Acetylene removal

The BASF process uses /V-methy1pyrro1idinone as the solvent to purify acetylene in the cracked gas effluent. Alow pressure prescmbbing is used to remove naphthalenes and higher acetylenes. The cracked gas is then compressed to 1 MPa (10 atm) and fed to the main absorption tower for acetylene removal. Light gases are removed from the top of this tower. 

The depropanizer overhead, Cj and lighter feed is compressed to about 300 psi and then passed over a fixed bed of acetylene removal catalyst, generally palladium on alumina. Because of the very large amount of hydrogen contained in this stream, the operating conditions are critical to selectively hydrogenate the acetylene without degrading the valuable ethylene to ethane. 

Stone Webster Eng., Corp. Acetylene extraction C2s and C3s Proven extraction design uses DMF solvent. Full acetylene removal 5 1998... 

After separation of the mixed olefins the product work up is similar to that in a steam cracker using LPG feedstock. Small amounts of carbon dioxide are removed and the hydrocarbon gases are dried before passing to a de-ethaniser column. The C2- fraction is passed to an acetylene removal unit before methane is removed from the C2 stream. This comprises 98-i-% ethylene, the remainder being ethane. The C3+ stream is split between the C3 fraction (98% propylene) and C4+. The work up of the C4 stream to produce linear butenes (not shown in the figure) is likely to be less problematic than the corresponding C4 stream from steam crackers, which is highly complex and cannot be separated by fractionation alone. The process produces little product above C5. 

Shaw Energy Chemicals Acetylene extraction C s and C s separately Proven extraction design uses DMF solvent. Complete C acetylene removal. C3 (MAPD) is separate product. 6-1- 2000... 

The data obtained with activated alumina F-10 as support are shown in Table I. In this table the surface area has been calculated on two bases, Se being the area per gram of catalyst and iS, the area per gram of support. iScx is the area of the exhausted catalyst per gram of catalyst. The catalytic activity is expressed as per cent acetylene removed from the air-acetylene mixture, As being the activity after three hours operation and Ao the activity at the beginning of the run. Under X are recorded the relative concentrations of silver nitrate and under Y those of metallic silver, as determined by the intensity of x-ray diffraction, the subscripts/ and x referring, respectively, to fresh catalysts and those partially exhausted by four hours of use. 

Isomerization also results when sodium amide is used as the base in the double dehydrohalogenation. All possible triple-bond isomers are formed, but sodium amide is such a strong base that it deprotonates the terminal acetylene, removing it from the equilibrium. The acetylide ion becomes the favored product. When water is added to quench the reaction, the acetylide ion is protonated to give the terminal alkyne. 

In another vinyl fluoride preparation method, hydrofluoric acid is added to acetylenet 1 to produce 1,1-difluoroethane. Next, 1,1-difluoroethane is pyro-lyzed over an aluminum salt and a molecule of hydrofluoric acid is removed, thereby producing VF. The product is passed through soda lime in towers to remove hydrofluoric acid followed by acetylene removal in ammoniacal cupric chloride. Oxygen is separated by distillation. 

Process conditions depend on the type of gas being treated and the catalyst employed. Acetylene removal from cracked gas streams containing sulfur, carbon monoxide, and a large excess of hydrogen can be carried out with nickel/cobalt/chromium/sulfur-based catalysts at 300° to 500°F and 50 to 500 psig. Such an operation will provide a product stream containing less than 10 ppmv acetylene. 

Small amounts of acetylene (C2H2) must be removed from ethylene (C2H4) before the latter can be used to make polyethylene. Acetylene removal usually is accomplished by selective catalytic hydrogenation ... 

Hydrogenation of methylacetylene and propadiene, its isomer (MAPD) in the separated C3 stream is very similar to tail-end acetylene removal. The possible reactions are ... 

Sodium acetyllde. Replace the ammonia - addition tube by a wide tube reaching almost to the bottom of the flask (or use the device depicted in Fig. II, 7, 12, b) and pass acetylene (Fig. VI, 16, 1, c) into the suspension of sodamide in liquid ammonia maintain the bath temperature at about — 35° so that little ammonia is lost. Continue the passage of acetylene until a uniformly black liquid is formed (usually 4r-5 hours) (7). Carefully watch the wide gas entry tube if much solid collects inside this tube, remove it before the tube is completely blocked. Add liquid ammonia, if necessary, to restore the original volume (ca. 3 5 litres). 

The mixture was then cooled to 30-40°C and the dissolved acetylene was sucked Over" in a water-pump vacuum (10-20 mmHg) and condensed in a receiver cooled at -78°C. The contents of the receiver were shaken three times with 20-ml portions of ice-water in a small separating funnel or dropping funnel in order to remove small amounts of tert.-butyl alcohol. After drying over a very small amount of... 

A mixture of 0.30 mol of the tertiairy acetylenic alcohol, 0.35 mol of acetyl chloride (freshly distilled) and 0.35 mol of /V/V-diethylaniline was gradually heated with manual swirling. At 40-50°C an exothermic reaction started and the temperature rose in a few minutes to 120°C. It was kept at that level by occasional cooling. After the exothermic reaction had subsided, the mixture was heated for an additional 10 min at 125-130°C, during which the mixture was swirled by hand so that the salt that had been deposited on the glass wall was redissolved. After cooling to below 50°C a mixture of 5 ml of 36% HCl and 200 ml of ice-water was added and the obtained solution was extracted with small portions of diethyl ether. The ethereal solutions were washed with water and subsequently dried over magnesium sulfate. The solvent was removed by evaporation in a water-pump vacuum... 

A mixture of 0.10 mol of the acetylenic alcohol, 0.12 mol of triethylamine and 200 ml of dichloromethane (note 1) was cooled to -50°C. Methanesulfinyl chloride (0.12 mol) (for its preparation from CH3SSCH3, (08300)30 and chlorine, see Ref. 73) was added in 10 min at -40 to -50°0. A white precipitate was formed immediately. After the addition the cooling bath was removed and the temperature was allowed to rise to -20°0, then the mixture was vigorously shaken or stirred with 100 ml of water. The lower layer was separated off and the aqueous layer was extracted twice with 10-ml portions of CH2CI2. The combined solutions were dried over magnesium sulfate and concentrated in a water-pump vacuum (note 2). The yields of the products, which are pure enough (usually 96%) for further conversions, are normally almost quantitative. 

Monosubstitution of acetylene itself is not easy. Therefore, trimethylsilyl-acetylene (297)[ 202-206] is used as a protected acetylene. The coupling reaction of trimethylsilylacetylene (297) proceeds most efficiently in piperidine as a solvent[207]. After the coupling, the silyl group is removed by treatment with fluoride anion. Hexabromobenzene undergoes complete hexasubstitution with trimethylsilylacetylene to form hexaethynylbenzene (298) after desilylation in total yield of 28% for the six reactions[208,209]. The product was converted into tris(benzocyclobutadieno)benzene (299). Similarly, hexabutadiynylben-zene was prepared[210j. 

Alcohols are stronger acids than acetylene and so the position of equilibrium lies to the left Methoxide ion is not a strong enough base to remove a proton from acetylene... 

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