Octane number reforming

Naphthas with different initial and final boiling points were compared by pilot reactor testing. The pilot reactor unit consisted of isothermal, once-through reactors with on-line GCs for full product analysis and octane number determination. Octane numbers, reformate yields and composition as well as gas yields were measured as a function of reaction temperature at 16 bar reaction pressure and a molar Hj/HC ratio of 4.3. Catalyst deactivation was studied over two weeks periods at high severity conditions, i.e. 102.4 RON and a Hj/HC ratio of 2.2. Test results, with emphasis on the yields of benzene and other aromatics, reformate and hydrogen yields as well as catalyst deactivation, are presented. 

By varying both initial and final boiling points of the feedstock, octane numbers, reformate yields and composition as well as gas yields were measured in a once-through, isothermal pilot reactor. The effect of the feedstock boiling point properties on catalyst deactivation was also studied. 

In Figure 5.4, the temperature required to produce 100 research clear octane number reformate is shown as a function of time on stream in the reforming of a 99-17VC boiling range naphtha containing approximately 43, 45, and 12% by volume, respectively, of cycloalkanes, alkanes, and aromatic... 

The studies of n-heptane and methylcyclopentane conversion provide insight into the advantages of platinum-iridium and platinum-rhenium catalysts over catalysts containing only one of the transition metal components, that is, platinum, iridium, or rhenium. If, for example, we consider an iridium-alumina catalyst for the reforming of a petroleum naphtha fraction, we find that it produces a substantially higher octane number reformate than a platinum on alumina catalyst under normal reforming conditions. The iridium-alumina catalyst will also exhibit a lower rate of formation of carbonaceous residues on the surface, with the result that the maintenance of activity with time will be much superior to that of a platinum-alumina catalyst. 

Figure 5.5 Comparison of activities of alumina-supported platinum-iridium and platinum-rhenium catalysts for the reforming of a 70-190°C boiling range Persian Gulf naphtha at 490°C and 28.2 atm to produce 98 research octane number reformate (33). (Reprinted with permission from Elsevier Scientific Publishing Company.)...

In Figures 5.7 and 5.8, data are presented for the reforming of a 65-150°C boiling range Persian Gulf naphtha at a temperature of 488°C to produce 96 research octane number reformate (33). The pressure was 28.2 atm, except for a period at 35.0 atm in the approximate time interval from hour 1460 to hour 1710 in each run. The naphtha had a density of 0.7243 g/cm3 and contained, on a liquid volume percentage basis, 70.2% alkanes, 21.1% cycloalkanes, and 8.6% aromatic hydrocarbons. 

Reforming at 28.2 atm and 490°C to produce 98 research octane number reformate. The yields are averages for 1600 hours on stream. 

The preceding information indicates the paths to follow in order to obtain stocks of high octane number by refining. The orientation must be towards streams rich in aromatics (reformate) and in isoparaffins (isomerization, alkylation). The olefins present essentially in cracked gasolines can be used only with moderation, considering their low MONs, even if their RONs are attractive. 

A key process in the production of gasoline, catalytic reforming is used to increase the octane number of light crude fractions having high paraffin and naphthene contents (C7-C8-C9) by converting them to aromatics. 

As a complementary process to reforming, isomerization converts normal paraffins to iso-paraffins, either to prepare streams for other conversions nCi —> /C4 destined for alkylation or to increase the motor and research octane numbers of iight components in the gasoiine pooi, i.e., the C5 or Cs-Ce fractions from primary distillation of the crude, or light gasoline from conversion processes, having low octane numbers. 

We cite isomerization of Cs-Ce paraffinic cuts, aliphatic alkylation making isoparaffinic gasoline from C3-C5 olefins and isobutane, and etherification of C4-C5 olefins with the C1-C2 alcohols. This type of refinery can need more hydrogen than is available from naphtha reforming. Flexibility is greatly improved over the simple conventional refinery. Nonetheless some products are not eliminated, for example, the heavy fuel of marginal quality, and the conversion product qualities may not be adequate, even after severe treatment, to meet certain specifications such as the gasoline octane number, diesel cetane number, and allowable levels of certain components. 

Benzene, toluene, and xylene are made mosdy from catalytic reforming of naphthas with units similar to those already discussed. As a gross mixture, these aromatics are the backbone of gasoline blending for high octane numbers. However, there are many chemicals derived from these same aromatics thus many aromatic petrochemicals have their beginning by selective extraction from naphtha or gas—oil reformate. Benzene and cyclohexane are responsible for products such as nylon and polyester fibers, polystyrene, epoxy resins (qv), phenolic resins (qv), and polyurethanes (see Fibers Styrene plastics Urethane POLYiffiRs). 

The octane number R + M jT) of such reformates is typically in the range of 88.9—94.5, depending on severity of the reforming operation. Toluene itself has a blending octane number of 103—106, which, as shown in Table 19, is exceeded only by oxygenated compounds such as methyl tert-huty ether, ethanol, and methanol. 

Increasing the octane number of a low-octane naphtha fraction is achieved by changing the molecular structure of the low octane number components. Many reactions are responsible for this change, such as the dehydrogenation of naphthenes and the dehydrocyclization of paraffins to aromatics. Catalytic reforming is considered the key process for obtaining benzene, toluene, and xylenes (BTX). These aromatics are important intermediates for the production of many chemicals. 

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