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{{Short description|Method that converts a mixture or solution into two or more distinct products}}
{{Chemical engineering }}
A '''separation process''' is a method that converts a mixture or solution of chemical substances into two or more distinct product mixtures.<ref>{{cite book|editor-first=Ian D. |editor-last=Wilson|editor2-first= Edward R. |editor2-last=Adlard |editor3-first=Michael |editor3-last=Cooke |editor4-first=Colin F. |display-editors = 3 |editor4-last=Poole |title=Encyclopedia of separation science|year=2000|publisher=Academic Press|location=San Diego|isbn=978-0-12-226770-3}}</ref> At least one product mixture of the separation is enriched in one or more of the source mixture's constituents. In some cases, a separation may fully divide the mixture into pure constituents.  Separations exploit differences in chemical properties or physical properties (such as size, shape, mass, density, or chemical affinity) between the constituents of a mixture.

Processes are often classified according to the particular differences they use to achieve separation. If no single difference can be used to accomplish the desired separation, multiple [[unit operation|operations]] can often be combined to achieve the desired end.
 
With a few exceptions, [[chemical element|element]]s or [[Chemical compound|compound]]s exist in nature in an impure state.  Often these raw materials must go through a separation before they can be put to productive use, making separation techniques essential for the modern industrial economy.  

The purpose of separation may be ''analytical'', i.e. to identify the size of each fraction of a mixture is attributable to each component without attempting to harvest the fractions. The purpose of a separation may maybe ''preparative'', i.e. to "prepare" fractions for input into processes that benefit when components are separated.

Separations may be performed on a small scale, such as in a [[laboratory]] for analytical purposes. Separations may also be performed on a large scale, such as in a [[chemical plant]].

==Complete and incomplete separation==
Some types of separation require complete purification of a certain component. An example is the production of [[aluminum]] metal from [[bauxite]] ore through [[Hall–Héroult process|electrolysis refining]]. In contrast, an incomplete separation process may specify an output to consist of a mixture instead of a single pure component. A good example of an incomplete separation technique is [[petroleum|oil]] refining. Crude oil occurs naturally as a mixture of various [[hydrocarbon]]s and impurities. The refining process splits this mixture into other, more valuable mixtures such as [[natural gas]], [[gasoline]] and [[Oil#Chemical feedstock|chemical feedstocks]], none of which are pure substances, but each of which must be separated from the raw crude.

In both cases of complete and incomplete separation, a series of separations may be necessary to obtain the desired end products. In the case of oil refining, crude is subjected to a long series of individual [[distillation]] steps, each of which produces a different product or [[Reaction intermediate#Chemical_processing_industry|intermediate]].

==List of separation techniques==
*[[Sponge]], adhesion of atoms, ions or molecules of gas, liquid, or dissolved solids to a surface
*[[Centrifugation]] and [[cyclonic separation]], separates based on density differences
*[[Chelation]]
*[[Filtration]]

===Chromatography===
[[Chromatography]] separates dissolved substances by different interaction with (i.e., travel through) a material.
*[[High-performance liquid chromatography]] (HPLC)
*[[Thin-layer chromatography]] (TLC)
*[[Countercurrent chromatography]] (CCC)
*[[Droplet countercurrent chromatography]] (DCC)
*[[Paper chromatography]]
*[[Ion chromatography]]
*[[Size-exclusion chromatography]]
*[[Affinity chromatography]]
*[[Centrifugal partition chromatography]]
*[[Gas chromatography]] and [[Inverse gas chromatography]]

*[[Crystallization]]
*[[Decantation]]
*[[Demister (vapor)]], removes liquid droplets from gas streams
*[[Distillation]], used for mixtures of liquids with different boiling points
*[[Drying]], removes liquid from a solid by vaporization or evaporation

===Electrophoresis===
[[Electrophoresis]], separates organic molecules based on their different interaction with a [[gel]] under an electric potential (i.e., different travel)
*[[Capillary electrophoresis]]

*[[Electrostatic separation]], works on the principle of corona discharge, where two plates are placed close together and high voltage is applied. This high voltage is used to separate the ionized particles.
*[[Elutriation]]
*[[Evaporation]]

===Extraction===
*[[Extraction (chemistry)|Extraction]]
**[[Leaching (chemistry)|Leaching]]
**[[Liquid-liquid extraction]]
**[[Solid phase extraction]]
**[[Supercritical fluid extraction]]
**[[Subcritical fluid extration]]

*[[Field flow fractionation]]

===Flotation===
*[[Froth flotation|Flotation]]
**[[Dissolved air flotation]], removes suspended solids non-selectively from slurry by bubbles that are generated by air coming out of solution
**[[Froth flotation]], recovers valuable, hydrophobic solids by attachment to air bubbles generated by mechanical agitation of an air-slurry mixture, which floats, and are recovered
**[[Deinking]], separating hydrophobic ink particles from the hydrophilic paper pulp in [[paper recycling]]

*[[Flocculation]], separates a solid from a liquid in a colloid, by use of a flocculant, which promotes the solid clumping into flocs
*[[Filtration]] – [[Mesh]], bag and paper filters are used to remove large particulates suspended in fluids (e.g., [[fly ash]]) while [[Membrane technology|membrane processes]] including [[microfiltration]], [[ultrafiltration]], [[nanofiltration]], [[reverse osmosis]], [[dialysis (biochemistry)]] utilising [[synthetic membrane]]s, separates [[micrometre]]-sized or smaller species
*[[Fractional distillation]]
*[[Fractional freezing]]
*[[API oil-water separator|Oil-water separation]], gravimetrically separates suspended oil droplets from waste water in [[oil refinery|oil refineries]], [[petrochemical]] and [[chemical plant]]s, [[natural gas processing]] plants and similar industries
*[[Magnetic separation]]
*[[Precipitation (chemistry)|Precipitation]]
*[[Recrystallization (chemistry)|Recrystallization]]
*[[Scrubber|Scrubbing]], separation of particulates (solids) or gases from a gas stream using liquid.
*[[Sedimentation]], separates using vocal density pressure differences
**[[Gravity separation]]
*[[Sieving]]
*[[Stripping (chemistry)|Stripping]]
*[[Sublimation (physics)|Sublimation]]
*[[Souders-Brown equation|Vapor-liquid separation]], separates by gravity, based on the Souders-Brown equation
*[[Winnowing]]
*[[Zone refining]]

==See also==
*{{annotated link|Analytical chemistry}}
*{{annotated link|High-performance liquid chromatography}}
*{{annotated link|Unit operation}}
*{{annotated link|Filtration}}

==References==
{{Reflist}}

==Further reading== 
* {{cite report|author=National Academies of Sciences, Engineering, and Medicine|year=2019|title=A Research Agenda for Transforming Separation Science|place=Washington, DC|publisher=The National Academies Press|doi=10.17226/25421}}

==External links==
*[http://amrita.olabs.co.in/?sub=73&brch=2&sim=96&cnt=1 Separation of Mixtures Using Different Techniques], instructions for performing classroom experiments
*[http://amrita.olabs.co.in/?sub=73&brch=2&sim=39&cnt=1 Separation of Components of a Mixture], instructions for performing classroom experiments


{{Separation processes}}
{{Analytical chemistry}}
{{Branches of chemistry}}
{{Authority control}}

[[Category:Analytical chemistry]]
[[Category:Unit operations]]
[[Category:Separation processes]]