Catalysts desulfurization catalyst

The conversion of CO to CO2 can be conducted in two different ways. In the first, gases leaving the gas scmbber are heated to 260°C and passed over a cobalt—molybdenum catalyst. These catalysts typically contain 3—4% cobalt(II) oxide [1307-96-6] CoO 13—15% molybdenum oxide [1313-27-5] MoO and 76—80% alumina, JSifDy and are offered as 3-mm extmsions, SV about 1000 h . On these catalysts any COS and CS2 are converted to H2S. Operating temperatures are 260—450°C. The gases leaving this shift converter are then scmbbed with a solvent as in the desulfurization step. After the first removal of the acid gases, a second shift step reduces the CO content in the gas to 0.25—0.4%, on a dry gas basis. The catalyst for this step is usually Cu—Zn, which may be protected by a layer of ZnO. 

The effectiveness of a naphtha desulfurization catalyst is tested by reducing thiophene with hydrogen at 660 K and 30 atm. Particle diameter is... 

Spectra of a spent bauxite-based desulfurization catalyst pellet ( 7 x 13 mm, examined in air) are shown in Fig. 9. The outside of the pellet was black and the single-beam spectrum S showed some of the continuum absorption found with chars. The compensated spectrum S/So, however, showed appreciable spectral structure. The broad band near 750 cm is probably due to the bauxite, and the absorptions near 3000, 1320 and 1000 cm-- - to a mixture of hydrocarbons and thio species formed during the reaction. The feature near 1640 cm l is probably caused by an olefinnic species. 

Fig. 14.19 Recovery of nickel, vanadium, and molybdenum from spent desulfurizing catalyst. Copyright 2004 by Taylor Francis Group, LLC... 

Use a gasoline desulfurization catalyst system to minimize gasoline sulfur contents... 

Another novel catalyst modification has been suggested in which the active Co-Mo-S catalyst is used in combination with an acidic catalyst such as a zeolite. This combination has the potential of opening another reaction pathway by isomerization of the alkyl groups on molecules such as 4,6-DMDBT to positions that do not sterically interfere with adsorption or oxidative addition. This is illustrated in Fig. 33. Gates and co-workers reported many years ago that the 2,8- and 3,7-dimethyldibenzothiophenes are much more easily desulfurized than 4,6-DMDBT (see Table XII) (26). Therefore, a combination of an isomerization catalyst and a desulfurization catalyst could be synergistic for removing dialkylbenzothiophenes. 

Figure 9. Desulfurization catalyst analysis after pilot plant test...

Topsoe, H., Clausen, B. S., Topsoe, N.-Y. and Pedersen, E. Ind. Eng. Chem. Fundam. 25 (1986) 25. Recent basic research in hydro-desulfurization catalysts. 

Natural materials such as manganese nodules and bauxite have been considered as catalysts for demetallation. These materials are attractive for applications where the catalyst is disposed after deactivation since conventional CoMo/A1203 desulfurization catalysts may be too expensive. The nodules also have their metallurgical value increased after accumulating Ni and V. 

The spatial distribution of deposited Ni and V in the reactor bed is determined by the activity of the catalyst and phenomenologically parallels that for profiles in individual pellets. Metals will tend to deposit near the reactor inlet with a highly active catalyst. A more even distribution or one skewed toward the reactor outlet is obtained for catalyst with less activity, as shown by Pazos et al. (1983). Generally with a typical small-pore (60-A), high-surface-area desulfurization catalyst, metals will concentrate near the inlet (Sato et al., 1971 Tamm et al., 1981). Fleisch et al. (1984) observed concentration maximums a short distance into the catalyst bed, as a probable consequence of the consecutive reaction path. 

In contrast, recent work (4-12) has shown that Raman spectroscopy can be used to study Ti) adsorption on oxides, oxide supported metals and on bulk metals [including an unusual effect sometimes termed "enhanced Raman scattering" wherein signals of the order of 10 - 106 more intense than anticipated have been reported for certain molecules adsorbed on silver], (ii) catalytic processes on zeolites, and (iii) the surface properties of supported molybdenum oxide desulfurization catalysts. Further, the technique is unique in its ability to obtain vibrational data for adsorbed species at the water-solid interface. It is to these topics that we will turn our attention. We will mainly confine our discussion to work since 1977 (including unpublished work from our laboratory) because two early reviews (13,14) have covered work before 1974 and two short recent reviews have discussed work up to 1977 (15,16). 

In the present context, the deposition of coke on a desulfurization catalyst will seriously affect catalyst activity with a marked decrease in the rate of desulfurization (Chapter 5). In fact, it has been noted that even with a deasphalted feedstock, i.e., a heavy feedstock from which the asphaltenes have previously been removed, the accumulation of carbonaceous deposits on the catalyst is still substantial. It has been suggested that this deposition of carbonaceous material is due to the condensation reactions that are an integral part of any thermal (even hydrocracking) process in which heavy feedstocks are involved. 

Hydrodesulfurization catalysts are normally used as extrudates or as porous pellets, but the particle size and pore geometry have an important influence on process design-especially for the heavier feedstocks. The reaction rates of hydro-desulfurization catalysts are limited by the diffusion of the reactants into, and the products out of, the catalyst pore systems. Thus, as the catalyst particle size is decreased, the rate of desulfurization is increased (Figure 5-9) (Frost and (Nottingham, 1971) but the pressure differential across the catalyst bed also diminishes and a balance must be reached between reaction rate and pressure drop across the bed. 

Fresh Activity Comparisons. The nine catalysts have been divided into two groups in order to simplify the activity comparisons. Group A is made up of the more active desulfurization catalysts and includes Mobil HCL-2, Mobil HCL-3, American Cyanamid HDS-1443, and Amocat 1A. Group B included Mobil HCL-1, Harshaw 618X, American Cyanamid HDN-1197, and Amocat IB. 

It was thought that some desulfiding of the catalyst might occur, by a reaction similar to that reported by Ivanovskil for iron sulfide desulfurization catalysts (15) ... 

However, Michaud et al. and Landau et al reported that the use of an acid zeolite catalyst and classical HDS catalyst bifunctional catalyst was a very efficient way to desulfurize alkylated DBT. In this case, they observed that acid zeolite catalyst achieves isomerization of the more hindered sulfur atom alkylated DBT (viz. 46DMDBT) to compounds for which the sulfur atom is not anymore hindered by the methyl groups (viz. 37DMDBT). 

Normally, commercial HDS reactors are operated under adiabatic conditions. The heat removal is achieved by the addition of quench fluids. Mhaskar and Shah27 carried out a similar analysis for reactors which are operated non-isothermally under the conditions of either constant wall temperature or constant wall heat flux. For simplicity, they assumed that the catalyst desulfurization activity function

rate equation proposed by Szepe,55 namely,... 

The molecular size distributions and the size-distribution profiles for the nickel-, vanadium-, and sulfur-containing molecules in the asphaltenes and maltenes from six petroleum residua were determined using analytical and preparative scale gel permeation chromatography (GPC). The size distribution data were useful in understanding several aspects of residuum processing. A comparison of the molecular size distributions to the pore-size distribution of a small-pore desulfurization catalyst showed the importance of the catalyst pore size in efficient residuum desulfurization. In addition, differences between size distributions of the sulfur- and metal-containing molecules for the residua examined helped to explain reported variations in demetallation and desulfurization selectivities. Finally, the GPC technique also was used to monitor effects of both thermal and catalytic processing on the asphaltene size distributions. 

Both asphaltene and maltene molecular size distributions were compared with the pore size distribution of a small pore desulfurization catalyst. Figure 4 shows the Kuwait maltene and asphaltene size distributions along with the catalyst pore size distribution. Most of the maltene molecules are small enough to diffuse into the catalytic pores. In contrast, the Kuwait asphaltenes have a... 

Figure 2 illustrates the relationship in the micro-, pilot- and commercial reactors between the desulfurization activities and metal on catalysts (MOC). In the micro-reactor, the metal which cannot be sufficiently removed by the upstream catalyst due to low liquid mass velocity deactivated the downstream desulfurization catalyst, thereby shortening the life of the catalyst system. 

Spent caustic (3800 tons/year) is sent off-site for recovery of remaining caustic value and naphthenic acids. Most catalysts are recycled for recovery of additional activity or metals. Spent cracking catalyst (6(K) tons/year) is sent to Amoco s Whiting, Indiana, refinery for use as equilibrium catalyst. Spent ultraforming catalyst is returned to metals reclaimers to recover platinum for reuse in new catalyst. Spent desulfurization catalyst and polymer catalyst are nonhazardous and are buried in an on-site landfill. Sludges from the oil/water separator are a listed hazardous waste under RCRA regulations. They are combined with other solid wastes, such... 

A spent resid hydrotreating catalyst was regenerated on a seni-commercial scale using a proprietary process in which the Nl+V metals were first extracted and Chen the catalyst was decoked (ref. 14). The catalyst was a high surface area GoCrNo/ganuna-alumina desulfurization catalyst that had... 

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