Types of Distillation
Some essential types of distillation include:
Simple distillation
Fractional distillation
Steam distillation
Vacuum distillation
Air-sensitive vacuum distillation
Short path distillation
Zone distillation
Simple Distillation
This method is only effective for mixtures wherein the boiling points of the liquids are considerably different (a minimum difference of 25oC).
Raoult’s law governs the purity of the distillate (the purified liquid).
Fractional Distillation
Fractional distillation is often used to separate mixtures of liquids that have similar boiling points. It involves several vaporization-condensation steps (which take place in a fractioning column). This process is also known as rectification. The apparatus required to perform a fractional distillation on a mixture is listed below.
Round-bottom flask or distilling flask
A source of heat, which can be a fire or a hot bath.
Receiving flask to collect the condensed vapors
Fractioning column
Thermometer to measure the temperature in the distilling flask
Condenser
Standard Glassware.
When heated, the liquid mixture is converted into vapors that rise into the fractioning column. The vapors now cool and condense on the walls of the condenser. The hot vapors emanating from the distilling flask directly heat the condensed moisture, creating new mists.
Many such vaporization-condensation cycles take place, and the purity of the distillate improves with every process. An illustration depicting a fractional distillation setup is provided below.
Fractional Distillation
Commonly used condensers in laboratories include Liebig condensers and Graham condensers.
Steam Distillation
Steam distillation is often used to separate heat-sensitive components in a mixture.
This is done by passing steam through the mixture (which is slightly heated) to vaporize some of it. The process establishes a high heat transfer rate without the need for high temperatures.
The resulting vapor is condensed to afford the required distillate.
The steam distillation process is used to obtain essential oils and herbal distillates from several aromatic flowers/herbs.
Vacuum Distillation
Vacuum distillation is ideal for separating mixtures of liquids with very high boiling points.
To boil these compounds, heating to high temperatures is an inefficient method. Therefore, the pressure of the surroundings is lowered instead.
The lowering of the pressure enables the component to boil at lower temperatures. Once the vapor pressure of the element is equal to the surrounding pressure, it is converted into vapor.
These vapors are then condensed and collected as the distillate. The vacuum distillation method is also used to obtain high-purity samples of compounds that decompose at high temperatures.
Air-Sensitive Vacuum Distillation
For compounds that are sensitive to air and readily react with it, the vacuum distillation process is carried out, but the vacuum must be replaced with an inert gas once the process is complete. Such a process is often referred to as air-sensitive vacuum distillation.
Short Path Distillation
Short path distillation is used to purify a small quantity of an unstable compound at high temperatures. This is done under lowered pressure levels and generally involves the distillate traveling a minimal distance before being collected (hence the name ‘short path’). The reduced distance traveled by the distillate in this method also reduces the wastage along the walls of the apparatus.
Zone Distillation
The process of zone distillation involves the partial melting of a substance and the condensation of the resulting vapors to obtain a pure distillate. This is carried out in a long container with the help of a zone heater.
Important Applications
The method of distillation has a considerable history, dating back to 3000 BC. Evidence suggests that the distillation of alcohol was developed as far back as the 9th century. Some critical applications of distillation are listed below.
Distillation plays an essential role in many water purification techniques. Many desalination plants incorporate this method to obtain drinking water from seawater.
Distilled water has numerous applications, such as in lead-acid batteries and low-volume humidifiers.
Many fermented products such as alcoholic beverages are purified with the help of this method.
Many perfumes and food flavorings are obtained from herbs and plants via distillation.
Oil stabilization is an essential type of distillation that reduces the vapor pressure of crude oil, enabling safe storage and transportation.
Air can be separated into nitrogen, oxygen, and argon by employing the process of cryogenic distillation.
Distillation is also employed on an industrial scale to purify the liquid products obtained from chemical synthesis.
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