What Is Distillation?

Lucy Bell-Young

by Lucy Bell-Young

16th November 2017

Most of us have heard of distilled water before, and assume it to be fancy bottled water siphoned from mountainous valleys. Well, I hate to break it to you, but what you’re thinking of is spring water. Distilled water isn’t actually recommendedfor human consumption, and the distillation process is much less idyllic than your mountain-fed stream – but it’s a lot more interesting.

Distillation is a widely used method that allows the separation of different components from a liquid mixture. This is achieved through a process of selective evaporation and condensation.

A Separation Process

Unlike deionisation, distillation is a physical separation process, not a chemical reaction. To separate a mixture of substances, the liquid is heated to convert different components into gases. The gas is then condensed back into liquid form and collected. This method is called simple distillation, and is the process used to create distilled water. But there are many types of processes, all of which yield a variety of applications.

An example Reagent's distilled water product

ReAgent provide businesses across the UK with a selection of products, including distilled water which can be bought in quantities up to 1000L. Shop now to view our wide range of products!

Types of Distillation

  1. Steam Distillation

This process is employed to extract essential oils from plants, such as Eucalyptus, and is used on a wide scale in the manufacturing of aromatic products like perfume. The compounds encountered here can be temperature sensitive, meaning that they would decompose if subjected to simple distillation, for example.

However, when these compounds are exposed to steam, their boiling points are minimised. This means that they are able to boil and vaporise without risk of decomposition. Therefore, using steam is ideal for materials where the flavour and aroma need to be preserved. Glass vials containing essential oils extracted from plants

  1. Vacuum Distillation

This is the preferred method when manufacturing pharmaceuticals with long-chain molecules or polymers. It is similar to steam distillation in that both methods are used for temperature sensitive materials in order to prevent undesired reactions or thermal decomposition.

Whereas the use of steam causes the component to boil well below its boiling point, vacuum distillation reduces the pressure above the liquid mixture to less than its vapour pressure. The lower the environmental pressure, the lower the temperature the substances boil at.

The difference between the two lies in the fact that vacuum distillation can be carried out without using any heat, while steam consumes a lot of heat. For this reason, vacuum distillation has taken the edge.

  1. Fractional Distillation

Substances like gasoline occur when distillation is used to fractionate the chemical compounds of a mixture. Like with other methods, the solution is boiled first. The vapours then pass through a fractionating column and condense on the column’s packing material.

The aim of this process is to yield a sample of the more volatile component of the mixture. Unlike less volatile substances, these components do not condense on the column’s packing material. Instead, they collect near the top of column and have higher purity.

Fractional distillation is often used in oil refineries in order to separate useful substances from crude oil. These substances include, but are not limited to gasoline, kerosene, diesel, and refinery gas.

  1. Destructive Distillation

This is used to break down organic substances, like wood or coal, and turn them into solids, liquids, or gases. This thermochemical decomposition of raw material is achieved by heating them to a high temperature, and is carried out in order to collect the compounds it leaves behind. This process is also referred to as Pyrolysis.

In order to successfully carry out destructive distillation, the feedstock must be heated in a closed container so that there is an absence of oxygen. This because, when there is a lack of air, the material produces a variety of by-products instead of burning.

There are a plethora of compounds we can collect by employing destructive distillation:

  • Tar, turpentine, and the solid residue of charcoal can all be obtained from the burning of wood
  • Coke fuel, coal tar and gas, and liquor ammonia are produced when coal undergoes Pyrolysis
  • Destructive distillation of natural rubber led to the discovery of Isoprene, which is responsible for the creation of synthetic rubbers.

Whether the products obtained are solids, liquids, or gases depends on the temperature used in the process.

Coke fuel is a by-product of destructive distillation

Coke fuel is a by-product of destructive distillation

  1. Double & Reverse Distillation

Double distillation is simply when the process is repeated on the collected liquid. This is done in order to improve the purity of the final product.

As we know by now, distillation is generally used to separate a mixture of liquids, or to break down organic substances. However, it can also be reversed so that gases are converted to a liquid state. This reverse process is called the liquefaction of gases.

The most common, practical application of liquefied gases is the compact storage they offer. Since liquids take up significantly less space than gases, it means that the transportation of substances like liquefied petroleum gas (LPG) are much more efficient.

Liquefaction occurs when gas molecules move closer together, which can be facilitated by increasing the pressure and decreasing the temperature.


There are many products that can be formed by using distillation. From the separation of crude oil into its different components, to using essential oils from flowers to create perfumes, the possibilities are endless. Perhaps the most common by-product, however, is distilled water which also has a range of common usages.

At ReAgent, we not only offer high quality products that are provided with full batch traceability, we also offer a personalised touch to make sure that you get your money’s worth. Whether you want customised packaging, bespoke blending, or even personalised labelling, ReAgent have your back. Why not get in touch with us today about your business needs?


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