Petroleum products hydrodesulfurization

In order to accomplish sulfur removal, use is still made of extraction and chemical treatment of various petroleum fractions as a means of removing certain sulfur types from petroleum products, but hydrodesulfurization is the only method generally applicable to the removal of all types of sulfur compounds. 

Petroleum products undergo catalytic hydrodesulfurization and re-forming processes. Catalysts in automobile exhaust systems convert pollutants (hydrocarbons, CO, NO) to... 

Midoux, N. and J. C. Charpentier. Apparent Diffusivity and Tortuosity in a Liquid Filled Porous Catalyst used for Hydrodesulfurization of Petroleum Products. Chem. Eng. Science 28 (1973) 2108. 

Two approaches for desulfurization, namely, hydrodesulfurization (HDS) and sulfur removal by adsorption, are used with the former being the most mature technology. HDS is a catalytic hydrogenation process that removes sulfur from fossil fuels. In this process, tiie organosulfur compound such as ethanethiol (C2H5SH), a sulfur compound present in some petroleum products, is converted to H2S and sulfur-free organic compounds ethane (C2Hg) by reaction with H2 in the presence of a catalyst as shown below ... 

Thermal Cracking. In addition to the gases obtained by distillation of cmde petroleum, further highly volatile products result from the subsequent processing of naphtha and middle distillate to produce gasoline, as well as from hydrodesulfurization processes involving treatment of naphthas, distillates, and residual fuels (5,61), and from the coking or similar thermal treatment of vacuum gas oils and residual fuel oils (5). 

This compound is notorious as a hard sulfide that cannot be removed from petroleum by current hydrodesulfurization processing. Oxidation by tert-butyl hydroperoxide occurs readily when 1 is used as the catalyst. After trying several combinations, this was the most effective 0.5 mmol of DMDBT, 1.75 mmol B OOH, and 0.05 mol% of 1 were placed in refluxing toluene (384 K). A quantitative yield of the dioxide was obtained in 2h. The oxidation product is insoluble in toluene and can readily be removed by filtration (42). 

Liberated gasses are drawn off at the top of the tower with the naptha. The gas is recovered to manufacture refrigerated liquefied petroleum gas (LPG). The naptha is condensed at a temperature of about 52 °C (125 °F). Part of the condensed naptha is normally returned to the top of the tower. The naptha product stream is split into light naptha for gasoline blending and heavy naptha for further reforming. Inside the tower, kerosene is withdrawn at a temperature of about 149 °C (300 °F). Diesel is withdrawn at a temperature of 260 °C (500 °F). These middle distillates are usually brought up to specification with respect to sulfur content with hydrodesulfurization. The heavy oil... 

Hydrogen sulfide is a by-product of many industrial operations, eg, coking and the hydrodesulfurization of crude oil and of coal. Hydrodesulfurization is increasing in importance as the use of high sulfur crude oil becomes increasingly necessary (see Petroleum, refinery processes). A large future source of hydrogen sulfide may result if coal liquefaction attains commercial importance (see Coal CONVERSION processes). 

Thus, it has become possible to define certain general trends that occur in the hydrodesulfurization of petroleum feedstocks. One of the more noticeable facets of the hydrodesulfurization process is that the rate of reaction declines markedly with the molecular weight of the feedstock (Figure 4-6) (Scott and Bridge, 1971). For example, examination of the thiophene portion of a (narrowboiling) feedstock and the resulting desulfurized product provides excellent evidence that benzothiophenes are removed in preference to the dibenzothiophenes and other condensed thiophenes. The sulfur compounds in heavy oils and residua are presumed to react (preferentially) in a similar manner. 

An example of a product-inhibited conversion is the hydrodesulfurization of medium-to-heavy petroleum fractions. The removal of sulfur from such oils can generally be described as a second-order reaction in total sulfur [1]. This high apparent order is a reflection of the presence of a variety of sulfur-containing compounds that have widely differing reactivities for hydrodesulfurization and implies that a relatively large proponion of sulfur is removed from the oil by conversion of the bulk of more reactive compounds in an early stage of the reaction. The conversion of the more refractive sulfur compounds occurs far more slowly in a later stage. 

In a trickle bed reactor the gas and liquid flow (trickle) concurrently downward over a packed bed of catalyst particles. Industrial trickle beds are typically 3 to 6 m deep and up to 3 m in diameter and are filled with catalyst particles ranging irom to in. in diameter. The pores of the catalyst are filled with liquid. In petroleum refining, pressures of 34 to 100 atm and temperatures of 350 to 425°C are not uncommon. A pilot-plant trickle bed reactor might be about 1 m deep and 4 cm in diameter. Trickle beds are used in such processes as the hydrodesulfurization of heavy oil stocks, the hydrotreating of lubricating oils, and reactions such as the production of butynediol from acetylene and aqueous formaldehyde over a copper acetylide catalyst. It is on this latter type of reaction,... 

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