Centrifugal Molecular Still

Principle

• In this method, liquid feed is introduced into a vessel, which is rotated at very high speed (centrifugal action)

• On account of heating, vaporisation occurs from a film of liquid on the sides of the vessel

• The vapour (molecules) travels a short distance and gets condensed on the adjacent condenser

• Each molecule is condensed individually

• The distillate is subsequently collected

Construction

• It consists of a bucket-shaped vessel having a diameter of about 1 to 1.5 m

• It is rotated at high speed using a motor

• Radiant heaters are provided externally to heat the fluid in the bucket

• Condensers are arranged very close to the evaporating surface.

• Vacuum pump is connected to the entire vessel at the top

• Provisions are made for introducing the feed into the centre of the bucket, for receiving the product and residue for re-circulation

Working

• Vacuum is applied at the centre of the vessel. The bucket shaped vessel is allowed to rotate at high speed

• The feed is introduced from the centre of the vessel

• Due to centrifugal action of the rotating bucket, liquid moves outward over the surface of the vessel and forms a film

• Since, the radiant heaters heat the surface, the liquid evaporates directly from the film

• The vapour (molecules) travels its mean tree path and strikes the condenser. The condensate is collected into another vessel

• The residue is collected from the bottom of the vessel and is recirculated through the feed port for further distillation

Applications

Molecular distillation is used for the purification and separation of chemicals of low vapour pressure

1. Purification of chemicals such as tricresyl phosphate, dibutyl phthalate and dimethyl phthalate

2. More frequently used in the refining of fixed oils

3. Vitamin A is separated from fish liver oil. Vitamins are concentrated by this method from fish liver oils and other vegetable oils

4. Free fatty acids are distilled at 100°C

5. Steroids can be obtained between 100°C and 200°C, while triglycerides can be obtained from 200°C onwards.

Centrifugal Molecular Still - Pharmaceutical Engineering B. Pharm Third Semester PDF Notes