Desulfurization catalyst

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) ... 

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... 

The catalytic distillation desulfurization process developed by CDTech is significantly different from conventional hydrotreating.76 77 The most important portion of the CDTech desulfurization process is a set of two distillation columns loaded with desulfurization catalyst in a packed structure. In this process, the LCN, middle cut naphtha (MCN), and HCN are treated separately, under optimal conditions for each. The first column, called CDHydro, treats the lighter compounds of FCC gasoline and separates the heavier portion of the FCC gasoline for treatment in the second column. The second column, called CDHDS (catalytic distillation hydrodesulfurization), removes the sulfur from the heavier compounds of FCC gasoline. Figure 5.6... 

The two reactors are disposed in series. The first reactor is loaded with a big pore diameter demetallation catalyst designed to withstand high metal poisoning the second reactor is loaded with a smaller pore size desulfurization catalyst which gives a larger reaction area and therefore, a larger hydrotreatment capacity. 

The contribution of the catalyst in the second reactor at the end of the run and at different temperatures was determined using a bed composed of an unused demetallation catalyst and an aged desulfurization catalyst (1F2A). 

Figures 1 and 2 show the metals and sulfur contents of the products obtained in the pilot plant. Curve 1A corresponds to a bed simulating only the first reactor with aged demetallation catalyst IF corresponds to the first reactor with fresh catalyst, 1F2F corresponds to the first and second reactor with fresh catalyst, 1F2A corresponds to the first reactor with fresh catalyst and the second one with aged desulfurization catalyst.

Comparing curves 1A and 1 F, i.e. the quality of the product at the outlet of the first reactor and at the end of the cycle, we observe that the quality of the product can be maintained by increasing the temperature without exceeding the design temperature (425°C). The hydrotreatment levels obtained at 350°C with the fresh catalyst are obtained at approximately 385°C with the used desulfurization catalyst and at 390°C for the demetallation catalyst, this indicates that the catalyst has not yet collapsed due to plugging of its pores by metallic deposits, confirming the results obtained by aging the samples of this catalyst in a second cycle. 

The experiments were conducted on a Kuwait atmospheric resid with characteristics as given in Table 1. The catalysts tested were commercial resid desulfurization catalysts in the shape of 1/32" cylindrical extrudates. Important properties of the catalysts have been listed in Table 2. 

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