АЦЕТИЛЕН

Описание

Acetylene (100% purity) is odourless, but commercial purity has a distinctive garlic-like odour and is very soluble in alcohol and almost miscible with ethane. Acetylene is a flammable gas and kept under pressure in gas cylinders. Under certain conditions, acetylene can react with copper, silver, and mercury to form acetylides, compounds which can act as ignition sources. Brasses containing less than 65% copper in the alloy and certain nickel alloys are suitable for acetylene. Acetylene is not compatible with strong oxidisers such as chlorine, bromine pentafluoride, oxygen, oxygen difluoride and nitrogen trifluoride, brass metal, calcium hypochlorite, heavy metals such as copper, silver, mercury, and their salts, bromine, chlorine, iodine, fluorine, sodium hydride, caesium hydride, ozone, perchloric acid, and potassium.

Химические свойства

Acetylene (100% purity) is odorless but commercial purity has a distinctive garlic-like odor. It is very soluble in alcohol and almost miscible with ethane. Acetylene is a flammable gas and kept under pressure in gas cylinders. Under certain conditions, acetylene can react with copper, silver, and mercury to form acetylides, compounds that can act as ignition sources. Brasses contain a form acetylides, compounds that can act as ignition sources. Brasses containing less than 65% copper in the alloy and certain nickel alloys are suitable for acetylene. Acetylene is not compatible with strong oxidizers such as chlorine, bromine pentafl uoride, oxygen, oxygen difl uoride, and nitrogen trifl uoride, brass metal, calcium hypochlorite, heavy metals such as copper, silver, mercury, and their salts, bromine, chlorine, iodine, fl uorine, sodium hydride, cesium hydride, ozone, perchloric acid, or potassium.

Физические свойства

Acetylene, which is the simplest alkyne hydrocarbon, exists as a colorless, flammable, unstable gas with a distinctive pleasant odor (acetylene prepared from calcium carbide has a garlic smell resulting from traces of phosphine produced in this process). The term acetylenes is used generically in the petroleum industry to denote chemicals based on the carbon-carbon triple bond.

История

Acetylene was discovered in 1836 by Edmund Davy (1785-1857) who produced the gas while trying to make potassium metal from potassium carbide (K₂C₂). In 1859, Marcel Morren in France produced acetylene by running an electric arc between carbon electrodes in the presence of hydrogen. Morren called the gas produced carbonized hydrogen. Three years later, Pierre Eugène-Marcelin Berthelot (1827-1907) repeated Morren’s experiment and identified carbonized hydrogen as acetylene.

Использование

Illuminant, oxyacetylene welding, cutting, and soldering metals, signalling; pptg metals, particularly Cu; manufacture of acetaldehyde, acetic acid; fuel for motor boats.

Методы производства

The traditional method of producing acetylene is from reacting lime, calcium oxide (CaO), with coke to produce calcium carbide (CaC₂). The calcium carbide is then combined with water to produce acetylene:
2CaO_(s) + 5C_(s)→2CaC_2(g) + CO_2(g)
CaC_2(s) + 2H₂O_(l)→ C₂H_2(g) + Ca(OH)_2(aq)
Several processes for producing acetylene from natural gas and other petroleum products developed in the 1920s. Thermal cracking of methane involves heating methane to approximately 600℃ in an environment deficient in oxygen to prevent combustion of all the methane. Combustion of part of the methane mix increases the temperature to approximately 1,500℃, causing the remaining methane to crack according the reaction: 2CH_4(g) → C2H_2(g) + 3H_2(g). In addition to methane, ethane, propane, ethylene, and other hydrocarbons can be used as feed gases to produce acetylene.

Определение

A gaseous alkyne. Traditionally ethyne has found use in oxy-acetylene welding torches, since its combustion with oxygen produces a flame of very high temperature. It is also important in the organic chemicals industry for the production of chloroethene (vinyl chloride), which is the starting material for the production of polyvinyl chloride (PVC), and for the production of other vinyl compounds. Until recently, ethyne was manufactured by the synthesis and subsequent hydrolysis of calcium dicarbide, a very expensive procedure. Modern methods increasingly employ the cracking of alkanes.

Реакции

Acetylene reacts (1) with chlorine, to form acetylene tetrachloride C2H2Cl4 or CHCl2·CHCl2 or acetylene dichloride C2H2Cl2 or CHCl:CHCl, (2) with bromine, to form acetylene tetrabromide C2H2Br4 or CHBr2·CHBr2 or acetylene dibromide C2H2Br2 or CHBr:CHBr, (3) with hydrogen chloride (bromide, iodide), to form ethylene monochloride CH2:CHCl (monobromide, monoiodide), and 1,1-dichloroethane, ethylidene chloride CH3·CHCl2 (dibromide, diiodide), (4) with H2O in the presence of a catalyzer, e.g., mercuric sulfate HgO4S, to form acetaldehyde CH3·CHO, (5) with hydrogen, in the presence of a catalyzer, e.g., finely divided nickel heated, to form ethylene C2H4 or ethane C2H6, (6) with metals, such as copper or nickel, when moist, also lead or zinc, when moist and unpurified. Tin is not attacked. Sodium yields, upon heating, the compounds C2HNa and C2Na2. (7) With ammoniocuprous (or silver) salt solution, to form cuprous (or silver) acetylide C2Cu2, dark red precipitate, explosive when dry, and yielding acetylene upon treatment with acid, (8) with mercuric chloride solution, to form trichloromercuric acetaldehyde C(HgCl)3·CHO, precipitate, which yields with HCl acetaldehyde plus mercuric chloride.

Общее описание

A colorless gas with a faint garlic-like odor. Easily ignited and burns with a sooty flame. Gas is lighter than air. Flame may flash back to the source of a leak very easily. Under prolonged exposure to fire or heat the containers may rupture violently and rocket.

Реакции воздуха и воды

Highly flammable. Slightly soluble in water. Reacts with water to form toxic ammonia fumes.

Профиль реактивности

Acetylene reacts with alkali metals, forming Hydrogen gas. Acetylene can react explosively with bromine [Von Schwartz 1918. p.142 ]. Acetylene forms a sensitive acetylide when passed into an aqueous solution of mercuric nitrate, [Mellor 4:933. 1946-47]. An Acetylene torch used to drill through a plow frame, which was filled with hydrogen gas, produced an explosion [NIOSH, June 1998]. Acetylene reacts with silver, copper and lead to form sensitive, explosive salts. Since Acetylene is endothermic and effectively a reducing agent, it's reaction with oxidants can be very violent (examples: calcium hypochlorite, nitric acid, nitrogen oxide, ozone, trifluoromethyl hypofluorite, etc.). Contact of very cold liquefied gas with water may result in vigorous or violent boiling of the product and extremely rapid vaporization, due to the large temperature differences involved. If the water is hot, there is the possibility that a liquid "superheat" explosion may occur. Pressures may build to dangerous levels if liquid gas contacts water in a closed container [Handling Chemicals Safely 1980]. Acetylene and ammonia can form explosive silver salts in contact with Ag. (Renner, Hermann, Gunther Schlamp. "Silver, Silver Compounds, and Silver Alloys." Ullmann's Encyclopedia of Industrial Chemistry. Wiley-VCH Verlag GmbH & Co. KGaA. 2001.).

Опасность

The LEL of acetylene is reached well before asphyxiation can occur, and the danger of explosion is reached before any other health hazard is present. When fighting fires involving acetylene containers, the fire should be extinguished before closing the valve to the container. This is because the acetylene has such a wide flammable range that it can burn inside the container. Acetylene is incompatible with bromine, chlorine, fluorine, copper, silver, mercury, and their compounds. Acetylene has a four-digit UN identification number of 1001. The NFPA 704 designation is health 1, flammability 4, and reactivity 3. Reactivity is reduced to 2 when the acetylene is dissolved in acetone.

Угроза здоровью

Headache, dizziness and loss of consciousness may occur. Death from ``smothering'' may occur if oxygen content of the air is severely reduced by dilution with Acetylene.

Пожароопасность

Behavior in Fire: May explode in fire

Воспламеняемость и взрывоопасность

Acetylene is a highly flammable gas and forms explosive mixtures with air over an unusually wide range of concentrations (2 to 80%). Acetylene can polymerize exothermically, leading to deflagration. With a very high positive free energy of formation, acetylene is thermodynamically unstable and is sensitive to shock and pressure. Its stability is enhanced by the presence of small amounts of other compounds such as methane, and acetylene in cylinders is relatively safe to handle because it is dissolved in acetone. Acetylene fires can be fought with carbon dioxide, dry chemical, and halon extinguishers; firefighting is greatly facilitated by shutting off the gas supply.

Промышленное использование

Acetylene is a colorless, flammable gas with a garlic-like odor. Under compressed conditions, it is highly explosive; however, it can be safely compressed and stored in high-pressure cylinders if the cylinders are lined with absorbent material soaked with acetone. Users are cautioned not to discharge acetylene at pressures exceeding 15 psig (103 kPa), as noted by the red line on acetylene pressure gauges.
With its intense heat and controllability, the oxyacetylene flame can be used for many different welding and cutting operations including hardfacing, brazing, beveling, gouging, and scarfing. The heating capability of acetylene also can be utilized in the bending, straightening, forming, hardening, softening, and strengthening of metals.

Возможный контакт

Acetylene can be burned in air or oxygen and is used for brazing, welding, cutting, metallizing, hardening, flame scarfing; and local heating in metallurgy. The flame is also used in the glass industry. Chemically, acetylene is used in the manufacture of vinyl chloride, acrylinitrile, synthetic rubber; vinyl acetate; trichloroethylene, acrylate, butyrolactone, 1,4-butanediol, vinyl alkyl ethers, pyrrolidone, and other substances

хранилище

Acetylene should be kept stored in a cool, dry place in a tightly sealed container, and should only be used in a well-ventilated area. Cylinders should be separated from oxygen and other oxidizers by a minimum of 20 ft or by a barrier of non-combustible material at least 5 ft high, having a fi re resistance rating of at least 30 min. Storage in excess of 2500 cu ft is prohibited in buildings with other occupancies. Cylinders should be stored upright with a valve protection cap in place and fi rmly secured to prevent falling or being knocked over. The cylinders should be protected from physical damage and avoid dragging, rolling, sliding, or dropping the cylinder. During transport, workers should use a suitable hand truck for cylinder movement. Care should be taken to label “No Smoking” or “Open Flames” signs in the storage or use areas. There should be no sources of ignition. All electrical equipment should be explosion-proof in the storage and use areas.

Перевозки

UN1001 Acetylene, dissolved, Hazard Class: 2.1; Labels: 2.1-Flammable gas. Cylinders must be transported in a secure upright position, in a well-ventilated truck. Protect cylinder and labels from physical damage. The owner of the compressed gas cylinder is the only entity allowed by federal law (49CFR) to transport and refill them. It is a violation of transportation regulations to refill compressed gas cylinders without the express written permission of the owner

Несовместимости

The substance may polymerize due to heating. The substance decomposes on heating and increasing pressure, causing a fire and explosion hazard. The substance is a strong reducing agent and reacts violently with oxidants and with fluorine or chlorine under influence of light, causing fire and explosion hazard. Reacts with copper, silver, and mercury or their salts, forming shock-sensitive compounds (acetylides). The content of lines carrying acetylene must not exceed 63% copper. May form explosive mixture with air. Forms shock-sensitive mixture with copper and copper salts; mercury and mercury salts; and silver and silver salts. Reacts with brass, bromine, cesium hydride, chlorine, cobalt, cuprous acetylize; fluorine, iodine, mercuric nitrate; nitric acid, potassium, rubidium hydride; trifluoromethyl hypofluorite; and sodium hydride.

Утилизация отходов

Return refillable compressed gas cylinders to supplier. Consult with environmental regulatory agencies for guidance on acceptable disposal practices. Generators of waste containing this contaminant (≥100 kg/mo) must conform with EPA regulations governing storage, transportation, treatment, and waste disposal. Incineration.