Acetylene decomposition temperature

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. 

Acetylene may propagate decomposition flames in the absence of any oxidant above certain minimum conditions of pressure, temperature, and pipe diameter. Acetylene, unlike most other gases, can decompose in a detonative manner. Among the different types of flame arresters that have proven successful in stopping acetylene decomposition flames are hydraulic (liquid seal) flame arresters, packed beds, sintered metal, and metallic balls (metal shot). 

Figure 1 indicates an example of how pretreatment of the Incoloy 800 reactor had a very large effect on the acetylene conversion (or on the kinetics of acetylene decomposition). The coke-coated Incoloy 800 reactor (the coke had been deposited on this reactor when butadiene reacted at 500°-700°C.) used in Run 14 resulted in much lower acetylene conversions in the range of 450° to 550°C compared with the same Incoloy 800 reactor after the coke had been burned off with oxygen and after the reactor had been contacted with hydrogen until nearly all surface oxides were eliminated. Most conversion results for the 11 gas samples collected during Run 15 are shown in Figure 1. Gas Samples 1 through 3 at 350°, 400°, and 450°C, respectively, indicated almost no acetylene conversions. A small amount of carbon dioxide was produced at 450°C, indicating some metal oxides had still been present on the surface after the hydrogen pretreatment. The temperature was then increased to 500°C, and the conversions then increased from 66% to 99% during the first 23 min (Samples 4 and 5). Some carbon oxide production was noted in Sample 4 but none in Sample 5 or in any later samples of the run presumably...

Various forms of radiation have been used to produce ions in sufficient quantitites to yield neutral products for subsequent analysis. In principle, it should be possible to use intense beams of UV below ionization threshold for this purpose. To date, however, efforts to collect neutrals from resonant multiphoton ionization (REMPI) have not succeeded. In one experiment, 1 mbar of gaseous -propyl phenyl ether was irradiated at room temperature with a 0.1 W beam of 266 nm ultraviolet (from an 800 Hz laser that gives 8 n pulses) concurrent with a 0.5 W beam at 532 nm. The beams were intense enough not only to ionize the ether in the mass spectrometer, but also to excite it so that it expels propene. After several hours of irradiation < 10% of the starting material remained. Production of carbon monoxide and acetylene (decomposition products of the phenoxy group) could be detected by infrared absorption spectroscopy, but the yield of neutral propene (as measured by NMR spectroscopy) was infinitesimal. 

Polymerization and GycliZation. Acetylene polymerizes at elevated temperatures and pressures which do not exceed the explosive decomposition point. Beyond this point, acetylene explosively decomposes to carbon and hydrogen. At 600—700°C and atmospheric pressure, benzene and other aromatics are formed from acetylene on heavy-metal catalysts. 

Fig. 1. Pressure required for propagation of decomposition flame through commercially pure acetylene free of solvent and water vapor in long horizontal pipes. Gas initially at room temperature ignition by thermal nonshock sources. Curve shows approximate least pressure for propagation (0), detonation,...

The calculated detonation velocity in room temperature acetylene at 810 kPa is 2053 m/s (61). Measured values are about 1000-2070 m/s, independent of initial pressure but generally increasing with increasing diameter (46,60—64). In a time estimated to be about 6 s (65), an accidental fire-initiated decomposition flame in acetylene at ca 200 kPa in an extensive piping system traveled successively through 1830 m of 76—203-mm pipe, 8850 m of 203-mm pipe, and 760 m of 152-mm pipe. 

The predetonation distance (the distance the decomposition flame travels before it becomes a detonation) depends primarily on the pressure and pipe diameter when acetylene in a long pipe is ignited by a thermal, nonshock source. Figure 2 shows reported experimental data for quiescent, room temperature acetylene in closed, horizontal pipes substantially longer than the predetonation distance (44,46,52,56,58,64,66,67). The predetonation distance may be much less if the gas is in turbulent flow or if the ignition source is a high explosive charge. 

The pressure developed by decomposition of acetylene in a closed container depends not only on the initial pressure (or more precisely, density), but also on whether the flame propagates as a deflagration or a detonation, and on the length of the container. For acetylene at room temperature and pressure, the calculated explosion pressure ratio, / initial > deflagration and ca 20 for detonation (at the Chapman-Jouguet plane). At 800 kPa (7.93... 

Decomposition Flame Arresters Above certain minimum pipe diameters, temperatures, and pressures, some gases may propagate decomposition flames in the absence of oxidant. Special in-line arresters have been developed (Fig. 26-27). Both deflagration and detonation flames of acetylene have been arrested by hydrauhc valve arresters, packed beds (which can be additionally water-wetted), and arrays of parallel sintered metal elements. Information on hydraulic and packed-bed arresters can be found in the Compressed Gas Association Pamphlet G1.3, Acetylene Transmission for Chemical Synthesis. Special arresters have also been used for ethylene in 1000- to 1500-psi transmission lines and for ethylene oxide in process units. Since ethylene is not known to detonate in the absence of oxidant, these arresters were designed for in-line deflagration application. 

The catalytic decomposition of acetylene was carried out in a flow reactor at atmospheric pressure. A ceramic boat containing 20-100 mg of the catalyst was placed in a quartz lube (inner diameter 4-10 mm, length 60-100 cm). The reaction mixture of 2.5-10% C2H2 (Alphagaz, 99.6%) in Nj (Alphagaz, 99.99%) was passed over the catalyst bed at a rate of 0.15-0.59 mol C2H2 g h for several hours at temperatures in the range 773-1073 K. 

The predominant gaseous products of the decomposition [1108] of copper maleate at 443—613 K and copper fumarate at 443—653 K were C02 and ethylene. The very rapid temperature rise resulting from laser heating [1108] is thought to result in simultaneous decarboxylation to form acetylene via the intermediate —CH=CH—. Preliminary isothermal measurements [487] for both these solid reactants (and including also copper malonate) found the occurrence of an initial acceleratory process, ascribed to a nucleation and growth reaction. Thereafter, there was a discontinuous diminution in rate (a 0.4), ascribed to the deposition of carbon at the active surfaces of growing copper nuclei. Bassi and Kalsi [1282] report that the isothermal decomposition of copper(II) adipate at 483—503 K obeyed the Prout—Tompkins equation [eqn. (9)] with E = 191 kJ mole-1. Studies of the isothermal decompositions of the copper(II) salts of benzoic, salicylic and malonic acids are also cited in this article. 

Triazoles have been obtained via microwave-assisted [3-i-2] cycloaddition, under solvent-free conditions [54], starting from organic azides and acetylenic amides at 55 °C for 30 min (Scheme 23). The complete conversion of the reagents into AT-substituted-1,2,3-triazoles 69 was achieved without decomposition and side products. A control reaction carried out at the same temperature in an oil bath did not give the cycHc products, not even after 24 h of reaction time. 

The addition of (TMS)3SiH to a number of monosubstituted acetylenes has also been studied in some detail. These reactions are highly regioselective (anti-Markovnikov) and give terminal (TMSlsSi-substituted alkenes in good yields. High cis or trans stereoselectivity is also observed, depending on the nature of the substituents at the acetylenic moiety. For example, the reaction of the alkynes 23 and 24 with (TMSlsSiH, initiated either by EtsB at room temperature (method or by thermal decomposition of di-ferf-butyl peroxide at 160 °C... 

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