Whereas distillation affects a separation by utilizing the differing volatilities of the components of a mixture, liquid-liquid extraction makes use of the different extent to which the components can partition into a second immiscible solvent. Since then many other processes have been developed by the petroleum, chemical, metallurgical, nuclear, pharmaceutical and food processing industries.
The first commercially-successful liquid-liquid extraction operation was developed for the petroleum industry in 1909 when Edeleanu’s process was employed for the removal of aromatic hydrocarbons from kerosene, using liquid sulfur dioxide as solvent.
Solvent extraction is an old, established process and together with distillation constitute the two most important industrial separation procedures. In practical terms, however, many solutes may be present in the initial solution and die extracting ‘solvent’ may be a mixture of solvents designed to be selective for one or more solutes, depending upon their chemical type. In its simplest form, this involves the extraction of a solute from a binary solution by bringing it into contact with a second immiscible solvent in which the solute is soluble. Liquid-liquid (or solvent) extraction is a countercurrent separation process for isolating the constituents of a liquid mixture.
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