Distillation 8301 225898774 2008-07-15T22:38:38Z 65.46.253.42 /* History */ copy edit [[Image:Simple distillation apparatus.svg|thumb|right|Laboratory distillation set-up: '''1: '''Heat source '''2: '''Still pot '''3: '''Still head '''4: '''Thermometer/Boiling point temperature '''5: '''Condenser '''6: '''Cooling water in '''7: '''Cooling water out '''8: '''Distillate/receiving flask '''9: '''Vacuum/gas inlet '''10: '''Still receiver '''11: '''Heat control '''12: '''Stirrer speed control '''13: '''Stirrer/heat plate '''14: '''Heating (Oil/sand) bath '''15:''' Stiring means e.g. magnetic follower (shown), anti-bumping granules or mechanical stirrer '''16: '''Cooling bath.]] '''Distillation''' is a method of [[separation process|separating]] [[chemical substance]]s based on differences in their [[Volatility (physics)|volatilities]] in a boiling liquid mixture. Distillation usually forms part of a larger chemical process, and is thus referred to as a [[unit operation]]. Commercially, distillation has a number of uses. It is used to separate [[crude oil]] into more fractions for specific uses such as [[transport]], [[power generation]] and heating. Water is distilled to remove impurities, such as salt from sea water. Air is distilled to separate its components - notably [[oxygen]], [[nitrogen]] and [[argon]] - for industrial use. Distillation of [[Fermentation (food)|fermented]] [[solutions]] has been used since ancient times to produce [[distilled beverages]] with a higher alcohol content. ==History== Early forms of distillation were known to [[Babylonia]]n [[Alchemy|alchemists]] in [[Mesopotamia]] (in what is now [[Iraq]]) from at least the [[2nd millennium BC]].<ref>Martin Levey (1956). "Babylonian Chemistry: A Study of Arabic and Second Millennium B.C. Perfumery", ''Osiris'' '''12''', p. 376-389.</ref> Archaeological excavations in northwest [[Pakistan]] have yielded evidence that the distillation of alcohol was known in [[Pakistan]] since 500 BCE, <ref name=Allchin/> but only became common between 150 BCE- 350 CE.<ref name=Allchin>Allchin 1979</ref> Distillation was later known to [[Greek language|Greek]] alchemists from the 1st century AD,<ref name=Russell>{{cite book | title = Chemistry, Society and Environment: A New History of the British Chemical Industry | author = Colin Archibald Russell | publisher = [[Royal Society of Chemistry]] | year = 2000 | isbn = 0854045996 | pages = p.69}}</ref><ref>{{cite book | title = Science, Medicine, and History: Essays on the Evolution of Scientific Thought and Medical | author = Edgar Ashworth Underwood | publisher = [[Oxford University Press]] | pages = 251}}</ref><ref name=Simmonds>{{cite book | title = Alcohol: With Chapters on Methyl Alcohol, Fusel Oil, and Spirituous Beverages | author = Charles Simmonds | year = 1919 | publisher = Macmillan and Co. Ltd | pages = 6}}</ref> and the later development of large-scale distillation apparatus occurred in response to demands for spirits.<ref name=Russell/> [[Hypathia of Alexandria]] is credited with having invented an early distillation apparatus,<ref> Biology, Joan Solomon, Pat O'Brien, Peter Horsfall, Nelson Thornes, p.41</ref> and the first exact description of apparatus for distillation is given by Zosimos of [[Alexandria]] in the fourth century.<ref name=Simmonds/> Primitive tribes of India used a method of distillation for producing ''Mahuda'' liquor. This crude and ancient method is not very effective.<ref>Forbes 1970: 53-54</ref> [[Image:Alembic.png|right|200px|thumb|Distillation by [[retort]] using the [[alembic]].]] In the 8th century, alchemists in the Middle East produced distillation processes to purify [[chemical substance]]s for [[Industry|industrial]] purposes such as isolating natural [[ester]]s ([[perfume]]s) and producing pure [[alcohol]].<ref name=Briffault>[[Robert Briffault]] (1938). ''The Making of Humanity'', p. 195.</ref> The first among them was the [[Persian Empire|Persian]] [[Geber|Jabir ibn Hayyan]] (Geber) ''circa'' 800 AD, who is credited with the invention of numerous chemical apparatus and processes that are still in use today. In particular, his [[alembic]] was the first [[still]] with [[retort]]s which could fully purify chemicals, a precursor to the [[pot still]], and its design has served as inspiration for modern micro-scale distillation apparatus such as the Hickman stillhead.<ref>[http://www.chemistry.mcmaster.ca/~chem2o6/labmanual/microscale/ms-distn.html Microscale Laboratory Techniques - Distillation] from McMaster University</ref> [[Petroleum]] was first distilled by another [[Persian Empire|Persian]], [[al-Razi]] (Rhazes) in the 9th century, for producing [[kerosene]],<ref name=Ajram>{{cite book | author = Kasem Ajram | year = 1992 | title = Miracle of Islamic Science | pages = Appendix B | publisher = Knowledge House Publishers | isbn = 0911119434}}</ref> while [[steam distillation]] was invented by [[Avicenna]] in the early 11th century, for producing [[essential oil]]s.<ref>{{cite journal |author=A. Wolf, G. A. Bray, B. M. Popkin |year=2007 |title=A short history of beverages and how our body treats them |journal=Obesity Reviews |doi=10.1111/j.1467-789X.2007.00389.x |volume=9 |pages=151 }}</ref> As the works of Middle Eastern scribes made their way to India and became a part of Indian alchemy, several texts dedicated to distillation made their way to Indian libraries.<ref name=Forbes1/> Among these was a treatise written by a scholar from Bagdad in 1034 titled ''Ainu-s-Sana'ah wa' Auna-s-Sana'ah''.<ref name=Forbes1>Forbes 1970: 42</ref> Scholar Al-Jawbari travelled to India.<ref name=Forbes2>Forbes 1970: 45</ref> By the time of the writing of the ''[[Ain-e-Akbari]]'', the process of distillation was well known in India.<ref name=Forbes3>Forbes 1970: 54</ref> In 1500, [[Germany|German]] alchemist Hieronymus Braunschweig published ''Liber de arte destillandi'' (The Book of the Art of Distillation)<ref>http://www.alchemywebsite.com/bookshop/mohs32.html</ref> the first book on the subject, followed in 1512 by a much expanded version. In 1651, [[John French (doctor)|John French]] published [http://www.levity.com/alchemy/jfren_ar.html The Art of Distillation] the first major English compendium of practice, though it has been claimed<ref>''Industrial Engineering Chemistry'' (1936) page 677</ref> that much of it derives from Braunschweig's work. This includes diagrams with people in them showing the industrial rather than bench scale of the operation. As [[alchemy]] evolved into the science of [[chemistry]], vessels called [[retort]]s became used for distillations. Both alembics and retorts are forms of [[Laboratory glassware|glassware]] with long necks pointing to the side at a downward angle which acted as air-cooled [[Condenser (heat transfer)|condensers]] to [[Condensation|condense]] the distillate and let it drip downward for collection. Later, copper alembics were invented. Riveted joints were often kept tight by using various mixtures, for instance a dough made of rye flour.<ref>[http://www.copper-alembic.com/manufacturing/specs_sealing.php Sealing Technique], accessed [[16 November]] [[2006]].</ref> These alembics often featured a cooling system around the beak, using cold water for instance, which made the condensation of alcohol more efficient. These were called [[pot still]]s. Today, the retorts and pot stills have been largely supplanted by more efficient distillation methods in most industrial processes. However, the pot still is still widely used for the elaboration of some fine alcohols such as [[cognac (drink)|cognac]], [[Scotch whisky]], [[tequila]] and some [[vodka]]s. Pot stills made of various materials (wood, clay, stainless steel) are also used by [[Rum-runner|bootlegger]]s in various countries. Small pot stills are also sold for the domestic production<ref>[http://www.essentialoil.com/alembic5.html Traditional Alembic Pot Still], accessed [[16 November]] [[2006]].</ref> of flower water or [[essential oils]]. Early forms of distillation were batch processes using one vaporization and one condensation. Purity was improved by further distillation of the condensate. Greater volumes were processed by simply repeating the distillation. Chemists were reported to carry out as many as 500 to 600 distillations in order to obtain a pure compound<ref name=Othmer>D. F. Othmer (1982) ''Distillation - Some Steps in its Development'', in W. F. Furter (ed) ''A Century of Chemical Engineering'' ISBN 0-306-40895-3</ref>. In the early 19th century the basics of modern techniques including pre-heating and reflux were developed, particularly by the French<ref name=Othmer/>, then in 1830 a British [[Patent]] was issued to [[Aeneas Coffey]] for a whiskey distillation column<ref>A. Coffey British Patent 5974, 5 August 1830</ref>, which worked continuously and may be regarded as the [[archetype]] of modern petrochemical units. In 1877, [[Ernest Solvay]] was granted a U.S. Patent for a tray column for [[ammonia]] distillation<ref>US Patent 198699 Improvement in the Ammonia-Soda Manufacture</ref> and the same and subsequent years saw developments of this theme for oil and spirits. With the emergence of [[chemical engineering]] as a discipline at the end of the 19th century, scientific rather than empirical methods could be applied. The developing [[petroleum]] industry in the early 20th century provided the impetus for the development of accurate design methods such as the [[McCabe-Thiele method]] and the [[Fenske equation]]. The availability of powerful computers has also allowed direct [[computer simulation]] of distillation columns. ==Applications of distillation== The application of distillation can roughly be divided in four groups: [[#Laboratory scale distillation|laboratory scale]], [[#Industrial distillation|industrial distillation]], distillation of herbs for perfumery and medicinals ([[herbal distillate]]) and [[#Distillation in food processing|food processing]]. The latter two are distinct from the former two in that the distillation is not used as a true purification method but rather to transfer all [[Volatility (chemistry)|volatile]]s from the source materials to the distillate. The main difference between laboratory scale distillation and industrial distillation is that laboratory scale distillation is often performed batch-wise, whereas industrial distillation often occurs continuously. In [[batch distillation]], the composition of the source material, the vapors of the distilling compounds and the distillate change during the distillation. In batch distillation, a still is charged (supplied) with a batch of feed mixture, which is then separated into its component fractions which are collected sequentially from most volatile to less volatile, with the bottoms (remaining least or non-volatile fraction) removed at the end. The still can then be recharged and the process repeated. In [[continuous distillation]], the source materials, vapors and distillate are kept at a constant composition by carefully replenishing the source material and removing fractions from both vapor and liquid in the system. This results in a better control of the separation process. ==Idealized distillation model== The [[boiling point]] of a liquid is the temperature at which the [[vapor pressure]] of the liquid equals the pressure surrounding the liquid. The [[normal boiling point]] of a liquid is the special case at which the vapor pressure of the liquid equals the ambient [[atmospheric pressure]]. A liquid in a container at a pressure below atmospheric pressure will boil at temperature lower than the normal boiling point, and a liquid in a container at a pressure higher than atmospheric pressure will boil at a temperature higher than the normal boiling point. It is a common misconception that in a liquid mixture at a given pressure, each component boils at the boiling point corresponding to the given pressure and the vapors of each component will collect separately and purely. This, however, does not occur even in an idealized system. Idealized models of distillation are essentially governed by [[Raoult's law]] and [[Dalton's law]], and assume that [[Vapor-liquid equilibrium|vapor-liquid equilibria]] are attained. Raoult's law assumes that a component contributes to the total [[vapor pressure]] of the mixture in proportion to its percentage of the mixture and its vapor pressure when pure, or succintly: partial pressure equals mole fraction multiplied by vapor pressure when pure. If one component changes another component's vapor pressure, or if the volatility of a component is dependent on its percentage in the mixture, the law will fail. Dalton's law states that the total vapor pressure is the sum of the vapor pressures of each individual component in the mixture. When a multi-component liquid is heated, the vapor pressure of each component will rise, thus causing the total vapor pressure to rise. When the total vapor pressure reaches the pressure surrounding the liquid, [[boiling]] occurs and liquid turns to gas throughout the bulk of the liquid. Note that a mixture with a given composition has one boiling point at a given pressure, when the components are mutually soluble. An implication of one boiling point is that lighter components never cleanly "boil first". At boiling point, all volatile components boil, but for a component, its percentage in the vapor is the same as its percentage of the total vapor pressure. Lighter components have a higher partial pressure and thus are concentrated in the vapor, but heavier volatile components also have a (smaller) partial pressure and necessarily evaporate also, albeit being less concentrated in the vapor. Indeed, batch distillation and fractionation succeed by varying the composition of the mixture. In batch distillation, the batch evaporates, which changes its composition; in fractionation, liquid higher in the fractionation column contains more lights and boils at lower temperatures. The idealized model is accurate in the case of chemically similar liquids, such as [[benzene]] and [[toluene]]. In other cases, severe deviations from Raoult's law and Dalton's law are observed, most famously in the mixture of [[ethanol]] and water. These compounds, when heated together, form an [[azeotrope]], in which the boiling temperature of the mixture is lower than the boiling temperature of each separate liquid. Virtually all liquids, when mixed and heated, will display azeotropic behaviour. Although there are [[computational chemistry|computational methods]] that can be used to estimate the behavior of a mixture of arbitrary components, the only way to obtain accurate [[vapor-liquid equilibrium]] data is by measurement. It is not possible to ''completely'' purify a mixture of components by distillation, as this would require each component in the mixture to have a zero [[partial pressure]]. If ultra-pure products are the goal, then further [[Separation of chemicals|chemical separation]] must be applied. When a binary mixture is evaporated and the other component, e.g. a salt, has zero partial pressure for practical purposes, the process is simpler and is called [[evaporation]] in engineering. ===Batch distillation=== {{main|Batch distillation}} [[Image:BatchDistill.svg|thumb|left|250px|A batch still showing the separation of A and B.]] Heating an ideal mixture of two volatile substances A and B (with A having the higher volatility, or lower boiling point) in a batch distillation setup (such as in an apparatus depicted in the opening figure) until the mixture is boiling results in a vapor above the liquid which contains a mixture of A and B. The ratio between A and B in the vapor will be different from the ratio in the liquid: the ratio in the liquid will be determined by how the original mixture was prepared, while the ratio in the vapor will be enriched in the more volatile compound, A (due to Raoult's Law, see above). The vapor goes through the condenser and is removed from the system. This in turn means that the ratio of compounds in the remaining liquid is now different from the initial ratio (i.e. more enriched in B than the starting liquid). The result is that the ratio in the liquid mixture is changing, becoming richer in component B. This causes the boiling point of the mixture to rise, which in turn results in a rise in the temperature in the vapor, which results in a changing ratio of A : B in the gas phase (as distillation continues, there is an increasing proportion of B in the gas phase). This results in a slowly changing ratio A : B in the distillate. If the difference in vapor pressure between the two components A and B is large (generally expressed as the difference in boiling points), the mixture in the beginning of the distillation is highly enriched in component A, and when component A has distilled off, the boiling liquid is enriched in component B. ===Continuous distillation=== {{main|Continuous distillation}} Continuous distillation is an ongoing distillation in which a liquid mixture is continuously (without interruption) fed into the process and separated fractions are removed continuously as output streams as time passes during the operation. Continuous distillation produces at least two output fractions, including at least one [[Volatility (chemistry)|volatile]] distillate fraction, which has boiled and been separately captured as a vapor condensed to a liquid. There is always a bottoms (or residue) fraction, which is the least volatile residue that has not been separately captured as a condensed vapor. ===General improvements=== Both batch and continuous distillations can be improved by making use of a [[fractionating column]] on top of the distillation flask. The column improves separation by providing a larger surface area for the vapor and condensate to come into contact. This helps it remain at equilibrium for as long as possible. The column can even consist of small subsystems ('trays' or 'dishes') which all contain an enriched, boiling liquid mixture, all with their own vapor-liquid equilibrium. There are differences between laboratory-scale and industrial-scale fractionating columns, but the principles are the same. Examples of laboratory-scale fractionating columns (in increasing efficacy) include: * [[Condenser (laboratory)#Air condenser|Air condenser]] * [[Vigreux column]] (usually laboratory scale only) * [[Packed bed|Packed column]] (packed with glass beads, metal pieces, or other chemically inert material) * [[Spinning band distillation]] system ==Laboratory scale distillation== Laboratory scale distillations are almost exclusively run as batch distillations. The device used in distillation, sometimes referred to as a ''[[still]]'', consists at a minimum of a '''reboiler''' or ''pot'' in which the source material is heated, a '''condenser''' in which the heated [[gas|vapour]] is cooled back to the liquid [[phase (matter)|state]], and a '''receiver''' in which the concentrated or purified liquid, called the '''distillate''', is collected. Several laboratory scale techniques for distillation exist (see also [[:Category:Distillation|distillation types]]). ===Simple distillation===<!-- This section is linked from [[Fractional distillation]] --> In '''simple distillation''', all the hot vapors produced are immediately channeled into a condenser which cools and condenses the vapors. Therefore, the distillate will not be pure - its composition will be identical to the composition of the vapors at the given temperature and pressure, and can be computed from [[Raoult's law]]. As a result, simple distillation is usually used only to separate liquids whose boiling points differ greatly (rule of thumb is 25 °C),<ref>[http://www.iupac.org/didac/Didac%20Eng/Didac05/Content/ST07.htm ST07 Separation of liquid - liquid mixtures (solutions)], DIDAC by [[IUPAC]]</ref> or to separate liquids from involatile solids or oils. For these cases, the vapor pressures of the components are usually sufficiently different that Raoult's law may be neglected due to the insignificant contribution of the less volatile component. In this case, the distillate may be sufficiently pure for its intended purpose. ===Fractional distillation=== {{main|Fractional distillation}} For many cases, the boiling points of the components in the mixture will be sufficiently close that Raoult's law must be taken into consideration. Therefore, '''fractional distillation''' must be used in order to separate the components well by repeated vaporization-condensation cycles within a packed fractionating column. As the solution to be purified is heated, its vapors rise to the [[fractionating column]]. As it rises, it cools, condensing on the condenser walls and the surfaces of the packing material. Here, the condensate continues to be heated by the rising hot vapors; it vaporizes once more. However, the composition of the fresh vapors are determined once again by Raoult's law. Each vaporization-condensation cycle (called a ''[[theoretical plate]]'') will yield a purer solution of the more volatile component.<ref>[http://wulfenite.fandm.edu/labtech/fractdistill.htm Fractional Distillation]</ref> In reality, each cycle at a given temperature does not occur at exactly the same position in the fractionating column; ''theoretical plate'' is thus a concept rather than an accurate description. More theoretical plates lead to better separations. A [[spinning band distillation]] system uses a spinning band of [[Polytetrafluoroethylene|Teflon]] or metal to force the rising vapors into close contact with the descending condensate, increasing the number of theoretical plates.<ref>[http://www.brinstrument.com/fractional-distillation/spinning_band_distillation.html Spinning Band Distillation] at B/R Instrument Corporation (accessed [[8 September]] [[2006]])</ref> ===Steam distillation=== {{main|Steam distillation}} Like [[vacuum distillation]], '''steam distillation''' is a method for distilling compounds which are heat-sensitive. This process involves using bubbling steam through a heated mixture of the raw material. By Raoult's law, some of the target compound will vaporize (in accordance with its partial pressure). The vapor mixture is cooled and condensed, usually yielding a layer of oil and a layer of water. Steam distillation of various [[aromatic]] herbs and flowers can result in two products; an [[essential oil]] as well as a watery [[herbal distillate]]. The [[essential oils]] are often used in perfumery and [[aromatherapy]] while the watery distillates have many applications in [[aromatherapy]], [[food processing]] and [[skin care]]. [[Image:Vacuum distillation of DMSO at 70C.jpg|left|200px|thumb|[[Dimethyl sulfoxide]] usually boils at 189 °C. Under a vacuum, it distills off into the receiver at only 70 °C.]] [[Image:perkin triangle distillation apparatus.svg|225px|thumb|'''Perkin Triangle Distillation Setup'''<br> '''1:''' Stirrer bar/anti-bumping granules '''2:''' Still pot '''3:''' Fractionating column '''4:''' Thermometer/Boiling point temperature '''5:''' Teflon tap 1 '''6:''' Cold finger '''7:''' Cooling water out '''8:''' Cooling water in '''9:''' Teflon tap 2 '''10:''' Vacuum/gas inlet '''11:''' Teflon tap 3 '''12:''' Still receiver]] ===Vacuum distillation=== {{main|Vacuum distillation}} Some compounds have very high boiling points. To boil such compounds, it is often better to lower the pressure at which such compounds are boiled instead of increasing the temperature. Once the pressure is lowered to the vapor pressure of the compound (at the given temperature), boiling and the rest of the distillation process can commence. This technique is referred to as '''vacuum distillation''' and it is commonly found in the laboratory in the form of the [[rotary evaporator]]. This technique is also very useful for compounds which boil beyond their [[decomposition temperature]] at atmospheric pressure and which would therefore be decomposed by any attempt to boil them under atmospheric pressure. ===Air-sensitive vacuum distillation=== Some compounds have high boiling points as well as being [[air sensitive]]. A simple vacuum distillation system as exemplified above can be used, whereby the vacuum is replaced with an inert gas after the distillation is complete. However, this is a less satisfactory system if one desires to collect fractions under a reduced pressure. To do this a "pig" adaptor can be added to the end of the condenser, or for better results or for very air sensitive compounds a [[Perkin triangle]] apparatus can be used. The Perkin triangle, has means via a series of glass or [[Polytetrafluoroethylene|Teflon]] taps to allows fractions to be isolated from the rest of the [[still]], without the main body of the distillation being removed from either the vacuum or heat source, and thus can remain in a state of [[reflux]]. To do this, the sample is first isolated from the vacuum by means of the taps, the vacuum over the sample is then replaced with an inert gas (such as [[nitrogen]] or [[argon]]) and can then be stoppered and removed. A fresh collection vessel can then be added to the system, evacuated and linked back into the distillation system via the taps to collect a second fraction, and so on, until all fractions have been collected. ===Short path distillation=== [[Image:short path distillation apparatus.svg|thumb|right|Short path vacuum distillation apparatus with vertical condenser (cold finger), to minimize the distillation path; '''1: ''' Still pot with stirrer bar/anti-bumping granules '''2: ''' Cold finger - bent to direct condensate '''3: ''' Cooling water out '''4: ''' cooling water in '''5: ''' Vacuum/gas inlet '''6: ''' Distillate flask/Distillate.]] '''Short path distillation''' is a distillation technique that involves the distillate traveling a short distance, often only a few [[centimeter]]s. A classic example would be a distillation involving the distillate traveling from one glass bulb to another, without the need for a condenser separating the two chambers. This technique is often used for compounds which are unstable at high temperatures. The advantage is that the heating temperature can be considerably lower (at this reduced pressure) than the boiling point of the liquid at standard pressure, and that the distillate only has to travel a short distance before condensing. The [[Kugelrohr]] is a kind of a short path distillation apparatus. ===Other types=== * In [[rotary evaporation]] a vacuum distillation apparatus is used to remove bulk [[solvent]]s from a sample. Typically the vacuum is generated by a water [[aspirator]] or a [[membrane pump]]. * In a [[kugelrohr]] a short path distillation apparatus is typically used (generally in combination with a (high) vacuum) to distill high boiling (> 300 °C) compounds. The apparatus consists of an oven in which the compound to be distilled is placed, a receiving portion which is outside of the oven, and a means of rotating the sample. The vacuum is normally generated by using a high vacuum pump. * The process of [[reactive distillation]] involves using the reaction vessel as the still. In this process, the product is usually significantly lower-boiling than its reactants. As the product is formed from the reactants, it is vaporized and removed from the reaction mixture. This technique is an example of a continuous vs. a batch process; advantages include less downtime to charge the reaction vessel with starting material, and less workup. * [[Destructive distillation]] involves the strong heating of solids (often organic material) in the absence of oxygen (to prevent combustion) to evaporate various high-boiling liquids, as well as [[thermolysis]] products. The gases evolved are cooled and condensed as in normal distillation. The destructive distillation of [[wood]] to give [[methanol]] is the root of its common name - ''wood alcohol''. * [[Pervaporation]] is a method for the separation of mixtures of liquids by partial vaporization through a non-porous [[Artificial membrane|membrane]]. * [[Dry distillation]], despite its name, is not truly distillation, but rather a chemical reaction known as [[pyrolysis]] in which solid substances are heated in a strongly [[redox|reducing]] atmosphere and any volatile fractions are collected. * [[Extractive distillation]] is defined as distillation in the presence of a miscible, high boiling, relatively non-volatile component, the solvent, that forms no azeotrope with the other components in the mixture. * [[Flash evaporation]] (or partial evaporation) is the partial vaporization that occurs when a saturated liquid stream undergoes a reduction in pressure by passing through a throttling [[valve]] or other throttling device. This process is one of the simplest unit operations. *[[Freeze distillation]] is an analogous method of purification using [[freezing]] instead of evaporation. It is not truly distillation, and does not produce products equivalent to distillation. This process is used in the production of [[American-style lager#Ice beer|ice beer]] and [[ice wine]] to increase [[ethanol]] and [[sugar]] content, respectively. *Codistillation is distillation which is performed on mixtures in which the two compounds are not miscible. ==Azeotropic distillation== {{main|Azeotropic distillation}} Interactions between the components of the solution create properties unique to the solution, as most processes entail nonideal mixtures, where [[Raoult's law]] does not hold. Such interactions can result in a constant-boiling '''[[azeotrope]]''' which behaves as if it were a pure compound (i.e., boils at a single temperature instead of a range). At an azeotrope, the solution contains the given component in the same proportion as the vapor, so that evaporation does not change the purity, and distillation does not effect separation. For example, [[ethyl alcohol]] and [[Water (molecule)|water]] form an azeotrope of 95.6% at 78.1 °C. If the azeotrope is not considered sufficiently pure for use, there exist some techniques to break the azeotrope to give a pure distillate. This set of techniques are known as '''azeotropic distillation'''. Some techniques achieve this by "jumping" over the azeotropic composition (by adding an additional component to create a new azeotrope, or by varying the pressure). Others work by chemically or physically remove or sequester the impurity. For example, to purify ethanol beyond 95%, a drying agent or a [[desiccant]] such as [[potassium carbonate]] can be added to convert the soluble water into insoluble [[water of crystallization]]. [[Molecular sieve]]s are often used for this purpose as well. Immiscible liquids, such as water and toluene, easily form azeotropes. Commonly, these azeotropes are referred to as a low boiling azeotrope because the boiling point of the azeotrope is lower than the boiling point of either pure component. The temperature and composition of the azeotrope is easily predicted from the vapor pressure of the pure components, without use of Raoult's law. The azeotrope is easily broken in a distillation set-up by using a liquid-liquid separator ( a decanter ) to separate the two liquid layers that are condensed overhead. Only one of the two liquid layers is refluxed to the distillation set-up. High boiling azeotropes, such as a 20 weight percent mixture of hydrochloric acid in water also exist. As implied by the name, the boiling point of the azeotrope is greater than the boiling point of either pure component. To break azeotropic distillations and cross distillation boundaries, such as in the DeRosier Problem, it is necessary to increase the composition of the light key in the distillate. ===Breaking an azeotrope with unidirectional pressure manipulation=== A vacuum distillation can be used to "break" an azeotropic mixture. Varying the temperature of the vapour generating flask when distilling an azeotrope from cold to the solutions boiling point does not produce a continuously sliding ratio of product to contaminate in the distillate. The two separate boiling points still remain, they merely overlap; these can be thought of as required activation energies for the release of a particular vapour. By exposing an azeotrope to a vacuum, it's possible to bias the boiling point of one away from the other by exploiting the difference between each components vapour pressure. When the bias is great enough, the two boiling points no longer overlap and so the azeotropic band disappears. This method is not without drawbacks. As an example, exposing a solution of water and ethanol to a 70 torr vacuum will allow for absolute ethanol to be distilled. However, due to the low pressure atmosphere, the ethanol vapour requires a significantly cooler condenser surface to liquefy, going from 78.3 °C at atmospheric pressure to 24.5 °C at 70 torr; failure to provide such results in the vapours passing through the condenser and into the vacuum source. This can also affect the efficiency of the condenser, as the liquefying temperature drops towards the minimum the condensing equipment can cool to, the thermal gradient across the liquefying surfaces reduces and, so with it, the rate at which heat can be extracted from the vapour. Conversely, increasing a distillation pressure can also break an azeotrope, but will bring with it the possibility of thermal decomposition, for organic compounds in particular, and may be more beneficial to high temperature tolerant distillations, such as those of the metallic salts. ===Pressure-swing Distillation=== This method of distillation can be used to separate azeotropic mixtures and relies on a principle similar to vacuum distillation, that being the manipulation of boiling points by altering the pressure of the atmosphere to which a solution is exposed. It might be chosen over pure vacuum distillation of an azeotrope if that solution, for instance, had such a low liquefying point at the pressure required to break the azeotrope that the equipment was unable to provide for it, allowing the product to stream out of the condenser and into the vacuum source. Here, rather than manipulate just one boiling point, one or more are altered, one after the other; with the number of pressure alternations being determined by the number of components in the feed solution considered to be contaminants. This could be beneficial to a purification as it is likely to create less extreme thermal requirements. Simply, instead of swinging distillation pressure in one direction alone in an attempt to break the azeotrope in one step, the break is performed in two or more steps with pressure swung in two directions to create an operating band centered around more accessible temperatures; perhaps going from a negative pressure to atmospheric and on to a positive pressure. In essence, pressure-swing distillation is an attempt to reduce extreme conditions by dispersing the manipulation load across the equipment generating the distillation environment. If a continuous feed is desired, or the distillation pressures required are extreme enough to warrant specialised design, each step may require a physically separate column. If only a batch run is required and the same column can perform under all the required pressures, this single column may suffice; with the vapour generating flask being emptied after the first distillation, the first distillate run back to the start and the distillation rerun under the second pressure conditions, and so on. Selection of which component the distillate should be biased towards may be made based on the energy required to evaporate it from the feed solution. Pressure-swing distillation is employed during the purification of [[ethyl acetate]] after its catalytic synthesis from ethanol. ==Industrial distillation== [[Image:Colonne distillazione.jpg|right|thumb|250px|Typical industrial distillation towers]] {{main|Continuous distillation}} Large scale '''industrial distillation''' applications include both batch and continuous fractional, vacuum, azeotropic, extractive, and steam distillation. The most widely used industrial applications of continuous, steady-state fractional distillation are in [[oil refinery|petroleum refineries]], [[petrochemical]] and [[chemical plant]]s and [[natural gas processing]] plants. Industrial distillation<ref name=Kister>{{cite book|author=Kister, Henry Z.|title= [[Distillation Design]]|edition=1st Edition |publisher=McGraw-Hill|year=1992|id=ISBN 0-07-034909-6}}</ref><ref name=Perry>{{cite book|author=Perry, Robert H. and Green, Don W.|title=[[Perry's Chemical Engineers' Handbook]]|edition=6th Edition| publisher=McGraw-Hill|year=1984|id=ISBN 0-07-049479-7}}</ref> is typically performed in large, vertical cylindrical columns known as '''distillation towers''' or '''distillation columns''' with diameters ranging from about 65 centimeters to 16 meters and heights ranging from about 6 meters to 90 meters or more. When the process feed has a diverse composition, as in distilling [[crude oil]], liquid outlets at intervals up the column allow for the withdrawal of different ''fractions'' or products having different [[boiling points]] or boiling ranges. The "lightest" products (those with the lowest boiling point) exit from the top of the columns and the "heaviest" products (those with the highest boiling point) exit from the bottom of the column and are often called the '''bottoms'''. [[Image:Distillation Column.png|frame|left|Diagram of a typical industrial distillation tower]] Large-scale industrial towers use [[reflux]] to achieve a more complete separation of products. Reflux refers to the portion of the condensed overhead liquid product from a distillation or fractionation tower that is returned to the upper part of the tower as shown in the schematic diagram of a typical, large-scale industrial distillation tower. Inside the tower, the downflowing reflux liquid provides cooling and condensation of the upflowing vapors thereby increasing the efficacy of the distillation tower. The more reflux is provided for a given number of [[theoretical plate]]s, the better is the tower's separation of lower boiling materials from higher boiling materials. Alternatively, the more reflux is provided for a given desired separation, the fewer theoretical plates are required. Such industrial fractionating towers are also used in air separation, producing liquid [[oxygen]], [[liquid nitrogen]], and high purity [[argon]]. Distillation of [[chlorosilane]]s also enables the production of high-purity [[silicon]] for use as a [[semiconductor]]. [[Image:Bubble Cap Trays.PNG|frame|right|Section of an industrial distillation tower showing detail of trays with bubble caps]] Design and operation of a distillation tower depends on the feed and desired products. Given a simple, binary component feed, analytical methods such as the [[McCabe-Thiele method]]<ref name=Perry/><ref name=SeaderHenley>{{cite book | author = Seader, J. D., and Henley, Ernest J. | title = Separation Process Principles | publisher = Wiley | location = New York | year = | id = ISBN 0-471-58626-9}}</ref> or the [[Fenske equation]]<ref name=Perry/> can be used. For a multi-component feed, [[simulation]] models are used both for design and operation. Moreover, the efficiencies of the vapor-liquid contact devices (referred to as "plates" or "trays") used in distillation towers are typically lower than that of a theoretical 100% efficient [[equilibrium stage]]. Hence, a distillation tower needs more trays than the number of theoretical vapor-liquid equilibrium stages. In industrial uses, sometimes a packing material is used in the column instead of trays, especially when low pressure drops across the column are required, as when operating under vacuum. [[Image:Vacuum Column.jpg|thumb|left|183px|Large-scale, industrial vacuum distillation column<ref>[http://resources.schoolscience.co.uk/SPE/knowl/4/2index.htm?vacuum.html Energy Institute website page]</ref>]] This packing material can either be random dumped packing (1-3" wide) such as [[Raschig ring]]s or [[structured packing|structured sheet metal]]. Liquids tend to wet the surface of the packing and the vapors pass across this wetted surface, where [[mass transfer]] takes place. Unlike conventional tray distillation in which every tray represents a separate point of vapor-liquid equilibrium, the vapor-liquid equilibrium curve in a packed column is continuous. However, when modeling packed columns, it is useful to compute a number of "theoretical stages" to denote the separation efficiency of the packed column with respect to more traditional trays. Differently shaped packings have different surface areas and void space between packings. Both of these factors affect packing performance. Another factor in addition to the packing shape and surface area that affects the performance of random or structured packing is the liquid and vapor distribution entering the packed bed. The number of [[Theoretical plate|theoretical stages]] required to make a given separation is calculated using a specific vapor to liquid ratio. If the liquid and vapor are not evenly distributed across the superficial tower area as it enters the packed bed, the liquid to vapor ratio will not be correct in the packed bed and the required separation will not be achieved. The packing will appear to not be working properly. The [[Theoretical plate|height equivalent of a theoretical plate]] (HETP) will be greater than expected. The problem is not the packing itself but the mal-distribution of the fluids entering the packed bed. Liquid mal-distribution is more frequently the problem than vapor. The design of the liquid distributors used to introduce the feed and reflux to a packed bed is critical to making the packing perform to it maximum efficiency. Methods of evaluating the effectiveness of a liquid distributor to evenly distribute the liquid entering a packed bed can be found in references.<ref name=Moore>''Random Packing, Vapor and Liquid Distribution: Liquid and gas distribution in commercial packed towers'', Moore, F., Rukovena, F., Chemical Plants & Processing, Edition Europe, August 1987, p. 11-15 </ref><ref name=Spiegel>''Structured Packing, Liquid Distribution: A new method to assess liquid distributor quality'', Spiegel, L., Chemical Engineering and Processing 45 (2006), p. 1011-1017 </ref> Considerable work as been done on this topic by Fractionation Research, Inc. (commonly known as FRI).<ref name=Kunesh>''Packed Tower Distributors: Commercial Scale Experiments That Provide Insight on Packed Tower Distributors'', Kunesh, J. G., Lahm, L., Yanagi, T., Ind. Eng. Chem. Res., 1987, vol. 26, p. 1845-1850 [http://www.fri.org FRI] (click on "Available Materials" and scroll to "Staff Publications")</ref> ==Distillation in food processing== ===Distilled beverages=== {{main|Distilled beverage}}'' [[Carbohydrate]]-containing plant materials are allowed to ferment, producing a dilute solution of [[ethanol]] in the process. Spirits such as [[whiskey]] and [[rum]] are prepared by distilling these dilute solutions of ethanol. Other components than ethanol are collected in the condensate, including water, esters, and other alcohols which account for the flavor of the beverage. ==References== {{reflist}} ==Further reading== * {{cite book| last = Forbes| first = R. J. | title = A Short History of the Art of Distillation from the Beginnings up to the Death of Cellier Blumenthal| publisher = BRILL| date = 1970| isbn = 9004006176}} * Needham, Joseph (1954). ''Science and Civilisation in China (vol. 4)'' Cambridge University Press: ISBN 052108573X * Allchin, F. R. (Mar., 1979). ''India: The Ancient Home of Distillation?''. ''Man'', New Series, Vol. 14, No. 1 , pp. 55-63. Royal Anthropological Institute of Great Britain and Ireland. ==Gallery== {|class="wikitable" |[[Image:Retort-in-operation-early-chemistry.PNG|100px]]|| Chemistry on its beginnings used [[retort]]s as [[laboratory equipment]] exclusively for distillation processes. |- |[[Image:Distillation of dry and oxygen-free toluene.jpg|100px]]|| A simple set-up to distill dry and oxygen-free [[toluene]]. |- |[[Image:Vacuum Column.png|100px]]||Diagram of an industrial-scale vacuum distillation column as commonly used in [[Oil refinery|oil refineries]] |- |[[Image:Rotary evaporator1.jpg|100px]]|| A [[rotary evaporator]] is able to distill solvents more quickly at lower temperatures through the use of a [[vacuum]]. |- |[[Image:Semi-microscale distillation.jpg|100px]]|| Distillation using semi-microscale apparatus. The jointless design eliminates the need to fit pieces together. The pear-shaped flask allows the last drop of residue to be removed, compared with a similarly-sized [[round-bottom flask]] The small holdup volume prevents losses. A pig is used to channel the various distillates into three receiving flasks. If necessary the distillation can be carried out under vacuum using the vacuum adapter at the pig. |} == External links == {{Wiktionary}} {{commonscat|Distillation}} *[http://lorien.ncl.ac.uk/ming/distil/distil0.htm Introduction to Distillation, University of Newcastle upon Tyne, UK] *[http://www.agcom.purdue.edu/AgCom/Pubs/AE/AE-117.html Alcohol distillation] *[http://www.distilling.com/ American Distilling Institute] *[http://www.cheresources.com/extrdist.shtml Extractive Distillation] *[http://www.members.tripod.com/historycheme/h_distill.html Case Study: Petroleum Distillation] * {{cite web|url=http://www.cheric.org/research/kdb/hcvle/hcvle.php|title=Binary Vapor-Liquid Equilibrium Data|publisher=Chemical Engineering Research Information Center|format=searchable database|accessdaymonth=5 May|accessyear=2007}} {{Distillation}} {{Separation processes}} [[Category:Distillation| ]] [[Category:Unit operations]] [[Category:Chemical engineering]] [[Category:Alchemical processes]] [[Category:Separation processes]] [[Category:Laboratory techniques]] [[Category:Phase changes]] [[bs:Destilacija]] [[bg:Дестилация]] [[ca:Destil·lació]] [[cs:Destilace]] [[da:Destillation]] [[de:Destillation]] [[el:Απόσταξη]] [[es:Destilación]] [[eo:Distilado]] [[fr:Distillation]] [[gl:Destilación]] [[id:Distilasi]] [[it:Distillazione]] [[he:זיקוק]] [[lt:Distiliacija]] [[hu:Desztilláció]] [[nl:Destillatie]] [[ja:蒸留]] [[no:Destillasjon]] [[pl:Destylacja]] [[pt:Destilação]] [[ro:Distilare]] [[ru:Дистилляция]] [[simple:Distillation]] [[sk:Destilácia]] [[sr:Дестилација]] [[fi:Tislaus]] [[sv:Destillation]] [[ta:வடித்திறக்கல்]] [[vi:Chưng cất]] [[tr:Damıtma]] [[uk:Перегонка]] [[ur:عمل تقطیر]] [[zh:蒸馏]]