Distillation Definition in Chemistry

In the most general sense, "distillation" means to purify something. For example, one you might distill the main point from a story. In chemistry, distillation refers to a particular method of purifying liquids:

Distillation Definition

Distillation is the technique of heating a liquid to create vapor which is collected when cooled separate from the original liquid. It's based on the different boiling point or volatility values of the components. The technique may be used to separate components of a mixture or to aid in purification.

The equipment used for distillation may be called a distillation apparatus or still. A structure designed to house one or more stills is termed a distillery.

Distillation Example

Pure water can be separated from salt water through distillation. Salt water is boiled to create form steam, but the salt remains in the solution. The steam is collected and allowed to cool back into salt-free water. The salt remains in the original container.

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What Is Distillation? Chemistry Definition

By Anne Marie Helmenstine, Ph.D.

Uses of Distillation

Distillation has many applications:

• It's used in chemistry to separate and purify liquids.
• Distillation is used to make alcoholic beverages, vinegar, and purified water.
• It's one of the oldest methods of desalinating water. Distilled water dates back to at least 200 AD, when it was described by Greek philosopher Alexander of Aphrodisias.
• Distillation is used on an industrial scale to purify chemicals.
• The fossil fuel industry uses distillation to separate components of crude oil to make chemical feedstock and fuel.

Types of Distillation

Types of distillation include:

Batch Distillation - A mixture of two volatile substances is heated until it boils. The vapor will contain a higher concentration of the more volatile component, so more of it will be condensed and removed from the system. This changes the ratio of components in the boiling mixture, raising its boiling point. If there is a large difference in the vapor pressure between the two components, the boiled liquid will become higher in the less volatile component, while the distillate will be mostly the more volatile component.

Batch distillation is the most common type of distillation used in a laboratory.

Continuous Distillation - Distillation is ongoing, with new liquid fed into the process and separated fractions continuously removed. Because new material is input, the concentrations of the components should not change as in batch distillation.

Simple Distillation - In simple distillation, vapor enters a condenser, cools, and is collected. The resulting liquid has a composition identical to that of the vapor, so simple distillation is used when components have greatly different boiling points or to separate volatile from non-volatile components.

Fractional Distillation - Both batch and continuous distillation may incorporate fractional distillation, which involves use of a fractionating column above the distillation flask. The column offers more surface area, allowing for more efficient condensation of vapor and an improved separation. A fractionating column may even be set up to include subsystems with separate liquid-vapor equilibrium values.

Steam Distillation - In steam distillation, water is added to the distilling flask. This lowers the boiling point of the components so they may be separated at a temperature below their decomposition point.

Other types of distillation include vacuum distillation, short-path distillation, zone distillation, reactive distillation, pervaporation, catalytic distillation, flash evaporation, freeze distillation, and extractive distillation,