A colorless, highly flammable or explosive gas, C2H2, used for metal welding and cutting and as an illuminant. Also called ethyne.
acetylenic a·cet'y·len'ic (ə-sĕt'l-ĕn'ĭk) adj.
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A colorless, highly flammable or explosive gas, C2H2, used for metal welding and cutting and as an illuminant. Also called ethyne.
acetylenic a·cet'y·len'ic (ə-sĕt'l-ĕn'ĭk) adj.Background
Acetylene is a colorless, combustible gas with a distinctive odor. When acetylene is liquefied, compressed, heated, or mixed with air, it becomes highly explosive. As a result special precautions are required during its production and handling. The most common use of acetylene is as a raw material for the production of various organic chemicals including 1,4-butanediol, which is widely used in the preparation of polyurethane and polyester plastics. The second most common use is as the fuel component in oxy-acetylene welding and metal cutting. Some commercially useful acetylene compounds include acetylene black, which is used in certain dry-cell batteries, and acetylenic alcohols, which are used in the synthesis of vitamins.
Acetylene was discovered in 1836, when Edmund Davy was experimenting with potassium carbide. One of his chemical reactions produced a flammable gas, which is now known as acetylene. In 1859, Marcel Morren successfully generated acetylene when he used carbon electrodes to strike an electric arc in an atmosphere of hydrogen. The electric arc tore carbon atoms away from the electrodes and bonded them with hydrogen atoms to form acetylene molecules. He called this gas carbonized hydrogen.
By the late 1800s, a method had been developed for making acetylene by reacting calcium carbide with water. This generated a controlled flow of acetylene that could be combusted in air to produce a brilliant white light. Carbide lanterns were used by miners and carbide lamps were used for street illumination before the general availability of electric lights. In 1897, Georges Claude and A. Hess noted that acetylene gas could be safely stored by dissolving it in acetone. Nils Dalen used this new method in 1905 to develop long-burning, automated marine and railroad signal lights. In 1906, Dalen went on to develop an acetylene torch for welding and metal cutting.
In the 1920s, the German firm BASF developed a process for manufacturing acetylene from natural gas and petroleum-based hydrocarbons. The first plant went into operation in Germany in 1940. The technology came to the United States in the early 1950s and quickly became the primary method of producing acetylene.
Demand for acetylene grew as new processes were developed for converting it into useful plastics and chemicals. In the United States, demand peaked sometime between 1965 and 1970, then fell off sharply as new, lower-cost alternative conversion materials were discovered. Since the early 1980s, the demand for acetylene has grown slowly at a rate of about 2-4% per year.
In 1991, there were eight plants in the United States that produced acetylene. Together they produced a total of 352 million lb (160 million kg) of acetylene per year. Of this production, 66% was derived from natural gas and 15% from petroleum processing. Most acetylene from these two sources was used on or near the site where it was produced to make other organic chemicals. The remaining 19% came from calcium carbide. Some of the acetylene from this source was used to make organic chemicals, and the rest was used by regional industrial gas producers to fill pressurized cylinders for local welding and metal cutting customers.
In Western Europe, natural gas and petroleum were the principal sources of acetylene in 1991, while calcium carbide was the principal source in Eastern Europe and Japan.
Raw Materials
Acetylene is a hydrocarbon consisting of two carbon atoms and two hydrogen atoms. Its chemical symbol is C2H2. For commercial purposes, acetylene can be made from several different raw materials depending on the process used.
The simplest process reacts calcium carbide with water to produce acetylene gas and a calcium carbonate slurry, called hydrated lime. The chemical reaction may be written as CaC2 + 2 H2O → C2H2 + Ca(OH)2.
Other processes use natural gas, which is mostly methane, or a petroleum-based hydrocarbon such as crude oil, naphtha, or bunker C oil as raw materials. Coal can also be used. These processes use high temperature to convert the raw materials into a wide variety of gases, including hydrogen, carbon monoxide, carbon dioxide, acetylene, and others. The chemical reaction for converting methane into acetylene and hydrogen may be written 2 CH4 → C2H2 + 3 H2. The other gases are the products of combustion with oxygen. In order to separate the acetylene, it is dissolved in a solvent such as water, anhydrous ammonia, chilled methanol, or acetone, or several other solvents depending on the process.
The Manufacturing
Process
There are two basic conversion processes used to make acetylene. One is a chemical reaction process, which occurs at normal temperatures. The other is a thermal cracking process, which occurs at extremely high temperatures.
Here are typical sequences of operations used to convert various raw materials into acetylene by each of the two basic processes.
Chemical reaction process
Acetylene may be generated by the chemical reaction between calcium carbide and water. This reaction produces a considerable amount of heat, which must be removed to prevent the acetylene gas from exploding. There are several variations of this process in which either calcium carbide is added to water or water is added to calcium carbide. Both of these variations are called wet processes because an excess amount of water is used to absorb the heat of the reaction. A third variation, called a dry process, uses only a limited amount of water, which then evaporates as it absorbs the heat. The first variation is most commonly used in the United States and is described below.
Thermal cracking process
Acetylene may also be generated by raising the temperature of various hydrocarbons to the point where their atomic bonds break, or crack, in what is known as a thermal cracking process. After the hydrocarbon atoms break apart, they can be made to rebond to form different materials than the original raw materials. This process is widely used to convert oil or natural gas to a variety of chemicals.
There are several variations of this process depending on the raw materials used and the method for raising the temperature. Some cracking processes use an electric arc to heat the raw materials, while others use a combustion chamber that burns part of the hydrocarbons to provide a flame. Some acetylene is generated as a coproduct of the steam cracking process used to make ethylene. In the United States, the most common process uses a combustion chamber to heat and burn natural gas as described below.
Storage and Handling
Because acetylene is highly explosive, it must be stored and handled with great care. When it is transported through pipelines, the pressure is kept very low and the length of the pipeline is very short. In most chemical production operations, the acetylene is transported only as far as an adjacent plant, or "over the fence" as they say in the chemical processing business.
When acetylene must be pressurized and stored for use in oxy-acetylene welding and metal cutting operations, special storage cylinders are used. The cylinders are filled with an absorbent material, like diatomaceous earth, and a small amount of acetone. The acetylene is pumped into the cylinders at a pressure of about 300 psi (2,070 kPa), where it is dissolved in the acetone. Once dissolved, it loses its explosive capability, making it safe to transport. When the cylinder valve is opened, the pressure drop causes some of the acetylene to vaporize into gas again and flow through the connecting hose to the welding or cutting torch.
Quality Control
Grade B acetylene may have a maximum of 2% impurities and is generally used for oxyacetylene welding and metal cutting. Acetylene produced by the chemical reaction process meets this standard. Grade A acetylene may have no more than 0.5% impurities and is generally used for chemical production processes. Acetylene produced by the thermal cracking process may meet this standard or may require further purification, depending on the specific process and raw materials.
The Future
The use of acetylene is expected to continue a gradual increase in the future as new applications are developed. One new application is the conversion of acetylene to ethylene for use in making a variety of polyethylene plastics. In the past, a small amount of acetylene had been generated and wasted as part of the steam cracking process used to make ethylene. A new catalyst developed by Phillips Petroleum allows most of this acetylene to be converted into ethylene for increased yields at a reduced overall cost.
Where to Learn More
Books
Brady, George S., Henry R. Clauser, and John A. Vaccari. Materials Handbook, 14th edition. McGraw-Hill, 1997.
Kroschwitz, Jacqueline I. and Mary Howe-Grant, ed. Encyclopedia of Chemical Technology, 4th edition. John Wiley and Sons, Inc., 1993.
Other
Acetylene Pamphlet G-1. Compressed Gas Association, 1990.
Compressed Gas Association. http://www.cganet.com.
[Article by: Chris Cavette]
An organic compound with the formula C2H2 or HC&tbnd;CH. The first member of the alkynes, acetylene is a gas with a narrow liquid range; the triple point is −81°C (−114°F). The heat of formation (ΔH°f) is +227 kilojoules/mole, and acetylene is the most endothermic compound per carbon of any hydrocarbon. The compound is thus extremely energy-rich and can decompose with explosive force. At one time acetylene was a basic compound for much chemical manufacturing. It is highly reactive and is a versatile source of other reactive compounds.
The availability of acetylene does not depend on petroleum liquids, since it can be prepared by hydrolysis of calcium carbide (CaC2), obtained from lime (CaO), and charcoal or coke (C). In modern practice, methane (CH4) is passed through a zone heated to 1500°C (2732°F) for a few milliseconds, and acetylene is then separated from the hydrogen in the effluent gas.
The main use of acetylene is in the manufacture of compounds derived from butyne-1,4-diol. The latter is obtained by condensation of acetylene with two moles of formaldehyde and is converted to butyrolactone, tetrahydrofuran, and pyrrolidone. Two additional products, vinyl fluoride and vinyl ether, are also based on acetylene.
Because of the very high heat of formation and combustion, an acetylene-oxygen mixture provides a very high temperature flame for welding and metal cutting. For this purpose acetylene is shipped as a solution in acetone, loaded under pressure in cylinders that contain a noncombustible spongy packing. See also
For more information on acetylene, visit Britannica.com.
A colorless gas, when mixed with oxygen, burns at a temperature of about 3500°C; used in welding.
A colorless, combustible, explosive gas, the simplest triple-bonded hydrocarbon.
| Acetylene | |
|---|---|
| IUPAC name | Ethyne |
| Identifiers | |
| CAS number | |
| SMILES | C#C |
| Properties | |
| Molecular formula | C2H2 |
| Molar mass | 26.0373 g/mol |
| Density | 1.09670 kg/m³ gas |
| Melting point |
-84 °C |
| Boiling point |
-80.8 °C |
| Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references |
|
Acetylene (systematic name: ethyne) is a hydrocarbon belonging to the group of alkynes. It is considered to be the simplest of all alkynes as it consists of two hydrogen atoms and two carbon atoms. Acetylene is an unsaturated organic compound because its four atoms are triple bonded through a covalent bond.
The carbon-carbon triple bond leaves the carbon atoms with two sp hybrid orbitals for sigma bonding, placing all four atoms in the same straight line, with CCH bond angles of 180°.
Acetylene was discovered in 1836 by Edmund Davy who identified it as a "new carburet of hydrogen." It was rediscovered in 1860 by French chemist Marcellin Berthelot, who coined the name "acetylene." The Nobel Laureate Gustaf Dalén was blinded by an acetylene explosion.
The principal raw materials for acetylene manufacture are calcium carbonate (limestone) and coal. The calcium carbonate is first converted into calcium oxide and the coal into coke, then the two are reacted with each other to form calcium carbide and carbon monoxide:
Calcium carbide (or calcium acetylide) and water are then reacted by any of several methods to produce acetylene and calcium hydroxide. This reaction was discovered by Friedrich Wohler in 1862.
Calcium carbide synthesis requires an extremely high temperature, ~2000 degrees Celsius, so the reaction is performed in an electric arc furnace. This reaction was an important part of the late-1800s revolution in chemistry enabled by the massive hydroelectric power project at Niagara Falls.
Acetylene can also be manufactured by the partial combustion of methane with oxygen, or by the cracking of hydrocarbons.
Berthelot was able to prepare acetylene from methyl alcohol, ethyl alcohol, ethylene, or ether, when he passed any one of these as a gas or vapour through a red-hot tube. Berthelot also found acetylene was formed by sparking electricity through mixed cyanogen and hydrogen gases. He was also able to form acetylene directly by combining pure hydrogen with carbon using electrical discharge of a carbon arc.
Walter Reppe discovered that acetylene can react at high pressures with heavy metal
This is industrially used to produce 1,4-butynediol from formaldehyde and acetylene:
Approximately 80 percent of the acetylene produced annually in the United States is used in chemical synthesis. The remaining 20 percent is used primarily for oxyacetylene gas welding and cutting due to the high temperature of the flame; combustion of acetylene with oxygen produces a flame of over 3300 °C (6000 °F), releasing 11.8 kJ/g. Oxyacetylene is the hottest burning common fuel gas.[3]. Cyanogen, a more exotic gas, produces a flame of over 4525°C (8180°F) when it burns in oxygen.[4]
Acetylene is also used in the acetylene ('carbide') lamp, once used by miners (not to be confused with the Davy lamp), on vintage cars, and still sometimes used by cavers. In this context, the acetylene is generated by dripping water from the upper chamber of the lamp onto calcium carbide (CaC2) pellets in the base of the lamp.
In former times a few towns used acetylene for lighting, including Tata in Hungary where it was installed on 24 July 1897, and North Petherton, England in 1898.
In modern times acetylene is sometimes used for carburization (that is, hardening) of steel when the object is too large to fit into a furnace.[3]
Acetylene has been proposed as a carbon feedstock for molecular manufacturing using nanotechnology. Since it does not occur naturally, using acetylene could limit out-of-control self-replication.
Acetylene is used to volatilize carbon in radiocarbon dating. The carbonaceous material in the archeological sample reacted in a small specialized research furnace with lithium metal to form lithium carbide (also known as lithium acetylide). The carbide can then be reacted with water, as usual, to form acetylene gas to be fed into mass spectrometer to sort out the isotopic ratio of carbon 14 to carbon 12.
The Future
The use of acetylene is expected to continue a gradual increase in the future as new applications are developed. One new application is the conversion of acetylene to ethylene for use in making a variety of polyethylene plastics. In the past, a small amount of acetylene had been generated and wasted as part of the steam cracking process used to make ethylene. A new catalyst developed by Phillips Petroleum allows most of this acetylene to be converted into ethylene for increased yields at a reduced overall cost.[5]
Due to the carbon-to-carbon triple bond, acetylene gas is fundamentally unstable, and will decompose in an exothermic reaction if compressed to any great extent. Acetylene can explode with extreme violence if the pressure of the gas exceeds about 100 kPa (≈14.5 psi) as a gas or when in liquid or solid form, so it is shipped and stored dissolved in acetone or dimethylformamide (DMF), contained in a metal cylinder with porous filling (Agamassan), which renders it safe to transport and use.
There are strict regulations on the shipment of dangerous gas cylinders throughout the world. The use of dissolved acetylene is decreasing rapidly, due to favourable flameless welding processes.
Inhaling acetylene may cause dizziness, headache and nausea.[6] It may also contain toxic impurities: the Compressed Gas Association Commodity Specification for acetylene has established a grading system for identifying and quantifying phosphine, arsine, and hydrogen sulfide content in commercial grades of acetylene in order to limit exposure to these impurities. The sulfur, phosphorus and arsenic are carryovers from the synthesis ingredient coke, an impure form of carbon and different, organic impurities would be expected from the thermal cracking of hydrocarbons source.
While the impurities in acetylene can be toxic and even fatal, pure acetylene is of a very low toxicity (not counting the "narcotic" effects). Up to 80% percent, (v/v) acetylene has been administered to surgical patients as a general anaesthetic. The trade name for acetylene was "narcylene." It was used a fair amount experimentally in Germany in their impoverished 1920's, perhaps on several thousand patients. Medically, acetylene was considered to be nearly as safe as nitrous oxide and with a slightly higher potency, allowing for the use of higher percentages of oxygen in the blend; it is about 50% more potent. However, the use of acetylene and oxygen mixtures was dropped after several gas explosions inside patients' lungs. The energy of these explosions would be expected to exceed any of the flammable inhalation anesthetics due to the instability of the triple bond (cyclopropane would be nearly as bad). It was suggested that such an internal thorax explosion could not occur with air mixtures (without purified oxygen).
Acetylene has been infrequently abused in a manner akin to nitrous oxide abuse up through modern times, according to the literature. Such abuse can result in the death of the abuser due to toxicity of the above mentioned impurities phosphine, arsine, and hydrogen sulfide. Since the gas is charged (absorbed) into tanks soaked with acetone over a solid matrix, some acetone comes out with the gas, further contributing to the poisonings. The driver for this abusive behavior is better understood with the view of acetylene's anesthetic properties and addictive behaviors.
Impurities in acetylene are easily detectable by smell. Pure acetylene is a colorless and odorless gas. The characteristic garlic-like odor of technical grade acetylene is attributable to contamination by impurities. Impurities which may be present include: divinyl sulfide, ammonia, oxygen, nitrogen, phosphine, arsine, methane, carbon dioxide, carbon monoxide, hydrogen sulfide, vinyl acetylene, divinyl acetylene, diacetylene, propadiene, hexadiene, butadienyl acetylene, and methyl acetylene.
Mixtures with air containing between 3% and 82% acetylene are explosive on ignition. The minimum ignition temperature is 335 °C.[6] The majority of acetylene's chemical energy is what is not contained in the carbon-carbon triple bond; that is, it is greater than that of three carbon-carbon bonds spread out, but is disallowed therefrom because of the spaces between its mate carbon and all other carbons likewise shielded in charge.
Sometimes the plural "acetylenes" may refer to the class of organic chemical compounds known as alkynes which contain the -C≡C- group.
Acetylene is a moderately common chemical in the universe, often associated with the atmospheres of gas giants.[7] One curious discovery of acetylene is on Enceladus, a moon of Saturn. Natural acetylene is believed to form from either catalytic decomposition of long chain hydrocarbons or at temperatures ≥ 1,770 kelvin. Since such temperatures are highly unlikely on such a small distant body, this discovery is potentially suggestive of catalytic reactions within the moon, making it a promising site to search for prebiotic chemistry.[8][9]
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Nederlands (Dutch)
acetyleen(gas)
Français (French)
n. - acétylène
Deutsch (German)
n. - (chem.) Acetylen
Ελληνική (Greek)
n. - (χημ.) ακετυλένιο (κν. ασετυλίνη)
Português (Portuguese)
n. - acetileno (m) (Quím.)
Español (Spanish)
n. - acetileno
Svenska (Swedish)
n. - acetylengas
中文(简体) (Chinese (Simplified))
电石气, 乙炔
中文(繁體) (Chinese (Traditional))
n. - 電石氣, 乙炔
العربيه (Arabic)
(الاسم) أسيتيلين : غاز عديم أللون يستخدم في ألتلحيم
עברית (Hebrew)
n. - גז חסר-צבע המשמש לריתוך, אצטילין (גאז)
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