Chemical routes, phenol hydrogenation

AH commercial processes for the manufacture of caprolactam ate based on either toluene or benzene, each of which occurs in refinery BTX-extract streams (see BTX processing). Alkylation of benzene with propylene yields cumene (qv), which is a source of phenol and acetone ca 10% of U.S. phenol is converted to caprolactam. Purified benzene can be hydrogenated over platinum catalyst to cyclohexane nearly aH of the latter is used in the manufacture of nylon-6 and nylon-6,6 chemical intermediates. A block diagram of the five main process routes to caprolactam from basic taw materials, eg, hydrogen (which is usuaHy prepared from natural gas) and sulfur, is given in Eigute 2. 

Caprolactam (world production of which is about 5 million tons) is mostly produced from benzene through three intermediates cyclohexane, cyclohexanone and cyclohexanone oxime. Cyclohexanone is mainly produced by oxidation of cyclohexane with air, but a small part of it is obtained by hydrogenation of phenol. It can be also produced through selective hydrogenation of benzene to cyclohexene, subsequent hydration of cyclohexene and dehydrogenation of cyclohexanol. The route via cyclohexene has been commercialized by the Asahi Chemical Company in Japan for adipic acid manufacturing, but the process has not yet been applied for caprolactam production. 

The chief outlets are for polyurethane (di-isocyanates) 40%, rubber chemicals, herbicides minor users include dye makers (approx. 5%) and pharmaceutical manufacturers. Benzene is the feedstock and the traditional route is to nitrate this and then to reduce the nitrobenzene to aniline. Catalytic hydrogenation has displaced iron/ferrous chloride reduction in this and analogous reductions e.g. in the manufacture of toluidines. Amination of phenol manufactured from cumene (Vol. I, p. 366) has been patented (Figure 2.8). The yield claimed is 99% though the economic viability is uncertain. 

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