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Encyclopedia > Azeotrope
2-propanol/water Equilibria with an azeotrope.
2-propanol/water Equilibria with an azeotrope.

An azeotrope is a mixture of two or more compounds (molecules) which at a specific composition (ratio of compounds) maintains vapor and liquid phases which are in equilibrium and identical in composition. Due to the uniformity of liquid and vapor, chemical composition of the azeotrope cannot be changed by simple boiling (distillation). This constant composition will (almost always) occur at a minimum or maximum temperature over the composition space. The exception for binary mixtures is the rare double azeotrope. The exception for three or more components is the intermediate boiling azeotrope (saddle azeotrope). In a fake example, if there are 3 parts of liquid x to every 4 parts of liquid y, then you could not separate the 2 by boiling them because of the rates at which they boil. Image File history File links Download high resolution version (904x626, 136 KB) Summary 2propanol-Water Equilibria P=760 mm Hg Author: J.A. Freyre Licensing I, the creator of this work, hereby release it into the public domain. ... Image File history File links Download high resolution version (904x626, 136 KB) Summary 2propanol-Water Equilibria P=760 mm Hg Author: J.A. Freyre Licensing I, the creator of this work, hereby release it into the public domain. ... Isopropyl alcohol or isopropanol is a common name for 2-propanol, an alcohol commonly used for application to the skin, and popularly referred to as rubbing alcohol. ... This article focuses on water as it is experienced in everyday life. ... A chemical compound is a chemical substance formed from two or more elements, with a fixed ratio determining the composition. ... In chemistry, a molecule is an aggregate of at least two atoms in a definite arrangement held together by special forces. ... Vapor (US English) or vapour (British English) is the gaseous state of matter. ... A liquid will assume the shape of its container. ... Phase, from the Greek phasis, meaning appearance, has a number of related meanings in English. ... Boiling is the rapid vaporization of a liquid, which typically occurs when a liquid is heated to a temperature such that its vapor pressure is above that of the surroundings, such as air pressure. ... Strathisla whisky distillery in Keith, Scotland Distillation is a method of separation of substances based on differences in their vapor pressures. ...


In order to enrich a mixture past the azeotrope (or "break" the azeotrope), one may use several techniques:

  1. Use azeotropic distillation, by adding in a third component which will generate a lower boiling heterogenous azeotrope that can be broken by phase separating the two immiscible liquids and decanting.
  2. Use extractive distillation where a third compound is added near the top of a distillation column that reduces the volatility of one compound over another. For example, if you wanted to separate water from a type of alchohol by boiling, but they were at their azeotropic mixture, if you added salt to the mixture that would raise the boiling point of the water so you could boil more of the alchohol out of it.
  3. Use liquid-liquid extraction to separate the compounds by segregating them into two different liquid phases.
  4. Use a membrane to separate them, as in pervaporation.
  5. For azeotropes that change composition when pressure is changed, you can use pressure swing distillation by operating two distillation columns at different pressures, and recycle material between these two distillation columns. One column will remove a pure component (two-component systems) in the bottom of one distillation column, the other will remove a pure component in the bottom of a second distillation column, and the azeotrope (of two different compositions) will be fed to the other column.

The word azeotrope comes from the Greek "zein tropos", or "constant boiling". An azeotrope is said to be positive if the constant boiling point is at a temperature maximum, and negative when the boiling point is at a temperature minimum. The vast majority of azeotropes are minimum boiling. All liquid mixtures which are immiscible and which form azeotropes are minimum boiling . In chemistry, azeotropic distillation is any of a range of techniques used to break an azeotrope in distillation. ... Extractive Distillation is defined as distillation in the presence of a miscible, high boiling, relatively non-volatile component, the solvent, that forms no azeotrope with the other components in the mixture. ... In chemistry, liquid-liquid extraction (or more briefly, solvent extraction) is a useful method to separate components (compounds) of a mixture. ... It has been suggested that Net flux be merged into this article or section. ... Pervaporation is a method for the separation of mixtures of liquids by partial vaporization through a non-porous membrane. ... A substance is soluble in a fluid if it dissolves in the fluid. ...


Examples of azeotropes

The chemical compound nitric acid (HNO3), otherwise known as aqua fortis or spirit of nitre, is a colorless, corrosive liquid, a toxic acid which can cause severe burns. ... Water has the chemical formula of H2O, meaning that one molecule of water is composed of two hydrogen atoms and one oxygen atom. ... Perchloric acid has the formula HClO4 and is a colorless liquid soluble in water. ... Flash point -37. ... Ethanol, also known as ethyl alcohol or grain alcohol, is a flammable, colorless chemical compound, one of the alcohols that is most often found in alcoholic beverages. ... Sulfuric acid (British English: sulphuric acid), H2SO4, is a strong mineral acid. ... R-phrases , , , S-phrases , , , Flash point -20 °C Autoignition temperature 465 °C RTECS number AL31500000 Supplementary data page Structure & properties n, εr, etc. ... Methanol, also known as methyl alcohol or wood alcohol, is a chemical compound with chemical formula CH3OH. It is the simplest alcohol, and is a light, volatile, colourless, flammable, poisonous liquid with a very faint odor. ... PEL-TWA (OSHA) 50 ppm (240 mg/m3) IDLH (NIOSH) 500 ppm Flash point non-flammable RTECS number FS9100000 Supplementary data page Structure & properties n, εr, etc. ... Diethyl ether, also known as ether and ethoxyethane, is a clear, colorless, and highly flammable liquid with a low boiling point and a characteristic smell. ... Structural formula of halothane Halothane vapour is an inhalational general anaesthetic. ... Benzene, also known as C6H6, PhH, and benzol, is an organic chemical compound that is a colorless and flammable liquid with a pleasant, sweet smell. ...

See also

A eutectic or eutectic mixture is a mixture of two or more elements which has a lower melting point than any of its constituents. ...

External links

  • Azeotrope Databank
  • Update in Anaesthesia: The halothane/ether azeotrope - A reconsideration [1]
  • Azeotrope defined with a limerick.

  Results from FactBites:
 
Azeotrope mixtures with perfluorobutylethylene - Patent 6793840 (0 words)
An azeotropic composition of from 51 to 50 mole percent of perfluorobutylethylene and from 49 to 50 mole percent of bromochloromethane, the composition having a boiling point of from 60.degree.
Azeotropic compositions are also characterized by a minimum or a maximum in the vapor pressure of the mixture relative to the vapor pressure of the neat components at a constant temperature.
The azeotropic compositions comprise 30.7 mole % PFBE and 69.3 mole % trans-DCE at 35.3.degree.
Re: Is it possible to lower the boiling point of water by adding a substance? (0 words)
The phenomenon to which you refer is that of forming an azeotrope, a mixture of two liquids which cannot be separated by distillation because the mixture has a lower boiling point than either of the pure liquids.
Azeotroping is why you cannot isolate ethanol by distillation without using a drying agent, something that preferentially soaks up water.
It sounds like what you are after is an azeotrope of some substance with water, in which water is the major component.
  More results at FactBites »

 
 

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