Azeotrope

Not to be confused with Allotrope.
Vapour-liquid equilibrium of 2-propanol/water showing positive azeotropic behaviour

An azeotrope (/əˈziːəˌtroʊp/)[1] or a constant heating point mixture is a mixture of two or more liquids whose proportions cannot be changed by simple distillation.[2] This happens because when an azeotrope is boiled, the vapour has the same proportions of constituents as the unboiled mixture. Knowing an azeotrope's behavior is important for distillation.

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). For both positive and negative azeotropes, it is not possible to separate the components by fractional distillation and azeotropic distillation is usually used instead.

For technical applications, the pressure-temperature-composition behavior of a mixture is the most important, but other important thermophysical properties are also strongly influenced by azeotropy, including the surface tension[3][4][5] and transport properties.[6][7]

  1. ^ "Azeotrope definition and meaning - Collins English Dictionary". www.collinsdictionary.com.
  2. ^ Moore, Walter J. Physical Chemistry, 3rd e Prentice-Hall 1962, pp. 140–142
  3. ^ Staubach, Jens; Stephan, Simon (28 September 2022). "Interfacial properties of binary azeotropic mixtures of simple fluids: Molecular dynamics simulation and density gradient theory". The Journal of Chemical Physics. 157 (12): 124702. doi:10.1063/5.0100728. ISSN 0021-9606.
  4. ^ McLure, I. A.; Edmonds, B.; Lal, M. (1973). "Extremes in Surface Tension of Fluorocarbon + Hydrocarbon Mixtures". Nature Physical Science. 241 (107): 71–71. doi:10.1038/physci241071a0. ISSN 0300-8746.
  5. ^ Schäfer, Elisabeth; Sadowski, Gabriele; Enders, Sabine (January 2014). "Interfacial tension of binary mixtures exhibiting azeotropic behavior: Measurement and modeling with PCP-SAFT combined with Density Gradient Theory". Fluid Phase Equilibria. 362: 151–162. doi:10.1016/j.fluid.2013.09.042. ISSN 0378-3812.
  6. ^ "95/05209 Transport properties of ternary near-azeotropic mixtures". Fuel and Energy Abstracts. 36 (5): 365. September 2009. doi:10.1016/0140-6701(95)96948-c. ISSN 0140-6701. Retrieved 24 March 2007.
  7. ^ Fertig, David; Hasse, Hans; Stephan, Simon (December 2002). "Transport properties of binary Lennard-Jones mixtures: Insights from entropy scaling and conformal solution theory". Journal of Molecular Liquids. 367: 120401. doi:10.1016/j.molliq.2022.120401. ISSN 0167-7322.