Hydrodesulfurization reaction selectivity

Table 4-2 Heats of Reaction for Selected Hydrodesulfurization Reactions... 

Figure 6.8.3 Equilibrium data of selected hydrotreating reactions (equilibrium constants of the three hydrodesulfurization reactions shown in Scheme 6.8.1).

The primary determinant of catalyst surface area is the support surface area, except in the case of certain catalysts where extremely fine dispersions of active material are obtained. As a rule, catalysts intended for catalytic conversions utilizing hydrogen, eg, hydrogenation, hydrodesulfurization, and hydrodenitrogenation, can utilize high surface area supports, whereas those intended for selective oxidation, eg, olefin epoxidation, require low surface area supports to avoid troublesome side reactions. 

The breadth of reactions catalyzed by cobalt compounds is large. Some types of reactions are hydrotreating petroleum (qv), hydrogenation, dehydrogenation, hydrodenitrification, hydrodesulfurization, selective oxidations, ammonoxidations, complete oxidations, hydroformylations, polymerizations, selective decompositions, ammonia (qv) synthesis, and fluorocarbon synthesis (see Fluorine compounds, organic). 

The foregoing reactions are highly exothermic and significantly raise reaction temperatures. The MRG process, however, docs not involve such adverse side reactions with use of a special, selective hydiodesulfuriziiig catalyst (developed by Japan Gasoline Co. and Nikki Chemical). The MRG process uses part of product gas for hydrodesulfunzation, and even if it contains only 20-25% hydrogen and as high as 20-23% carbon oxides, only the proper hydro desulfurization reactions take place, The MRG process features a recycle use of product gas for hydrodesulfurization purposes without any special treatment. 

The objective of the present work is to evaluate the effect of a wide range of process or reaction variables— reaction temperature, hydrogen partial pressure, catalyst loading, and reaction time—on hydrodesulfurization and hydrogenation of filtered liquid product (coal-derived liquid) obtained from the coal dissolution stage in the presence of a commercial presulfided Co-Mo-Al catalyst. The selectivity for desulfurization over hydrogenation (Se) is used to rate the effectiveness of the above mentioned process variables. Se is defined as the fraction of sulfur removal per unit (g) of hydrogen consumed, that is,... 

A new explanation for catalyst synergy between two solid phases of a catalyst has recently been advanced by Delmon (174) in studies of hydrodesulfurization (HDS) with mixtures of MoS2 and Co9S8. Both the activity and the selectivity of the HDS reaction increased if the contact between the admixed phases was improved. Spiltover hydrogen from the Co9S8 partially reduces the MoS2 modest reduction creates hydrogenation sites and further reduction creates HDS sites. 

The noble metal component may be either palladium or platinum the effect of the concentration of both metals on methylpentane as well as on dimethylbutane selectivity in C6 hydroisomerization on lanthanum and ammonium Y-zeolite with Si/Al of 2.5 has been studied by M.A. Lanewala et al. (5). They found an optimum of metal content for that reaction between 0.1 and 0.4 wt.-%. The noble metal has several functions (i) to increase the isomerization activity of the zeolite (ii) to support the saturation of the coke precursors and hence prevent deactivation, as was shown by H.W. Kouvenhoven et al. (6) for platinum on hydrogen mordenite (iii) to support the hydrodesulfurization activity of the catalysts in sulfur containing feedstocks. 

Investigations of functioning catalysts with Mossbauer spectroscopy have been performed for a wide range of samples and applications. The reactions include hydrodesulfuration 15), the Fischer-Tropsch reaction (20,180), selective oxidation or oxidative dehydrogenation (181-186), and acetonitrile synthesis (187). 

The activity and selectivity of 12.5% M0/AI2O3 nitrided at various temperatures for the hydrodesulfurization (HDS) of dibenzothiophene and the effect of re-treatment of NH3 on dibenzothiophene HDS were studied. The nitrided catalyst was significantly more active toward the scission of the C-S bond from dibenzothiophene with hydrogenation of dibenzothiophene. The sulfur species accumulated on the surface of the nitrided M0/AI2O3 catalysts by replacement of nitrogen species after reaction was analyzed by XPS measurement. The formation of molybdenum sulfide during the HDS dibenzothiophene led to a decrease in the activity of the nitrided catalyst, which approached that of the sulfided catalyst. 

Trickle-bed reactors are widely used in hydrotreating processes, i.e., hydrodesulfurization of gasoline and diesel fuel, in petroleum refining, chemical, petrochemical, and biochemical processes. The knowledge of hydrodynamic parameters is vital in the design of a TBR because the conversion of reactants, reaction yield, and selectivity depend not only on reaction kinetics, operating pressure, and temperature, but also on the hydrodynamics of the reactor. Special care is also required to prevent flow maldistribution, which can cause incomplete catalyst wetting in some parts... 

Sulfided Mo-Y and Ni-Mo-Y catalysts were tested in thiophene hydrodesulfurization and hydrogenation of pentene-1 and cyclopentene. Catalysts were prepared by thermal decomposition of supported Mo(CO)g encaged in Y and stabilized Y zeolites. Cracking ability in both reactions is related to the surface acidity of catalysts but is not parallel to their HDS activity. H S generates protonic acidity over NaY and KY zeolites. Synergetic effect between Ni and Mo sulfided species in HDS reaction was observed. The presence of extra-lattice aluminum in stabilized forms of Y-zeolites favours selectivity towards formation of isopentane and cyclopentane during hydrogenation. 

Platinum (metal)- and acid (oxide)-catalyzed processes were developed to convert petroleum to high-octane fuels. Hydrodesulfurization catalysis removed sulfur from the crude to prevent catalyst deactivation. The discovery of microporous crystalline alumina silicates (zeolites) provided more selective and active catalysts for many reactions, including cracking, hydrocracking, alkylation, isomerization, and oligomerization. Catalysts that polymerize ethylene, propylene, and other molecules were discovered. A new generation of bimetallic catalysts that were dispersed on high-surface-area (100-400 m /g) oxides was synthesized. 

Selective hydrogenation is of importance industrially. It is used in the manufacture and in the purification of ethylene, in removing substituted acetylenes from butadiene, in lowering the olefin content of cracked naphthas while leaving the aromatics unchanged, and in various other petroleum-processing reactions such as hydrodesulfurization. 

The majorify of sulfur compounds (thioles and sulfides) have been successfully removed from liquid fuel using a hydrodesulfurization process where high temperature and high pressure are required [7-9, 159]. As mentioned in section 2.5 some sulfur species are very resistant to hydrodesulfurization and those include thiophenic compounds, especially dibenzothiophene and 4,6 dimethyldibenzothiophene [148]. Various methods based on extraction and adsorption have been proposed to remove these compounds [7, 8, 13,145, 147-149, 151-158]. In the extraction route, sulfiir species are first oxidized and then extracted using organic solvents as, for instance acetonitrille [13, 149]. On the other hand, an adsorption process is usually tailored to enhance either adsorption forces, selectivity, or to impose a chemical reaction. So fer the enhancement in the removal of thiophenic compounds was reported on materials where n-complexation can occur as on Cu-Y zeolites [151, 153], or on alumina with highly dispersed sodium [147]. In the latter case, mono- and disodium thiophene metallates are formed. Another desulfurization methods use formation and subsequent precipitation of S-alkylsulfonium salts [148]. 

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