Catalyst sulfidic

The cracking of diphenylmethane (DPM) was carried out in a continuous-flow tubular reactor. The liquid feed contained 29.5 wt.% of DPM (Fluka, >99%), 70% of n-dodecane (Aldrich, >99% solvent) and 0.5% of benzothiophene (Aldrich, 95% source of H2S, to keep the catalyst sulfided during the reaction). The temperature was 673 K and the total pressure 50 bar. The liquid feed flow rate was 16.5 ml.h and the H2 flow rate 24 l.h (STP). The catalytic bed consisted of 1.0 g of catalyst diluted with enough carborundum (Prolabo, 0.34 mm) to reach a final volume of 4 cm. The effluent of the reactor was condensed at high pressure. Liquid samples were taken at regular intervals and analyzed by gas chromatography, using an Intersmat IGC 120 FL, equipped with a flame ionization detector and a capillary column (Alltech CP-Sil-SCB). 

Although the hydrogenation activity of metal sulfides is lower by several orders of magnitude than that of metal catalysts, sulfides allow operations under conditions that are impractical for metals. They are generally used as highly dispersed materials on a high surface area support, such as y-alumina, in fixed bed operation. Most important is catalyst design to minimize deactivation due to the deposition of metals (V, Ni) in the feed and of coke at the mouths of the pores. Metal sulfides can also be used as finely dispersed phases in continuous slurry reactors to reduce the mass transport limitations of heavy oils. 

Catalyst selectivity is somewhat meaningless unless the term is defined. There also are selective catalysts that do not meet the technical or practical definition of hydrogen selectivity. Such catalysts are sulfur-poisoned catalyst. Sulfided nickel catalyst produces high trans-isomers, has lower activity than conventional nickel, exhibits longer reaction times, and is used for specialty applications (e.g., coating fats and hard butters). 

Three different long duration vanadium deposition experiments, I, II and III, have been carried out. Experiment I was a test under reference conditions. Experiment II was carried out to determine the influence of quinoline on the vanadium deposition process. Experiment III was carried out to determine the effect of a low HjS partial pressure on the vanadium deposition profiles. Each experiment was split into two parts A and B. Experiment A is the first part of the vanadium deposition experiment. At the end of experiment A, the reactor was removed fi om the microflow equipment and catalyst pellets fi om every tray were collected and analysed. After this short stop, the reactor was mounted again in the microflow equipment, the catalyst sulfided and the experiment B started. Details on the reaction conditions of the three experiments are summarized in Table 2. 

Mo " ". Cobalt became also essentially sulfided and S is characteristic of a sulfide S -. We may conclude that the presulfided catalyst after the activation results in giving similar active metal forms to those in the catalyst sulfided by a mixture of H2S and H2. 

Molybdenum trioxide supported on alumina is the precursor of molybdenum disulfide based hydrodesulflirisation catalysts. Sulfiding of supported M0O3 is facilitated by bound water. INS spectroscopy was used to determine the nature of the water in hydrated M0O3/AI2O3 [92, 93]. The librational modes of co-ordinated water (Fig. 7.22) are observed in INS spectra when the water molecule is bound through the oxygen atom ( 9.2). 

Catalytic measurements. The high pressure reactor for benzene hydrogenation has been previously described (8). The reaction was conducted at 598 K under 4 0 bars total pressure. The benzene feed contained 1.5 % by weight of dimethyldisulfide (DMDS) which was fully decomposed on the catalyst, so that the H2S/H2 and benzene/H2 molar ratios during reaction amounted to 10-4 and 4xl0-3 respectively. The catalyst mass was 0.4 g and the liquid feed rate 1.6 jtl mn . Catalyst sulfidation was performed in the reactor itself but at atmospheric pressure, using a H2-H2S feed. Details of the complete procedure are following ... 

The catalytic activities for the functionalities viz. HDS and HYD were evaluated at 400 C on catalysts sulfided at 400 C using CS2/H2 mixture. The catalytic activity for thiophene hydrodesulfurization and cyclohexene hydrogenation are presented in Fig. 4. as a function of... 

As might be expected, ease of desulfurization depends on the type of carbon-sulfur bonds involved. Alkyl sulfides and polysulfides possess weak carbon-sulfur bonds and react rapidly and completely under hydroprocessing conditions, as their uses in catalyst sulfiding agents testify. Sulfur incorporated in thiophene systems have both stronger C(sp2)-S bonds than alkyl C(sp3)-S bonds and the sulfur as well is in the aromatic five-membered thiophene ring system. Table 8.12... 

If initial catalyst sulfiding is to be done with sulfur dioxide-containing SRU tail gas, the reactor effluent must be isolated, bypassing the quench system. 

Regarding catalyst sulfidation, the pseudo steady-state activities (1) after a lineout period (dopping the feed with 500 ppm sulfur during some time) or (2) sulfiding before the reaction, were found to depend on the hydrocarbon feed used. The different behavior is explained in terms of the range of turnover numbers, the relative strength as an adsorbing species, and ensemble size require-... 

Experimental data indicated that the isotope exchange process is described by first order equations, and in most cases, e.g., on supported C0M0/AI2O3 catalysts by a superposition of two curves representing two types of sulfur mobility, the more and the less mobile i.e., rapidly and slowly exchangeable sulfur. In general, the H2S molar radioactivity a (in percent of the initial molar radioactivity of catalyst sulfide sulfur), as a function of the produced H2S-[X(cm )], is given (Fig. 7) as a superposition of curves... 

It is of interest to compare the Smob/Scat data with Sexc/Scat obtained in studies on the S-exchange of catalyst sulfide with H2S.I 1 The degree of MoOx sulfidation was 63% if sulfided with thiophene, [ 1 that by the H2S-sulfided sample — 48%.t l The fraction of exchangeable sulfur in the... 

---