Liquefaction of gases
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Liquefaction of gasesis physical conversion of agasinto aliquidstate (condensation). The liquefaction of gases is a complicated process that uses various compressions and expansions to achieve high pressures and very low temperatures, using, for example,turboexpanders.
Uses
[edit]Liquefactionprocesses are used for scientific, industrial and commercial purposes. Many gases can be put into a liquid state at normalatmospheric pressureby simple cooling; a few, such ascarbon dioxide,require pressurization as well. Liquefaction is used for analyzing the fundamental properties of gas molecules (intermolecular forces), or for the storage of gases, for example:LPG,and inrefrigerationandair conditioning.There the gas is liquefied in thecondenser,where theheat of vaporizationis released, and evaporated in theevaporator,where the heat of vaporization is absorbed.Ammoniawas the first suchrefrigerant,and is still in widespread use in industrial refrigeration, but it has largely been replaced by compounds derived frompetroleumandhalogensin residential and commercial applications.
Liquid oxygenis provided to hospitals for conversion to gas for patients with breathing problems, andliquid nitrogenis used in the medical field forcryosurgery,by inseminators to freezesemen,and by field and lab scientists to preserve samples. Liquefiedchlorineis transported for eventual solution in water, after which it is used for water purification, sanitation ofindustrial waste,sewage and swimming pools, bleaching of pulp and textiles and manufacture ofcarbon tetrachloride,glycoland numerous other organic compounds as well asphosgenegas.
Liquefaction ofhelium(4He) with the precooledHampson–Linde cycleled to aNobel PrizeforHeike Kamerlingh Onnesin 1913. At ambient pressure the boiling point ofliquefied heliumis 4.22 K (−268.93 °C). Below 2.17 K liquid4He becomes asuperfluid(Nobel Prize1978,Pyotr Kapitsa) and shows characteristic properties such as heat conduction throughsecond sound,zeroviscosityand thefountain effectamong others.
The liquefaction of air is used to obtainnitrogen,oxygen,andargonand other atmosphericnoble gasesby separating the air components byfractional distillationin acryogenic air separation unit.
History
[edit]Liquid air
[edit]Linde's process
[edit]Air is liquefied by theLinde process,in which air is alternately compressed, cooled, and expanded, each expansion results in a considerable reduction in temperature. With the lower temperature the molecules move more slowly and occupy less space, so the air changes phase to become liquid.
Claude's process
[edit]Air can also be liquefied byClaude's process in which the gas is allowed to expandisentropicallytwice in two chambers. While expanding, the gas has to do work as it is led through anexpansion turbine.The gas is not yet liquid, since that would destroy the turbine.[citation needed]Commercial air liquefication plants bypass this problem by expanding the air atsupercriticalpressures.[1]Final liquefaction takes place byisenthalpicexpansion in athermal expansion valve.
See also
[edit]- Air Liquide
- Air Products & Chemicals
- Air separation
- The BOC Group
- Chemical engineer
- Compressibility factor
- Fischer–Tropsch process
- Gas separation
- Gas to liquids
- Hampson–Linde cycle
- Industrial gases
- The Linde Group
- Liquefaction
- Liquefaction point
- Louis Paul Cailletet
- Messer Group
- Praxair
- Siemens cycle
- Turboexpander
References
[edit]- ^Greenwood, Harold Cecil (1919).Industrial Gases.D. Van Nostrand. p.87.