Section: 6 | Azeotropic Data for Binary Mixtures |
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The table 'Azeotropic Binary Mixtures: Temperature, Pressure, and Composition' has 807 more rows than appear in the book.
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John R. Rumble, ed., CRC Handbook of Chemistry and Physics, 103rd Edition (Internet Version 2022), CRC Press/Taylor & Francis, Boca Raton, FL.
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J. Gmehling, J. Menke, J. Krafczyk, K. Fischer, J.-C. Fontaine and H. V. Kehiaian

In this table, important parameters are given for 808 azeotropic binary mixtures.

Binary homogeneous (single-phase) liquid mixtures having an extremum (maximum or minimum) vapor pressure P at constant temperature T, as a function of composition, are called azeotropic mixtures, or simply azeotropes. The composition is usually expressed as mole fractions, where x1 for component 1 in the liquid phase and y1 for component 1 in the vapor phase are identical. Mixtures that do not show a maximum or minimum are called zeotropic. A maximum (minimum) of the P(x1) or P(y1) curves corresponds to a minimum (maximum) of the boiling temperature T at constant P, plotted as a function of x1 or y1 [see T(x1) and T(y1) curves, Types I and III, in Figure 1]. Azeotropes in which the pressure is a maximum (temperature is a minimum) are often called positive azeotropes, while pressure-minimum (temperature-maximum) azeotropes are called negative azeotropes. The coordinates of an azeotropic point are the azeotropic temperature TAz, pressure PAz, and the vapor-phase composition y1,Az, which is the same as the liquid-phase composition x1,Az.

In the two-phase liquid-liquid region of partially miscible (heterogeneous) mixtures, the vapor pressure at constant T (or the boiling temperature at constant P) is independent of the global composition x1 of the two coexisting liquid phases between the equilibrium compositions x1′ and x1″ (x1′ < x1″).

The constant vapor pressure (boiling temperature) above the two-phase region of certain partially miscible mixtures is usually larger (smaller) than the vapor pressure (boiling temperature) at any other liquid-phase composition in the homogeneous region. In this case, the vapor-phase composition is inside the miscibility gap. Mixtures of this type are called heteroazeotropic mixtures, or simply heteroazeotropes. (Figure 1, Type II), as opposed to the other types of azeotropes, called homoazeotropes.

Only in a few cases partially miscible mixtures present a positive or negative azeotropic point in the single-phase region, outside the miscibility gap, similar to the azeotropic points of homogeneous mixtures (Figure 1, Types IV and VI).

A few binary mixtures, for example the system perfluorobenzene + benzene, may present two azeotropic points at constant temperature (pressure), a positive and a negative one. They are called double azeotropic mixtures, or simply double azeotropes. (Figure 1, Type V).

The knowledge of the occurrence of azeotropic points in binary and higher systems is of special importance for the design of distillation processes. The number of theoretical stages of a distillation column required for the separation depends on the separation factor α12, i.e., the ratio of the Ki -factors (Ki = yi/xi ) of the components i (i = 1, 2). The required separation factor can be calculated with the following simplified relation (Ref. 1)

α12 = K1/K2 = (y1/x1)/(y2/x2) = (γ1P1s)/(γ2P2s)      (1)

where γi is the activity coefficient of component i in the liquid phase and Pis is the vapor pressure of the pure component i.

In distillation processes, only the difference between the separation factor and unity (α12 – 1) can be exploited for the separation. If the separation factor is close to unity, a large number of theoretical stages is required for the separation. If the binary system to be separated shows an azeotropic point (α12 = 1), the separation is impossible by ordinary distillation, even with an infinitely large number of stages.

Following eq. (1) azeotropic behavior will always occur in homogeneous binary systems when the vapor pressure ratio P1s /P2s is equal to the ratio of the activity coefficients γ2/γ1.

Various thermodynamic methods based on gE—models (Wilson, NRTL, UNIQUAC) or group contribution methods (UNIFAC, modified UNIFAC, ASOG, PSRK) can be used for either calculating or predicting the required activity coefficients for the components under given conditions of temperature and composition (Ref. 2).

Because of the importance of azeotropic data for the design of distillation processes, compilations have been available in book form for quite some time (Refs. 3-7). The most recent printed data collection was published in 1994 (Ref. 8). A revised and extended version appeared in 2004 (Ref. 9).

A collection of approximately 47,400 zeotropic and azeotropic data sets, compiled from 6600 references, are stored in a comprehensive computerized data bank (Ref. 10). The references from the above-mentioned compilations and from the vapor-liquid equilibrium part of the Dortmund Data Bank (Ref. 11) were supplemented by references found from CAS online searches, private communications, data from industry, etc. Over 24,000 zeotropic data and over 20,000 azeotropic data are available for binary systems. Nearly 90% of the binary azeotropic data show a pressure maximum. In most cases (ca. 90%) these are homogeneous azeotropes, and in approximately 7–8% of the cases heterogeneous azeotropes are reported. Less than 10% of the data stored show a pressure minimum. Approximately 21,000 of the datasets stored were published after 1970.

The table below provides information about azeotropes for selected binary systems. Mixtures are listed alphabetically by the name of the first component, followed by the name of the second component. For convenience in searching, each row is duplicated with the components reversed. 

Column headings for the table are as follows.

Column heading Definition
Component 1 Name of first component; mixtures are listed alphabetically by first component; for convenience in searching, each row is duplicated with the components reversed
Mol. form. 1 Molecular formula of first component, in Hill order
Component 2 Name of second component
Mol. form.2 Molecular formula of second component, in Hill order
TAZ Azeotropic temperature, in K
Y1,AZ Vapor-phase composition of first component
PAZ Azeotropic pressure, in kPa
Type Azeotropic type, see definition of symbols below

The explanation of the type of azeotrope is given by the following codes.

O: Homogeneous azeotrope in a completely miscible system
L: Homogeneous azeotrope in a partially miscible system
E: Heterogeneous azeotrope
X: Pressure maximum
N: Pressure minimum
D: Double azeotrope
C: System contains a supercritical compound


  1. Gmehling, J. and Brehm, A., Grundoperationen, Thieme-Verlag, Stuttgart, 1996.
  2. Gmehling, J. and Kolbe, B., Thermodynamik, VCH-Verlag, Weinheim, 1992.
  3. Lecat, M., Doctoral Dissertation, 1908.
  4. Lecat, M., L’Azeotropisme, Monograph, L’Auteur, Brussel, 1918.
  5. Lecat, M., Tables Azeotropiques, Monograph, Lamertin, Brussel 1949.
  6. Ogorodnikov, S. K., Lesteva, T. M., and Kogan V. B., Azeotropic Mixtures, Khimia, Leningrad, 1971.
  7. Horsley, L. H., Azeotropic Data III, American Chemical Society, Washington, 1973. []
  8. Gmehling, J., Menke, J., Krafczyk, J., and Fischer, K., Azeotropic Data, 2 Volumes, VCH Verlag, Weinheim, 1994.
  9. Gmehling, J., Menke, J., Krafczyk, J., and Fischer, K., Azeotropic Data, Second Edition, 3 Volumes, VCH Verlag, Weinheim, 2004.
  10. Gmehling, J., Menke, J., Krafczyk, J., and Fischer, K., A Data Bank for Azeotropic Data, Status and Applications, Fluid Phase Equilib. 103, 51, 1995. []
  11. Dortmund Data Bank,

figure 1 described below

  • Figure 1 Different types of binary azeotropic systems: I — homogeneous pressure-maximum azeotrope in a completely miscible system (OX); II — heterogeneous pressure-maximum azeotrope (EX); III — homogeneous pressure-minimum azeotrope in a completely miscible system (ON); IV — homogeneous pressure-maximum azeotrope in a partially miscible system (LX); V–D: double azeotrope (OND, OXD); VI — homogeneous pressure-minimum azeotrope in a partially miscible system (LN). A — y1(x1); B — P(x1) and P(y1); C — T(x1) and T(y1). Continuous line — (x1); Dashed line — (y1).

Azeotropic Binary Mixtures: Temperature, Pressure, and Composition

Component 1Mol. form. 1Component 2Mol. form. 2TAz/Ky1,AzPAz/kPaType
Continued on next page...
Acetic acidC2H4O2DecaneC10H22390.050.9250101.33OX
Acetic acidC2H4O22,4-DimethylpyridineC7H9N435.450.3022101.33ON
Acetic acidC2H4O2HeptaneC7H16364.950.4490101.33OX
Acetic acidC2H4O2HexaneC6H14341.400.0839101.33OX
Acetic acidC2H4O23-Methyl-2-butanol, (±)-C5H12O392.650.7210101.33ON
Acetic acidC2H4O22-MethylpyridineC6H7N417.270.5120101.33ON
Acetic acidC2H4O2NonaneC9H20386.050.8250101.33OX
Acetic acidC2H4O2OctaneC8H18378.850.6870101.33OX
Acetic acidC2H4O2PyridineC5H5N411.250.5780101.33ON
Acetic acidC2H4O2UndecaneC11H24391.150.9720101.33OX
Acetic acidC2H4O2Vinyl butanoateC6H10O2386.450.5750101.33OX
Acetic acidC2H4O2o-XyleneC8H10389.750.8640101.33OX
Acetic acidC2H4O2p-XyleneC8H10388.400.8200101.33OX
Acetic anhydrideC4H6O3OctaneC8H18397.650.3500129.80OX
Acetic anhydrideC4H6O31-OcteneC8H16367.530.284053.88OX

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