Acetylene, hydrogenation production

Much more important is the hydrogenation product of butynediol, 1,4-butanediol [110-63-4]. The intermediate 2-butene-l,4-diol is also commercially available but has found few uses. 1,4-Butanediol, however, is used widely in polyurethanes and is of increasing interest for the preparation of thermoplastic polyesters, especially the terephthalate. Butanediol is also used as the starting material for a further series of chemicals including tetrahydrofuran, y-butyrolactone, 2-pyrrohdinone, A/-methylpyrrohdinone, and A/-vinylpyrrohdinone (see Acetylene-DERIVED chemicals). The 1,4-butanediol market essentially represents the only growing demand for acetylene as a feedstock. This demand is reported (34) as growing from 54,000 metric tons of acetylene in 1989 to a projected level of 88,000 metric tons in 1994. 

Since both complete hydrogenation of acetylene or any hydrogenation of the ethylene results in the production of a less valuable product such as ethane, conditions must be chosen carefiiUy and a catalyst must be used that is both sufficiently active for acetylene hydrogenation and extremely selective to avoid ethylene hydrogenation. Since hydrogenation of acetylenic bonds proceeds stepwise and since acetylene is more strongly adsorbed on the catalytic... 

The total yield of hydrogen under the conditions of these measurements was about 1.6 molecules/100 e.v. If one-half resulted from the primary dissociation also leading to acetylene ion, a yield of 0.8 acetylene ions/100 e.v. may be estimated. This value is a minimum since acetylene ion production can also be accompanied by hydrogen atom formation and is highly uncertain but consistent with the mass spectral fragmentation pattern of acetylene and W which lead to an estimate of ca. 0.94 acetylene ions/100 e.v. 

The aqueous Co(CN)52- solutions under H2 have been found to catalyze hydrogenolysis of C4-unsaturated alcohols to butenes but, more remarkably, with acetylenic alcohols besides hydrogenated products secondary nitriles are also formed by addition of HCN (stoichiometric with respect to cobalt) (195) ... 

Meyer et a/. obtained in low yields thiophene, 2-methylthiophene, benzo[6]thiophene, traces of thienothiophene 1, and some other products on passing a mixture of acetylene, hydrogen (or methane), and hydrogen sulfide at 640°-670° through a tube filled wth FeSj. 

Other chemicals present in acrylonitrile production or in other non-acrylonitrile operations on sites of the companies in the epidemiological study by Blair et al. (1998) include acetylene, hydrogen cyanide, propylene, ammonia, acetic acid, phosphoric acid, lactonitrile, hydroquinone, sodium hydroxide, sulfuric acid, acrylamide, acetone cyanohydrin, melamine, methyl methaciydate, zweto-methylstyrene, urea, methacrylonitrile, butadiene, ammonium hydroxide and ammonium sulfate (Zey et al., 1989, 1990a,b Zey McCammon, 1990). 

Hydrocarbons with suitably acidic (allylic, benzylic, propargylic, acetylenic) hydrogens can be transformed to organometallic derivatives, which then can react with alkylating agents to yield alkylated products. 

Acetylene, when adsorbed on active nickel catalysts, undergoes self-hy-drogenation with the production of ethylene [91], although the extent of this process is less than with ethylene. Similar behaviour has been observed with alumina- and silica-supported palladium and rhodium [53], although with both of these metals ethane is the sole self-hydrogenation product some typical results for rhodium—silica are shown in Fig. 21. 

Percentage composition of C4-products from acetylene hydrogenation over alumina-supported Group VIII metals Initial C2H2/H2 1. 

In 1954 R. P. Eischens, W. A. Pliskin, and S. A. Francis (5) of the Texaco Research Center in New York published the first infrared spectra of chemisorbed species, namely of carbon monoxide adsorbed on the silica-supported finely divided metal catalysts of Ni, Pd, Pt, and Cu. Also, in 1956, Pliskin and Eischens (5) were the first to obtain spectra of the hydrocarbons ethylene (ethene), acetylene (ethyne), and propene adsorbed on an oxide-supported metal catalyst, Ni/Si02. Eischens and his colleagues followed this up with further studies of chemisorbed zj-alkenes and their surface-hydrogenation products on Ni/Si02 (7). 

Acetylene hydrogenation. Selective hydrogenation of acetylene to ethylene is performed at 200°C over sulfided nickel catalysts or carbon-monoxide-poisoned palladium on alumina catalyst. Without the correct amount of poisoning, ethane would be the product. Continuous feed of sulfur or carbon monoxide must occur or too much hydrogen is chemisorbed on the catalyst surface. Complex control systems analyze the amount of acetylene in an ethylene cracker effluent and automatically adjust the poisoning level to prepare the catalyst surface for removing various quantities of acetylene with maximum selectivity. 

The high concentration of oxygen in the feed for the 20% oxygen system causes an over oxidation of the carbon species to CO, reducing the selectivity towards acetylene. This product flexibility could be useful in that it would allow for hydrogen to be produced... 

Cracked gases are cooled and fractionated to remove fuel oil and water (2-5) then compressed (6), processed for acid-gas removal (8) and dried (9). The C3 and lighter material is separated as an overhead product in the depropanizer (10) and acetylene is hydrogenated in the acetylene converter (11). The acetylene converter effluent is processed in the demethanizer system (12-14) to separate the fuel gas and hydrogen products. The demethanizer bottoms is sent to the deethanizer (15) from which the overhead flows to the C2-splitter (16), which produces the polymer-grade ethylene product and the ethane stream, which is typically recycled to the furnaces as a feedstock. The deethanizer bottoms flows to the C3-splitter (18) where the polymer-grade propylene is recovered... 

A more effective acetylene hydrogenation catalyst to ethylene would also facilitate the development of coal to ethylene via the acetylene route, which is at present restricted to the use of acetylene for the production of vinyl chloride. 

Acetylene (HCsCH) and benzene are very similar in their LCVD characteristics. Both compounds form plasma polymers with the least amount of hydrogen production (type I monomer), and their characteristics of copolymerization with N2 and/or H2O are nearly identical if we consider that one molecule of benzene is equivalent to three molecules of acetylene. Analysis of the gas phase in both closed and flow systems are given in Tables 7.5 and 7.6. 

This compound has been photolyzed in the gas phase with a Pyrex reaction vessel and a medium pressure mercury arc without the use of any filters. Under these conditions the effective radiation is that emitted between 290 and 334 ray in the mercury spectrum with the major contribution from the lines at 313 m,u. The volatile products produced were ethylene, acetylene, hydrogen, and nitrogen. To explain the relative yields of these compounds the following mechanism was suggested ... 

According to this the overall rate, v, ol acetylene and hydrogen production should be given by the equation... 

Metal- and alloy-containing membranes are currently applied mainly in ultrapure hydrogen production. Pilot plants with palladium alloy tubular membrane catalyst were used in Moscow for hydrogenation of acetylenic alcohols into ethylenic ones. In the Topchiev Institute of Petrochemical Synthesis, a laboratory-scale reactor of the same type was tested... 

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