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Distillation | Chemistry | Research Starters | EBSCO Research Back Browse Subject Areas Copy URL Copy URL Distillation Distillation is a widely used technique for purifying liquid mixtures by boiling and subsequently condensing the vapors, allowing for the separation of components based on their boiling points. Practiced since ancient times, distillation plays a crucial role in various industries, including petroleum, petrochemicals, and pharmaceuticals. The basic principle involves heating a liquid to its boiling point, converting it into vapor, and then cooling the vapor to collect it as a liquid—this process can effectively isolate individual components from mixtures. There are various forms of distillation, such as simple, fractional, and vacuum distillation, each suited for different applications and mixtures. For instance, fractional distillation is particularly useful for separating liquids with close boiling points, while vacuum distillation lowers boiling points by reducing pressure, making it ideal for heat-sensitive substances. Distillation is also applied in desalination processes to produce chemically pure water. In the modern context, the technique is evolving with advancements that aim to improve energy efficiency and reduce environmental impacts, particularly in response to the rising costs of raw materials and sustainability concerns. Overall, distillation remains an essential method in both laboratory and industrial settings for the purification of a wide range of substances. Authored By : Stewart, Martin V., BS, PhD 1 of 3 Authored By : Stewart, Martin V., BS, PhD Published In : 2024 2 of 3 Published In : 2024 Related Topics : State of matter ; Boiling points ; Condensation ; Alcoholic drink ; Petrochemical products ; Liquefaction Of Gases ; Crystallization ; John Dalton ; Organic Compounds ; Hazardous waste ; Chromatography ; Gas chromatography (GC) ; High-performance liquid chromatography (HPLC) ; Chemical Engineering ; Chemical synthesis ; Chemical industry ; Energy conservation ; Sustainability ; Fossil fuel reserves ; Solar power State of matter ; Boiling points ; Condensation ; Alcoholic drink ; Petrochemical products ; Liquefaction Of Gases ; Crystallization ; John Dalton ; Organic Compounds ; Hazardous waste ; Chromatography ; Gas chromatography (GC) ; High-performance liquid chromatography (HPLC) ; Chemical Engineering ; Chemical synthesis ; Chemical industry ; Energy conservation ; Sustainability ; Fossil fuel reserves ; Solar power 3 of 3 On This Page Full Article Full Article Distillation Summary Distillation is a process for purifying liquid mixtures by collecting vapors from a boiling substance and condensing them back into the original liquid. Various forms of this technique, practiced since antiquity, continue to be used extensively in the petroleum, petrochemical, coal tar, chemical, and pharmaceutical industries to separate mixtures of mostly organic compounds as well as to isolate individual components in chemically pure form. Distillation has also been employed to acquire chemically pure water, including potable water through the desalination of seawater. Definition and Basic Principles Matter commonly exists in one of three physical states solid, liquid, or gas. Any phase of matter can be changed reversibly into another at a temperature and pressure characteristic of that particular sample. When a liquid is heated to a temperature called the boiling point , it begins to boil and is transformed into a gas. Unlike the melting point of a solid, the boiling point of a liquid is proportional to the applied pressure, increasing at high pressures and decreasing at low pressures. When a mixture of several miscible liquids is heated, the component with the lowest boiling point is converted to the gaseous phase preferentially over those with higher boiling points, which enriches the vapor with the more volatile component. The distillation operation removes this vapor and condenses it back to the liquid phase in a different receiving flask. Thus, liquids with unequal boiling points can be separated by collecting the condensed vapors sequentially as fractions. Distillation also removes nonvolatile components, which remain behind as a residue. Background and History Applications of fundamental concepts such as evaporation, sublimation, and condensation were mentioned by Aristotle and others in antiquity. However, many historians consider distillation to be a discovery of Alexandrian alchemists (300 BCE to 200 CE), who added a lid (called the head) to the still and prepared oil of turpentine by distilling pine resin. The Arabians improved the apparatus by cooling the head (which came to be known as the alembic) with water, which allowed the isolation of a number of essential oils by distilling plant material and, by 800 CE, permitted the Islamic scholar Jbir ibn Hayyn to obtain acetic acid from vinegar. Alembic stills and retorts were widely employed by alchemists of medieval Europe. The first fractional distillation, also called differential distillation, was developed by Taddeo Alderotti in the thirteenth century. The first comprehensive manual of distillation techniques was Liber de arte distillandi de simplicibus , written by Hieronymus Brunschwig and published in 1500 in Strasbourg, France. The first account of the destructive distillation of coal was published in 1726. Large-scale continuous stills with fractionating towers similar to modern industrial stills were devised for the distillation of alcoholic beverages in the first half of the nineteenth century and later adapted to coal and oil refining. Laboratory distillation similarly advanced with the introduction of the Liebig condenser around 1850. The modern theory of distillation was developed by Ernest Sorel and reduced to engineering terms in his Distillation et Rectification Industrielles (1899). How It Works Simple Distillation. A difference in boiling point of at least 25 degrees Celsius is generally required for successful separations with simple distillation. The glass apparatus for laboratory-scale distillations consists of a round-bottomed boiling flask, a condenser, and a receiving flask. Vapors from the boiling liquid are returned to the liquid state by the cooling action of the condenser and are collected as distillate in the receiving flask. An air condenser may be sufficient for high-boiling liquids, but often, a jacketed condenser—in which a cooling liquid such as cold water is circulated—is required. The design of many styles of condensers, such as the Liebig condenser and the West condenser, enhances the cooling effect of the circulating liquid. An adapter called a still head connects the condenser to the boiling flask at a 45-degree angle and is topped with a fitting in which a thermometer is inserted to measure the temperature of the vapor (the boiling point). A second take-off adapter is often used to attach the receiving flask to the condenser at a 45-degree angle so that it is vertical and parallel to the boiling flask. One should never heat a closed system, so the take-off adapter contains a sidearm for connection to either a drying tube or a vacuum source for distillations under reduced pressure. The apparatus was formerly assembled by connecting individual pieces with cork or rubber stoppers, but the ground-glass joints of modern glassware make these stoppers unnecessary. Fractional Distillation. When the boiling points of miscible liquids are within about 25 degrees Celsius, simple distillation does not yield separate fractions. Instead, the process produces a distillate whose composition contains varying amounts of the components, being initially enriched in the lower-boiling and more volatile one. The still assembly is modified to improve efficiency by placing a distilling column between the still head and the boiling flask. This promotes multiple cycles of condensation and revaporization. Each of these steps is an equilibration of the liquid and gaseous phases and is, therefore, equivalent to a simple distillation. Thus, the distillate from a single fractional distillation has the composition of one obtained from numerous successive simple distillations. Still heads that allow higher reflux ratios and distilling columns with greater surface areas permit more contact between vapor and liquid, which increases the number of equilibrations. Thus, a Vigreux column having a series of protruding fingers is more efficient than a smooth column. Even more efficient are columns packed with glass beads, single- or multiple-turn glass or wire helices, ceramic pieces, copper mesh, or stainless-steel wool. The limit of efficiency is approached by a spinning-band column that contains a very rapidly rotating spiral of metal or Teflon over its entire length. Applications and Products Batch and Continuous Distillation. Distilling very large quantities of liquids as a single batch is impractical, so industrial-scale distillations are often conducted by continuously introducing the material to be distilled. Continuous distillation is practiced in petrochemical and coal-tar processing and can also be used for the low-temperature separation and purification of liquefied gases such as hydrogen, oxygen, nitrogen, and helium. Vacuum Distillation. Heating liquids to temperatures above about 150 degrees Celsius is generally avoided to conserve energy, minimize the difficulty of insulating the still head and the distilling column, and prevent the thermal decomposition of heat-sensitive organic compounds. A vacuum distillation takes advantage of the fact that a liquid boils when its vapor pressure equals the external pressure, which causes the boiling point to be lowered when the pressure decreases. For example, the boiling point of water is 100 degrees Celsius at a pressure of 101.3 kilopascals (kPa), but this drops to 79 degrees Celsius at 45.5 kPa and rises to 120 degrees Celsius at 198.5 kPa. Vacuum distillation can be