Hydrotreating reactions hydrodesulfurization

Trickle-bed reactors are used in catalytic hydrotreating (reaction with H2) of petroleum fractions to remove sulfur (hydrodesulfurization), nitrogen (hydrodenitrogena-tion), and metals (hydrodemetallization), as well as in catalytic hydrocracking of petroleum fractions, and other catalytic hydrogenation and oxidation processes. An example of the first is the reaction in which a sulfur compound is represented by diben-zothiophene (Ring and Missen, 1989), and a molybdate catalyst, based, for example, on cobalt molybdate, is used ... 

Transition metal sulfides of the 3" row show high activity in hydrotreating reactions and some of them are studied as potential promoters of conventional catalysts in order to improve their performance. Carbon supported Pt sulfide was highly active in hydrodesulfurization (HDS) of thiophene and hydrodenitrogenation (HDN) of quinoline and pyridine [1,2]. The Pt/silica-alumina sulfide catalyst has been investigated as the promising candidate for deep HDS [3]. 

Figure 6.8.3 Equilibrium data of selected hydrotreating reactions (equilibrium constants of the three hydrodesulfurization reactions shown in Scheme 6.8.1).

The breadth of reactions catalyzed by cobalt compounds is large. Some types of reactions are hydrotreating petroleum (qv), hydrogenation, dehydrogenation, hydrodenitrification, hydrodesulfurization, selective oxidations, ammonoxidations, complete oxidations, hydroformylations, polymerizations, selective decompositions, ammonia (qv) synthesis, and fluorocarbon synthesis (see Fluorine compounds, organic). 

If reaction (2-13) follows reaction (2-12) instantaneously, the effect will not be noticeable in the H2 signal [12]. In spite of these limitations, we conclude that TPS with mass spectrometric detection is a highly useful technique for studying the sulfidation of hydrotreating catalysts. We shall return to the sulfidation of molybdenum oxides in the chapters on photoemission (Chapter 3), ion spectroscopy (Chapter 4), and in a case study on hydrodesulfurization catalysts in Chapter 9. 

While the definitions of the various hydroprocesses are (as has been noted above) quite arbitrary, it may be difficult, if not impossible, to limit the process to any one particular reaction in a commercial operation. The prevailing conditions may, to a certain extent, minimize, cracking reactions during a hydrotreating operation. However, with respect to the heavier feedstocks, the ultimate aim of the operation is to produce as much low-sulfur liquid products as possible from the feedstock. Any hydrodesulfurization process that has been designed for application to the heavier oils and residua may require that hydrocracking and hydrodesulfurization occur simultaneously. 

In most applications, the reaction occurs between a dissolved gas and a liquid-phase reactant in the presence of a solid catalyst. In some cases, the liquid is an inert medium and the reaction takes place between the dissolved gases at the solid surface. These reactors have many diverse applications in catalytic processes and are used extensively in the chemical industry. Trickle-bed reactors have been developed by the petroleum industry for hydrodesulfurization, hydrocracking, and hydrotreating of various petroleum fractions of relatively high boiling point. Under reaction conditions, the hydrocarbon feed is frequently a vapor-liquid mixture that reacts at liquid hourly space velocities (LHSV in volume of fresh feed, as liquid/volume of bed, hr) in the... 

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,... 

Zeolites containing transition metai offer interesting possibilities to combine acid properties and a hydrogenation function in bifunctional catalysts. For hydrotreating, e.g. for hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) reactions, both functions are essential the acid properties are provided by the zeolite, the hydrogenation activity by the sulfided transition metal cations [1,2]. It can be expected that these catalysts will be attractive alternatives to alumina supported Co-Mo and Ni-Mo hydrotreating catalysts because of their superior catalytic properties. 

Trickle-bed reactors are widely used in hydrotreating processes, i.e., hydrodesulfurization of gasoline and diesel fuel, in petroleum refining, chemical, petrochemical, and biochemical processes. The knowledge of hydrodynamic parameters is vital in the design of a TBR because the conversion of reactants, reaction yield, and selectivity depend not only on reaction kinetics, operating pressure, and temperature, but also on the hydrodynamics of the reactor. Special care is also required to prevent flow maldistribution, which can cause incomplete catalyst wetting in some parts... 

Trickle bed reactors have grown rapidly in importance in recent years because of their application in hydrodesulfurization of naphtha, kerosene, gasoil, and heavier petroleum fractions hydrocracking of heavy gasoil and atmospheric residues hydrotreating of lube oils and hydrogenation processes. In trickle bed operation the flow rates are much lower than those in absorbers. To avoid too low effectiveness factors in the reaction, the catalyst size is much smaller than that of the packing used in absorbers, which also means that the overall void fraction is much smaller. 

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