Benzene hydrogenation conversion

Benzene hydrogenation was used to probe metal site activity. A 12/1 H2/benzene feed was passed over the catalysts at 700 kPa with a weight hourly space velocity of 25. The temperature was set to 100°C and the conversion of benzene to cyclohexane was measured after 2 hours at temperature. The temperature was then increased at 10°C increments and after two hours, the conversion remeasured. 

The isolated Ru(0) nanoparticles were used as solids (heterogeneous catalyst) or re-dispersed in BMI PP6 (biphasic liquid-liquid system) for benzene hydrogenation studies at 75 °C and under 4 bar H2. As previously described for rhodium or iridium nanoparticles, these nanoparticles (heterogeneous catalysts) are efficient for the complete hydrogenation of benzene (TOP = 125 h ) under solventless conditions. Moreover, steric substituent effects of the arene influenced the reaction time and the decrease in the catalytic TOP 45, 39 and 18h for the toluene, iPr-benzene, tBu-benzene hydrogenation, respectively, finally. The hydrogenation was not total in BMI PPg, a poor TOE of 20 h at 73% of conversion is obtained in the benzene hydrogenation. 

Study the effect of varying space time on the fractional conversions Xj and X2 and evaluate the compositions of benzene, hydrogen, diphenyl and triphenyl. 

Because of the scarcity of electronic paramagnetic resonance data, and because of the frequent unreliability of the data from paramagnetism, boiling point elevation, spectrophotometry, and ortho-para hydrogen conversion, most published radical dissociation constants can be accepted only with reservations. An error of 50 % is not at all improbable in many cases. We are therefore not yet in a position to explain, or rather to test our explanations of, small differences in dissociation constants. Table I shows the values of K corresponding to various hexaarylethanes in benzene at 25°. Because of the order of magnitude differences in Table I, however, it is likely that some of the expected large effects, such as steric and resonance effects, exist. 

Hydrogenation of Benzene Benzene hydrogenation is a facile reaction and is indicative of the number of surface Ni atoms available for catalysis. The activity of the catalysts in the benzene hydrogenation reaction was investigated at 453 Cyclohexane was the only product of the reaction. Benzene conversion (Table 11.4) increased with increasing Ni content (samples 2A—4A) up to 20 wt.%. 

Molybdenum nitride itself has been dispersed on platinum clusters dispersed in EMT zeolite. In this study, coverage of platinum particles by molybdenum deposition was investigated and was reported to suppress the activity for benzene hydrogenation and enhance the heptane conversion. With respect to bare Pt for heptane conversion, the aromatisation activity was reduced, whereas isomerisation and hydrogenolysis were observed. 

Catalytic Activity. An aliquot (20-50 mg) of the sample used for dispersion measurement was reactivated for one hour at 300° C under hydrogen. The rate of benzene hydrogenation was measured in a conventional flow reactor at low conversion (<2%) to avoid heat and mass transfer limitations. The pressure of benzene was 56 torr and that of hydrogen was 704 torr under these conditions the reaction is zero order for benzene. 

Cyclohexane is an essential intermediate for the synthesis of nylon-6,6. The purity level required for the use of cyclohexane, especially for its oxidation, is higher than 99%. This purity can be obtained by the benzene hydrogenation technique. The conversion is highly exothermic and is favored by low temperature, and high hydrogen partial pressure. 

Other instances of compensatory behavior in reactions on alloys have been described and discussed in the literature [see, for example, Bond (5) para-hydrogen conversion (pp. 170-172), olefin hydrogenation (pp. 248-250), benzene hydrogenation (pp. 321), and decomposition of formic acid (pp. 426-429)]. 

Fig. 5.6. Above Activity in benzene hydrogenation, as % of conversion at 100°C per m2 total surface area of unsupported alloys, as a function % Cu in Ni. Below Conversion with a standard amount catalyst as a function of temperature. (1) pure Ni (2) 10% Cu-Ni alloy (3) thermodynamic limit at reaction conditions (for other details see [1]).

The HDS reaction for a feed with the composition 15% Bz + 85% n-C5 + 30 ppmw sulfur is already completed at about 170°C, as shown in Figure 7.5. This shows that HYSOPAR is an efficient hydrodesulfiirization (HDS) catalyst under these conditions despite the effect of sulfur on benzene hydrogenation activity. To complete the benzene conversion the temperature needs to be increased from 225-235°C to 250-260°C with 30 ppmw S in the feed. At these high temperatures, thermodynamic equilibrium between nC5 and iC5 was practically reached, indicating that the impact of S on isomerization is not pronounced. Some ring cleavage of cyclic compounds was also observed, accompanied by an increase in gas production. The results are summarized in table 7.7. 

Theoretical equations, which predict the loss of catalyst activity due to sulfur poisoning in hydrogenation reactions, are presented in this paper. The integration of the partial differential equations resulting from a consideration of sulfur poisoning, hydrogenation, and a catalyst active site balance leads to an analytical solution. When these equations were applied to deactivation data obtained for commercial benzene hydrogenation catalysts, conversions measured experimentally as a function of time were fit quite well by these equations. 

A comparison of Figures 1 and 2 shows that at 16 hours (T = 1.44), the benzene conversion for Catalyst A is around 45% but greater than 60% for thiophene. Similarly, a comparison of Figures 1 and 4 shows that at 16 hours (T=0.29) for Catalyst C , benzene conversion is still about 78% but the conversion of thiophene is around 40%. These results suggest that Catalyst C is less susceptible to thiophene poisoning which results in better benzene conversion over the life of the catalyst. This makes Catalyst C a good choice for benzene hydrogenation unless the amount of residual sulfur in the product exceeds specifications. 

The benzene hydrogenation was carried out at atmospheric pressure in a flow system provided with a fixed bed reactor. The activity tests were made under the following conditions T = 773 K, = 0.05 atm, PH2 - 0.95 atm, benzene flow rate = 2 cra h K Conversion was always less than lOX, The feed was doped with thiophene in concentrations between 0 and 50 ppm of S. 

Supported-Pt-catalysts were prepared by wet impregnation technique using H2PtClg solution. Supported platinum salt was reduced at 473 K and 773 K, H2, CO adsorption and electron microscopy were used to measure the metal dispersion. On table 1 are reported Pt dispersion,infrared vrQ for CO adsorbed on Pt and the catalytic data on benzene hydrogenation and n-hexane conversion. 

The magnitude of the effect is not unreasonable for promotion by nickel. The original activity was 0.040 (cm /minute at 310° and a space velocity of about 600 hour i). After 3 x lO s nvt, two samples had activities of 0.100 and 0.148 and, after repreparation, of 0.510 and 0.376. Apparent activation energies were 41 kcal/mole before irradiation, 17-18 after irradiation, and 17-20 after repreparation. Emmett and Skau (63) found zero conversion in benzene hydrogenation at 200° over a nearly pure copper catalyst (5 X 10 % Ni) and about 2% conversion on one containing 0.1 % nickel. These experiments are not easily compared quantitatively with Tet nyi s because of the different temperatures, but they demonstrate the promoting effect of a known addition of nickel. 

The isomerization of n-hexane at 250 °C, 26 bar. a H2/hydrocar-bon (HC) molar ratio of 22.4, and a WHSV of 3.3 g.g". h over fresh Pd-NiSMM led to a conversion of 56 %, almost without cracking. This isomerization activity was totally and irreversibly destroyed after injection of about 10 molecules pyridine per g Pd-NiSMM. Benzene hydrogenation over the poisoned catalyst (260 °C, 26 bar, H2/HC = 25) showed that the hydrogenation function of the catalyst was still active enough to hydrogenate benzene totally to cyclohexane, indicating that the metallic sites had only been partially poisoned, it at all. 

The dehydrogenation of cyclohexane and the dehydrocyclization of / -hexane to yield benzene are strongly endothermic, so that increasing temperature markedly improves the extent of conversion to benzene. Hydrogen partial pressure obviously has a marked effect on the extent of formation of benzene, and from the viewpoint of equilibria alone, it is advantageous to operate at as high a temperature and as low a hydrogen partial pressure as possible to maximize the yield of the aromatic hydrocarbon. 

Irradiation of 1,3,5-hexatriene (81) in the vapor phase leads to the formation of 1,3-cyclohexadiene (82), benzene, hydrogen, and 1,2,4-hexatriene (83), in addition to a liquid polymer 63>. Determination of the quantum yield 64> led to the conclusion that 83 may originate from an electronically excited molecule, while benzene and hydrogen occur from a vibrationally excited ground state molecule (1,3-cyclohexadiene) formed by internal conversion from the electronically excited molecule. 

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