Distillation

 

Distillation is one of the most very process for separation the components of a solution. The solution is heated to form a vapor of the more volatile components in the system, and vapor is then cooled, condensed, and collected as pure liquid. By repeating vaporization and condensation, individual components in the solution can be recovered in a pure state. Essences and many pure products from the oil refinery industry are processed via distillation.

Principles

Distillation is a technique by which a liquid mixture is separated into fractions with higher concentrations of certain components by using differences in relative volatility. The mechanism involved in distillation is the differences in volatility between individual components. With sufficient heat applied, vapours are formed from the liquid solution. The liquid product is subsequently condensed from the vapour phase by removal of the heat. Therefore, heat is used as the separating agent during distillation. In general, distillation can be carried out either with or without reflux involved. For the case of single-stage differential distillation, the liquid mixture is heated to form a vapour that is in equilibrium with the residual liquid. The vapour is then condensed and removed from the system without any liquid allowed to return to the still pot. This vapour is richer in the more volatile component than the liquid removed as the bottom product at the end of the process. However, when products of much higher purity are desired, part of the condensate has to be brought into contact with the vapour on its way to the condenser and recycled to the still pot. This procedure can be repeated many times to increase the efficiency of separation of mixture. This  process is called as rectification.

 Objectives

Distillation is used to separate the liquid mixture into two or more separated components. In a basic distillation column, a feed stream enters in the middle of the column and two fractions leave, one at the top and other at the bottom. Component with lower boiling points will be concentrated in the fraction leaving the top while component with higher boiling point will be concentrated in the stream at the bottom. Separation is achieved by controlling the column temperature and pressure to take advantage of differences in the relative volatility of the components of mixture and therefore has tendency to change phase. The lighter and lower boiling point components evaporate and travel up the column to form the top product and the heavier, higher boiling point components condense and travel down the column to form the bottom product.

Principle of Separation

Distillation takes advantage of the difference in relative volatility of the feed mixture components. Generally for two or more compounds at a given pressure and temperature, there will be a difference in the vapour and liquid compositions at equilibrium due to component partial pressure. Distillation exploits this by bringing liquid and gas phases into contact at temperatures and pressures that promote the desired separation. During this contact, the components with the lower volatility (typically lower boiling point) preferentially move into the liquid phase while more volatile components move into the vapour phase. A distillation column may use either trays or a packed bed to bring the gas and liquid into contact. For a column using trays, we can consider the changes to gas and liquid phase compositions as they both enter and exit a single tray. The liquid entering the tray will contact the gas exiting the tray, Fig.2. The hotter vapour phase heats the incoming liquid phase as it bubbles through the tray, evaporating the light components which then leaves the tray with the vapour phase. Conversely, the cooling of the vapour phase by the liquid phase will cause the heavier components of the vapour phase to condense and exit the tray with the liquid phase.

1.     Applications

Distillation has been used widely to separate volatile components from non-volatile compounds. In industrial settings such as oil refineries and natural gas processing plants, this separation process is undertaken using a distillation column. 

Di  Distillation is used in industries to proceed many commercial processes; Production of gasoline,  , xylene, alcohol, paraffin, kerosene,  distilled water and many other liquids. Distillation is used for purification of solvents and liquid products from there reaction mixture.

3.      It is used in the manufacturing of distilled water, double distilled water used in laboratories and pharmaceutical industries. toxic and expensive organic solvents that are extensively used in the extraction, synthesis and analysis can be recovered by distillation for economic benefits as well as for  protection of environmental.

5.      Distillation is used in the separation of volatile oils such as clove oil, cardamom oil, anise oil,  eucalyptus oil etc. from the plant extracts.

6.      It can also be used in the isolation of volatile components from a mixture of two or more volatile liquids. It can be used as a quality control method for alcohol content in liquid formulations. The alcohol is separated from formulations by distillation and alcohol content is determined.

8.      It can be used to liquefy and separate gases from the air. For example: nitrogen, oxygen, and argon are distilled from the air.

9.      Distillation is used in crude fermentation broths to separate alcoholic spirits.

10.  It can also be used in the fractionation of crude oil into gasoline and heating oil.

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