Disadvantages of Short-Path Distillation

lanphan

5 years ago

What is a Short-Path Distillation?

The short path distillation is a technique that removes solvents form mixtures through evaporation, which is mainly used for liquid-liquid separation. The principle is that the pressure difference between the boiling film and condensing surface is the driving force of the steam flow, and the minimum pressure will cause the flowing of steam. Under the 1mbar, the operation requires that there is the shortest distance between the boiling surface and condensing surface. The evaporator manufactured based on the principle is called the short-path distillation. The short-path distillation (molecular distillation) is equipped with a inside condenser which is opposite to the heating surface, and make the operation pressure reduce to under 0.001mbar. Its relative low boiling temperature is very suitable for the material with heat sensitive and high boiling point.

Disadvantages of Short-Path Distillation

Although the short-path distillation is one of the high-efficiency techniques, it still has some disadvantages.

Compared to the traditional distillation equipment, the short-path distillation is more expensive. And when using the short-path distillation, the system pressure must be ensured to achieve a high degree of vacuum, which requires a high sealing performance of the material. Moreover, the distance between the evaporating surface and the condensing surface should be moderate. As a result, it’s relatively difficult to process the equipment and the cost is quite high. And it’s well known that mixtures can be evaporated and then solvents get extracted during the operation of the short-path distillation. It takes a really short distance for the extracted gas solvents to go from the evaporation flask into the condenser. Thus the extracted gas solvents can get lost easily and be left in the short distance in this process.

Advantages of Short-Path Distillation

Generally, the advantages of the short-path distillation outweigh its disadvantages. Most people will still choose the short-path distillation to do evaporation and distillation.

Firstly, the short-path distillation has a higher degree of separation compared with the conventional distillation, which is capable of separating the substances that are not easily separated by conventional distillation.

Secondly, there is no boiling and bubbling phenomena. The short-path distillation is a free evaporation at the liquid surface and carried out at low pressure. Because there is no dissolved air in the liquid, the entire liquid can’t be boiled or bubbled in the distillation.

Thirdly, the pure and safe products can be obtained by using the short-path distillation. The operation process is simple and the less devices are used.

Short-Path Distillation VS. Wiped Film Evaporator

Although both of the short-path distillation and the wiped film evaporator can be used for evaporation, they vary from each other in three aspects, which can be concluded as follows.

The working principles are different. The short-path distillation makes use of the different free paths of molecules under high vacuum condition to separate components, which doesn’t need heat the material to the boiling point. But the wiped film evaporator utilizes different boiling points of each component to separate them, which requires a higher working temperature than the short-path distillation.
The structures are different. The short-path distillation has an internal condenser, with a quite small distance between the condenser and the heating wall. The separated materials are collected from the bottom of the instrument. But the wiped fielm evaporator has an external condenser and the separated materials are recycled from the top of the instrument.
The efficiency is different. When using the short-path distillation, a relatively high purity components can be obtained, but the cost is high.

Rotary Evaporator VS. Short-Path Distillation

The similarity between the rotary evaporator and short-path distillation is that both of them are devices to extract solvents from mixtures through evaporation. There are both one evaporation flask to get solvents evaporated and receiving flasks to receive extracted solvents in these two devices.

The differences between the rotary evaporator and short-path distillation are:

Rotary evaporator is more efficient than short-path distillation to remove solvents from mixtures. Because rotary evaporator runs in vacuum environment, which is very protective for the purity of extracted solvents. However, short-path distillation can loss few extracted gas solvents along the short distance from evaporation flask to receiving flask
Rotary evaporator and short-path distillation have different structures and parts. For rotary evaporator, there is one receiving flask in the whole equipment and one evaporation flask. And for short path distillation, there are two or three receiving flasks in the whole equipment and one evaporation flask.

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