Kinetic models / networks reforming

Mechanistic and experimental studies generally result in the creation of a kinetic network that quantitatively describes the path a particular reactant takes. Given the complexity of the reforming reactions and the number of species involved, many researchers have taken a lumped approach towards describing the kinetics. In a lumped approach, many different molecules are placed into a single group or lump. The reaction kinetics then assumes that all species in a lump behave identically. Recently, some researchers have presented models that involve hundreds of reaction species and thousands of reactions [16,18], However, there is little published information about these complex kinetic models validated against industrial operation. 

After choosing a representative kinetic model, we must decide how to represent the remaining units for a truly integrated model. Researchers have applied many of the kinetic networks described in the previous section in integrated process models. Figure 5.8 is an overview the key features of an integrated process model for a three-section reformer. This overview applies to both semi-regenerative fixed bed and CCR reformers. 

The reaction network in the reactor model is similar to the network presented by Froment etal. [12] and Taskar [4], However, the reaction network supports higher aromatics up to C14. While these typically are not expected in reformer feeds, the kinetic model can handle them as well. In addition, the reactor model includes paths for the undesired hydrogenolysis reactions. These highly exothermic reactions do not occur in any significant degree in stable reforming units. However, older reactors may display this behavior so it is important to model them as well. 

Start-of-cycle kinetic lumps in KINPTR are summarized in Table V. A C5-light gas lump is required for mass balance. Thirteen hydrocarbon lumps are defined. The reforming kinetic behavior can be modeled without splitting the lumps into their individual isomers (e.g., isohexane and n-hexane). Also, the component distribution within the C5- lump can be described by simple correlations, as discussed later. The start-of-cycle reaction network that defines the interconversions between the 13 kinetic lumps is shown in Fig. 9. This reaction network results from kinetic studies on pure components and narrow boiling fractions of naphthas. It includes the basic reforming reactions... 

A detailed study of many of the reactions is out of the scope of this work. We refer readers to Fromentet al. [10,11,12] for detailed experimental and mechanistic studies. These studies are very useful in the course of detailed catalyst design and kinetic network generation [15,16,17,18], However, neither of these topics is the subject of the current work. We present these reactions in the context of an integrated process model. As mentioned earlier in this work, the typical reactions in the reforming process are dehydrogenation, dehydrocyclization, isomerization and hydrocracking. Table 5.2 shows examples of these reaction classes. 

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