Chemistry:Separation process

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Short description: Method that converts a mixture or solution into two or more distinct products
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A separation process is a method that converts a mixture or a solution of chemical substances into two or more distinct product mixtures, [1] a scientific process of separating two or more substance in order to obtain purity. At least one product mixture from 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 properties they exploit to achieve separation. If no single difference can be used to accomplish the desired separation, multiple operations can often be combined to achieve the desired end.

With a few exceptions, elements or compounds 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: to identify the size of each fraction of a mixture is attributable to each component without attempting to harvest the fractions.
  • preparative: to "prepare" fractions for input into processes that benefit when components are separated.

Separations may be performed on a small scale, as in a laboratory for analytical purposes, or on a large scale, 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 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 oil refining. Crude oil occurs naturally as a mixture of various hydrocarbons and impurities. The refining process splits this mixture into other, more valuable mixtures such as natural gas, gasoline and chemical feedstocks, none of which are pure substances, but each of which must be separated from the raw crude.

In both complete separation and incomplete separation, a series or cascade 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 intermediate.

List of separation techniques

  • 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

See also

References

  1. ↑ Wilson, Ian D.; Adlard, Edward R.; Cooke, Michael et al., eds (2000). Encyclopedia of separation science. San Diego: Academic Press. ISBN 978-0-12-226770-3. 

Further reading

  • National Academies of Sciences, Engineering, and Medicine (2019). A Research Agenda for Transforming Separation Science (Report). Washington, DC: The National Academies Press. doi:10.17226/25421. ISBN 978-0-309-49170-9. 

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