Hunter-Nash Method for Liquid-Liquid Extraction: Summary

The answers to the ConcepTests are given below and will open in a separate window. 
Key points from this module:
  • Liquid-liquid extraction takes advantage of the partial miscibility of components.
  • Liquid-liquid extraction uses counter-current flow to extract a solute from one liquid phase to another.
  • The extract from a liquid-liquid extraction is the solvent that is enriched in the solute; the raffinate is the feed stream has been depleted of some solute.
  • Liquid-liquid extraction is ideally carried out at steady state.
  • Streams leaving a stage in liquid-liquid extraction are assumed to be in phase equilibrium.
  • When two streams of different compositions are mixed, the composition of the mixture will be on a line that connects the compositions of the two streams on a ternary phase diagram.
  • The mixing point has the overall composition of a mixture of feed and solvent.
  • The operating point is determined from rearrangement of an overall mass balance.
  • The lever rule can be used on a ternary phase diagram to determine the ratio of stream flow rates if the stream compositions and the overall composition are known.
From studying this module, you should now be able to:
  • Graphically locate the mixing point on a ternary phase diagram.
  • Graphically locate the operating point on a ternary phase diagram.
  • Determine the extract composition for liquid-liquid extraction, given feed and solvent compositions and flow rates, and the desired raffinate composition.
  • Use mass balances and ternary phase diagrams to determine the outlet compositions from a liquid-liquid extraction.
  • Use a ternary phase diagram to determine the number of stages needed for liquid-liquid extraction.
Prepared by John L. Falconer, Department of Chemical and Biological Engineering, University of Colorado Boulder