Steam distillation
- 1. Steam distillation By: Mrs. D. R. Mali Asssitant Professor Pharmaceutical Chemistry GES’s Sir Dr. M. S. Gosavi College of Pharmaceutical Education and Research, Nashik.
- 2. Distillation is the process of separating the components or substances from a liquid mixture by using selective boiling and condensation. It may result : Complete separation (pure components), or Partial separation (selected components in high conc.) In industrial chemistry, distillation is a unit operation of practically universal importance. A physical separation process, not a chemical reaction.
- 3. Aspecial type of distillation Temperature sensitive materials like natural aromatic compounds. It once was a popular laboratory method for purification of organic compounds. Distillation at lower temperatures, reducing the deterioration of the desired products.
- 4. Steam distillation may be applied under reduced pressure: if the substances to be distilled are very sensitive to heat. After distillation the vapours are condensed. 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. When a mixture of two practically immiscible liquids is heated liquid exerts its own vapour pressure as a function of temperature as if the other constituent were not present. 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.
- 6. In this way, many organic compounds insoluble in water can be purified at a temperature well below the point at which decomposition occurs. 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.
- 8. • A round-bottomed flask (C) • A glass inlet tube which reaches almost to the bottom of the flask • A steam generator (D) • Water condenser (double surface type) (E) • An additional a still-head (B) • Receiver (F)
- 9. The flask is clamped at an angle. To prevent the solution in C from being splashed into the entrance of the outlet tube. An addition a still-head is used in place of the outlet tube, since spray will be trapped in the still-head, and returned as a steady stream of liquid to the flask C.
- 10. A vigorous current of steam blown in from D. The mixture in C is thus rapidly heated The vapour of the organic compound mixed with steam passes over and is condensed in E. If the flask C contains a large volume of material or material which requires prolonged distillation, it should be heated by a Bunsen burner.
- 11. If the organic compound which is being steam-distilled is freely soluble in water, an aqueous solution will ultimately collect in the receiver F. The compound must then be isolated by ether extraction, etc. Alternatively, a water-insoluble compound, if liquid, will form a separate layer in F, or if solid, will probably crystallise in the aqueous distillate.
- 13. 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 obtained in the industrial scale. It is used to separate intermediate or final products during synthesis of complex organic compounds. Also widely used in petroleum refineries and petrochemical plants.