Naphthene, dehydrogenation

Except for naphthene dehydrogenation, which only requires a Pt site for catalysis, all the other major reactions require an interaction between sites. Ring and paraffin isomerization require the platinum function for dehydrogenation to olefin, the acid function for carbon skeletal rearrangement, and the metal function again for hydrogenation of the olefin. 

A typical reformer temperature profile for an inlet temperature of 783 K is shown in Fig. 5 for a three-reactor design. Only 15-20% of the total catalyst is used in the first reactor because of the rapid temperature decrease which results from naphthene dehydrogenation (Fig. 6). Note there is a 70 K temperature drop in this reactor. The activation energies are such that reaction rates are very low at the bottom of the first reactor. Thus, more catalyst in the first reactor would not provide additional conversion. 

In order to minimize the temperature drop at the reactor inlet caused by the rapid, endothermic naphthene dehydrogenation, the catalyst bed was diluted by a low-surface, chloride-free alumina. The degree of dilution was varied in three different zones of the reactor, with the highest dilution at the reactor inlet. The first zone, comprising 33% of the reactor volume, contained only 6% of the total amount of catalyst. The temperature drop at the reactor inlet, measured with the axial thermocouple, did not exceed 5°C. 

Aromatics are produced by naphthene dehydrogenation and olefin cyclization... 

The paraffins dehydrogenation occurs by a mechanism similar to the one of naphthenes dehydrogenation ... 

Naphthene Dehydrogenation > Paraffin Dehydrogenation > Naphthene Isomerization... 

The chemistry of catalytic reforming includes the reactions listed in Table 18. All are desirable except hydrocracking, which converts valuable Cs-plus molecules into light gases. The conversion of naphthenes to aromatics and the isomerization of normal paraffins provide a huge boost in octane. H2 is produced by dehydrocyclization of paraffins and naphthene dehydrogenation, which are shown in Figure 15. 

We can also view the reactor temperature and flow profile by selecting the Reactors section in the Results Tab, as shown in Figure 5.66. Again, we note that the predicted temperature drop for each reactor bed compares well with the measured temperature drop. Most of the temperature change is due to the naphthene dehydrogenation reactions. Since we made reasonable predictions of the aromatic content, we expect the reactor temperatures to agree as well. 

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