Types of Distillation | Method with Interesting Examples in Detail

Distillation is the process of separating a substance from a liquid mixture by evaporating and subsequent cooling into a separate chamber. There are different types of distillation, like

1. Simple distillation
2. Fractional distillation
3. Steam distillation
4. Vacuum distillation
5. Azeotropic distillation
6. Double distillation
7. Triple distillation

Types of distillation in detail

Simple distillation

• Here, a liquid mixture is heated in a conical flask either with a burner or heating mantle.

• This heats up the liquid mixture, and the substance in the mixture with lower boiling points evaporates first.

• This vapor, rising from the top, is allowed to pass through a cooling chamber.

• The resultant liquid formed from cooled vapor is collected in a separate flask.

Fractional distillation

• This is similar to simple distillation but has an additional separation mechanism and a fractionating column in the equipment.

• As seen in the image above, a fractionating column is present in between the flask and condenser.

• This fractionating column has beads inside the column, creating a hindrance to rising vapor.

• Due to this, some of the vapor gets in contact with the beads, converts back into liquid, and drains back into the flask with the liquid mixture.

• This process leads to the escape of only a vaporable portion of liquid into the condenser.

• Thus, this procedure helps obtain a pure form of substance that is not achieved by simple distillation.

Steam distillation

• As the name indicates, steam is used here for the separation of the liquid mixture.

• A steady flow of steam is passed into a liquid mixture in the round-bottom flask.

• This steam carries away one of the liquids from the container and gets cooled in the cooling chamber.

• The fluid formed by cooling the vapor is collected separately.

• This type of distillation is used to separate high-boiling substances from non-volatile impurities.

For example, turpentine oil boils in pure form at 160°C. When mixed with water, this turpentine oil boils at 96°C.

At this temperature, the vapor pressure of water is 647mm Hg, and that of oil is 113 mm Hg.

The combined sum is 760mmHg, which is equivalent to atmospheric pressure.

So, to separate turpentine from impurities, it is mixed with water and then distilled by passing steam.

The steam carries turpentine vapors and gets cooled in a condenser.

This is collected in a separate flask, and it can be easily separated since the water and turpentine oil are immiscible.

Vacuum distillation

• This is similar to simple distillation, with the only exception being the use of a vacuum to evaporate liquid at low temperatures.

• A liquid boils and converts into vapor when the vapor pressure is equal to the atmospheric pressure.

• In this procedure, low pressure or vacuum is applied to remove the atmospheric pressure.

• Due to this, evaporation occurs at relatively low temperatures. The vapor forms, which is then separated and cooled.

Thus, vacuum distillation is very useful for separating heat-sensitive substances.

Azeotropic distillation

• This process, as the name indicates, involves specific changes in the material during the distillation process.

• When a mixture contains two liquids with similar boiling points, they cannot be efficiently separated using simple distillation.

• Hence, one of the substance’s boiling points is enhanced due to changes in its chemistry.

• Due to this, the other one boils first, and it is allowed to evaporate and cool into a separate flask.

• An example of azeotropic distillation is a mixture of water and ethanol. Both have similar boiling points.

• So, glycerin is added to this mixture to enhance the boiling point of water.

• Now, when this mixture is heated, ethyl alcohol boils first and evaporates out.

• The ethyl alcohol is collected separately as the vapors get cooled.

Double distillation

• Here, two simple distillation flasks are connected in a series, like in the image below.

• In this method, the condensate from the first distillation is allowed to reach the 2nd flask.

• In the 2nd flask, the condensate is again heated to form vapors

• This formed vapor again cools down to form liquid.

• This method is routinely used to obtain double-distilled water.

Triple distillation

• Here, the condensate from double distillation is heated to vapor to reach 3rd flask as shown in the image below.

• The formed vapors are cooled like above to get a triple-distilled liquid. Triple distilled water can be obtained by this method.

• Triple-distilled water is widely used for reasearch in analytical chemistry as it is free of toxins and other contaminants.

• This water is preferred for laboratory research like HPLC chromatography, making buffers, etc.

• This method of multiple distillations is said to remove dissolved salts and other substances leading to minimization of conductivity and enhancement of the purity of water.