atmospheric pressure, the temperature that is to be attained is relatively lower; if it is greater than one atmospheric pressure, the temperature to be attained is relatively higher.

In some circumstances, it might not be possible to perform this. Some of those instances are as follows:

  • When separating materials with very high boiling points, we have to supply more heat to raise the temperature of the mixture. As a result, the procedure uses more energy and is more expensive.
  • If the mixture contains any thermally unstable components, raising the temperature too high could cause the components to decompose and have an impact on their qualities.
  • The process becomes energy-intensive if we have a binary combination in which one component boils at a high temperature while the other is non-volatile in nature.
  • We can easily handle these situations using the method of steam distillation.

Steam Distillation Principle

In the previous blog, we saw Raoult’s law which states that the partial pressure of each component in a miscible ideal mixture is equal to the product of its vapour pressure and mole fraction.

Pa = Xa * Pv

Steam distillation process

Hence it is clear that the liquid components can’t exert their actual vapour pressure but a corrected vapour pressure (or what we call the partial pressure) which is always less than its pure component vapour pressure ( since mole fraction is always less than 1 )

But, in the case of liquid mixtures in which the components are non-miscible, they can exert their entire vapour pressure as its partial pressure. That is, the total pressure becomes equal to the sum of the individual vapour pressures for immiscible liquid mixtures. Their combined vapour pressures can easily reach the external pressure before the vapour pressure of either of the individual components cross it. Hence the boiling point of the mixture would be lesser than the boiling point of either of the components.

Now, let us assume that water is one of the components in the immiscible mixture. Then we can bring that mixture to a boil at under 100 0C in one atmosphere ( Boiling Point of water at 1 ATM = 100 0C ) if we keep the pressure constant at 1 ATM. In other words, we can lower the operating pressure needed to boil the mixture by introducing steam.

The main concept behind steam distillation is that we use steam to help create the pressure needed to balance the operating pressure. We must be careful to only employ components that are immiscible with water while using steam.

Steam Distillation Process

Consider a binary mixture where component A is a high-boiling component and component B is a non-volatile component. Let’s say A is insoluble in water. We feed the mixture into the column. Using a steam coil, we raise the feed mixture’s temperature. A sparger forces the steam through another steam line. Steam enters the column through the feed mixture and adds to the vapour pressure. When it reaches the working pressure, it causes the creation of vapours of A at a significantly lower temperature. The non-volatile component is eliminated as residue but remains in the feed. Steam and Component A is routed via a condenser where they are easily separated after condensation.

Steam Distillation Advantages

We frequently use steam distillation since it has various advantages over other extraction methods. They are as follows:

  1. the process produces organic compounds devoid of solvents;
  2. Additional separation procedures are not necessary;
  3. It has a huge processing capacity on an industrial scale;
  4. Inexpensive equipment

Shall we wrap up?


In this blog, we saw the process of steam distillation, its advantages and its applications.

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