|
|
| Line 1: |
Line 1: |
| '''Liquid–liquid extraction''' also known as '''solvent extraction''' and '''partitioning''', is a method to separate compounds based on their relative [[solubility|solubilities]] in two different [[miscibility|immiscible]] liquid<ref>5222
| | 55 yr old Office Manager Fahy from Richibucto, has lots of pursuits which include jogging, [http://www.comoganhardinheiro101.com como ganhar dinheiro na internet] and keep. Finds the charm in visiting spots all over the entire world, of late only returning from Vredefort Dome. |
| 0
| |
| 0.
| |
| 0
| |
| ..0
| |
| .0
| |
| .
| |
| 0..0.0
| |
| 0
| |
| 0
| |
| 0.00
| |
| 0
| |
| 0.0
| |
| 0
| |
| 0.0.
| |
| 0
| |
| 0
| |
| </ref>s, usually water and an [[solvent|organic solvent]]. It is an extraction of a substance from one liquid into another liquid phase. Liquid–liquid extraction is a basic technique in chemical laboratories, where it is performed using a [[separatory funnel]]. This type of process is commonly performed after a chemical reaction as part of the [[Work-up (chemistry)|work-up]].
| |
| | |
| The term ''partitioning'' is commonly used to refer to the underlying chemical and physical processes involved in ''liquid–liquid extraction'' but may be fully synonymous. The term ''solvent extraction'' can also refer to the separation of a substance from a mixture by preferentially dissolving that substance in a suitable solvent. In that case, a soluble compound is separated from an insoluble compound or a complex matrix.
| |
| | |
| Solvent extraction is used in [[nuclear reprocessing]], ore processing, the production of fine [[organic compound]]s, the processing of [[perfume]]s, the production of [[vegetable fats and oils|vegetable oils]] and [[biodiesel]], and other industries.
| |
| | |
| Liquid–liquid extraction is possible in non-aqueous systems: In a system consisting of a molten metal in contact with [[molten salt]]s, metals can be extracted from one phase to the other. This is related to a [[mercury (element)|mercury]] [[electrode]] where a metal can be reduced, the metal will often then dissolve in the mercury to form an [[amalgam (chemistry)|amalgam]] that modifies its electrochemistry greatly. For example, it is possible for [[sodium]] [[cation]]s to be reduced at a mercury [[cathode]] to form [[sodium amalgam]], while at an inert electrode (such as platinum) the sodium cations are not reduced. Instead, water is reduced to hydrogen. A [[detergent]] or fine [[solid]] can be used to stabilize an [[emulsion]], or [[third phase]]..
| |
| | |
| ==Measures of effectiveness==
| |
| | |
| ===Distribution ratio===
| |
| In solvent extraction, a distribution ratio is often quoted as a measure of how well-extracted a species is. The distribution ratio (''D'') is equal to the [[concentration]] of a [[solution|solute]] in the organic phase divided by its concentration in the aqueous phase. Depending on the system, the distribution ratio can be a function of temperature, the concentration of chemical species in the system, and a large number of other parameters.
| |
| | |
| Note that ''D'' is related to the Δ''G'' of the extraction process.
| |
| | |
| Sometimes, the distribution ratio is referred to as the [[partition coefficient]], which is often expressed as the [[logarithm]]. Note that a distribution ratio for [[uranium]] and [[neptunium]] between two inorganic solids ([[zirconolite]] and [[perovskite]]) has been reported.<ref>http://www-ssrl.slac.stanford.edu/pubs/activity_rep/ar98/2370-vance.pdf</ref>
| |
| In solvent extraction, two immiscible liquids are shaken together. The more [[Chemical polarity|polar]] solutes dissolve preferentially in the more polar solvent, and the less polar solutes in the less polar solvent. In this experiment, the nonpolar halogens preferentially dissolve in the nonpolar mineral oil.
| |
| | |
| ===Separation factors===
| |
| The separation factor is one distribution ratio divided by another; it is a measure of the ability of the system to separate two solutes. For instance, if the distribution ratio for [[nickel]] (D<sub>Ni</sub>) is 10 and the distribution ratio for [[silver]] (D<sub>Ag</sub>) is 100, then the silver/nickel separation factor (SF<sub>Ag/Ni</sub>) is equal to D<sub>Ag</sub>/D<sub>Ni</sub> = SF<sub>Ag/Ni</sub> = 10.
| |
| | |
| ===Decontamination factor===
| |
| This is used to express the ability of a process to remove a [[contaminant]] from a product. For instance, if a process is fed with a mixture of 1:9 [[cadmium]] to [[indium]], and the product is a 1:99 mixture of [[cadmium]] and [[indium]], then the decontamination factor (for the removal of cadmium) of the process is 0.11 / 0.01 = 11.
| |
| | |
| ===Slopes of graphs===
| |
| The easy way to work out the extraction mechanism is to draw graphs and measure the slopes. If for an extraction system the ''D'' value is proportional to the square of the concentration of a reagent (''Z'') then the slope of the graph of log<sub>10</sub>(''D'') against log<sub>10</sub>(<nowiki>[[</nowiki>''Z''<nowiki>]]</nowiki>) will be two.
| |
| | |
| ==Techniques==
| |
| | |
| ===Batchwise single stage extractions===
| |
| This is commonly used on the small scale in chemical labs. It is normal to use a [[separating funnel]]. For instance, if a chemist were to extract [[anisole]] from a [[mixture]] of [[water]] and 5% [[acetic acid]] using [[diethyl ether|ether]], then the anisole will enter the organic phase. The two phases would then be separated.
| |
| | |
| The acetic acid can then be scrubbed (removed) from the organic phase by shaking the organic extract with [[sodium bicarbonate]]. The acetic acid reacts with the [[sodium bicarbonate]] to form [[sodium acetate]], [[carbon dioxide]], and [[water]].
| |
| | |
| ===Multistage countercurrent continuous processes===
| |
| [[Image:Coflore ACX.png|thumb|Coflore continuous countercurrent extractor]]
| |
| | |
| These are commonly used in [[industry]] for the processing of [[metals]] such as the [[lanthanides]]; because the separation factors between the lanthanides are so small many extraction stages are needed. In the multistage processes, the aqueous [[raffinate]] from one extraction unit is fed to the next unit as the aqueous feed, while the organic phase is moved in the opposite direction. Hence, in this way, even if the separation between two metals in each stage is small, the overall system can have a higher decontamination factor.
| |
| | |
| Multistage [[Countercurrent exchange|countercurrent]] arrays have been used for the separation of [[lanthanides]]. For the design of a good process, the distribution ratio should be not too high (>100) or too low (<0.1) in the extraction portion of the process. It is often the case that the process will have a section for scrubbing unwanted [[metals]] from the organic phase, and finally a [[stripping (chemistry)|stripping]] section to obtain the metal back from the organic phase.
| |
| | |
| Multistage Podbielniak contactor centrifuges produce three to five stages of theoretical extraction in a single countercurrent pass, and are used in fermentation-based pharmaceutical and food additive production facilities.
| |
| | |
| Centrifugal extractors mix and separate in one unit. Two liquids will be intensively mixed between the spinning rotor and the stationary housing at speeds up to 6000 RPM. This develops great surfaces for an ideal mass transfer from the aqueous phase into the organic phase. At 200 – 2000 g both phases will be separated again. Centrifugal extractors minimize the solvent in the process, optimize the product load in the solvent and extract the aqueous phase completely. Counter current and cross current extractions are easily established.
| |
| | |
| ===Extraction without chemical change===
| |
| Some solutes such as [[noble gas]]es can be extracted from one phase to another without the need for a chemical reaction (see [[Absorption (chemistry)|absorption]]). This is the simplest type of solvent extraction. When a solvent is extracted, two immiscible liquids are shaken together. The more polar solutes dissolve preferentially in the more polar solvent, and the less polar solutes in the less polar solvent. Some solutes that do not at first sight appear to undergo a reaction during the extraction process do not have distribution ratio that is independent of concentration. A classic example is the extraction of [[carboxylic acids]] ('''HA''') into nonpolar media such as [[benzene]]. Here, it is often the case that the carboxylic acid will form a dimer in the organic layer so the distribution ratio will change as a function of the acid concentration (measured in either phase).
| |
| | |
| For this case, the extraction constant ''k'' is described by ''k'' = [['''HA'''<sub>organic</sub>]]<sup>2</sup>/[['''HA'''<sub>aqueous</sub>]]
| |
| | |
| ===Solvation mechanism===
| |
| Using solvent extraction it is possible to extract [[uranium]], [[plutonium]], or [[thorium]] from acid solutions. One solvent used for this purpose is the [[organophosphate]] [[tri-n-butyl phosphate]]. The [[PUREX]] process that is commonly used in [[nuclear reprocessing]] uses a mixture of tri-n-butyl phosphate and an [[inert]] [[hydrocarbon]] ([[kerosene]]), the uranium(VI) are extracted from strong nitric acid and are back-extracted (stripped) using weak nitric acid. An organic soluble uranium [[complex (chemistry)|complex]] [UO<sub>2</sub>(TBP)<sub>2</sub>(NO<sub>3</sub>)<sub>2</sub>] is formed, then the organic layer bearing the uranium is brought into contact with a [[Concentration|dilute]] nitric acid solution; the equilibrium is shifted away from the organic soluble uranium complex and towards the free TBP and [[uranyl nitrate]] in dilute nitric acid. The plutonium(IV) forms a similar complex to the uranium(VI), but it is possible to strip the plutonium in more than one way; a [[reducing agent]] that converts the [[plutonium]] to the trivalent [[oxidation state]] can be added. This [[oxidation state]] does not form a stable complex with TBP and [[nitrate]] unless the nitrate concentration is very high (circa 10 mol/L nitrate is required in the aqueous phase). Another method is to simply use dilute nitric acid as a stripping agent for the plutonium. This PUREX chemistry is a classic example of a [[solvation]] [[wiktionary:Extraction|extraction]].
| |
| | |
| Here in this case D<sub>U</sub> = k [[Tributyl phosphate|TBP]]<sup>2</sup>[[NO<sub>3</sub>]]<sup>2</sup>
| |
| | |
| ===Ion exchange mechanism===
| |
| Another extraction mechanism is known as the [[ion exchange]] mechanism. Here, when an ion is transferred from the aqueous phase to the organic phase, another [[ion]] is transferred in the other direction to maintain the charge balance. This additional ion is often a [[hydrogen ion]]; for ion exchange mechanisms, the distribution ratio is often a function of [[pH]]. An example of an ion exchange extraction would be the extraction of [[americium]] by a combination of [[terpyridine]] and a [[carboxylic acid]] in ''tert''-[[butyl]] [[benzene]]. In this case
| |
| | |
| ''D''<sub>Am</sub> = ''k'' [[terpyridine]]<sup>1</sup>[[carboxylic acid]]<sup>3</sup>[[Hydron (chemistry)|H+]]<sup>−3</sup>
| |
| | |
| Another example is the extraction of [[zinc]], [[cadmium]], or [[lead]] by a di[[alkyl]] phosphinic acid (R<sub>2</sub>PO<sub>2</sub>H) into a nonpolar [[diluent]] such as an [[alkane]]. A non-[[Polar molecule|polar]] diluent favours the formation of uncharged non-polar [[metal]] complexes.
| |
| | |
| Some extraction systems are able to extract metals by both the solvation and ion exchange mechanisms; an example of such a system is the americium (and [[lanthanide]]) extraction from [[nitric acid]] by a combination of 6,6'-''bis''-(5,6-di[[pentyl]]-1,2,4-triazin-3-yl)-[[2,2'-bipyridine]] and 2-bromo[[hexanoic acid]] in ''tert''-[[butyl]] [[benzene]]. At both high- and low-nitric acid concentrations, the metal distribution ratio is higher than it is for an intermediate nitric acid concentration.
| |
| | |
| ===Ion pair extraction===
| |
| It is possible by careful choice of counterion to extract a metal. For instance, if the [[nitrate]] concentration is high, it is possible to extract [[americium]] as an [[anionic]] nitrate complex if the mixture contains a [[lipophilic]] [[quaternary ammonium salt]].
| |
| | |
| An example that is more likely to be encountered by the '' 'average' '' chemist is the use of a [[phase transfer catalyst]]. This is a charged species that transfers another [[ion]] to the organic phase. The ion reacts and then forms another ion, which is then transferred back to the aqueous phase.
| |
| | |
| For instance, the 31.1 [[kilojoule|kJ]] [[mole (unit)|mol]]<sup>−1</sup> is required to transfer an [[acetate]] anion into nitrobenzene,<ref>{{cite journal|last=Scholz|first=F.|coauthors=S. Komorsky-Lovric, M. Lovric|date=February 2000|title=A new access to Gibbs energies of transfer of ions across liquid|journal=Electrochemistry Communications|publisher=[[Elsevier]]|volume=2|issue=2|doi=10.1016/S1388-2481(99)00156-3|pages=112–118|unused_data=liquid interfaces and a new method to study electrochemical processes at well-defined three-phase junctions}}</ref> while the energy required to transfer a chloride anion from an aqueous phase to nitrobenzene is 43.8 kJ mol<sup>−1</sup>.<ref>{{cite journal|last=Danil de Namor|first=A.F.|coauthors=T. Hill|year=1983|journal=[[Journal of the Chemical Society]], [[Faraday Transactions]]|page=2713}}</ref> Hence, if the aqueous phase in a reaction is a solution of [[sodium acetate]] while the organic phase is a nitrobenzene solution of [[benzyl chloride]], then, when a phase transfer catalyst, the acetate anions can be transferred from the aqueous layer where they react with the [[benzyl]] [[chloride]] to form benzyl acetate and a chloride anion. The chloride anion is then transferred to the aqueous phase. The transfer energies of the anions contribute to that given out by the reaction.
| |
| | |
| A 43.8 to 31.1 kJ mol<sup>−1</sup> = 12.7 kJ mol<sup>−1</sup> of additional energy is given out by the reaction when compared with energy if the reaction had been done in [[nitrobenzene]] using one [[equivalent weight]] of a [[tetraalkylammonium]] acetate.
| |
| | |
| === Aqueous two-phase extraction ===
| |
| ''Aqueous two-phase extraction'', also known as ''two-phase liquid extraction'', is a unique form of solvent extraction. In an aqueous two-phase extraction, compounds are still separated based on their solubility, but the two immiscible phases are both water-based, an [[aqueous two phase system]].
| |
| | |
| Aqueous two-phase extractions can have a number of advantages over traditional solvent extraction. Solvents are often destructive to proteins, making the traditional extraction impossible for purifying proteins. In addition, organic solvents can be flammable, and their use can cause both environmental and health concerns. Aqueous-two phase extractions do not require solvents, and so avoid these concerns.
| |
| | |
| ====Types of aqueous two-phase extractions====
| |
| | |
| =====Polymer–polymer systems=====
| |
| In a Polymer–polymer system, both phases are generated by a dissolved polymer. The heavy phase will generally be [[Polyethylene glycol]] (PEG), and the light phase is generally a [[polysaccharide]]. Traditionally, the polymer used is [[dextran]]. However, dextran is relatively expensive, and research has been exploring using less expensive polysaccharides to generate the light phase.
| |
| | |
| If the target compound being separated is a protein or enzyme, it is possible to incorporate a ligand to the target into one of the polymer phases. This improves the target's affinity to that phase, and improves its ability to partition from one phase into the other. This, as well as the absence of solvents or other denaturing agents, makes polymer–polymer extractions an attractive option for purifying proteins.
| |
| | |
| The two phases of a polymer–polymer system often have very similar densities, and very low surface tension between them. Because of this, demixing a polymer–polymer system is often much more difficult than demixing a solvent extraction. Methods to improve the demixing include [[centrifugation]], and application of an [[electric field]].
| |
| | |
| =====Polymer–salt systems=====
| |
| Aqueous two-phase systems can also be generated by introducing a high concentration of salt to a polymer solution. The polymer phase used is generally still PEG. Generally, a [[kosmotropic]] salt, such as Na<sub>3</sub>PO<sub>4</sub> is used, however PEG–NaCl systems have been documented when the salt concentration is high enough.
| |
| | |
| Since polymer–salt systems demix readily they are easier to use. However, at high salt concentrations, proteins generally either denature, or precipitate from solution. Thus, polymer–salt systems are not as useful for purifying proteins.
| |
| | |
| =====Ionic liquids=====
| |
| [[Ionic liquids]] are ionic compounds with low melting points. While they are not technically aqueous, recent research has experimented with using them in an extraction that does not use organic solvents.
| |
| | |
| ==== Applications ====
| |
| *DNA purification: The ability to purify DNA from a sample is important for many modern biotechnology processes. However, samples often contain nucleases that degrade the target DNA before it can be purified. It has been shown that DNA fragments will partition into the light phase of a polymer–salt separation system. If ligands known to bind and deactivate nucleases are incorporated into the polymer phase, the nucleases will then partition into the heavy phase and be deactivated. Thus, this polymer–salt system is a useful tool for purifying DNA from a sample while simultaneously protecting it from nucleases.
| |
|
| |
| *Food Industry: The PEG–NaCl system has been shown to be effective at partitioning small molecules, such as peptides and nucleic acids. These compounds are often flavorants or odorants. The system could then be used by the food industry to isolate or eliminate particular flavors.
| |
| | |
| ==Kinetics of extraction==
| |
| It is important to investigate the rate at which the solute is transferred between the two phases, in some cases by an alteration of the contact time it is possible to alter the selectivity of the extraction. For instance, the extraction of [[palladium]] or [[nickel]] can be very slow because the rate of ligand exchange at these metal centers is much lower than the rates for [[iron]] or [[silver]] complexes.
| |
| | |
| ==Aqueous complexing agents==
| |
| If a complexing agent is present in the aqueous phase then it can lower the distribution ratio. For instance, in the case of iodine being distributed between water and an inert organic solvent such as [[carbon tetrachloride]] then the presence of [[iodide]] in the aqueous phase can alter the extraction chemistry.
| |
| | |
| Instead of <math>D_{\mathrm{I}^{+2}}</math> being a constant it becomes <math>D_{\mathrm{I}^{+2}}</math> = ''k''[[I<sub>2</sub>.<sub>Organic</sub>]]/[I<sub>2</sub>.<sub>Aqueous</sub>] [[I<sup>-</sup>.<sub>Aqueous</sub>]]
| |
| | |
| This is because the [[iodine]] reacts with the [[iodide]] to form I<sub>3</sub><sup>-</sup>. The I<sub>3</sub><sup>-</sup> anion is an example of a [[polyhalide]] [[anion]] that is quite common.
| |
| | |
| ==Industrial process design==
| |
| In a typical scenario, an industrial process will use an extraction step in which solutes are transferred from the aqueous phase to the organic phase; this is often followed by a scrubbing stage in which unwanted solutes are removed from the organic phase, then a stripping stage in which the wanted solutes are removed from the organic phase. The organic phase may then be treated to make it ready for use again.
| |
| | |
| After use, the organic phase may be subjected to a cleaning step to remove any degradation products; for instance, in PUREX plants, the used organic phase is washed with [[sodium carbonate]] solution to remove any dibutyl hydrogen phosphate or butyl dihydrogen phosphate that might be present.
| |
| | |
| ==Equipment==
| |
| Two layers separating during a liquid–liquid extraction.
| |
| [[File:Separation02.ogg|frame|left|An organic [[MTBE]] solution is extracted with [[aqueous]] sodium bicarbonate solution. This base removes [[benzoic acid]] as [[benzoate]] but leaves non-acidic [[benzil]] (yellow) behind in the upper organic phase.]]
| |
| {{clear}}
| |
| | |
| While solvent extraction is often done on a small scale by synthetic lab chemists using a [[separatory funnel]] or [[Craig apparatus]], it is normally done on the industrial scale using machines that bring the two liquid phases into contact with each other. Such machines include [[centrifugal contactor]]s, [[Thin Layer Extraction]], [[spray column]]s, [[pulsed columns]], and [[mixer-settler]]s.
| |
| | |
| ==Extraction of metals==
| |
| The extraction methods for a range of metals include:<ref>{{cite web|url=http://www.cognis.com/NR/rdonlyres/62A4BDA0-2B5F-4579-9761-968114B57A2A/0/thesolve.pdf|title=The Solvent Extraction of Some Major Metals|last=Mackenzie|first=Murdoch|publisher=Cognis GmbH|accessdate=2008-11-18}}</ref>
| |
| | |
| *Cobalt – The extraction of cobalt from [[hydrochloric acid]] using alamine 336 in ''[[meta]]''-[[xylene]].<ref>M. Filiz, N.A. Sayar and A.A. Sayar, ''Hydrometallurgy'', 2006, '''81''', 167–173.</ref> Cobalt can be extracted also using Cyanex 272 {''bis''-(2,4,4-trimethylpentyl) phosphinic acid}.
| |
| | |
| *Copper – Copper can be extracted using hydroxy[[oxime]]s as extractants, a recent paper describes an extractant that has a good selectivity for copper over [[cobalt]] and [[nickel]].<ref>Yoshinari Baba, Minako Iwakuma and Hideto Nagami, ''Ind. Eng. Chem. Res'', 2002, '''41''', 5835–5841.</ref>
| |
| <!-- *An excellent demonstration of copper solvent extraction by the University of Queensland Hydrometallurgy Group can be viewed at the following link: www.youtube.com/watch?v=Iph-z5QY2_8 -->
| |
| | |
| *Neodymium – This rare earth is extracted by di(2-ethyl-hexyl)phosphoric acid into [[hexane]] by an ion exchange mechanism.<ref>J. M. Sánchez, M. Hidalgo, M. Valiente and V. Salvadó, ''Solvent Extraction and Ion Exchange'', 1999, '''17''', 455–474.</ref>
| |
| | |
| *Nickel – Nickel can be extracted using di(2-ethyl-hexyl)phosphoric acid and [[tributyl phosphate]] in a hydrocarbon diluent (Shellsol).<ref>{{cite web | url = http://www.biomet.com.au/Extract/NiCoFS.htm | publisher = BioMetallurgical Pty Ltd | author = Lee W. John | title = A Potential Nickel / Cobalt Recovery Process}}</ref>
| |
| | |
| *Palladium and platinum – Dialkyl sulfides, tributyl phosphate and alkyl amines have been used for extracting these metals.<ref>{{cite web|url=http://www.halwachs.de/solvent-extraction.htm|title=Precious Metals Refining By Solvent Extraction |publisher=Halwachs Edelmetallchemie und Verfahrenstechnik |accessdate=2008-11-18}}</ref><ref>P. Giridhar, K.A. Venkatesan, T.G. Srinivasan and P.R. Vasudeva Rao, ''Hydrometallurgy'', 2006, '''81''', 30–39.</ref>
| |
| | |
| *Zinc and cadmium – The zinc and cadmium are both extracted by an ion exchange process, the ''N,N,N′,N′''-tetrakis(2-pyridylmethyl)ethylenediamine (TPEN) acts as a masking agent for the zinc and an extractant for the cadmium.<ref>{{cite journal | author = K. Takeshita, K. Watanabe, Y. Nakano, M. Watanabe | title = Solvent extraction separation of Cd(II) and Zn(II) with the organophosphorus extractant D2EHPA and the aqueous nitrogen-donor ligand TPEN | journal = [[Hydrometallurgy]] | year = 2003 | volume = 70 | pages = 63–71}}</ref> In the modified Zincex process, zinc is separated from most divalent ions by solvent extraction. D2EHPA (Di (2) ethyl hexyl phosphoric acid) is used for this. A zinc ion replaces the proton from two D2EHPA molecules. To strip the zinc from the D2EHPA, sulfuric acid is used, at a concentration of above 170g/l (typically 240-265g/l).
| |
| | |
| ==References==
| |
| *Sikdar, Cole, et al. Aqueous Two-Phase Extractions in Bioseparations: An Assessment. Biotechnology 9:254. 1991
| |
| *Szlag, Giuliano. A Low-Cost Aqueous Two Phase System for Enzyme Extraction. Biotechnology Techniques 2:4:277. 1988
| |
| *Dreyer, Kragl. Ionic Liquids for Aqueous Two-Phase Extraction and Stabilization of Enzymes. Biotechnology and Bioengineering. 99:6:1416. 2008
| |
| *Boland. Aqueous Two-Phase Systems: Methods and Protocols. Pg 259-269
| |
| *http://ull.chemistry.uakron.edu/chemsep/extraction/
| |
| {{Reflist}}
| |
| | |
| {{Separation processes}}
| |
| {{Chemical equilibria}}
| |
| | |
| {{DEFAULTSORT:Liquid-liquid extraction}}
| |
| [[Category:Unit operations]]
| |
| [[Category:Laboratory techniques]]
| |
| [[Category:Separation processes]]
| |
| [[Category:Flavor technology]]
| |
| [[Category:Articles containing video clips]]
| |