Benzene pressure

In the benzene carrier system57 (Ar = C6H5) using 20-160 torr benzene pressure over the temperature range 475-527 °C, approximately 3-6 % of the methyl radicals are removed by reaction (6). An additional 1-5 % are found as ethylene and propane (less than 2 % under most conditions used). At all temperatures, kl is independent of pressure above approximately 8 torr. The Arrhenius equations for the decomposition at infinite pressure (P > 8 cm) and at 18 mm respectively are... 

Harada, S. and Schelly, Z. A. (1982). Reversed micelle of dodecylpyridinium iodide in benzene. Pressure-jump relaxation kinetic and equilibrium study of the solubilization of 7,7,8,8-tetracyanoquinodimethane. J. Phys. Chem., 86, 2098-102. 

An estimate of the specific frequency factor can be made according to the principles laid down in IV, 2. Assuming that the kinetics of the benzene hydrogenation is about zero order in the benzene pressure and first order in the hydrogen pressure, one would expect. 

A model compound here is benzene. Both the benzene hydrogenation (de-aro-matization of oil) as well as the dehydrogenation of cyclohexane into benzene (e.g. upon naphtha reforming) are of practical interest. Hydrogenation of benzene looks similar to the hydrogenation of olefins. For example, in a certain region of reaction conditions, the reaction is near to first order in hydrogen pressure and zero order in benzene pressure [78]. (N.B. A more exact analysis of the kinetics is available too, see ref. 81). However, there also seem to be some important differences. 

With the above assumptions, the total activation energy calculated from equation (4) should be about 19 Kcal/jmole. The discrepancy can be attributed to inaccuracies in the estimation of the heat of reaction (1) and (2). This order of magnitude analysis indicates that the model can roughly account for the third order dependence on hydrogen pressure and first order dependence on benzene pressure. 

The rate constant obtained for Reaction 1 was 3.6 0.7 X 107M 1 sec."1 independent of benzene pressure from 2 to 8 cm. (However, at 1 cm. benzene, low enough pulse intensity could not be used to overcome the importance of Reactions 2, 3, and 4 relative to 1, and the apparent rate constant obtained was higher.) Within 20%, the same rate constant for Reaction 1 was obtained in systems containing 30 to 90 atm. Ar plus about 2 atm. C02, 50 at jyLp]p% bouL2iaftnvj Q, and 15 atm. COo... 

A typical oscilloscope trace is shown in Figure 5. (The decay rate did not change when the argon pressure was varied from 58 to 95 atm., or when the benzene pressure was changed from 2 to 8 cm.). The absorption did not decay to zero, but seemed to reach a plateau of about half of the maximum optical density. Because of noise and the difficulty of establishing the plateau, first and second order tests on such decay... 

Figure 2.7 Test of Model I for benzene hydrogenation (a) Variable benzene pressure, (b) Variable hydrogen pressure. 

Fig. 18 Sorption isosteres of the sorbate ethylbenzene from simultaneous sorption of the binary mixture of ethylbenzene and benzene pressure as a function of the reciprocal temperature at constant loading (in mmolg" ) (1) 0.10 (2) 0.15 (3) 0.20 (4) 0.25 (5) 0.30...

Benzene adsorption has been performed at a benzene pressure P = 75 mbar. Samples were previously evacuated at 300 C overnight under 5.10" bar... 

Experimentally the UV sources are provided by two dye lasers giving a minimum of 2 x 250 pJ UV-light of 10 ns pulse duration in the range 260 - 285 nm. The benzene pressure was between 10 pbar and 200 pbar. The electrodes were biased with 16 V and the ion current following laser irradiation was collected by a gated integrator. Details can be found in Fig. 3. In thi way a complete ionization spectrum for several selected intermediate ( vibronic levels could be recorded fjom slightly ne-... 

The first criterion is most easily examined. In pure benzene vapor excited at 2536 A or longer wave lengths, both the quantum yield and the observed singlet state lifetime show only a very shallow dependence on benzene pressure above 10 torr. Addition of foreign gases such as hydrocarbons to these experiments also has little (but sometimes finite) effect on fluorescence yields " or lifetimes. Even in the extreme collisional limit of condensed phase at 77°K, the fluorescence yield of 0.2 matches that of the vapor. - (Condensed phase yields drop to about 0.05 at 300°K, but this is probably a special thermal effect somewhat apart from a collision-induced electronic decay. See Section IVC.)... 

Fig. 12. Relative fluorescence quantum yields of benzene vapor at 300 K as a function of exciting wave. Those data indicated by squares are normalized to the point at 2536 A and arc from excitation with lines from a mercury arc. Those data indicated by circles are from another set obtained with light from a Xe arc coupled with a monochromator whose bandpa.ss is about 6-15 A. They are normalized to the average in that set between 2530 and 2590 A. The two sets are independent and not normalized to each other. All quantum yields are obtained from mixtures of benzene and cyclohexane with benzene pressures in the range 0.5 to 3 torr and cyclohexane between 35 and 50 torr. Data from Noyes and Harter.

The benzene sorption isotherms for the several materials prepared with the auxiliary organic show the large sorption capacity characteristic of MCM-41. The isotherms show a gradual shift in capillary condensation to higher benzene pressure with increasing mesitylene content. The material formed with the... 

Figure 7.14. Activity versus benzene pressure for 4.8% Fe/GMC, Ph2 = 600 Torr 414K - (O), 448K - (A) 473K - ( ). Solid lines represent predicted behavior using parameter values in Table 7.9. (Reprinted from ref. 24, copyright 1983, with permission from Elsevier)...

Figure 1. (a) Photoemission spectra N(E) for clean Ni(l 11), O = 5.4 eV (full curve), and after exposure to 2.4 L of benzene at room temperature (broken curve). TTie energy of the unpolarized photons was 21.2 eV, and electrons were collected by the energy analyzer over a large solid angle, (b) Adsorbate-induced difference in emission AA ( ). i.e., the difference between the broken and the full curves in (a). AO = -1.4 eV. (c) AA ( ) for a condensed benzene layer formed at 7" = 150 K at a benzene pressure of 4.6 x lO" Pa. AO = -1.6 eV. (d) Gas-phase photoelectron spectra of benzene. The energy scale in (d) has been shifted so that the assigned levels line up with those in (c). Note that the 7t-level is shifted between (b) and (c). (From Ref. 2.)... 

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