Azeotropes: Summary
The answers to the ConcepTests are given below and will open in a separate window.
Key points from this module:
- At an azeotrope, the pressure is either a maximum or minimum.
- At an azeotrope, xi = yi. That is, the composition of the vapor is identical to the composition of the liquid that it is in equilibrium with.
- A maximum temperature azeotrope corresponds to a minimum pressure azeotrope.
- For a binary mixture, a maximum temperature azeotrope occurs when the interactions between unlike molecules are much stronger than the interactions between like molecules.
- The activity coefficients are greater than one for a mixture with a maximum-temperature azeotrope.
- As a mixture boils in a batch system, the temperature increases. This means the temperature will approach the azeotrope temperature for a maximum-temperature azeotrope, and further separation by distillation will not be possible.
- A minimum temperature azeotrope corresponds to a maximum pressure azeotrope.
- For a binary mixture, a minimum temperature azeotrope occurs when the interactions between unlike molecules are much weaker than the interactions between like molecules.
- The activity coefficients are less than one for a mixture with a minimum-temperature azeotrope.
From studying this module, you should now be able to:
- Explain the properties of an azeotrope.
- Explain which type of mixing (endothermic or exothermic) occurs for a maximum-temperature or minimum-temperature azeotrope.
- Determine vapor-liquid equilibrium compositions at another liquid composition and the same temperature, given vapor-liquid equilibrium data for a binary mixture at one liquid composition and temperature.
- Explain how an azeotrope can make separation by distillation difficult.
Prepared by John L. Falconer, Department of Chemical and Biological Engineering, University of Colorado Boulder