Construction of Temperature-Composition Diagrams for Immiscible Liquids

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This Demonstration leads you through a step-by-step procedure to construct a temperature-composition diagram for two immiscible liquids (water and an organic) at a fixed pressure. In each step, you can drag a line or point to a different location to make a guess and then check the "solution" box to see the correct answer. You can only move forward or select "new problem" to start over at a different temperature and a different organic compound. For any step, check "hint" for help. In some steps, saturation pressures are calculated from Antoine's equation at the selected temperature.

Contributed by: Rachael L. Baumann (January 2018)
Additional contributions by: John L. Falconer
(University of Colorado Boulder, Department of Chemical and Biological Engineering)
Open content licensed under CC BY-NC-SA



Immiscible components do not mix in the liquid phase. For the benzene-water system, each exerts its own saturation pressure ( and ) when present as a liquid; the calculations are analogous if toluene or -hexane is the organic molecule. The saturation temperature for each component is calculated from the Antoine equation by setting the saturation pressure equal to the system pressure :


where units are bar for ; , and are Antoine constants; and is the saturation temperature (°C).

Benzene condenses (dew point curve) at a temperature where its partial pressure () equals its saturation pressure:



This equation is solved for , where is the mole fraction of benzene in the vapor phase and is pressure (bar).

The temperature where water condenses (dew point curve) is obtained from the corresponding equations for water:



The screencast video at [1] explains how to use a similar Demonstration.


[1] Immiscible Liquids on a Pressure-Composition Diagram [Video]. (Jan 23, 2018)

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