Catalysts for HDS

Involvement of Ni resulted in great enhancement of HDS activity MoNi/NaY proved to be a highly active and selective catalyst for HDS of benzothiophene to ethylbenzene, and other products were scarcely observed. No change in the activity was observed during 4 hours. 

The presence of V3S4 crystals can only be attributed either to an autocatalytic mechanism of this type or the migration of the deposited metals. It is known that deposited Ni and V sulfides possess some catalytic activity (see Section IV). Slurry processes have been proposed which utilize Ni and V deposited from the oil onto a slurry material (Bearden and Aldridge, 1981). Studies have appeared in the literature demonstrating that nearly all of the transition metals are catalytically active for HDS reactions and presumably for HDM (Harris and Chianelli, 1984). Rankel and Rollmann (1983) impregnated an alumina catalyst base with Ni and V and concluded that these sulfides display an order of magnitude lower activity than the standard Co-Mo sulfide catalyst for HDS reactions, but exhibited similar activity for HDM reactions. 

If one considers that the Monolith catalyst was intrinsically more active than the Nalcomo 474 catalyst then the observed superiority of the Monolith catalyst should be essentially the same, or at least be comparable, when tested on two different feeds. But as explained earlier the observed surface activities of the two catalysts for HDS are almost equal in the case of Raw Anthracene Oil, while, on Synthoil liquid the observed surface activity of the Monolith is about four times that of the Nalcomo 474 catalyst. Therefore, there is some basis to... 

Kushiyama et al (129) reported that phosphorus also promotes the activity of highly divided unsupported molybdenum and cobalt-molybdenum sulfide catalysts for HDS (and HDM) of crude oil, with a maximum at a P/(Co + Mo) atomic ratio of 2. This result warrants attention because it shows that phosphorus may directly modify the active sulfide phase(s) even in the absence of the alumina support. 

In 1992, novel mesoporous molecular sieve MCM-41 was invented by Mobil researchers.90 91 The novel mesoporous molecular sieve of MCM-41 type has also been examined as support for Co-Mo/MCM-41 catalyst for HDS. Al-MCM-41 has been synthesized with improved aluminum incorporation into framework92 94 and applied to prepare Co Mo/MCM-41 for deep HDS of diesel fuels95-97 and for HDS of petroleum resid.94... 

Haldor Topsoe has commercialized more active catalysts for HDS. Its TK-554 catalyst is analogous to AkzoNobel s KF 756 catalyst, while its newer, more active catalyst is termed TK-574. For example, in pilot-plant studies, under conditions... 

The promotional ratio is defined here as the ratio of the activity of the Co-Mo composite catalyst to that of the host Mo sulfide catalyst. The promotional ratio is plotted in Fig. 8 against N(Mo-Mo) of the host Mo sulfides. It is evident that the promotional ratio increases as the dispersion of the Mo sulfide increases. It is demonstrated that highly dispersed Mo sulfides lead to the formation of highly dispersed and highly active Co-Mo sulfide catalysts for HDS. 

Figure 8. Promotional ratio of the Co-Mo/AI2O3 catalyst for HDS as a function of N(Mo-Mo) of the host Mo sulfide species.

With respect to the metal recovery for reuse, the study of Lee et al deserves attention. These authors used the oil-soluble compounds of Mo, W, Ni and Co as the precursors for dispersed metal-sulfide catalysts. For single metals, the best performance was observed for the Mo catalyst. The combination of Co -1- Mo gave the most active catalyst for HDS, whereas Ni + Mo was best for HCR. In this study, the fixed bed of extmdates made either of the microporous AC or of y-Al203 was placed downstream of the reaction zone with the aim to remove metals from the product streams. For the former, the overall conversion increased with time on stream. This was attributed to the accumulation of metals on AC. Thus, the metal-deposited AC exhibited catalytic activity. It was noted that the efficiency of the metal removal using the AC extrudates was rather high. It is believed that there are a number of methods that are suitable for the recovery of metals that were trapped by the AC. For example, combustion of the AC will leave behind ash with a high concentration of metals. In this study, an AR containing 26 ppm of V + Ni was used as the feed. 

TMS catalyst, used in refineries, are mixed sulfides of cobalt-molybdenum (CoMo) or nickel-molybdenum (NiMo) with a promoter atomic ratio Co(Ni)/[Co(Ni) -I- Mo(W)] between 0.2 and 0.4 (2), supported on high surface area materials such as alumina to increase dispersion of the active component of the catalyst. Although CoMo sulfide is the favorite catalyst for HDS reactions, the use of NiMo sulfide is preferred in HDN reactions and hydrogenation processes, to treat feedstock with a high concentration of unsaturated compounds. 

The set of kinetic experiments was conducted in a bench-scale HDT unit. The plant consisted of two FBRs in series (-500 cm of catalyst in each reactor) which were loaded with a triple layer of catalyst extrudates a front-end HDM catalyst, a mid-end catalyst with balanced HDM/HDS activity, and a tail-end highly active catalyst for HDS and HCR. Catalysts were activated in situ by sulfiding with spiked straight-run gas oil (1.46 wt% sulfur, also containing 1.0 wt% dimethyl disulfide). The feedstock was an AR (343°C-i-) from a Mexican heavy crude oil (13°API). 

The recent search for sorbents for liquid fuel desulfurization has taken two paths, both based on trial-and-error. One approach has been simply testing the commercial sorbents. The other approach has an origin in HDS catalysis. This approach is aimed at sorbents that are good catalysts for HDS, with the hope that such sorbents would form a bond with the sulfur atom of the thiophenic compounds. Forming such a bond may require above-ambient temperatures. The commercialized process discussed above, S Zorb, is based on an interesting hybrid of catalyst and sorbent. The use of r-complexation is an entirely different approach and will be discussed separately. 

Substantial progress has been made in fundamental understanding and practical applications of hydrotreating catalysis and metal sulfide-based catalysts for HDS, as discussed in several excellent reviews" . The following discussion focuses on deep desulfurization of polycyclic sulfur compounds as shown in Scheme 1. 

Researchers at Haldor Topsoe and their collaborators in academic institutions have contributed significantly to both the advances in research on fundamental aspects of catalytically active sites of transition metal sulfides and the development of new and more active commercial hydrotreating catalysts and processes . Haldor Topsoe has commercialized more active catalysts for HDS. Its TK-554 catalyst is analogous to Akzo Nobel s KF 756 catalyst, while its newer, more active catalyst is termed TK-574. For example, in pilot plant studies, under conditions where TK-554 produces 400 ppmw sulfur in SRGO, I K 574 will produce 280 ppmw. Under more severe conditions, TK-554 will produce 60 ppmw, while TK 574 will produce 30 ppmw, and similar benefits are found with a mixture of straight run and... 

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