A Basic Primer on Liquid-Liquid Extraction

Chemical engineers are often faced with the task to design challenging separation processes for product recovery or purification. This article looks at the basics of one powerful and yet overlooked separation technique liquid-liquid extraction. There are other unit operations used to separate compounds, such as distillation, which is taught extensively in chemical engineering curriculums. If a separation is feasible by distillation and is economical, there is no reason to consider liquid-liquid extraction (LLE). However, distillation may not be a feasible solution for a number of reasons, such as:

  • If it requires a complex process sequence (several distillation columns)
  • If the components to be removed or recovered have low volatility
  • If it results in high CapEx and OpEx
  • In these instances, LLE may be the best separation technology to pursue.