Hydro-desulfurization

Identifying sulfur compounds in crude oils and their products is of little use to a refiner because all sulfur compounds can easily be hydro-desulfurized to hydrogen sulfide and the corresponding hydrocarbon. 

The primary purpose of the energy conversion facility is the production of liquid or gaseous fuels most of the sulfur will be removed from these products. Liquid fuel streams will be hydro-desulfurized to meet combusion standards, with the sulfur transferred to the gas phase. In the case of oil shale, extensive hydrotreatment will be required to remove the refractory nitrogen compounds from the oil. With this degree of treatment, the sulfur will also be removed. 

The foregoing reactions are highly exothermic and significantly raise reaction temperatures. The MRG process, however, docs not involve such adverse side reactions with use of a special, selective hydiodesulfuriziiig catalyst (developed by Japan Gasoline Co. and Nikki Chemical). The MRG process uses part of product gas for hydrodesulfunzation, and even if it contains only 20-25% hydrogen and as high as 20-23% carbon oxides, only the proper hydro desulfurization reactions take place, The MRG process features a recycle use of product gas for hydrodesulfurization purposes without any special treatment. 

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. 

Data obtained using this equation showed that a change in hydrogen sulfide concentration from 1 to 12% (by volume) could reduce by 50% the rate constants for the easy-to-desulfurize and the difficult-to-desulfurize reactions. On the basis of the data available from kinetic investigations, the kinetics of residuum hydro-desulfurization may be represented by the following general equation ... 

Removal of the metal contaminants is not usually economical, or efficient, during rapid regeneration. In fact, the deposited metals are believed to form sulfates during removal of carbon and sulfur compounds by combustion that produce a permanent poisoning effect. Thus, if fixed-bed reactors are to be used for residuum or heavy oil hydrodesulfurization (in place of the more usual distillate hydro-desulfurization) it may be necessary to first process the heavier feedstocks to remove the metals (especially vanadium and nickel) and so decrease the extent of catalyst bed plugging. Precautions should also be taken to ensure that plugging of the bed does not lead to the formation of channels within the catalyst bed which will also reduce the efficiency of the process and may even lead to pressure variances within the reactor because of the distorted flow patterns with eventual damage. 

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. 

The extent of the hydrocracking is, like the hydrodesulfurization reaction, dependent upon the temperature, and both reaction rates increase with increase in temperature. However, the rate of hydrocracking tends to show more marked increases with temperature than the rate of hydrodesulfurization. The overall effect of the increase in the rate of the hydrocracking reaction is to increase the rate of carbon deposition on the catalyst. This adversely affects the rate of hydro-desulfurization hydrocracking reactions are not usually affected by carbon deposition on the catalyst since they are more dependent upon the noncatalytic scission of covalent bonds brought about by the applied thermal energy. 

Poisoning is not always bad. There are situations where a catalyst is intentionally poisoned to decrease activity towards an undesirable reaction. In the hydro-desulfurization and -demetallization of a petroleum feedstock the catalyst is presulfided prior to introducing the feed to decrease its activity and minimize cracking reactions that will produce unwanted gases. Another is the use of ammonia to slightly poison a Pt catalyst used in the hydrogenation of fats and oils to decrease undesirable oversaturation. 

There are different grades of Stoddard Solvent depending upon the type and level of posttreatment. These treatments include hydro-desulfurization, solvent extraction, and hydrogenation. These successive treatments result in lower and lower aromatics in the final product. 

CF-2 series catalyst was designed to show good hydroconversion and hydrodesulfiarization (HDS), and to be loaded into the latter part of reactors. CF-3 series catalyst showed good hydroconversion and hydrodemetallization (HDM) in addition to hydro-desulfurization. CF-500 series catalyst was designed to have excellent hydrodemetallization and metal uptake capacity. Their performance features are shown in Table 1. 

Whitehurst, D.D. Isoda, T. Mochida, I. Present state of the art and future challenges in the hydro-desulfurization of polyaromatic sulfur compounds. Adv. Catal. 1998, 4, 345 71. 

Primary steam reforming Secondary steam reforming Carbon monoxide conversion Carbon monoxide methanation Ammonia synthesis Sulfuric acid synthesis Methanol synthesis Oxo synthesis Ethylene oxide Ethylene dichloride Vinylacetate Butadiene Maleic anhydride Phthalic anhydride Cyclohexane Styrene Hydrodealkylation Catalytic reforming Isomerization Polymerization (Hydro)desulfurization Hydrocracking... 

Moon and Ihm (1996) used NdNis as an unsupported catalyst in thiophene hydro-desulfurization. But the intermetallic compound itself is not active and activation was... 

Blomberg et al. separated the different t) s of sulphur compounds in hydro desulfurization (HDS) feed and product to follow the hydrogenation of the different types and species of sulphur-containing compounds (Figure 8) [36]. In order to enable maximum detector selectivity and linearity, the authors modified (the electronics of) an existing sulphur chemiluminescence detector, so that it could adequately follow the narrow peaks. 

Austenitic steels provide excellent corrosion, oxidation, and sulfidation resistance with high creep resistance, toughness, and strength at temperatures greater than 565 °C. Thus they are used in refineries for heater tubes, heater tube supports, and in amine, fluid catalytic cracking (FCC), catalytic hydro-desulfurization (CHD) sulfur, and hydrogen plants. 

Figure 13.8 Schematic representation of membrane reforming reactor integrated with a gas turbine (1) Combustion chamber (2) hydro-desulfurization unit (3) convective furnace (4) and (5) membrane modules for H2 separation (6) H2 compressor.

Reactions that require elimination of trace quantities of certain compounds (hydro-desulfurization reactions in refineries, deep hydrogenation, or other intrinsically slow reactions) are normally kinetic controlled. The trickle bed reactor in the cocurrent downflow mode is a popular multiphase reactor for such apphcations. The... 

Describe hydro desulfurization, hydrocracking, and fluid coking... 

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