Coking selective hydrogenation

The data shown in Table II show interactions between matrix surface area and chemical composition at constant conversion. As expected, the increased matrix surface area of Matrix C caused increased coke and hydrogen yields compared to the lower surface area Matrix B, at constant silica content. However, the very low surface area of Matrix A does not compensate for the poorer selectivity due to its lower silica content relative to Matrices B and C. 

On non-zeolitic particles in the absence of a vanadium passivator, vanadium (when present at the 0.4 wt% level) makes a greater contribution to contaminant coke and hydrogen yields than nickel at constant surface area and metals loading. Incorporation of a vanadium passivator into the catalyst matrix can greatly alter the selectivity effects of vanadium, and can essentially negate its effect on non-zeolitic particles as in the case of magnesium. 

It is now suggested that in the absence of Mo 2 as a hydrogen activating phase the thermal coke formation is substantial. A very limited amount of Mo is already sufficient to dissociate hydrogen which leads to termination of radicals, thus preventing their condensation to coke. This explains the strong drop of the coke selectivity going from zero to 0,2% Mo,... 

Keywords Selective Hydrogenation of Acetylene, Coking, Pretreatment, Nickel Aluminate... 

Supported and coprecipitated nickel catalyst represent an interesting alternative, from the economical point of view, to other selective hydrogenation catalysts such as Pt or Pd, of higher performance but also with a higher price. In the present study, a coprecipitated NiO/NiAl 04 catalyst has been selected to cany out the selective hydrogenation of acetylene to ethylene as a test reaction. One important characteristic of this process is the large amount of coke which may be generated [l]. 

It follows that regeneration may consist of either (i) removal of IS sometimes poisons, most often inhibitors or fouling agents, e.g., coke (hydrogenation catalysts, e.g., selective hydrogenation of pyrolysis gasoline) or (ii) redispersion of the active species (platinum catalysts) or (iii) both (hydrodesulfurization or catalytic reforming catalysts). 

The term aging generally describes a loss in the activity—or selectivity—observed in a catalytic process after a certain period of reaction time. Aging may result from some change in the nature or number of catalyst sites, or in the accessibility of the sites to reactant molecules. Thus, such factors as formation of hydrogen-deficient organic residues ( coke ), selective adsorption of impurities from the charge ad-... 

Activity, Selectivity and Coking of Bimetallic Ni-Co-Spinel Catalysts in Selective Hydrogenation Reactions. 

On the other side, the addition of a second metal like Re, Ir or Sn, which increases the stability of Pt/Al203 catalyst, has been studied extensively in the literature. In summary, the effect of Sn is ascribed to i) a reduction of the number of Lewis sites [17] ii) an increase of selective hydrogenation of coke precursors (dienes) [18] Hi) a suppression of hydrogenolysis reactions [19]. Moreover, Sn can promote alkane oligomerization or even Diels-Alder type reactions [20]. 

The effects have been studied of the total or partial substitution of Ni by Cu or Co on the physicochemical properties and catalytic activity of Ni (Co,Cu)-Zn-Al catalysts used for the selective hydrogenation of acetylene. In addition, the influence of the hydrogen concentration in the feed on the activity, selectivity and coke formation on the catalysts has been investigated. The results obtained in this work could be explained by the formation, to different degrees, of bimetallic clusters of Ni-Cu and Ni-Co in the quaternary Ni-Co-Zn-Al and Ni-Cu-Zn-Al catalysts. The formation of these bimetallic clusters would be responsible for the diminution of methane and ethane, both undesirable products. 

This work deals with the study of the coke formation on H-mordenite during the benzene transalkylation with C9 aromatics, under several reaction conditions, in order to evaluate the condition which results in the lowest catalyst deactivation for industrial purposes. It was found that coke was produced in all samples but it was maintained around 4% (weight) without damage to activity and selectivity to toluene and xylenes. The coke was hydrogenated and could be easily removed. The soluble coke was mostly constituted by aliphatic hydrocarbons, while the insoluble coke was amorphous. These results were explained by the mordenite structure as well as by the presence of hydrogen. The best condition to perform the reaction depends much more on the selectivity to toluene and xylenes rather than on coke production. 

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