Cyclohexene Hydrogenation and Dehydrogenation

Peer-reviewed journals [74,122] proceedings [20,73,123-126] sections in re-views [90,94,97]. 

Thepresentinvestigationswerelargelymotivatedtoshowfheserial-screeningca-pabilities ofthe reactor concept used. The speed ofprocess-parameter changes, consumption of small volumes only, preciseness ofkinetic information, and ro-bustnessweremajormicroreactorpropertiesutilized. 

ChemicalMicroProcessEngineering Fundamentals,ModelUngandReactions VolkerHessel,SteffenHardt,HolgerL6we 

Copyright 2004WILEY-VCHVerlagGmbH Co.KGaA,Weinheim ISBN 3-527-30741-9 

For certainprocessparameters,completeconversionisachievedina5 pm channel, whereas zero conversionisgivenfora 50 pm channel. Similarly,thecatalyst 

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Figure 15. Turnover rate for cyclohexene hydrogenation and dehydrogenation as a function of particle size. Reaction conditions are lOTorr CeHio, 200 Torr H2, and 310K for hydrogenation and 448 K for dehydrogenation, respectively [18].

Consistent with this model It has been shown on platinum (223) that the reaction occurs on the surface covered with a near monolayer of carbonaceous species In an apparently structure-insensitive loanner but that cyclohexene hydrogenation and dehydrogenation reactions proceed on the clean metal surface In a structure sensitive manner and in addition there Is then a striking variation In catalytic behaviour between various crystal surfaces ... 

X. Su, K. Y. Rung, J. Lahtinen, Y. R. Shen, G. A. Somorjai, 1-3 and 1-4 cyclohexadiene reaction intermediates in cyclohexene hydrogenation and dehydrogenation on Pt(lll) crystal surface a combined reaction kinetics and surface vibrational spectroscopy study using sum frequency generations, J. Mol. Catal. A 1999, 141, 9-19. 

R. Nassar, J. Hu, J. Palmer, W. Dai, Modeling of cyclohexene hydrogenation and dehydrogenation reactions in a continuous-flow microreactor, Catal. Today 2007, 120, 121-124. 

It was found that cyclohexene passed over vanadium trioxide catalyst at 250-450° in the presence of hydrogen shows no hydrogen disproportionation, but, depending on the temperature, a direct hydrogenation and dehydrogenation reaction approaching equilibrium values. 

Hydrogenation and dehydrogenation reactions of many compounds, such as cyclohexene, common alkanes such as ethane, cyclohexane, aromatic compounds such as benzene, unsaturated compounds such as fatty oils and aldehydes, and their respective catalyst chemistries have been studied in microreactors. The combinatorial chemistry-style approach that has been popular in biomedical and pharmaceutical research has been extended to catalyst discovery in hydrogenation... 

Another pertinent example is provided by the manufacture of caprolactam [135]. Current processes are based on toluene or benzene as feedstock, which can be converted to cyclohexanone via cyclohexane or phenol. More recently, Asahi Chemical [136] developed a new process via ruthenium-catalysed selective hydrogenation to cyclohexene, followed by zeolite-catalysed hydration to cyclo-hexanol and dehydrogenation (Fig. 1.49). The cyclohexanone is then converted to caprolactam via ammoximation with NH3/H202 and zeolite-catalysed Beckmann rearrangement as developed by Sumitomo (see earlier). 

Dehydrogenation and hydrogenation of cyclohexene Hydrogenation of butadiene Dehydrogenation of isopropyl alcohol... 

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. 

Fig. 4.1. Chromatograms of the original sample (I) and the products of hydrogenation at 200°C (II) and dehydrogenation at 325°C (III) [55]. Carrier gas, hydrogen flow-rate, 60 ml/min column, 600 X 0.6 cm I.D. sorbent, 20% polyethylene glycol 4000 on solid support. Peaks 1 = air 2 =n-octane 3=octene-l 4 = octene-2 5 = n-propylcycIopentene-1 6 = cyclohexene 7 = 1-isopropylcyclo-hexene-l 8 =n-propylcyclohexene 9 = ethylcyclohexene 10 = isopropylcyclohexane 11 = product from the dehydrogenation of propylcyclopentane 12 = n-octane 13 = ethylbenzene 14 = isopropylbenzene. From ref. 55,...

Catalysts were prepared by impregnation of Pt inside the pore structure of carbon fibers. Care was taken to eliminate the active metal from the external surface of the support. A very high dispersion of Pt was measured. Four reactions were carried out in a fixed-bed reactor competitive hydrogenation of cyclohexene and 1-hexene, cyclization of 1-hexene, n-heptane conversion and dehydrogenation of cyclohexanol. Three types of carbon fibers with a different pore size and Pt-adsorption capacity along with a Pt on activated carbon commercial catalyst were tested. The data indicate a significant effect of the pore size dimension on the selectivity in each system. The ability to tailor the pore structure to achieve results drastically different from those obtained with established supports is demonstrated with heptane conversion. Pt on open pore carbon fibers show higher activity with the same selectivity as compared with Pt on activated carbon catalysts. 

On metallic catalysts, cyclohexene can either be hydrogenated or dehydrogenated to benzene, depending on the temperature and hydrogen pressure the first is favoured at low temperatures, but it can also disproportionate to give cyclohexane and benzene ... 

Moreover, if cyclohexene is present merely because equilibrium is established between olefin in the gas phase and olefin on the surface, it would be expected that in the dehydrogenation of ethylcyclohexane, thermodjmamic equilibrium between styrene, hydrogen, and ethylbenzene would be established. If, however, cyclohexene plays an important and specific part in the reaction, and is desorbed after formation to be... 

The process involves three steps partial hydrogenation of MPD to 3-amino-2-cyclohexene-l-imine (3-ACI), hydrolysis of the imine to 3-amino-2-cyclohexene-1-one (3-ACO), and dehydrogenation of 3-ACO to MAP (scheme 6.37). 

The reactivity of cyclohexene is much higher than that for benzene hydrogenation and cyclohexane dehydrogenation, particularly using noble metals as catalysts. Good results has been reported over 0.35 wt% Pt, Ir, Rh, Re, U, Ptir, PtRe, or PtU/y-Al203 catalysts in a pulsed MSR at 250 °C [24] or in a continuous MSR (thiophene, pyridine, and cyclohexene conversions of 94.3, 100, and 90.3%, respectively) [25]. 

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