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Dry distillation is the
heat In thermodynamics, heat is defined as the form of energy crossing the boundary of a thermodynamic system by virtue of a temperature difference across the boundary. A thermodynamic system does not ''contain'' heat. Nevertheless, the term is ...
ing of
solid Solid is one of the four fundamental states of matter (the others being liquid, gas, and plasma). The molecules in a solid are closely packed together and contain the least amount of kinetic energy. A solid is characterized by structur ...
materials to produce gaseous products (which may condense into liquids or solids). The method may involve
pyrolysis The pyrolysis (or devolatilization) process is the thermal decomposition of materials at elevated temperatures, often in an inert atmosphere. It involves a change of chemical composition. The word is coined from the Greek-derived elements '' ...
or
thermolysis Thermal decomposition, or thermolysis, is a chemical decomposition caused by heat. The decomposition temperature of a substance is the temperature at which the substance chemically decomposes. The reaction is usually endothermic as heat is re ...
, or it may not (for instance, a simple mixture of ice and glass could be separated without breaking any chemical bonds, but organic matter contains a greater diversity of molecules, some of which are likely to break). If there are no chemical changes, just phase changes, it resembles classical
distillation Distillation, or classical distillation, is the process of separating the components or substances from a liquid mixture by using selective boiling and condensation, usually inside an apparatus known as a still. Dry distillation is the he ...
, although it will generally need higher temperatures. Dry distillation in which chemical changes occur is a type of
destructive distillation Destruction may refer to: Concepts * Destruktion, a term from the philosophy of Martin Heidegger * Destructive narcissism, a pathological form of narcissism * Self-destructive behaviour, a widely used phrase that ''conceptualises'' certain kind ...
or cracking.


Uses

The method has been used to obtain liquid
fuel A fuel is any material that can be made to react with other substances so that it releases energy as thermal energy or to be used for work. The concept was originally applied solely to those materials capable of releasing chemical energy b ...
s from
coal Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other elements, chiefly hydrogen, sulfur, oxygen, and nitrogen. Coal is formed when ...
and
wood Wood is a porous and fibrous structural tissue found in the stems and roots of trees and other woody plants. It is an organic materiala natural composite of cellulose fibers that are strong in tension and embedded in a matrix of lignin ...
. It can also be used to break down mineral
salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of salts; salt in the form of a natural crystalline mineral is known as rock salt or halite. Salt is present in vast quant ...
s such as
sulfate The sulfate or sulphate ion is a polyatomic anion with the empirical formula . Salts, acid derivatives, and peroxides of sulfate are widely used in industry. Sulfates occur widely in everyday life. Sulfates are salts of sulfuric acid and many ...
s () through
thermolysis Thermal decomposition, or thermolysis, is a chemical decomposition caused by heat. The decomposition temperature of a substance is the temperature at which the substance chemically decomposes. The reaction is usually endothermic as heat is re ...
, in this case producing
sulfur dioxide Sulfur dioxide (IUPAC-recommended spelling) or sulphur dioxide (traditional Commonwealth English) is the chemical compound with the formula . It is a toxic gas responsible for the odor of burnt matches. It is released naturally by volcanic a ...
(SO2) or
sulfur trioxide Sulfur trioxide (alternative spelling sulphur trioxide, also known as ''nisso sulfan'') is the chemical compound with the formula SO3. It has been described as "unquestionably the most important economically" sulfur oxide. It is prepared on an ind ...
(SO3) gas which can be dissolved in water to obtain
sulfuric acid Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid ( Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen and hydrogen, with the molecular fo ...
. By this method sulfuric acid was first identified and artificially produced. When substances of vegetable origin, e.g.
coal Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other elements, chiefly hydrogen, sulfur, oxygen, and nitrogen. Coal is formed when ...
, oil shale,
peat Peat (), also known as turf (), is an accumulation of partially Decomposition, decayed vegetation or organic matter. It is unique to natural areas called peatlands, bogs, mires, Moorland, moors, or muskegs. The peatland ecosystem covers and ...
or
wood Wood is a porous and fibrous structural tissue found in the stems and roots of trees and other woody plants. It is an organic materiala natural composite of cellulose fibers that are strong in tension and embedded in a matrix of lignin ...
, are heated in the absence of air (dry distillation), they decompose into gas, liquid products and coke/
charcoal Charcoal is a lightweight black carbon residue produced by strongly heating wood (or other animal and plant materials) in minimal oxygen to remove all water and volatile constituents. In the traditional version of this pyrolysis process, ...
. The yield and chemical nature of the decomposition products depend on the nature of the raw material and the conditions under which the dry distillation is done. Decomposition within a temperature range of 450 to about 600°C is called carbonization or low-temperature degassing. At temperatures above 900°C, the process is called
coking Coking is the heating of coal in the absence of oxygen to a temperature above 600 °C to drive off the volatile components of the raw coal, leaving a hard, strong, porous material of high carbon content called coke. Coke consists almost en ...
or high-temperature degassing. If coal is gasified to make
coal gas Coal gas is a flammable gaseous fuel made from coal and supplied to the user via a piped distribution system. It is produced when coal is heated strongly in the absence of air. Town gas is a more general term referring to manufactured gaseous ...
or carbonized to make coke then
coal tar Coal tar is a thick dark liquid which is a by-product of the production of coke and coal gas from coal. It is a type of creosote. It has both medical and industrial uses. Medicinally it is a topical medication applied to skin to treat pso ...
is among the by-products.


Wood

When wood is heated above 270°C it begins to carbonize. If air is absent, the final product (since there is no oxygen present to react with the wood) is charcoal. If air (which contains oxygen) is present, the wood will catch fire and burn when it reaches a temperature of about 400–500°C and the fuel product is wood ash. If wood is heated away from air, first the moisture is driven off. Until this is complete, the wood temperature remains at about 100–110°C. When the wood is dry its temperature rises, and at about 270°C, it begins to spontaneously decompose. This is the well known exothermic reaction which takes place in charcoal burning. At this stage evolution of the by-products of wood carbonization starts. These substances are given off gradually as the temperature rises and at about 450°C the evolution is complete. The solid residue, charcoal, is mainly carbon (about 70%) and small amounts of tarry substances which can be driven off or decomposed completely only by raising the temperature to above about 600°C. In the common practice of charcoal burning using internal heating of the charged wood by burning a part of it, all the by-product vapors and gas escapes into the atmosphere as smoke. The by-products can be recovered by passing the off-gases through a series of water to yield so-called wood vinegar ( pyroligneous acid) and the non-condensible wood gas passes on through the condenser and may be burned to provide heat. The wood gas is only usable as fuel and consists typically of 17% methane; 2% hydrogen; 23% carbon monoxide; 38% carbon dioxide; 2% oxygen and 18% nitrogen. It has a gas calorific value of about 10.8 MJ/m3 (290 BTU/cu.ft.) i.e. about one third the value of natural gas. When
deciduous In the fields of horticulture and Botany, the term ''deciduous'' () means "falling off at maturity" and "tending to fall off", in reference to trees and shrubs that seasonally shed leaves, usually in the autumn; to the shedding of petals, ...
tree woods are subjected to distillation, the products are
methanol Methanol (also called methyl alcohol and wood spirit, amongst other names) is an organic chemical and the simplest aliphatic alcohol, with the formula C H3 O H (a methyl group linked to a hydroxyl group, often abbreviated as MeOH). It is ...
(wood alcohol) and
charcoal Charcoal is a lightweight black carbon residue produced by strongly heating wood (or other animal and plant materials) in minimal oxygen to remove all water and volatile constituents. In the traditional version of this pyrolysis process, ...
. The distillation of
pine A pine is any conifer tree or shrub in the genus ''Pinus'' () of the family (biology), family Pinaceae. ''Pinus'' is the sole genus in the subfamily Pinoideae. The World Flora Online created by the Royal Botanic Gardens, Kew and Missouri Botanic ...
wood causes
Pine tar Pine tar is a form of wood tar produced by the high temperature carbonization of pine wood in anoxic conditions (dry distillation or destructive distillation). The wood is rapidly decomposed by applying heat and pressure in a closed container; ...
and pitch to drip away from the wood and leave behind charcoal. Birch tar from
birch bark Birch bark or birchbark is the bark of several Eurasian and North American birch trees of the genus ''Betula''. The strong and water-resistant cardboard-like bark can be easily cut, bent, and sewn, which has made it a valuable building, craftin ...
is a particularly fine tar, known as "
Russia Russia (, , ), or the Russian Federation, is a transcontinental country spanning Eastern Europe and Northern Asia. It is the largest country in the world, with its internationally recognised territory covering , and encompassing one-ei ...
n oil", suitable for
leather Leather is a strong, flexible and durable material obtained from the tanning, or chemical treatment, of animal skins and hides to prevent decay. The most common leathers come from cattle, sheep, goats, equine animals, buffalo, pigs and hog ...
protection. The by-products of wood tar are
turpentine Turpentine (which is also called spirit of turpentine, oil of turpentine, terebenthene, terebinthine and (colloquially) turps) is a fluid obtained by the distillation of resin harvested from living trees, mainly pines. Mainly used as a special ...
and
charcoal Charcoal is a lightweight black carbon residue produced by strongly heating wood (or other animal and plant materials) in minimal oxygen to remove all water and volatile constituents. In the traditional version of this pyrolysis process, ...
.
Tar kiln Tar is a dark brown or black viscous liquid of hydrocarbons and free carbon, obtained from a wide variety of organic materials through destructive distillation. Tar can be produced from coal, wood, petroleum, or peat. "a dark brown or black bit ...
s are dry distillation ovens, historically used in Scandinavia for producing
tar Tar is a dark brown or black viscous liquid of hydrocarbons and free carbon, obtained from a wide variety of organic materials through destructive distillation. Tar can be produced from coal, wood, petroleum, or peat. "a dark brown or black bi ...
from wood. They were built close to the forest, from
limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms w ...
or from more primitive holes in the ground. The bottom is sloped into an outlet hole to allow the tar to pour out. The wood is split into dimensions of a finger, stacked densely, and finally covered tight with dirt and moss. If oxygen can enter, the wood might catch fire, and the production would be ruined. On top of this, a fire is stacked and lit. After a few hours, the tar starts to pour out and continues to do so for a few days.


See also

* Coal oil *
Destructive distillation Destruction may refer to: Concepts * Destruktion, a term from the philosophy of Martin Heidegger * Destructive narcissism, a pathological form of narcissism * Self-destructive behaviour, a widely used phrase that ''conceptualises'' certain kind ...
*
Gasworks A gasworks or gas house is an industrial plant for the production of flammable gas. Many of these have been made redundant in the developed world by the use of natural gas, though they are still used for storage space. Early gasworks Coal ...
*
Pitch (resin) Pitch is a viscoelastic polymer which can be natural or manufactured, derived from petroleum, coal tar, or plants. Various forms of pitch may also be called tar, bitumen, or asphalt. Pitch produced from plants is also known as resin. Some produ ...
*
Syngas Syngas, or synthesis gas, is a mixture of hydrogen and carbon monoxide, in various ratios. The gas often contains some carbon dioxide and methane. It is principly used for producing ammonia or methanol. Syngas is combustible and can be used as ...
*
Tar Tar is a dark brown or black viscous liquid of hydrocarbons and free carbon, obtained from a wide variety of organic materials through destructive distillation. Tar can be produced from coal, wood, petroleum, or peat. "a dark brown or black bi ...


References

Distillation Pyrolysis {{chem-stub