What is Fractional Distillation?

Fractional Distillation, also known as Fractionation, is the technique of separating volatile components with different boiling points in a mixture into different parts, which is used for the purification of chemicals or the separation of mixtures in order to obtain some certain components. Without new material produced in the process, Fractional Distillation merely separates mixtures which is regarded as a physical change.

Working Principle of Fractional Distillation

Fractional Distillation can complete multiple vaporization-condensation processes in one operation by utilizing fractional columns.

After boiling a mixture, the vapor enters the fractional column and is partially condensed. The condensate contacts the rising vapor during the descending process, and they exchange heat. The high boiling point components in the vapor are condensed while the low boiling point components still rise in vapor state. The low boiling point components in the condensate are vaporized under heating while the high boiling point components still drop in liquid form. Hence, the low boiling point components increase in the rising vapor, and the high boiling point increase in the falling condensate. It can be considered as continuous ordinary distillation after multiple such heat exchanges. As a result, the low boiling point components and high boiling point components are separated. The vapor of low boiling point components constantly increase and then is distilled out. The high boiling point components continuously flow back into the distillation flask.

Simple Distillation VS. Fractional Distillation

Actually, Fractional Distillation can be regarded as multiple distillations. But there are several differences between them, which can be concluded as follows:

Different Purposes

Fractional Distillation is often used to separate components with small boiling point differences, while simple distillation is usually used to separate components with large boiling point difference as well as separate liquids from solid impurities.

Different Pros and Cons

Fractional Distillation can purify liquids containing several different components better even though there are small boiling point differences. But it requires more energy, slower and more complex than Simple Distillation. So on the other hand, Simple Distillation is faster and simpler, requiring less energy. But it can only be used for the separation of relatively pure liquids and there should be a large boiling point differences between components. In conclusion, there are various pros and cons between Fractional Distillation and Simple Distillation.

Equipment Required for Fractional Distillation    

Short Path Distillation

Giving consideration to the above factors, the Short-Path Distillation can be used for Fractional Distillation. The Short-Path Distillation usually consists of a vacuum pump, a chiller, and the distillation part.

The working process of the Short-Path Distillation can be described as follows:

The material should be added from the top of the evaporator and continuously spread to the heating surface through the material covered on the rotor. Then, the scratch film is capable of scratching the material into a thin and flowing liquid film. During this process, the light molecular exceeded the heating surface form the condense liquid on inside condenser without any collision. Then, the molecular flows along the condenser tube, and discharges through the discharge tube on the bottom of the evaporator. The residue liquid (heavy molecule) is collected on the circular channel under the heating zone, and flows through the discharge tube on one side.   

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