Conversion rate, benzene

Benzene conversion Rate at 500 °F (g moles/hr-g catalyst) Rate at 600 °F (g moles/hr-g catalyst)... 

Quach et al found that the benzene conversion rate was best described by the Langmuir-Hinshelwood relation ... 

A convenient one-pot system was developed also for the conversion of highly chlorinated benzenes to less chlorinated ones at room temperature, with reasonable conversion rates using the system [(dppf)PdCl2]/NaBH4/TMEDA/THF [67]. Degradation to benzene could not be achieved. Removal of chlorines in meta-position was preferred over those in ortho- or para-positions. The effectiveness of the method has been tested on the PCB mixtures Aroclor 1242,1248, and 1254 at 67 °C. 

The conversion rates on a once"through basis are high as you can see from the material, balance, 2337 pounds of benzene/xylenes from 2400 pounds of toluene. 

Figure 12. Molecular structures of some monosubstituted benzenes studied via TRPES in order to determine the quantitative accuracy of the extracted internal conversion rates. Three different electronic substituents were used, C=0, C=C, and C=C, leading to different state interactions. The effects of vibrational dynamics were investigated via the use of methyl group (floppier), as in a-MeSTY and ACP, or a ring structure (more rigid), as in IND, side-group additions. Both BZA and ACP have favorable Type (I) ionization correlations, whereas STY, IND, a-MeSTY, and ACT have unfavorable Type (II) ionization correlations.

Figure 14. Excess vibrational energy dependence of the internal conversion rates of the first TtTt state of benzene and its derivatives.

The feedstock consists of a mixture of C8 aromatics typically derived from catalytically reformed naphtha, hydrotreated pyrolysis gasoline oran LPG aromatization unit. The feed may contain up to 40% ethylbenzene, which is converted either to xylenes or benzene by the Isomar reactor at a high-conversion rate per pass. Feedstocks may be pure solvent extracts or fractional heartcuts containing up to 25% nonaromatics. Hydrogen may be supplied from a catalytic reforming unit or any suitable source. Chemical hydrogen consumption is minimal. 

The limitation of conversion rates to between 25 and 30 per cent per pass, by avoiding an excessive temperature rise in the reaction medium, has the effea of preventing the production of hea > produas. On the other hand, this entails high benzene redrculation. The following are separated by flash and settling at the reaaor exit ... 

Ethyl benzene flow rate Ethyl benzene molecular weight Steam flow rate Water molecular weight Mixed feed temperature Inlet pressure Final conversion... 

Recently, the use of sulfolane solvent allowed better kinetic control of the oxidation chain, with an increase of the selectivity to 80% or greater, at ca 8% benzene conversion. The by-products were catechol (7%), hydroquinone (4%), 1,4-benzo-quinone (1%) and tar (5%) [53, 54]. According to these authors, a rather stable complex, formed by hydrogen bonding with sulfolane, promoted desorption and hindered the re-adsorption of phenol, protecting it from consecutive oxidation (Equation 18.7). Actually, the rate of oxidation of phenol in the presence of sulfolane was only 1.6 times that of benzene, while it was 10 times higher in the presence of acetone. 

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. 

Increasing the reaction temperature from 300 to 450 C led to an increase in reaction rate. Benzene conversion reached values up to 50% at 450°C with the fresh catalyst (Figure 3). 

Like the hydroxylation rate, the deactivation rate, too, increased with temperature. After 150 minutes time-on-stream of the catalyst, benzene conversion at 450 C was very close to the conversion at 400 C. Complete regeneration was achieved by heating the catalyst to 500°C under a flowing oxygen/nitrogen mixture (ratio 1 5). 

An increase of nitrous oxide feed concentration led to an increase inreaction rate and benzene conversion. On the other hand benzene conversion decreased with increasing benzene feed concentration (Table 2). Phenol yield basically changed in the same way as benzene conversion in all cases. Upon variation of the feed concentrations, the highest phenol production was obtained at 26% nitrous oxide and 12.5% benzene at T=400 C, W/F=92 gmin/mol and a catalyst time on stream of 40 minutes [5-7]. 

In summary, increasing feed concentration of nitrous oxide led to an increase of reaction rate with only little loss of selectivity to the desired product phenol. Absolute benzene conversion increased with increasing benzene feed concentration especially at high nitrous oxide... 

The direct oxidation of propylene by molecular oxygen is a low-selective reaction. The propylene oxide yield can be raised by limiting the conversion rate to a low value, about 10 to 15 per cent, by using more selective catalysts, or by achieving co-oxidation with a more oxidizable compound than propylene (acetaldehyde, isobutyraldehyde etc.). Many patents have been Hied concerning this process, but without any industrial implementation. Among them is the liquid phase oxidation of propylene on a rare earth oxide catalyst deposited on silica gel (USSR), or in the presence of molybdenum complexes in chlorobenzene or benzene (JFP Instiiut Francois du Petrole. Jefferson ChemicalX vapor phase oxidation on modified silver catalysts (BP British Petroleum IFP, or on ... 

The reaction rate remains constant up to high conversion rates (zero order in relation to benzene). Two side reactions must be avoided because they lower the cyclohexane purity. These are conversion to methylcydopentane and hydrocracking. The isomerization equilibrium of cyclohexane to methyicyclopentane corresponds to a conversion of 68 per cent at 200°C, reaching 83 per cent at 300°C. This makes it necessary to select a catalyst that does not favor this reaction. With nickel-based systems, the reaction appears only above 250°C. Moreover, the hydrogen must not contain impurities liable to poison the active phases introduced. 

Figure 3. Effect of feed rate on benzene conversion...

Figures 1 shows TEM images of the lwt%Ru/0.1wt%Cu/SiO2 catalysts activated with hydrogen before and after calcination. Metal particles (2-10 nm and 2-50 nm) in the sol-gel catalysts activated before and after calcination are smaller than those (3-50 nm and 20-60 nm) in the corresponding impregnation ones, respectively. In the comparison of the catalysts activated before and after calcination, the size of metal particles is smaller in the catalysts without calcination than in the corresponding catalysts with calcination. These are consistent with the fact that the sol-gel catalysts activated before calcination show faster rates in the benzene conversion than the sol-gel catalysts activated after calcination and the impregnation catalysts [7].

We are tempted to proceed a little bit further, and examine the development of the whole flowsheet in relation with the reaction system. Let s suppose that the feedstock is of high purity ethylene and benzene. Because recycling a gas is much more costly than a liquid, we consider as design decision the total conversion of ethylene. The benzene will be in excess in order to ensure higher conversion rate, but also to shift the equilibrium. The equilibrium calculation can predict with reasonable accuracy the composition of the product mixture for given reaction conditions. Then polyalkylates, mainly diethylbenzene can be reconverted to ethylbenzene in a second reactor. 

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