Xylene hydrogenation

Figure 14 Cross-section of a DCA host channel sliced parallel to the direction of the channel (carbon, hydrogen and oxygen atoms are represented by gray, white and black, respectively) with arrays of o-xylene (hydrogen atoms are omitted for clarity, and carbon atoms are represented by open circles).

This is manufactured in three steps ammoxidation of p-xylene, hydrogenation of the resulting dinitrile to diamine, oxygenation of diamine. 

The H2-chemisorption data indicated fliat the average platinum particle size was not affected by the metal uptakeAoading and all three catalysts had a platinum particle size of ca. 1.5 nm in diameter. The catalyst exhibited high activities in o-xylene hydrogenation. Cis and trans 1, 2-dimethylcyclohexane were the only reaction products. The hydrogenation rate was found to increase by increased hydrogen partial pressure. Coirplete hydrogenation of o-xylene could be achieved at 460 K at H2 to o-xylene molar ratio of 12. 

Cis I, 2-DMCH hexane was found to be the kinetically favored product whereas the selectivity to the formation of thermodynamically preferred tram-isomer increased by increasing the operation temperature (Figure 4). The selectivity to the formation of trans-isomer also increases by the enhanced conversion levels. In Table 3 the activity of the fiber supported catalysts in xylene hydrogenation is compared to that of a (4.2)Pt Al203 catalyst having approximately the same mean platinum particle diameter. The (2.1)Pt/SF-1173 catalyst which has the lowest pore volume (Figure 2) is exhibiting similar activity to that of the Pt/alumina catalyst. 

Figure 1.33. Kinetics of o-xylene hydrogenation The apparent activation energy defined as...

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. 

Such change in selectivity could be explained by assuming that gold, by a ligand effect, could change the electronic properties of platinum. The selectivity of o-xylene hydrogenation reaction (cis and trans dimethylcyclohexane) has shown to be sensitive to electronic density modifications... 

Using the rate expressions for benzene and toluene, determine the remaining rate expressions for ethylene, xylene, hydrogen, and diphenyl in the BTX system. 

Ostrovskii and Bukhavtsova published several experimental and theoretical works on capillary condensation in catalytic reactions. Capillary condensation was found to accompany some gas-phase catalytic processes, in particular hydrotreating of jet fuel fractions [7]. The effects of gas-liquid interfacial surface, intra-particle diffusion, and of the ratio of gas to liquid reaction rates under conditions of capillary condensation were estimated [8]. The experimental study of /j-xylene hydrogenation on Pt/Si02 (as a model reaction) was carried out in order to demonstrate the influence of capillary condensation on reaction kinetics and process dynamics, and corresponding model was proposed [9]. Finally, the poisoning of the catalyst under capillary condensation was also considered [10]. 

The model reaction of p-xylene hydrogenation was chosen in order to provide the mild conditions of the experiments in both gas and capillary condensed phases, and to avoid the influence of side reaction and catalyst deactivation. The recycle type of gradientless reactor was used that provides uniform temperature and concentration profiles within all the catalyst packing. The catalyst particles (0.25-0.50 mm) provide a negligible intraparticle limitation of mass- and heat-transfer. 

Bukhavtsova and Ostrovskii [9] have studied the effect of capillary condensation on the reaction rate of p-xylene hydrogenation in transitions by variations of the feedstock flow and temperature. In order to avoid the intraparticle diffusion limitation, the crushed catalyst particles were used (0.25-0.5 mm). 

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