Methylcyclopentane conversion, selectivity

Fig. 10. Selectivities in hexane conversions versus temperature for benzene formation (Be), hydrogenolysis (Hy), methylcyclopentane formation (MCP), isomerization (ISOM), and dehydrocyclization (Dehy) (9 wt. % Pt on inert Si02).

Sexton et al. (66) also examined the activity for the dehydrogenation of cyclohexane and conversion of methylcyclopentane of a series of PtSn alumina catalysts where the Sn/Pt ratio was varied. They found that the activity decreased as the Sn/Pt ratio increased. Selectivity for benzene formation from methylcyclopentane increased to a maximum at ca. 1.5 to 2.5 wt.% Sn (Sn/Pt = 4.9 to 8.2) and then declined. These conversions were conducted at normal pressures. 

The benzene selectivity in /i-hexane conversion over Pt/KL catalysts increases with conversion, but the selectivity for methylcyclopentane decreases (21). Lane et al. show that the MCP yield passes through a maximum between 40 and 60% conversion, 2-methylpentane and 3-methylpentane peak around 80% conversion, and hydrogenolysis products and benzene increases with -hexane conversion (29). The same reaction product distribution was found for a variety of supports, e.g., AI2O3, Si02, KL, and KY. On Pt/KY, Pt/NaY, and Pt/ALOj the 2MP/3MP ratios... 

Apart from the prevailing fragmentation, different C0 products were important at the two nH pressures. The initial higher selectivity of methylcyclopentane at p(nH)=10 Torr (Fig. la) points to a metallic activity [9, 12]. These centres seem to deactivate rapidly as the reaction proceeded. Higher nH pressures suppressed this initial Cg-cychzation. More isomers were formed at p(nH)=40 Torr (Fig. lb). Whereas the selectivity of both saturated Cc products decreased, that of aromatics increased exceemng linearity at hi er total conversion values. A fourfold increase of p(nH) caused about a tenfold increase in aromatization selectivity (Kgs la and b). 

The presence of gold with the palladium also improves the selectivity of such catalysts for the conversion of methylcyclopentane to benzene. In this case, reactions leading to the formation of C,-C6 alkanes as a result of the rupture of the five-membered ring structure in methylcyclopentane are inhibited relative to the aromatization reaction. Data from our 1973 patent (2), the application for which was filed in 1971, are shown in Table 2.2. 

In Table 5.3 data are presented for the conversion of methylcyclopentane at 500°C and 14.6 atm over the same catalysts for which data on n-heptane reactions are presented in Table 5.2, and also for a rhenium on alumina catalyst (33). The selectivity to benzene and to C,-C6 alkanes, expressed as percentages of the total conversion of methylcyclopentane to all products, is shown after 0.5 hour and after 24 hours on stream. The methylcyclopentane weight hourly space velocity was 40 grams per hour per gram of catalyst. The inlet stream to the reactor contained five moles of hydrogen per mole of methylcyclopentane. The methylcyclopentane contained 1 ppm sulfur, and the catalysts were pretreated in the same manner as they were in the n-heptane conversion studies. 

Table VII shows some results obtained in reforming methylcyclopentane, and it is noteworthy that there appear to be striking differences between these data and the earlier results with cyclohexane. When compared at similar space velocity and pressure conditions, the conversions (and particularly the selectivities) are markedly poorer than those in the cyclohexane case despite the use of higher temperatures. The selectivity would be still poorer at higher pressures.

Table VIII shows similar data on the conversion of n-hexane. Again, even at the favorable low pressure, the selectivity to benzene is relatively poor. As the temperature is increased, the selectivity to aromatization increases somewhat, but hydrocracking increases at an even greater rate. The data in Table VII show better conversion and selectivity for the aromatization of methylcyclopentane to benzene. It appears, therefore, that the rate-limiting step in hexane conversion is the conversion of hexane to methylcyclopentane. This could be explained by reference to...

Methylcyclopentane reacted with hydrogen on Rh/Si02 and Rh/Al203 at 500 K to give quantities of smaller alkanes that fell as the hydrogen pressure was raised 33 3 45-i48 product selectivities (>60 showed little dependence on this variable or on conversion up to In another study with RI1/AI2O3,... 

The chemical (Gif system) and the electrochemical conversion (Gif-Orsay system) have been compared in the oxidation of six saturated hydrocarbons (cyclohexane, 3-ethylpentane, methylcyclopentane, cis- and traus-decalin and adamantane). The results obtained for pyridine, acetone and pyridine-acetone were similar for both systems. Total or partial replacement of pyridine for acetone affects the selectivity for the secondary position and lowers the ratio ketone secondary alcohol. The formation of the same ratio of cis- and traws-decal-9-ol from either cis- or trans-deca in indicates that tertiary alcohols result from a mechanism essentially radical in nature. The C /C ratio between 6.5 and 32.7 rules out a radical mechanism for the formation of ketones and secondary alcohols. Ratios of 0.14 and 0.4 were reported for radical-type oxidations of adamantane and cis-decalin. Partial replacement of pyridine by methanol, ethanol or f-propanol results in diminished yields and a lower selectivity. Acetone gives comparable yields however, the C /C ratio drops to 0.2-10.7. 

This is a structure-sensitive reaction (RSS), and hence the intrinsic activity or turnover frequency (TOP) depends on the particle sizes. The hydrogenolysis reaction was also tested with the Pt/Al203 and promoted with Sn. The reaction was carried out at 1 atm and 573 K and a mixture of hydrogenolysis of methylcyclopentane (MCP)/H2 (1 10.5). The selectivity toward n-hexane, 2-methylpentane, and 3-methylpentane was determined for conversions less than 10 % and was presented in Table 3.2 [15]. 

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