Hydrodesulfurization reaction network

Thiophene is the typical model compound, which has been extensively studied for typifying gasoline HDS. Although, some results are not completely understood, a reaction network has been proposed by Van Parijs and Froment, to explain their own results, which were obtained in a comprehensive set of conditions. In this network, thiophene is hydrodesulfurized to give a mixture of -butenes, followed by further hydrogenation to butane. On the considered reaction conditions, tetrahydrothiophene and butadiene were not observed [43], The consistency between the functional forms of the rate equations for the HDS of benzothiophene and thiophene, based on the dissociative adsorption of hydrogen, were identical [43,44], suggesting equivalent mechanisms. 

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. 

Houalla, M. and Gates, B.C. (1978) Hydrodesulfurization of dibenzothi-ophene catalyzed by sulfided CoO-Mo03/y-A1203 the reaction network. AICHE f, 24, 1015. 

Whitehurst, Isoda, and Mochida write about catalytic hydrodesulfurization of fossil fuels, one of the important applications of catalysis for environmental protection. They focus on the relatively unreactive substituted di-benzothiophenes, the most difficult to convert organosulfur compounds, which now must be removed if fuels are to meet the stringent emerging standards for sulfur content. On the basis of an in-depth examination of the reaction networks, kinetics, and mechanisms of hydrodesulfurization of these compounds, the authors draw conclusions that are important for catalyst and process design. 

Reaction network for the hydrodesulfurization of dibenzothiophene and for the hydrogenation of acenaphthene and biphenyl... 

However, in many industrial processes a large number of chemical reactions occurs simultaneously. In petroleum refining operations dealing with feeds containing hundreds of components (i.e. gas oil catalytic cracking, n htha catalytic reforming, middle distillate hydrodesulfurization), where the complete analysis is a problem, the number of reactions becomes formidable and the reaction network may also become very complicated, so that components of the feed can be lumped into a small number of groups. 

In recent years, kinetic studies have concentrated on the HDS of dibenzothio-phene (DBT) derivatives as these species are by orders of magnitude less reactive than sulfur species such as thioles, sulfides, and thiophene, or benzothiophene (Figure 5.1.22). The reaction network of hydrodesulfurization is illustrated in Scheme 6.8.2 for the example of HDS of DBT on CoMo. 

Scheme 6.8.2 Reaction network of hydrodesulfurization ofdibenzothiophene catalyzed by CoMo at 300°C and 102 bar (Farrauto and Bartholomew, 1997 Houalla et a/., 1978).

Piins, R. Catalytic HydrodenitrogenatioiL Advances in Catalysis, 2001,46, 399-464. Houalla, M. Nag, N. K. Sapre, A. V. Broderick, D. H. Gates, B. C. Hydrodesulfurization of Dibenzothiophene Catalyzed by Sulfided C0O-M0O3/Y-AI2O3 The Reaction Network. AIChEJ. 1978,24,1015. 

Vanrysselberghe, V., Froment, G. Hydrodesulfurization of Ddibenzothiophene on a C0M0/AL2O3 Catalyst Reaction Network and Kinetics. Ind. Eng. Chem. Res. 1996, 35, 3311. 

These are all independent, so R = N each one represents a linkage class, so N" = N and each one yields two complexes, so N = 2N, and 6 = 0. The deficiency tends to become very large in systems where most of the components have brute chemical formulas that are multiples of each other, which give rise to strongly interconnected networks (very many compatible complexes exist, even if complexes with more than two members are excluded) it stays at 0 or 1 in most systems of the hydrodesulfurization type, where parallel reactions with (almost) no interconnection take place. 

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