About Extraction

Liquid-liquid extraction is a powerful separation technique that falls right behind distillation in the hierarchy of separation methods (see figure on the right).

Reasons to use extraction:

  • Separation not feasible by distillation
  • Break azeotropes
  • Energy requirements of distillation are prohibitive
  • A complex distillation sequence is required
  • The material is heat sensitive
  • The material is non-volatile

The general rule: If a separation can be made economically by distillation, there is no reason to consider extraction. However, in situations where distillation is not feasible for reasons such as a complex process sequence, high investment or operating costs, heat sensitive materials, or low volatility, extraction is often the best technology to use.

Extraction frequently involves additional steps to recover and recycle the solvent. A typical extraction process is shown below. About 3% of the operating cost is in the extractor, with the remaining 97% in solvent recovery. Also, the majority of the capital cost is in the equipment downstream of the extraction column. Therefore, it is extremely important to consider the solvent recovery aspects early in the project since they play such an important role in overall process economics.


Liquid-Liquid Extraction Applications by Industry


  • Washing of acids/bases, polar compounds from organics
  • Recovery of acrylic acid


  • Recovery of carboxylic acids from biomass such as fermentation broths
  • Recovery of oil from algae broths


  • Recovery of active materials from fermentation broths
  • Purification of vitamin products

Effluent Treatment

  • Recovery of phenol, DMF, DMAC
  • Recovery of acetic acid from dilute solutions

Polymer Processing

  • Recovery of caprolactam for nylon manufacture
  • Separation of catalyst from reaction products


  • Lube oil quality improvement
  • Separation of aromatics/aliphatics (BTX)


  • Separation of olefins/parafins
  • Separation of structural isomers

Food Industry

  • Decaffeination of coffee and tea
  • Separation of essential oils (flavors and fragrances)

Metals Industry

  • Recovery of cobalt and nickel
  • Recovery of rare earth elements

Inorganic Chemicals

  • Purification of phosphoric acid

Nuclear Industry

  • Purification of uranium