Cyclohexane from benzene hydrogenation

Several processes are used for the industrial production of caprolactam. Generally cyclohexanone is the key intermediate and it is produced by catalytic hydrogenation of phenol (ex benzene or toluene) or the catalytic autoxidation of cyclohexane (from benzene hydrogenation) as shown in Fig. 2.27. 

High purity cyclohexane is manufactured by hydrogenating benzene at 400-500°F and 500 psig. Some cyclohexane was earlier produced by fractionating naphtha but its purity of 85-90% was too low to compete with 99-t- percent purity from benzene hydrogenation. A number of cyclohexane processes based on benzene hydrogenation are available. 

The hydrogenation of aromatics has been a topic of interest since Sabatier s first synthesis of cyclohexane from benzene with metallic nickel. The role of Nb and Ta aryloxides as catalysts for this reaction was mentioned earlier. Another system that has been studied in detail comprises allyl and hydride complexes of cobalt, e.g., (i73-C3H5)Co[P(OMe)3]3. Like the Nb and Ta compounds cobalt gives cyclohexane with cis stereoselectivity. The active species is probably the hydride, generated from (allyl)CoL3 on hydrogenolysis, which reacts with arenes in a stepwise manner. 

Another application of hydrogenation is the manufacture of cyclohexane from benzene as shown by the following reaction. 

Cyclohexane, produced from the partial hydrogenation of benzene [71-43-2] also can be used as the feedstock for A manufacture. Such a process involves selective hydrogenation of benzene to cyclohexene, separation of the cyclohexene from unreacted benzene and cyclohexane (produced from over-hydrogenation of the benzene), and hydration of the cyclohexane to A. Asahi has obtained numerous patents on such a process and is in the process of commercialization (85,86). Indicated reaction conditions for the partial hydrogenation are 100—200°C and 1—10 kPa (0.1—1.5 psi) with a Ru or zinc-promoted Ru catalyst (87—90). The hydration reaction uses zeotites as catalyst in a two-phase system. Cyclohexene diffuses into an aqueous phase containing the zeotites and there is hydrated to A. The A then is extracted back into the organic phase. Reaction temperature is 90—150°C and reactor residence time is 30 min (91—94). 

Caprolactam [105-60-2] (2-oxohexamethyleiiiiriiQe, liexaliydro-2J -a2epin-2-one) is one of the most widely used chemical intermediates. However, almost all of the aimual production of 3.0 x 10 t is consumed as the monomer for nylon-6 fibers and plastics (see Fibers survey Polyamides, plastics). Cyclohexanone, which is the most common organic precursor of caprolactam, is made from benzene by either phenol hydrogenation or cyclohexane oxidation (see Cyclohexanoland cyclohexanone). Reaction with ammonia-derived hydroxjlamine forms cyclohexanone oxime, which undergoes molecular rearrangement to the seven-membered ring S-caprolactam. 

Type 66 nylon is a polyamide first commercialized by DuPont just prior to World War II. At that time, the needed hexamethylenediamine was made from adipic acid by reaction with ammonia to adiponitrile followed by reaction with hydrogen. The adipic acid then, like now, was made from cyclohexane. The cyclohexane, however, was derived from benzene obtained from coal. The ammonia was made from nitrogen in the air by reaction with hydrogen from water obtained in the water-gas shift reaction with carbon monoxide from the coal. So, in the 1950s, nylon was honestly advertised by DuPont as being based on coal, air, and water. 

Because hydrogen can easily be removed from a reaction stream, many dehydrogenations have been studied. These include dehydrogenation of methane to carbon,326 ethane to ethene,327,328 propane to propene,329 n-butane to butenes,330 isobutane to isobutene,331,332 cyclohexane to benzene,332-334 meth-ylcyclohexane to toluene 335 n-heptane to toluene,336 methanol to formaldehyde,330 and ethanol to acetaldehyde.337... 

Nixan [Nitrocyclohexane] A process for making cyclohexane oxime (an intermediate in the manufacture of nylon) from benzene by liquid phase nitration, followed by hydrogenation of the nitrobenzene. Invented by Du Pont and operated from 1963 to 1967. 

The isolation of benzene and cyclohexane from chlorobenzene and thiophenol, and cyclohexane from fluorobenzene, suggests the preferential reductive cleavage of the substituent prior to hydrogenation of the ring. However, fluorocyclohexane decomposes slowly to cyclohexene, which could give rise to the cyclohexane higher yields of fluorocyclohexane are obtained at lower temperatures. 

Fig. 9. Specific activities of Ni-Cu alloy catalysts for hydrogenolysis of (a) ethane to methane and (b) dehydrogenation of cyclohexane to benzene at 316 C. , Ethane hydrogenolysis at ethane and hydrogen partial pressures of 0.030 and 0.20 atm, respectively , cyclohexane dehydrogenation at cyclohexane and hydrogen pressures of 0.17 and 0.83 atm, respectively. From Sinfelt el al. (63).

Cyclohexane (hexahydrobenzene, melting point 6.5°C, boiling point 81°C, density 0.7791, flash point -20°C) can be quantitatively produced from benzene by hydrogenation over either a nickel or a platinum catalyst at 210°C and 350 to 500 psi hydrogen (Fig. 1). 

HDA1—hydrodealkylation of toluene to produce benzene CYHEX1—cyclohexane production by hydrogenation of benzene STYR1—styrene production from ethylbenzene XYL1—production of m-xylene from toluene... 

Zeolites have been used as (acid) catalysts in hydration/dehydration reactions. A pertinent example is the Asahi process for the hydration of cyclohexene to cyclo-hexanol over a high silica (Si/Al>20), H-ZSM-5 type catalyst [57]. This process has been operated successfully on a 60000 tpa scale since 1990, although many problems still remain [57] mainly due to catalyst deactivation. The hydration of cyclohexanene is a key step in an alternative route to cyclohexanone (and phenol) from benzene (see Fig. 2.19). The conventional route involves hydrogenation to cyclohexane followed by autoxidation to a mixture of cyclohexanol and... 

Simple alcohols can be obtained from the decomposition of peroxy acids in cyclohexane or benzene at reflux. This chain reaction, which is efficient for adamantane-l-carboxylic acid (equation 40), is unfortunately usually complicated by side reactions involving hydrogen abstraction from the substrate or sol-... 

The catalytic properties of H-, Li-, Na-, K-, Mg-, Ca-, Zn-, Cd-, and Al-forms of synthetic mordenite in the reactions of cyclohexane and n-pentane isomerization and benzene hydrogenation have been studied. The cation forms of mordenite that do not involve the metals of column VIII of the Mendeleyev Table show high activity in these reactions. To elucidate the mechanism of n-pentane isomerization, the kinetics of the reaction on H-mordenite have been studied. Carbonium ion is supposed to result from splitting off hydride ion from hydrocarbon molecule. Na-mordenite catalytic activity in benzene hydrogenation reaction decreases linearly with the increase of decationization. This indicates that cations are responsible for the catalytic activity of zeolite. The high activity of cations of nontransition metals in oxidation-reduction reactions seems to be quite unexpected and may provide evidence for some uncommon mechanism of benzene hydrogenation. 

Selective Hydrogenation of Benzene to Cyclohexene Obtaining trans substituted cyclohexanes suggested that desorbed cyclohexenes were intermediates in the hydrogenation of benzenes. The isolation of cyclohexene and substituted cyclohexenes from the hydrogenation of benzene and substituted benzenes was first reported for hydrogenations run over a Ru/C catalyst, but the maximum olefin concentrations observed in this early work were only 0.2-3.4%.7... 

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