Steam distillation

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Steam Distillation Apparatus
Steam distillation apparatus in a lab.

Steam distillation is a process used for the recovery of volatile compounds with high boiling point from solid or liquid, using saturated or superheated steam.[1]

Steam distillation apparatus

Steam distillation remains important in certain industrial sectors.[2]

Many organic compounds tend to decompose at high sustained temperatures. When separation by distillation at the normal pressures is not an option, steam is introduced into the distillation apparatus. The water vapor carries small amounts of the vaporized compounds to the condensation flask, where the condensed liquid phase-separates, allowing for easy collection. This process effectively allows for distillation at lower temperatures, reducing the deterioration of the desired products. If the substances to be distilled are very sensitive to heat, steam distillation may be applied under reduced pressure, thereby reducing the operating temperature further.

After distillation the vapors are condensed. Usually the immediate product is a two-phase system of water and the organic distillate, allowing for separation of the components by decantation, partitioning or other suitable methods.

Principle[edit]

When a mixture of two practically immiscible liquids is heated while being agitated to expose the surface of each liquid to the vapor phase, each constituent independently exerts its own vapor pressure as a function of temperature as if the other constituent were not present. Consequently, the vapor 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. 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.[3]

Applications[edit]

A boiling water distiller. Boiling tank on top and holding tank on the bottom.

Steam distillation is employed in the isolation of essential oils from natural sources.These essential oils are used as food additives, natural flavorings, and/or preservatives, and in cosmetics and pharmaceutical industries, due to their notable antimicrobial, antioxidant, and anti-inflammatory properties.[1] In this method, steam is passed through the plant material containing the desired oils. Eucalyptus oil and orange oil are obtained by this method on an industrial scale. Steam distillation is also sometimes used to separate intermediate or final products during the synthesis of complex organic compounds.[2]

Steam distillation is also widely used in petroleum refineries and petrochemical plants where it is commonly referred to as "steam stripping".[4][5]

Steam distillation also is an important means of separating fatty acids from mixtures and for treating crude products such as tall oils to extract and separate fatty acids, soaps and other commercially valuable organic compounds.[6]

Equipment[edit]

Hydrodistillation using the Clevenger-type apparatus (A) Power regulator; (B) Heating mantle with round bottom flask containing water and aromatic leaves; (C) Clevenger-type apparatus which returns the hydrosol to the still and maintains the essential oil phase, but only for essential oils that are less dense than water and therefore float; (D) The condenser.

On a lab scale, steam distillations are carried out using steam generated outside the system and piped through macerated biomass or steam generated in-situ using a Clevenger-type apparatus.[7]

See also[edit]

References[edit]

  1. ^ a b Prado, Juliana M.; Vardanega, Renata; Debien, Isabel C. N.; Meireles, Maria Angela de Almeida; Gerschenson, Lia Noemi; Sowbhagya, Halagur Bogegowda; Chemat, Smain (2015-01-01). Galanakis, Charis M., ed. Food Waste Recovery. San Diego: Academic Press. pp. 127–148. doi:10.1016/b978-0-12-800351-0.00006-7. ISBN 9780128003510. 
  2. ^ a b Fahlbusch, Karl-Georg; Hammerschmidt, Franz-Josef; Panten, Johannes; Pickenhagen, Wilhelm; Schatkowski, Dietmar; Bauer, Kurt; Garbe, Dorothea; Surburg, Horst (2003). "Flavors and Fragrances". Ullmann's Encyclopedia of Industrial Chemistry. doi:10.1002/14356007.a11_141. ISBN 3-527-30673-0. 
  3. ^ Martin's Physical Pharmacy & Pharmaceutical sciences, fifth edition, ISBN 0-7817-6426-2, Lippincott williams & wilkins
  4. ^ Beychok, M.R., The Design of Sour Water Strippers, Individual Paper 61, Proceedings of Seventh World Petroleum Congress, Mexico City, April 1967
  5. ^ Kister, Henry Z. (1992). Distillation Design (1st ed.). McGraw-Hill. ISBN 0-07-034909-6. 
  6. ^ M.M. Chakrabarty (9 November 2003). Chemistry and Technology of Oils & Fats. Allied Publishers. pp. 12–. ISBN 978-81-7764-495-1. 
  7. ^ Walton & Brown, Chemicals From Plants, Imperial College Press, 1999.