Applications of Benzene Hydrogenation

Benzene is the raw material for the two most important routes for the manufacture of polymers that are collectively referred to as Nylon. In the first route, cyclohexane is oxidised to adipic acid (HOOC—(CH2)4—COOH), and for this reason the full hydrogenation of benzene has commanded much attention. Because of the large heat of reaction, the process is best performed in the slurry phase, using an unsupported catalyst such as Raney nickel the process heat is removed by vaporisation of the cyclohexane, part of which is returned to the feed, which typically contains 20% benzene -f- 80% cyclohexane. Reaction conditions are 30-50 atm. hydrogen and temperatures of 453-503 K. In the second route, the starting compound is cyclohexene, and for some time efforts have been made to effect the partial hydrogenation of benzene to this molecule (see Section 10.2.7). 

Separation from unreacted benzene is easier than with cyclohexane, because an azeotrope is not formed. The quality of diesel fuels is improved by removal of aromatics, and hydrogenation has been explored as a means of eliminating them sulfur-tolerant catalysts are needed in this application. The combination of palladium - - platinum is sometimes found to be more thiotolerant than either separately, although this is not the case with model (Pt + PdVy-AhOs in the hydrogenation of tetralin.  

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