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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 1 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 2 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 3 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 4
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