Presulfiding treatments

Very fine particles of iron sulfide is one class of very promising catalysts because of lower cost and moderate activity. Presulfiding treatments for activation, ion exchange, and dispersed impregnation of catalysts or catalyst precursors are combined to enhance the catalytic activity and reduce the amount of catalyst required (69, 70). 

Furthermore, the effect of presulfiding with 5%H2S-H2 mixture on the catalytic activity of Rh/USY was examined. It was revealed that the catalytic activity of Rh/USY was enhanced by the presulfiding treatment as shown in Figure 2. This indicates that Rh/USY catalyst is not poisoned by sulfur compounds and this catalyst has high sulfur-tolerant ability in the hydrodesulfiirization of thiophene. 

The way sulfur treatment is applied gives rise to pronounced differences in selectivities21. A decrease in the overall alkene yield was observed when 1,3-butadiene was hydrogenated on presulfided Pd. In contrast, much improvement in selective alkene formation from isoprene was achieved when sulfur was present in the feed. In the latter case adsorption competition was suggested to account for the favorable effect of sulfur. 

In applications of this type, the sulfur content of the feedstock may vary from 100 ppm to 1% and the necessary degree of desulfurization to be effected by the treatment may vary from as little as 50% to more than 99%. If the sulfur content of the feedstock is particularly low, it will be necessary to presulfide the catalyst. For example, if the feedstock only has 100 to 200 ppm sulfur, several days may be required to sulfide the catalyst as an integral part of the desulfurization process even with complete reaction of all of the feedstock sulfur to, say,... 

The rapid-injection reactor is particularly suitable for applications involving catalysts that require specific pretreatment procedures. For example, in applications with catalysts requiring presulfiding, the catalyst treatment can be undertaken in the injection tube. Upon completion of pretreatment, the injection tube can be attached to the reactor and the contents added to the reactor when desired. 

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