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Azeotropes: Interactive Simulations

The first simulation will run in your browser. The second simulation was prepared using Mathematica. Download the free Wolfram player, and then download the simulation CDF file (link given below or click on figure to download). Screencasts below describe how to use the simulations.

Non-ideal VLE modeled by the Margules Equation

Try to answer these questions before determining the answer with the simulation. We suggest that you write down the reasons for your answers.

  1. If the two parameters in the Margules equations (A12, A21) are positive and large, what behavior is likely to be seen for a pressure-mole fraction plot?
  2. If the two parameters in the Margules equations (A12, A21) are negative and large, what behavior is likely to be seen for a temperature-mole fraction plot?
Simulation: Add a Component to a Mixture with an Azeotrope

Benzene and ethanol, which have an azeotrope at a benzene mole fraction of xB=0.6, are in vapor-liquid equilibrium (VLE) inside a cylinder fitted with a piston. Add either benzene or ethanol to the system by clicking the play button next to “inject isothermally”. The final state when the system returns to equilibrium after injection depends on which component is injected and how much is injected. The piston-cylinder shows the relative amounts of liquid and vapor, and the total moles in the liquid phase, nL, and in the vapor phase, nV, are displayed. The mole fraction of benzene in the liquid, xB, and the vapor, yB are also displayed. The P-x-y diagram shows the results of the mass balances and demonstrates why a given phase is the final state. To observe behavior for injecting a different number of moles or to inject the other component, click reset before clicking “inject isothermally” again.

Try to answer these questions before determining the answer with the simulation. We suggest that you write down the reasons for your answers.

Benzene and ethanol form a maximum pressure azeotrope. Initially a piston-cylinder contains liquid (5 mol, xB = 0.17) and vapor 0.5 mol, (yB = 0.36) in equilibrium.

  1. If 0.5 mol of benzene were added at constant temperature and pressure, what is the final state likely to be?
  2. If 5.0 mol of benzene were added at constant temperature and pressure, what is the final state likely to be?
  3. If 5.0 mol of ethanol were added at constant temperature and pressure, what is the final state likely to be?
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