Aromatic reaction network

The general reaction occurring in hydrodesulfurization has been described in Section 2.1.1. The most studied model compound is DBT. The reactivity towards hydrogenation of the phenyl substituents already mentioned (Section 2.1.1) is also observed in the hydroprocessing of sulfur compounds. The reactivity towards hydrogenolysis of the C-S bond masks the effects associated to aromatics hydrogenation. The DBT reaction network is sketched in Fig. 8 the pseudo-first-order reaction constants measured by Houalla [68] have been included. 

Girgis, M. J., and Gates, B. C., Catalytic Hydroprocessing of Simulated Heavy Coal Liquids. 2. Reaction Networks of Aromatic Hydrocarbons and Sulfur and Oxygen Heterocyclic Compounds. Ind. Eng. Chem. Res, 1994. 33 pp. 2301-2313. 

The reaction network proposed by Ouchiyama et al. for carbazole [316] considers an early oxidation product of degradation to be 2 -aminobiphenyl-2,3-diol. This compound is believed to result from dioxygenase attack at the 1 and 9a positions, resulting in the formation of l,9a-dihydroxy-l-hydrocarbazole. The reaction might be reversed by spontaneous cleavage of the adjacent C—N bond to restore aromaticity and yield back the 2 / -aminobiphenyl-2,3-diol. 

Fig. 9. Reforming lump reaction network. N, cyclopentane and cyclohexane naphthenes P, C6. paraffins A, aromatics C5-, pentane and lighter.

Prins summarizes advances in understanding of the reactions in catalytic hydrodenitrogenation (HDN), which is important in hydroprocessing of fossil fuels. Hydroprocessing is the largest application in industrial catalysis based on the amount of material processed. The chapter addresses the structures of the oxide precursors and the active sulfided forms of catalysts such as Ni-promoted Mo or W on alumina as well as the catalytically active sites. Reaction networks, kinetics, and mechanisms (particularly of C-N bond rupture) in HDN of aliphatic, aromatic, and polycyclic compounds are considered, with an evaluation of the effects of competitive adsorption in mixtures. Phosphate and fluorine promotion enhance the HDN activity of catalysts explanations for the effect of phosphate are summarized, but the function of fluorine remains to be understood. An account of HDN on various metal sulfides and on metals, metal carbides, and metal nitrides concludes this chapter. 

In conclusion to the short analysis on curing chemistry of epoxy-aromatic amine networks (for more detailed analysis see papers of K. Dusek and B. Rozenberg in this volume), one can say that the chemical structure of the polymers under consideration is mainly determined by the curing reaction in Eq. (I). Equation II becomes important only for polymers with an excess of epoxy groups at T 150 °C. This rather simple situation makes the analyzed polymers very suitable for basic investigations. 

In this section, we shall consider only T of epoxy-aromatic amine networks as well as the influence of side reactions on T . The magnitude of Tgxp will be analyzed in Sect. 6. 

A complefe identification and quantification of aromatics and carboxylic acids, during the oxidation of phenol for both unpromoted PC reaction (no iron present) and PC reaction coupled with Fe ions, will allow the formulation of a comprehensive reaction network for both systems and thus, a systematic comparison between them. Also, this will permit the development of a more defailed kinefic model fo incorporate most of the oxidation intermediates for bofh sysfems and will definitely help determine the role of Fe ions in PC reacfions. 

A similar diagram was presented in a previous study for the impromoted PC oxidation of phenol (Salaices et al., 2004). The reaction scheme introduced in this chapter incorporates all carboxylic acids detected in the oxidations of the various aromatic species, as well as the existing relationships among the intermediate species. A very important fact is that this newly developed reaction network describes the Fe-assisted PC oxidation of phenol as well as the unpromoted PC reaction. One important difference between the reaction scheme for the impromoted PC reaction and that of the Fe-assisted PC reaction is the step relating the formation of 1,2,4-THB from... 

Kinetic model i (KM i) aromatics only The first proposed model considers that those aromatic intermediates produced in small amoimts can be neglected and that all remaining aromatics are converted directly into CO2 and water (e.g., formation of carboxylic acids is neglected). A schematic representation of this reaction network is given in Figure 12. 

However, other results indicate that the P/Al catalyst has very low activity for C —N or C —C bond breaking 74, 81). A detailed kinetics study by Jian and Prins 81) showed that phosphorus addition decreases the C—N bond cleavage (rate constants k[ and k) in the reaction networks Figs. 33a and 33b) and the subsequent alkene hydrogenation (rate constant k() reactions in piperidine and DHQ HDN (see Table XIV). On the other hand, the presence of phosphorus increases aromatic ring hydrogenation of OPA... 

These results suggest that the influence on the hydrogenation reactions of the addition of phosphorus to catalysts should depend strongly on the molecules being converted, on the nature of the active sites, and on the reaction conditions (as noted for HDN). However, addition of phosphorus seems predominantly to increase aromatic hydrogenation, as has been shown for the HDN reaction networks. The effect of hydrogen partial pressure is inferred to be relatively important for hydrogenation reactions... 

The reaction network may be explained within the concept of the electrophylic substitution in the aromatic ring and the formation of a chemisorbed atomic oxygen species stabilized on strong Lewis acid sites, as it has been proposed in our previous papers [7, 10] ... 

Source A. V. Sapre and B. C. Gates, Hydrogenation of Aromatic Hydrocarbons Catalyzed by Sulfided C0O-M0O3 y-Al203. Reactivities and Reaction Networks, Industrial and Engineering Chemistry Process Design and Development 20 68-73 (1981). With permission. 

We have indicated only the core aromatic species in the scheme above because these reactions are all pseudo-first-order in these species and pseudo-zero-order in all other species when the reactions are carried out in concentrated sulfuric acid. This reaction network can also be written in symbolic form as... 

Besides the three basic forms presented previously, the literature offers a long list of rate expressions, which are basically combinations and variations of Equations 13.1-13.3. Depending on the available information about the reaction pathway, simplified reaction networks have been proposed to represent, for instance, reversible hydrogenation of aromatic rings, sequential... 

The cracking simulation model developed by the Laboratorium voor Petrochemische Techniek contains 1680 reaction networks for some 550 hydrocarbons. The components involved in the model are normal and iso-paraffins and olefins up to C25, 5- and 6-ring naphthenes up to C20 and aromatics up to C20. The computation of the reaction networks for the heavy components requires many hours. 

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