Distillation

Steam Distillation and azeotropic distillation by Tutumoni Kalita

1. PRESENTATION ON THE TOPIC : STEAM DISTILLATION AND AZEOTROPIC DISTILLATION SUBMITTED BY- TUTUMONI KALITA M.PHARM, 2 nd sem

2. Definition- Distillation is the process of separating the components or substances from a liquid mixture by using selective boiling and condensation. Distillation may result in essentially complete separation (nearly pure components), or it may be a partial separation that increases the concentration of selected components in the mixture. In either case, the process exploits differences in the  volatility of the mixture's components. In  industrial chemistry, distillation is a  unit operation  of practically universal importance, but it is a physical separation process, not a chemical reaction.

3. Steam distillation Steam distillation is a special type of  distillation (a  separation process) for temperature sensitive materials like natural   aromatic compounds . It once was a popular laboratory method for purification of organic compounds, but has become less common due to the proliferation of vacuum distillation. Steam distillation remains important in certain industries. This process effectively enables distillation at lower temperatures, reducing the deterioration of the desired products. If the substances to be distilled are

4. very sensitive to heat, steam distillation may be applied under reduced pressure, thereby reducing the operating temperature further. After distillation the vapours are condensed. Usually the immediate product is a two-phase system of water and the organic distillate, allowing separation of the components by decantation, partitioning or other suitable methods.

5. Principle- When a mixture of two practically   immiscible  liquids is heated while being agitated to expose the surface of each liquid to the vapour phase, each constituent independently exerts its own  vapour pressure  as a function of temperature as if the other constituent were not present. Consequently , the vapour pressure of the whole system increases. Boiling begins when the sum of the vapour pressures of the two immiscible liquids just exceeds the atmospheric pressure (approximately 101  kPa  at sea level). In this way, many organic compounds insoluble in water can be purified at a temperature well below the point at which decomposition occurs .

6. For example, the boiling point of  bromobenzene  is 156 °C and the boiling point of water is 100 °C, but a mixture of the two boils at 95 °C. Thus, bromobenzene can be easily distilled at a temperature 61 °C below its normal boiling point.

7. Apparatus-

8. Applications- It is employed in the manufacture of essential oils, for use in perfumes for example. In this method, steam is passed through plant material containing desired oils. Eucalyptus oil and orange oil are obtained by this ethod in the industrial scale. Steam distillation is also used to separate intermediate or final products during synthesis of complex organic compounds. Also widely used in petroleum refineries and petrochemical plants.

9. AZEOTROPIC DISTILLATION Azeotropic mixture- An azeotrope is a mixture of two or more liquids in such a ratio that its composition cannot be changed by simple distillation. This occurs because, when an azeotrope is boiled, the resulting vapour has the same ratio of constituents as the original mixture. Because their composition is unchanged by distillation, azeotropes are also called constant boiling mixtures.

10. Positive and negative azeotropes - Each azeotrope has a characteristic boiling point. The boiling point of an azeotrope is either less than the boiling point temperatures of any of its constituents (a positive azeotrope ), or greater than the boiling point of any of its constituents (a negative azeotrope ). A well-known example of a positive azeotrope is 95.63%  ethanol and 4.37% water (by mass) boils at 78.2 °C .  Ethanol boils at 78.4 °C, water boils at 100 °C, but the azeotrope boils at 78.2 °C, which is lower than either of its constituents. Indeed , 78.2 °C is the minimum temperature at which any ethanol/water solution can boil at atmospheric pressure . Positive azeotropes are also called minimum boiling mixtures or pressure maximum  azeotropes .

11. In general, a negative azeotrope boils at a higher temperature than any other ratio of its constituents. Negative azeotropes are also called maximum boiling mixtures or pressure minimum  azeotropes . An example of a negative azeotrope is hydrochloric acid at a concentration of 20.2% and 79.8% water (by mass). Hydrogen chloride boils at −84 °C and water at 100 °C, but the azeotrope boils at 110 °C, which is higher than either of its constituents. The maximum temperature at which any hydrochloric acid solution can boil is 110 °C .

12. Principle : It involves the addition of a new component called the entrainer , to the original feed mixture to form an azeotrope with one or more of the feed components. The azeotrope is then removed as either the distillate or the bottoms. The new component is added to the feed mixture to break the azeotrope that otherwise would be formed by feed components.

13. THANKYOU!