Chapter 9: 
      Liquid-Liquid Extraction (LLE) 
       
         Extraction is a process where one or more 
      solute(s) are removed from one liquid phase 
      (technically called a diluent) by transferring 
      that/those the solute(s) to another liquid phase 
      (or a solvent) 
       
         Since this is the operation between the two 
      liquid phases, no vaporisation is needed; thus, 
      extraction can be performed at low temperatures 
       
         Accordingly, extraction is suitable for sepa-
      rating materials that may decompose or de-
      nature at elevated temperatures 
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         Examples of the uses of extraction are 
            The separation of penicillin from the 
             broth (the liquid phase obtained from 
             biological processes) 
            The separation of aromatic-ring hydro-
             carbons (e.g., benzene, toluene) from 
             paraffins using sulpholane 
       
         It is important to note that, in many appli-
      cations, the downstream process that separates 
      solvent from the solute(s) is usually more expen-
      sive than the extraction operation itself 
       
         A complete extraction process is illustrated 
      in Figure 9.1 
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      Figure 9.1: A schematic diagram of a complete 
      liquid-liquid extraction process 
        (from “Separation Process Engineering” by Wankat, 2007) 
       
         In the extraction process, the feed, which 
      contains the first solvent (or the diluent) and 
      the solute is sent to the extraction unit (or the 
      extractor) 
       
       Another solvent (commonly called the solvent) 
      is also fed into the extractor, with the purpose to 
      remove the solute from the diluent 
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       Normally, the diluent + the remaining solute 
      is called the raffinate phase, while the second 
      solvent + the solute is called the extract phase 
       
       The extract phase (or the loaded solvent) is 
      then sent to the solvent recovery unit, to 
            separate the desired solute from the 
             extract phase 
            recover the second solvent, which can be 
             reused or recycled to be used again as the 
             solvent 
       
         Several types of extraction equipment are 
      employed in various industries; examples are 
      illustrated in Figure 9.2 
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