Dehydrogenation, of methylcyclohexan

Chemical Recuperation of Waste Heat by Catalytic Dehydrogenation of Methylcyclohexane under Superheated Liquid-Film Conditions... 

A fourth type of petroleum isomerization, which was commercialized on a small scale, involves the rearrangement of naphthenes. In the manufacture of toluene by dehydrogenation of methylcyclohexane, the toluene yield can be increased by isomerizing to methylcyclohexane the dimethylcyclopentanes also present in the naphtha feed. This type of isomerization is also of interest in connection with the manufacture of benzene from petroleum sources. 

Thus it appears that an interpretation not involving adsorption equilibria is reasonable in accounting for the observed kinetics of dehydrogenation of methylcyclohexane to toluene. However, some additional information, such as data on the heat of adsorption of toluene on supported platinum, would be desirable in establishing the correctness of this interpretation. 

PS-19c The dehydrogenation of methylcyclohexane (M) to produce toluene (T) was carried out over a 0.3% PT/AI2O3 catalyst in a differential c lytic reactor, The reaction is carried out in the presence of hydrogen (H,) to avoid coking [./. Phys. Ckem., 64, 1559 (I960)]. 

K. AH Jawad, EJ. Newson, and D.W.T. Rippin, Exceeding equilibrium conversion with a catalytic membrane reactor for the dehydrogenation of methylcyclohexane, Chem Eng. Sci. 49 2129 (1994). 

Example 9.7. Dehydrogenation of methylcyclohexane [10]. Methylcyclohexane (MCH) can be dehydrogenated to toluene over alumina-supported platinum ... 

Examples include hydrogenation of propanal over nickel, dehydrogenation of ethanol over copper-cobalt, dehydrogenation of methylcyclohexane to toluene over platinum, hydroformylation of olefins catalyzed by cobalt hydrocarbonyls on solid polymers, hydrogen-ion catalyzed hydration of olefins on ion exchangers, dehydrogenation of 1-butene to butadiene over chromia-alumina, and various hypothetical reactions. 

Another example is the dehydrogenation of methylcyclohexane to toluene and H2 under conditions such that the reaction is not limited by equilibrium. Still, the rate is not inhibited by toluene in spite of the intuitively evident stronger chemisorption of toluene than that of methylcyclohexane. Again, a Langmuir-Hinshelwood mechanism seems improbable. This conclusion receives strong support from the critieal observation that benzene added to the feed does not... 

The dehydrogenation of methylcyclohexane to toluene was studied by Sinfelt et al. [J.H. Sinfelt, H. Hurwitz and R.A. Shulman, J. Phys. Chem., 64, 1559 (I960)], over a 0.3% Pt on AI2O3 catalyst. The temperature range from 315 to 372°C was investigated, with methylcyclohexane partial pressures varying from 1.1 to 4.1 atm. Experimental rate data were well correlated by an equation of the form... 

J. Ali, A. Baiker, Dehydrogenation of methylcyclohexane to toluene in a pilot-scale membrane reactor, Appl. Catal. A 1997, 155(1), 41-57. 

Even if all of the criteria are satisfied, there is still the possibility that the reaction may proceed according to a different mechanism. Dehydrogenation of methylcyclohexane is an interesting example of this (Sinfelt, 1964). 

Dehydrogenation of cyclohexane was examined at 300 °C. Figure 16.6 shows the cyclohexane conversion at 300 °C and 4 bars and the conversion of methylcyclohexane at 275 °C, 300 °C, and 4 bars for comparison. It is obvious that the conversion of cyclohexane decreases with increasing feed rate, similarly to the dehydrogenation of methylcyclohexane, but is lower than that of methylcyclohexane. This is because the equilibrium conversion at the same temperature is higher as shown in Figure 16.2. 

Figure 16.7 shows the hydrogen flux observed in the dehydrogenation of cyclohexane at 300 °C and those in the dehydrogenation of methylcyclohexane at 275 and 300 °C. The lower hydrogen flux for the dehydrogenation of cyclohexane than that of methylcyclohexane at 300 °C may correspond to the lower cyclohexane... 

Ferreira, P., Rodriguez, I., Guerrero, A. (2002b). On the performance of porous vycor membranes for conversion enhancement in the dehydrogenation of methylcyclohexane to toluene. Journal of Catalysis, 212, 182—192. 

Kariya et al. performed dehydrogenation of methylcyclohexane and other cycloalkanes over platinum, palladium and rhodium monometallic and platinum/palladium, platinum/rhodium, platinum/molybdenum, platinum/tungsten, platinum/rhenium platinum/osmium and platinum/iridium catalysts supported on both petroleum coke active carbon and on alumina between 375 and 400 °C [279]. The platinum catalyst supported by petroleum active carbon showed the highest activity. While platinum was the most active monometallic catalyst, its activity could be increased by addition of molybdenum, tungsten and rhenium. 

Ferreira-Aparicio et al. reported the development of a laboratory-scale membrane reactor for the partial dehydrogenation of methylcyclohexane into toluene in a membrane reactor [527]. A platinum/alumina catalyst containing 0.83 wt% platinum was put into a porous stainless steel tube, which had been prior coated with a palladium membrane by electroless plating. At 350 °C reaction temperature and a pressure of 1.4 bar at the reaction side, 99% of the hydrogen product could be separated through the membrane, which had a thickness of 11 pm. However, the sweep stream required on the permeate side was more than 20 times higher than the hydrogen permeate flow rate that could be achieved. 

An example of application of these rules to the testing of rate parameters in the dehydrogenation of methylcyclohexane on Pt and Pt/Re catalysts was published by Van Trimpont et al. [1986] and to the dehydrogenation of ethylbenzene into styrene by Won Jae Lee and Froment [2008]. 

Sinfelt et al. (1960) obtained initial rate data using a differential reactor for the dehydrogenation of methylcyclohexane (Af) over a 0.3% Pt-Al203 catalyst in the presence of H2 to reduce coking. The reaction is ... 

Table 3,2 Rate Data for Dehydrogenation of Methylcyclohexane (Sinfelt et al. 1960)...

Problem 6-8 (Level 1) Toluene (T) can be produced by dehydrogenation of methylcyclohexane (M) over various transition metal catalysts ... 

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