Handling of acetylene

Reppe s work also resulted in the high pressure route which was estabUshed by BASF at Ludwigshafen in 1956. In this process, acetylene, carbon monoxide, water, and a nickel catalyst react at about 200°C and 13.9 MPa (2016 psi) to give acryUc acid. Safety problems caused by handling of acetylene are alleviated by the use of tetrahydrofuran as an inert solvent. In this process, the catalyst is a mixture of nickel bromide with a cupric bromide promotor. The hquid reactor effluent is degassed and extracted. The acryUc acid is obtained by distillation of the extract and subsequendy esterified to the desked acryhc ester. The BASF process gives acryhc acid, whereas the Rohm and Haas process provides the esters dkecdy. 

The necessity of establishing rules and regulations which have to be observed by gas producers and users was and stiU is obvious. The accidents, some of which were serious, occurring initially during the production and handling of acetylene (and oxygen) had to be prevented at all costs. 

Reyiews.—Recent reviews on areas of acetylenic chemistry include synthetic routes to average-ring-size cycloalkynes, a study of the bonding in metal-acetylene complexes, transition-metal complexes of acetylene, intramolecular cyclization reactions with acetylenic bond participation, oligomerization of acetylenes induced by metals of the nickel triad, an article on the handling of acetylenic compounds, and a book on preparative acetylenic chemistry. ... 

Industrially, large quantities of vinyl ethers can be prepared following Reppe s ethynylation reaction that involved reacting acetylene gas with alcohols [101]. Due to the challenges and hazards associated with the experiment as well as the required handling of acetylene gas (under pressure) alternative approaches to the synthesis of vinyl ethers are typically used in small laboratory settings. One such approach used common iridium complexes to catalyze... 

CH2=CHC = CCH = CH2. a colourless liquid which turns yellow on exposure to the air it has a distinct garlic-like odour b.p. 83-5°C. Manufactured by the controlled, low-temperature polymerization of acetylene in the presence of an aqueous solution of copper(I) and ammonium chlorides. It is very dangerous to handle, as it absorbs oxygen from the air to give an explosive peroxide. When heated in an inert atmosphere, it polymerizes to form first a drying oil and finally a hard, brittle insoluble resin. Reacts with chlorine to give a mixture of chlorinated products used as drying oils and plastics. 

The carbide route is the preferred method of operation for most industrial gas operations. It is well suited to small-scale consumers. The high cost of acetylene in industrial gas appHcations reflects these scale, handling, and shipping factors. 

When acetylene is recovered, absorption—desorption towers are used. In the first tower, acetylene is absorbed in acetone, dimethylformarnide, or methylpyroUidinone (66,67). In the second tower, absorbed ethylene and ethane are rejected. In the third tower, acetylene is desorbed. Since acetylene decomposition can result at certain conditions of temperature, pressure, and composition, for safety reasons, the design of this unit is critical. The handling of pure acetylene streams requires specific design considerations such as the use of flame arrestors. 

Absorption of water dining handling or storage of technical calcium cyanamide may cause explosions, owing to liberation of acetylene from the calcium carbide content (up to 2%). Precautions are discussed. 

Downstream of the compressor is a series of fractionators (generally the tallest towers in an ethylene plant) which separate the methane and hydrogen, the ethylene, the ethane, and the propane and heavier. All are heavy metallurgy to handle the pressures and insulated to maintain the low temperatures. There s also an acetylene hydrogenator or converter in there. Trace (very small) amounts of acetylene in ethylene can really clobber some of the ethylene derivative processes, particularly polyethylene manufacture. So the stream is treated with hydrogen over a catalyst to convert the little acetylene present into ethylene. 

Oxidation of ethyl alcohol was one of the two important commercial routes to acetaldehyde until the 1950s, The other, much older route was the hydration of acetylene. The chemical industry was always after a replacement of acetylene chemistry, not just for acetaldehyde production, but all its many applications. Acetylene was expensive to produce, and with its reactive, explosive nature, it was difficult to handle. In the 1950s, acetylene chemistry and the ethyl alcohol oxidation route were largely phased out by the introduction of the liquid phase direct oxidation of ethylene. Almost all the acetaldehyde produced uses the newer process. 

Solution of Gases in Liquids Certain gases will dissolve readily in hquids. In some cases in which the quantities are not large, this may be a practical storage procedure. Examples of gases that can be handled in this way are ammonia in water, acetylene in acetone, and hydrogen chloride in water. Whether or not this method is used depends mainly on whether the end use requires the anhydrous or the liquid state. Pressure may be either atmospheric or elevated. The solution of acetylene in acetone is also a safety feature because of the instability of acetylene. 

Mo and W hexacarbonyls, Mo(CO)6 and W(CO)6, alone do not induce polymerization of acetylenic compounds. However, UV irradiation toward these catalysts in the presence of halogenated compounds can form active species for polymerization of various substituted acetylenes. Carbon tetrachloride, CCI4, when used as the solvent for the polymerization, plays a very important role for the formation of active species, and thus cannot be replaced by toluene that is often used for metal chloride-based catalysts. Although these metal carbonyl-type catalysts are less active compared to the metal halide-based counterparts, they can provide high MW polymers. It is a great advantage that the metal carbonyl catalysts are very stable under air and thus handling is much easier. 

Explosibility. Liquid ethylene oxide is stable to detonating agents, but the vapor will undergo explosive decomposition. Pure ethylene oxide vapor will decompose partially however, a slight dilution with air or a small increase in initial pressure provides an ideal condition for complete decomposition. Copper or other acetylide-forming metals such as silver, magpesium, and alloys of such metals should not be used to handle or store ethylene oxide because of the danger of the possible presence of acetylene. Acetylides detonate readily and will initiate explosive decomposition of ethylene oxide vapor. In the presence of certain catalysts, liquid ethylene oxide forms a poly-condensate. 

For handling acetylene in chemical processes under pressure a special strategy has been developed to solve the specific problems of this chemical - the decomposition of the substance even under mild conditions. It is known that this reaction is generating a pressure increase of approximately factor 11 above the normal working pressure. Therefore the design pressure of all components of acetylene plants should be selected eleven times higher compared to the operating pressure. 

ACETYLENE. [CAS 74-86-2]. CH CH formula weight 26.04, mp — 81.5°C, bp —84 0, sp gr 0.905 (air = 1.000). Sometimes referred to as ethyne, ethine, or gaseous carbon (92.3% of the compound is C), acetylene is moderately soluble in H2O or alcohol, and exceptionally soluble in acetone (300 volumes of acetylene m 1 volume of acetone at 12 atmospheres pressure) The gas burns when ignited in air with a luminous sooty flame, requiring a specially devised burner for illumination purposes. An explosive mixture is formed with air over a wide range (about 3 to 80% acetylene), but safe handling is improved when the gas is dissolved in acetone, The heating value is 1455 Btu/ft--1 (8.9 Cal/nr). 

The substantial difference in the heats of reaction of ethane, ethene, and ethyne with bromine is reflected in a very important practical consideration in handling ethyne (acetylene), namely its thermodynamic stability relative to solid carbon and hydrogen gas. Unlike ethane, both ethene and ethyne can be shown from bond energies to be unstable with respect to formation of solid carbon and gaseous hydrogen ... 

Calcium carbide provides a fairly safe and easy-to-handle source of ethyne. Before the advent of battery-operated lights, portable lamps such as those used on bicycles, carnages, and miner s helmets were fueled by this material. Water was slowly dropped onto solid calcium carbide, and the ethyne that was generated was burned. This reaction is still used as a source of acetylene for welding torches. 

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