how to enhance yield in the liquid liquid extraction
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A-to-Z Guide to Thermodynamics,
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EXTRACTION, LIQUID-LIQUID
Thornton, J.D.
DOI: 10.1615/AtoZ.e.extraction_liquid-liquid
Liquid-liquid (or solvent) extraction is a countercurrent separation process for isolating the constituents of a liquid mixture. 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. 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.
Solvent extraction is an old, established process and together with distillation constitute the two most important industrial separation procedures. 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. Since then many other processes have been developed by the petroleum, chemical, metallurgical, nuclear, pharmaceutical and food processing industries.
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. This property is frequently characteristic of the chemical type so that entire classes of compounds may be extracted if desired. The petroleum industry takes advantage of this characteristic of the process and has used extraction to separate, for example, aromatic hydrocarbons from paraffin hydrocarbons of the same boiling range using solvents such as liquified sulfur dioxide, furfural and diethylene glycol. In general, extraction is applied when the materials to be extracted are heat-sensitive or nonvolatile and when distillation would be inappropriate because components are close-boiling, have poor relative volatilities or form azeotropes.
The simplest extraction operation is single-contact batch extraction in which the initial feed solution is agitated with a suitable solvent, allowed to separate into two phases after which the solvent containing the extracted solute is decanted. This is analagous to the laboratory procedure employing a separating funnel. On an industrial scale, the extraction operation more usually involves more than one extraction stage and is normally carried out on a continuous basis. The equipment may be comprised of either discrete mixers and settlers or some form of column contactor in which the feed and solvent phases flow countercurrently by virtue of the density difference between the phases.
Final settling or phase separation is achieved under gravity at one end of the column by allowing an adequate settling volume for complete phase disengagement.
Any one extraction operation gives rise to two product streams: the extracted feed solution, more usually termed the raffinate phase, and the solvent containing extracted solute termed the extract phase. This nomenclature is unique to liquid-liquid extraction processes and will be used from hereon.
Library Subscription: Guest
A-to-Z Guide to Thermodynamics,
Heat & Mass Transfer, and Fluids Engineering
HOMESEMANTIC MAPA-Z INDEXVISUAL GALLERYAUTHORSMY THERMOPEDIA
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
VISUAL MAP NAVIGATIONView in A-Z IndexRELATED CONTENT IN OTHER PRODUCTSInternational Heat Transfer ConferenceDigital LibraryInternational Centre for Heat and Mass Transfer Digital LibraryBegell HouseJournalsAnnual Review of Heat Transfer
EXTRACTION, LIQUID-LIQUID
Thornton, J.D.
DOI: 10.1615/AtoZ.e.extraction_liquid-liquid
Liquid-liquid (or solvent) extraction is a countercurrent separation process for isolating the constituents of a liquid mixture. 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. 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.
Solvent extraction is an old, established process and together with distillation constitute the two most important industrial separation procedures. 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. Since then many other processes have been developed by the petroleum, chemical, metallurgical, nuclear, pharmaceutical and food processing industries.
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. This property is frequently characteristic of the chemical type so that entire classes of compounds may be extracted if desired. The petroleum industry takes advantage of this characteristic of the process and has used extraction to separate, for example, aromatic hydrocarbons from paraffin hydrocarbons of the same boiling range using solvents such as liquified sulfur dioxide, furfural and diethylene glycol. In general, extraction is applied when the materials to be extracted are heat-sensitive or nonvolatile and when distillation would be inappropriate because components are close-boiling, have poor relative volatilities or form azeotropes.
The simplest extraction operation is single-contact batch extraction in which the initial feed solution is agitated with a suitable solvent, allowed to separate into two phases after which the solvent containing the extracted solute is decanted. This is analagous to the laboratory procedure employing a separating funnel. On an industrial scale, the extraction operation more usually involves more than one extraction stage and is normally carried out on a continuous basis. The equipment may be comprised of either discrete mixers and settlers or some form of column contactor in which the feed and solvent phases flow countercurrently by virtue of the density difference between the phases.
Final settling or phase separation is achieved under gravity at one end of the column by allowing an adequate settling volume for complete phase disengagement.
Any one extraction operation gives rise to two product streams: the extracted feed solution, more usually termed the raffinate phase, and the solvent containing extracted solute termed the extract phase. This nomenclature is unique to liquid-liquid extraction processes and will be used from hereon.
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