Early Acetylene Hydrogenation Catalysts

TABLE 3.23. Operation of Some Early Acetylene Hydrogenation Catalysts. 

Acrylonitrile was first produced in Germany and the United States on an industrial scale in the early 1940s. These processes were based on the catalytic dehydration of ethylene cyanohydrin. Ethylene cyanohydrin was produced from ethylene oxide and aqueous hydrocyanic acid at 60°C in the presence of a basic catalyst. The intermediate was then dehydrated in the liquid phase at 200°C in the presence of magnesium carbonate and alkaline or alkaline earth salts of fonnic acid. A second commercial route to acrylonitrile was the catalytic addition of hydrogen cyanide to acetylene. The last commercial plants using these process technologies were shut down in 1970 (Langvardt, 1985 Brazdil, 1991). 

The initial drive for acrylonitrile (AN) production (6.2 Mt/a in 2004 worldwide) was the discovery, in the late 1930s, of the synthetic rubber Buna N. Today nitrile rubbers represent only a minor outlet for AN which is utilized primarily for polymerization to give textile fibres (50%) and ABS resins (24%), and for dimerization to adiponitrile (10%). Early industrial processes depended on the addition of hydrogen cyanide to acetylene or to ethylene oxide, followed by the dehydration of intermediate ethylene cyanohydrin. Both processes are obsolete and are now supplanted by the ammoxidation of propylene (Equation 34) introduced in 1960 by Standard Oil of Indiana (Sohio). The reason for the success stems from the effectiveness of the catalyst and because propylene,... 

Up to the early 1980s VCM was produced by addition of hydrogen chloride to acetylene. In this process the gaseous reactants are brought into contact with the catalyst at slightly increased pressure and 100-250 °C [1]. Mercury(II) chloride on activated carbon is used as a catalyst in this heterogeneous process. Today, however, this reaction has no economical importance. Nowadays, VCM is exclusively produced by thermal decomposition of DCE. 

Methylhept-2-en-6-one, usually referred to simply as methylhep-tenone, is a useful synthon for the total synthesis of terpenes. One early synthesis of this intermediate employed the Carroll reaction, the substrate for which is prepared by the addition of acetylene to acetone and subsequent partial hydrogenation to 2-methylbut-3-en-2-ol, as shown in Scheme 4.5. Addition of acetylene to methylheptenone gives dehydrolinalool, which can be hydrogenated to linalool using a Lindlar catalyst. 

Early attempts to approach this problem were made by Kobosev and co-workers in the 1930s from the viewpoint of atomic dispersion and active ensembles. They studied the behavior of catalysts containing very small amounts of supported metal and were able to derive the number of atoms within the ensembles that were active for specific reactions (one atom for SO2 oxidation, two atoms for benzene hydrogenation, three atoms for ammonia synthesis, four atoms for acetylene oligomerization) (2a-c). These results as well as later ones have been reviewed by GiFdebrand (3). 

The acetylene process was developed in Germany in the early 1940s to supply the synthetic rubber industry [19]. Acetylene is reacted with hydrogen cyanide in an aqueous medium in the presence of catalytic amounts of cuprous chloride. The reaction is maintained at 80 90°C at a pressure of 1-2 atm. The reaction is highly exothermic forming a gaseous reactor effluent. This crude product is water-scrubbed and the pure acrylonitrile product is recovered from the resultant 1-3% aqueous solution by fractional distillation. The major drawbacks of this process are the large number of by-products formed by hydration, the loss of catalyst activity from hydrolysis reactions, and the buildup of ammonium chloride and tars. 

Linoleic acid was first synthesized via acetylenic intermediates in the early 1950s but it was not until 1961 that a general procedure for obtaining the natural methylene-interrupted polyenes was outlined (Os-bond et ai, 1961). This has been modified in useful ways by Kunau (1971) and, in the original or modified form, it has been used to prepare a large number of polyene acids (Sprecher, 1979). The necessary poly-ynoic acid is prepared first. This is a crystalline solid which can be thoroughly purified by crystallization, prior to partial hydrogenation with Lindlar catalyst. 

Catalysts suitable for selective hydrogenation of acetylenic compounds in cracked gas streams contain elements of group VI and VIII of the periodic table. An early catalyst was molybdenum sulfide supported on activated alumina (Key and Eastwood, 1946). This was followed by the development of cobalt molybdate and nickel based catalysts (Giaro, 1956 Barry, 1950). Modem catalysts for impure (sulfur-bearing) cracked gas streams typically contain nickel, cobalt, and chromium on a silica-alumina base (United Catalysts, 1993). 

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