Kinetics thiophene hydrodesulfurization

Gray MR, Ayasse AR, Chan EW, Veljkovic M. Kinetics of hydrodesulfurization of thiophenic and sulfide sulfur in Athabasca bitumen. Energy Fuels 1995 9 500-506. 

Frye, C.G Mosby, J. F. Kinetics of Hydrodesulfurization. Chem. Eng. Prog. 1967,63,66. Kilanowski, D. R. Teeuwen, H. De Beer, V. H. J. Gates, B. C. Schuit, B. C. A. Kwart, H. Hydrodesulfurization of Thiophene, Benzothiophene, Dibenzothiophene, and Relafed Compounds Cafalyzed by Sulfided C0O-M0O3/Y-AI2O3 Low-Pressure Reactivity Studies. J. Catal., 1978,55, 129. 

Although desulfurization is a process, which has been in use in the oil industry for many years, renewed research has recently been started, aimed at improving the efficiency of the process. Envii onmental pressure and legislation to further reduce Sulfur levels in the various fuels has forced process development to place an increased emphasis on hydrodesulfurization (HDS). For a clear comprehension of the process kinetics involved in HDS, a detailed analyses of all the organosulfur compounds clarifying the desulfurization chemistry is a prerequisite. The reactivities of the Sulfur-containing structures present in middle distillates decrease sharply in the sequence thiols sulfides thiophenes benzothiophenes dibenzothio-phenes (32). However, in addition, within the various families the reactivities of the Substituted species are different. 

Here we illustrate how to use kinetic data to establish a power rate law, and how to derive rate constants, equilibrium constants of adsorption and even heats of adsorption when a kinetic model is available. We use the catalytic hydrodesulfurization of thiophene over a sulfidic nickel-promoted M0S2 catalyst as an example ... 

Kinetics over the Mo(lOO) Crystal Surface. We have studied the hydrodesulfurization of thiophene over the initially clean Mo(lOO) single crystal surface in the temperature range 520K - 690K and at reactant pressures of 100 Torr < P(H ) 800 Torr and 0.1 Torr P(Th) < 10 Torr. Under these conditions the reaction is catalyzed at a constant rate for a period of approximately one hour after which the rate begins to decrease with time. The rates reported here are all initial rates of reaction calculated from data collected in the period over which they remain constant. 

Allied with design and preparation, catalyst testing is the exploratory screening of candidate catalysts. This phase does not yield either kinetics or process variables but merely ranks performance. Bench reactors used should be as simple and rapid as possible, for many samples are usually tested. For ease in operation and interpretation, model compound reactions are helpful. Thus, for example, cumene dealkylation is a model for catalytic cracking, and thiophene hydrogenolysts for hydrodesulfurization. Care must be taken to ensure that the model system does indeed parallel process performance. 

A major advantage of the models of Rieckmann and Keil [44] and Wood et al. [16] was that, unlike earlier studies, any general reaction kinetics could be incorporated into the computer simulation. This means that reactions of industrial interest, which are typically represented by Langmuir-Hinshelwood kinetics, could be represented. Wood et al. [16] chose the hydrodesulfurization of thiophene as an example reaction, using the kinetic measurements of Van Parijs et al. [45] in their simulations. The kinetic model assumes that first thiophene is hydrogenated to butene, then butene is hydrogenated to butane ... 

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. 

Fundamental studies of hydrodesulfurization kinetics often use thiophene (C4H4S) to represent the type of sulfur bonding present in larger molecules. A simplified scheme for the reaction is illustrated in Figure 3.14 and corresponds to... 

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