Distillation is the process of separating components of a mixture based on their different boiling points. Examples of distillation applications include filtering alcohol, desalination, petroleum refining, and extracting dissolved gases from air. Distillation has been used since at least 3000 BC in the Indus Valley.
Definition of Distillation
Distillation is a widely employed technique for separating mixtures based on the different conditions required to change the phase of its components. To separate a mixture of liquids, the liquid is heated to convert the components with different boiling points into vapor. The vapor is then condensed back into liquid form and collected. Repeating this process on the collected liquid to enhance product purity is known as fractional distillation. Although the term is primarily applied to liquids, a reverse process can also be used to separate gases by liquefying the components using changes in temperature and/or pressure.
A facility that performs distillation is called a distillery, and the equipment used is called a still.
Background
The earliest evidence of distillation comes from a terracotta distillation device dating back to 3000 BC in the Indus Valley of Pakistan. The Babylonians in Mesopotamia were also known to use distillation, potentially for making perfumes. The distillation of beverages occurred much later. In the 9th century, the Arab chemist Al-Kindi distilled alcohol in Iraq. Distillation of alcohols became prevalent in Italy and China starting in the 12th century.
Uses of Distillation
Distillation is utilized in various industrial processes, including the production of gasoline, pure water, xylene, alcohol, paraffin, kerosene, and numerous other liquids. Gasoline can be distilled, and nitrogen, oxygen, and argon can be separated from air.
Types of Distillation
There are several types of distillation, including simple distillation, fractional distillation (where different volatile “fractions” are collected as they form), and destructive distillation (in which a substance is heated until it breaks down into compounds for collection).
Simple Distillation
Simple distillation is used when the boiling points of two liquids are significantly different from each other or to separate liquids from solids or nonvolatile components. In simple distillation, a mixture is heated to convert the most volatile component into vapor.
Steam Distillation
Steam distillation is employed to separate heat-sensitive components. For example, steam distillation of flowers is used to produce essential oils and a water-based distillate.
Fractional Distillation
Fractional distillation is employed when the boiling points of the components in a mixture are close to each other, as determined by Raoult’s law. A fractionating column is used to separate the components through a series of distillations called rectification. In fractional distillation, a mixture is heated, and as the vapor rises, it enters the fractionating column. The vapor condenses on the packing material within the column. The heat of the rising vapor causes this liquid to vaporize again, carrying it along the column and eventually producing a higher purity sample of the more volatile component in the mixture.
Vacuum Distillation
Vacuum distillation is employed to separate components with high boiling points. Vacuum distillation is especially useful when the normal boiling point exceeds the decomposition temperature of a substance.
The earliest evidence of distillation comes from a terracotta distillation apparatus dating back to 3000 BC in the Indus Valley of Pakistan. Distillation is used in various industrial processes, including the production of gasoline, distilled water, xylene, alcohol, paraffin, kerosene, and many other liquids. Simple distillation may be used when the boiling points of two liquids are significantly different from each other or to separate liquids from solids or nonvolatile components. Fractional distillation is employed when the boiling points of the components in a mixture are close to each other, as determined using Raoult’s law. A fractionating column is used to separate the components through a series of distillations called rectification.
