Hunter-Nash Method for Liquid-Liquid Extraction: Interactive Simulations

These simulations were prepared using Mathematica. Download the free Wolfram player, and then download the simulation CDF file (link given below or click on figure to download). Try to predict the behavior when a parameter changes before using a slider to change that parameter. Screencasts below explain how to use these simulations.

The Hunter-Nash method uses material balances and a ternary phase diagram with phase separation to determine the number of equilibrium stages needed for liquid-liquid extraction (LLE). The system contains a solvent, a carrier, and a solute. Select a feed composition from the drop-down menu. The solvent mass flow rate is given, and the desired raffinate (refined product) composition RN is given. Select “plot points” to display the feed (F), solvent (S) or raffinate RN on the phase diagram. Select “mixing point” to see how the lever rule is used to determine the mixing point (M), and check “show E1” to see how the extract composition from the first stage is found. Next, select “operating point” to see how the operating point (P) is found. This also displays a schematic of the flow system. Finally, select “count stages” and move the “draw tie lines” slider to the right to see how to determine the number of stages and show the raffinate composition leaving each stage.

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 feed contains 45 mole% solute, is the raffinate mole percent higher or lower than 45%?
  2. If the mixing point is closer to the solvent composition than the feed composition, is the solvent or feed flow rate higher?
  3. What stream has a composition that is the same as the stream that would result if the feed flow stream were mixed with a flow stream corresponding to the operating point?
  4. The composition of E1 (the exit extract stream) is in equilibrium with what stream?

This Demonstration shows how to use the Hunter-Nash method on a right-triangle ternary phase diagram that uses mass fractions. The Hunter-Nash method uses material balances and a ternary phase diagram with phase separation to determine the number of equilibrium stages needed for liquid-liquid extraction (LLE). The solvent mass flow rate and the desired raffinate (refined product) composition are given. Select “plot points” and then drag the black feed point (labeled with a circled F) to a desired feed composition within a restricted range of compositions. Use buttons to view the compositions of the feed F, solvent S, or raffinate RN in the solute (blue), solvent (red) and carrier (green) phases. Select “mixing point” to see how the mixing point M and the extract composition E1 in the first stage are determined. Check “show E1” to show the extract composition. Next, select “operating point” to show how the operating point P is found. This also displays a schematic of the flow system and mass balances. The operating point is used to determine the number of stages. Finally, select “count stages” to use the “draw tie lines” slider to determine the number of stages and the extract and raffinate compositions in each stage. The solid orange lines follow the black tie lines, and the dashed blue lines trace back to the operating point. A diagram of the stages is shown above the ternary phase diagram.

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

  1. What is different about using the Hunter-Nash method on a right-triangle ternary phase diagram instead of an equilateral ternary phase diagram?
  2. Must the mixing point be inside the phase envelope for liquid-liquid extraction?