Xylenes reaction

Kramp, F., and S. E. Paulson, On the Uncertainties in the Rate Coefficients for OH Reactions with Hydrocarbons, and the Rate Coefficients of the 1,3,5-Trimethylbenzene and m-Xylene Reactions with OH Radicals in the Gas Phase, J. Phys. Chem. A., 102, 2685-2690 (1998). 

The Octafining process (114—116) was developed and commercialized by Adantic Richfield and Engelhard in the eady 1960s. The first-generation catalyst was prepared by mixing equal amounts of a silica—alumina cracking catalyst with Pt on alumina. The Pt content of the mixture was about 0.5 wt %. The EB approach to equilibrium was 88%, with an 80% selectivity to xylenes. Reaction conditions consist of temperature of 425-480°C pressure of 1.14—2.51 MPa H2/hydrocarbon ratio < 10 1 (preferably 4—6 1) and LHSV = 0.6-1.6/h. An equilibrium mixture of xylenes is produced. To maintain... 

Table III. m-Xylene Reactions Catalyzed by Aluminophosphate-Based Molecular Sieves...

In section 5.1.9, the important parameters affecting the reaction and transport rates in a single catalyst pellet for this reaction have been investigated. The o-Xylene reaction has shown very complex performance, and many interesting features have been observed. 

Table 3 presents data for the catalytic patterns of the samples Investigated in the m-xylene reaction. It is evident that m-xylene isomerization and disproportionation products typical of acidic catalysts appear when nitrogen is used as a carrier. This result indicates that the nickel-modification does not in principle change the reaction selectivity. The increase in the catalytic activity of the pure SAPO suggests that the introduction of nickel compounds during the hydrothermal synthesis of the SAPO-5 may effect the crystallization process, leading in this case to a catalyst with more expressed acidic properties. The selectivity remains... 

It was previously shown (15) that the selectivity for O-xylene hydrogenation (cis and trans dimethylcyclohexane) is sensitive to electronic density modification. In order to estimate electronic transfer on Pt catalysts induced by Au addition, Table 4 shows that it was not observed any change in selectivity for the 0-xylene reaction on Pt-Au catalysts. 

It has not been observed any change in selectivity for the o-xylene reaction on Pt-Au (Table 4), cis products an bimetallic catalysts are comparable to the monometallic catalysts. This result is in good agreement with the electronic affinities of Pt and Au which are comparable (2.1 eV and 2.3 eV respectively). Therefore, it is difficult to expect a ligand effect for the Pt-Au system. 

EXPLOSION and FIRE CONCERNS combustible with evolution of chlorine at 210°C (410°F) NFPA rating (not rated) may form explosive mixtures with xylene reaction with water or steam will produce poisonous and corrosive fumes incompatible with strong acids contact with easily oxidized materials (such as ammonia salts and sulfides), will result in fire and explosion heating to decomposition emits toxic fumes of chlorine and oxides of nitrogen use dry chemical, foam, carbon dioxide, or other extinguishing agent suitable for firefighting purposes. 

Table 4. m-Xylene reactions catalyzed by aluminophosphate-based molecular sieves... 

Figure 2.5 o-Xylene reaction rates over W0x/Zr02 with different tungsten loadings plotted as a function of (a) calcination temperature and (b) tungsten surface density (Taken from Barton, D.G., Soled, S.L., Meitzner, G.D., Puentes, G.A., and Iglesia, E., J. Catal. 1999,181, 57-72. With permission.)... 

In the case of p-xylene, reaction at low temperature forms the adduct at the unsubstituted 2,3 positions. A much smaller amount of the adduct corresponding to 1,2 attack is obtained. Note that in this case one of the carbons involved in attack is substituted. At higher temperature a dramatic reversal takes place in the ease of attack as reflected in the change in isomer ratio from 20 1 to 1 10 as is shown in Table 6.2. Bryce-Smith and Gilbert obtained these data on composition by isolation and fractional recrystallization. Therefore, it is not clear whether in the earlier studies the unreported isomer was not isolated or not identified i.e., was the yield higher than they reported earlier ... 

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