Benzene hydrogenation, temperature

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. 

Chemisorphon of the complexes [Cp MR2], [Cp MR3] or [MR4] (Cp = Cp, Cp M = Zr, Ti, Th R = Me, CH2 Bu, CH2TMS) onto superacidic sulfated zirconia (ZRS , where x refers to activation temperature) [81, 91] and sulfated y-alumina (AIS) [90] afforded active benzene hydrogenation catalysts and ethylene polymer-izahon catalysts. The most active catalyst system for the hydrogenation of benzene (arene Zr = 1.5 1, 25 °C, no solvent, 0.1 MPa H2) was [Cp ZrMe2] -ZRS400, which achieved a TOP of 970 h. The activity of this adsorbate catalyst rivals or exceeds those of the most active heterogeneous arene hydrogenahon catalysts known. The... 

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. 

The analogy between abnormally low CO and C2H4 adsorption, on the one hand, and low relative activity, on the other hand, that has been pointed out while discussing the ethylene hydrogenation hence occurs also for the benzene hydrogenation. Some further experiments on this reaction even show that the analogy is present in details. It has been discussed before that the inaccessibility to CO could not be observed when a catalyst such as 5421 is reduced at low temperatures but that it occurs only when the temperature of reduction is raised (Table II). The same can be said of the activity, as is shown in Fig. 31 the drop in activity is seen to occur at about the same temperature. The influence of surface inaccessibility on catalytic activity appears more pronounced than for adsorption. 

The grouping of the metals as to activity appears about the same in this reaction as for the equilibration of H2 and D2, although the differences are somewhat smaller. This may have to do with the higher temperature at which the benzene hydrogenation was studied. 

The insertion of elemental tellurium into C — Li or C — Na bonds is a convenient method for the preparation of alkali metal tellurolates. Many organic lithium compounds are commercially available or can be prepared, for instance, by halogen-lithium or hydrogen-lithium exchange. The reactions of the organic lithium compounds with elemental tellurium are performed in inert organic solvents such as diethyl other, tetrahydrofuran, tetrahydrofuran/hexane, or diethyl ether/benzene at temperatures (— 196° to + 20°) compatible with the stability of the organic lithium compound. The applicability of this reaction for the synthesis of aliphatic, aromatic, and heteroaromatic lithium tellurolates is documented in Table 1 (p. 155). 

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. 

Hydroisomerization is one of the few major refinery processes that allow refineries to cope with the future fuel regulations on the one side and the necessity to supply premium fuel with the necessary octane on the other side. Due to the limited volume the chemical industry can cope with in addition to the present level, future reduction of the aromatics in fuels will force the refineries to convert as much of the aromatics as possible to fuel components. One possible option is to feed the one-ring aromatics such as benzene to an isomerization unit. A state of the art hydroisomerization catalyst such as HYSOPAR is very active for benzene hydrogenation at temperatures as low as 100°C, where 100% hydrogenation is achieved, and can cope with up to 15 wt.-% of benzene in the feed. When sulfur in the range of 50 ppm is present in the feed, a partial inhibition of... 

Rate (Xi, X2) is the rate expression for benzene hydrogenation that depends on X, and X2. For example, the following rate equation could be used if the constants and were known at the reaction temperature ... 

Kehoe and Butt [J. P. Kehoe and J. B. Butt, AIChE /., 18 (1972) 347] have reported the kinetics of benzene hydrogenation of a supported, partially reduced Ni/kieselguhr catalyst. In the presence of a large excess of hydrogen (90 percent) the reaction is pseudo-first-order at temperatures below 200°C with the rate given by ... 

Dimethylhydrazino)diphenylphosphine may be prepared by the action of wnsym-dimethylhydrazinet on diphenylphosphinous chloride in benzene at temperatures just below room temperature. A 2 1 mol ratio provides an extra mol of the free base to act as a hydrogen chloride acceptor. The M7Wi/m-dimethylhydrazinium chloride, which is only very slightly soluble in benzene, may be easily removed by filtration. The hydrazinophosphine may then be recovered from the filtrate in good yield by evaporation of the solvent at room temperature under reduced pressure. 

Benzene Hydrogenation The benzene hydrogenation reaction over Ni/kieselguhr is highly exothermic and irreversible in the temperature range of 60 -200 C at an atmospheric pressure, Kehoe and Butt (1972) correlated the kinetics with an Eley-Kideal mechanism. Host of the parameters were measured via independent experiments or through literature correlations when experimentation could not be easily done-... 

For the case of thiophenol tiiis value is n = 6. The bond number has been determined for the series of poisorts already mentioned (ref. 14) with the aim of comparing it with the toxicity towards benzene hydrogenation at room temperature (the results are not still available). 

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