Distillation


Distillation, also classical distillation, is the process of separating the component substances of a liquid mixture of two or more chemically discrete substances; the separation process is realized by way of the selective boiling of the mixture and the condensation of the vapors in a still.
Distillation can operate over a wide range of pressures from 0.14 bar to nearly 21 bar and is capable of separating feeds with high volumetric flowrates and various components that cover a range of relative volatilities from only 1.17 to 81.2. Distillation provides a convenient and time-tested solution to separate a diversity of chemicals in a continuous manner with high purity. However, distillation has an enormous environmental footprint, resulting in the consumption of approximately 25% of all industrial energy use. The key issue is that distillation operates based on phase changes, and this separation mechanism requires vast energy inputs.
Dry distillation is the heating of solid materials to produce gases that condense either into fluid products or into solid products. The term dry distillation includes the separation processes of destructive distillation and of chemical cracking, breaking down large hydrocarbon molecules into smaller hydrocarbon molecules. Moreover, a partial distillation results in partial separations of the mixture's components, which process yields nearly pure components; partial distillation also realizes partial separations of the mixture to increase the concentrations of selected components. In either method, the separation process of distillation exploits the differences in the relative volatility of the component substances of the heated mixture.
In the industrial applications of classical distillation, the term distillation is used as a unit of operation that identifies and denotes a process of physical separation, not a chemical reaction; thus an industrial installation that produces distilled beverages, is a distillery of alcohol. These are some applications of the distillation process:

Iron Age

Early evidence of distillation was found on Akkadian tablets dated describing perfumery operations. The tablets provided textual evidence that an early, primitive form of distillation was known to the Babylonians of ancient Mesopotamia.

Classical antiquity

Greek and Roman terminology

According to British chemist T. Fairley, neither the Greeks nor the Romans had any term for the modern concept of distillation. Words like "distill" would have referred to something else, in most cases, a part of some process unrelated to what is now known as distillation. In the words of Fairley and German chemical engineer Norbert Kockmann, respectively:
According to Dutch chemical historian Robert J. Forbes, the word distillare when used by the Romans, e.g. Seneca and Pliny the Elder, was "never used in our sense".

Aristotle

knew that water condensing from evaporating seawater is fresh:
Letting seawater evaporate and condense into freshwater cannot be called "distillation" for distillation involves boiling, but the experiment may have been an important step towards distillation.

Alexandrian chemists

Early evidence of distillation has been found related to alchemists working in Alexandria in Roman Egypt in the 1st century CE.
Distilled water has been in use since at least, when Alexander of Aphrodisias described the process. Work on distilling other liquids continued in early Byzantine Egypt under Zosimus of Panopolis in the 3rd century.

Ancient India and China (1–500 CE)

Distillation was practiced in the ancient Indian subcontinent, which is evident from baked clay retorts and receivers found at Taxila, Shaikhan Dheri, and Charsadda in Pakistan and Rang Mahal in India dating to the early centuries of the Common Era. Frank Raymond Allchin says these terracotta distillation tubes were "made to imitate bamboo". These "Gandhara stills" were only capable of producing a very weak distillate, as there was no efficient means of collecting the vapors at low heat.
Distillation in China may have begun at the earliest during the Eastern Han dynasty.

Islamic Golden Age

Medieval Muslim chemists such as Jābir ibn Ḥayyān and Abū Bakr al-Rāzī experimented extensively with the distillation of various substances. The fractional distillation of organic substances plays an important role in the works attributed to Jābir, such as in the Seventy Books|, translated into Latin by Gerard of Cremona under the title Liber de septuaginta. The Jabirian experiments with fractional distillation of animal and vegetable substances, and to a lesser degree also of mineral substances, is the main topic of the De anima in arte alkimiae, an originally Arabic work falsely attributed to Avicenna that was translated into Latin and would go on to form the most important alchemical source for Roger Bacon.
The distillation of wine is attested in Arabic works attributed to al-Kindī and to al-Fārābī, and in the 28th book of al-Zahrāwī's Al-Tasrif. In the twelfth century, recipes for the production of aqua ardens by distilling wine with salt started to appear in a number of Latin works, and by the end of the thirteenth century it had become a widely known substance among Western European chemists. The works of Taddeo Alderotti describe a method for concentrating alcohol involving repeated distillation through a water-cooled still, by which an alcohol purity of 90% could be obtained.

Medieval China

The distillation of beverages began in the Southern Song and Jin dynasties, according to archaeological evidence. A still was found in an archaeological site in Qinglong, Hebei province, China, dating back to the 12th century. Distilled beverages were common during the Yuan dynasty.

Modern era

In 1500, German alchemist Hieronymus Brunschwig published Liber de arte distillandi de simplicibus, the first book solely dedicated to the subject of distillation, followed in 1512 by a much expanded version. Right after that, in 1518, the oldest surviving distillery in Europe, The Green Tree Distillery, was founded.
In 1651, John French published The Art of Distillation, the first major English compendium on the practice, but it has been claimed that much of it derives from Brunschwig's work. This includes diagrams with people in them showing the industrial rather than bench scale of the operation.
File:Hieronymus Brunschwig Liber de arte Distillandi CHF AQ13x3.jpg|thumb|Hieronymus Brunschwig's Liber de arte Distillandi de Compositis
As alchemy evolved into the science of chemistry, retorts became used for distillations. Both alembics and retorts are glass vessels with long necks pointing to the side at a downward angle to act as air-cooled condensers to condense the distillate and let it drip downward for collection. Later, copper alembics were used. Riveted joints were often kept tight by using various mixtures, for instance, a dough made of rye flour. These alembics often used a cooling system around the beak, using cold water for instance, which made the condensation of alcohol more efficient. These were called pot stills. 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 production of some fine alcoholic beverages including cognac, whisky and whiskey, tequila, rum, cachaça, and some vodkas. Pot stills made of various materials are also used by bootleggers in various countries. Small pot stills are also sold for use in the domestic production of flower water or essential oils.
Early forms of distillation involved 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 reportedly carried out as many as 500 to 600 distillations in order to obtain a pure compound.
In the early 19th century, the basics of modern techniques, including pre-heating and reflux, were developed. In 1822 Anthony Perrier developed one of the first continuous stills, and in 1826 Robert Stein improved that design to make his patent still. In 1830, Aeneas Coffey was granted a patent for improving the design further. Coffey's continuous still may be regarded as the archetype of modern petrochemical units. The French engineer Armand Savalle developed his steam regulator around 1846. In 1877, Ernest Solvay was granted a U.S. patent for a tray column for ammonia distillation; from that year there were further developments on distilling oils 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 by Ernest Thiele, and the Fenske equation. The first industrial plant in the United States to use distillation as a means of desalinating seawater opened in Freeport, Texas in 1961 with the hope of bringing water security to the region.
The availability of powerful computers enabled distillation columns to be simulated numerically.