Types of distillation | Method with Interesting Examples in Detail
Distillation is a process of separation of a specific 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
Here a liquid mixture is heated in a conical flask. This leads to evaporation of liquid with low boiling first. This vapor is allowed to cool while passing through the cooling chamber. The resultant liquid formed from cooled vapor is collected in a separate flask.
This is similar to simple distillation with the only addition of a fractionating column. This column is present in between the flask and condenser. This column helps to convert some of the vapor back to a liquid which drains back into the vial. This process leads to escape of only vaporable portion into the condenser. Thus this procedure helps in obtaining a pure form of substance than that achieved by simple distillation.
As the name indicates, here steam is used for separation of the liquid mixture. A steady flow of steam is passed into a liquid mixture present in a round bottom flask. This steam carries away one of the liquid from the container, gets cooled in the cooling chamber. The fluid formed by cooling is collected separately.
This type of distillation is used to separate high boiling substances from non-volatile impurities. For example, turpentine oil boils at 160°C in pure form. 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 113mmHg. 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 they can be easily separated since the water and turpentine oil are immiscible.
This is similar to simple distillation with the only exception is the use of vacuum to evaporate liquid at low temperatures. A liquid boils and converts into vapor when the vapor pressure is equal to atmospheric pressure. In this procedure, the vacuum is applied to remove the atmospheric pressure. Due to this, at relatively low temperature the vapor forms which is separated and cooled. Thus, vacuum distillation is very useful to separate heat-sensitive substances.
This process as the name indicates 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 boiling points is enhanced due to change in its chemistry. Due to this, the other one boils first, and it is allowed to evaporate and cool into a separate flask.
Example for 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: This is a method wherein the condensate from first distillation is again heated. This forms vapors and again cools down to for liquid. This method is routinely used to obtain double distilled water.
Triple distillation: Here the condensate from double distillation is heated to vapors. The formed vapors are cooled like above to get triple distilled liquid. Mostly water is obtained as triple distilled water. This water is preferred for laboratory research like HPLC chromatography, making buffers etc.
This method of multiple distillation is thought remove dissolved salts and other substances. It minimizes the conductivity and enhances the purity of water.