Catalytic reactions hydrodesulfurization

It is well known that the accessibility of the mesoporous materials would play an important role in catalysis, and catalytic activity depends on the free diffusion of the reactants, intermediates and products [5], Thus, a mesoporous molecular sieve with better mass transport pore would be a more suitable candidate for some industrial catalytic reactions of the largesized hydrocarbons in dehydrogenation, hydrocracking or hydrodesulfurization. 

For most reaction systems, the intrinsic kinetic rate can be expressed either by a power-law expression or by the Langmuir-Hinshelwood model. The intrinsic kinetics should include both the detailed mechanism of the reaction and the kinetic expression and heat of reaction associated with each step of the mechanism. For catalytic reactions, a knowledge of catalyst deactivation is essential. Film and penetration models for describing the mechanism of gas-liquid and gas-liquid-solid reactions are discussed in Chap. 2. A few models for catalyst deactivation during the hydrodesulfurization process are briefly discussed in Chap. 4. 

Many operations in chemical engineering require the contact of two liquid phases between which mass and heat transfer with reaction occurs. Examples are hydrometallurgical solvent extraction, nitrations and halogenations of hydrocarbons, hydrodesulfurization of crude stocks, emulsion polymerizations, hydrocarbon fermentations for single-cell proteins, glycerolysis of fats, and phase-transfer catalytic reactions. A most common method of bringing about the contact of the two phases is to disperse droplets of one within the other by mechanical agitation. 

In fine-chemicals production three-phase reaction systems are common for the hydrogenation and hydrogenolysis of different organic functional groups. Other reactions, such as heterogeneously catalyzed catalytic oxidations, hydrodesulfurizations, and reductive aminations are encountered less frequently. 

The removal of sulfur from organosulfur compounds is an important catalytic reaction during petroleum refining [198, 199]. A test reaction for this process is the hydrodesulfurization of thiophene to butenes. Describe the process [209]. The removal of nitrogen from organonitrogen compounds is equally important. Describe the process [210]. 

In this chemistry, it is natural to focus on models for the catalytic reactions that are most important economically or which are most poorly understood because of difficulties of direct study. One which best fits these criteria is the catalytic hydrotreatment of petroleum feedstocks, which is used to remove sulfur and other heteroatoms, which interfere with subsequent catalytic reactions such as petroleum reforming, from the hydrocarbons. Molybdemun sulfide is the most common metal sulfide used in this catalysis, and hydrogen activation and C-S bond hydrogenolysis are known to be key reactions occurring at the catalyst surface but details are difficult to obtain. Study of model binuclear and cluster complexes has elucidated mechanisms of several of the key reactions and Section 2.6 describes important recent advances in this field, with the focus being on models for hydrodesulfurization catalysts. 

The primary determinant of catalyst surface area is the support surface area, except in the case of certain catalysts where extremely fine dispersions of active material are obtained. As a rule, catalysts intended for catalytic conversions utilizing hydrogen, eg, hydrogenation, hydrodesulfurization, and hydrodenitrogenation, can utilize high surface area supports, whereas those intended for selective oxidation, eg, olefin epoxidation, require low surface area supports to avoid troublesome side reactions. 

Sulfided bimetallic clusters which mimic the metal composition of commercial hydrodesulfurization (HDS) catalysts have been prepared and their homogeneous catalytic behavior studied. Reaction of thiophenol with [Mo2Co2(/z4-S)... 

The studies of ammonia synthesis over Fe and Re and the hydrodesulfurization of thiophene over Mo, described above, illustrate the importance and success of our approach of studying catalysis over single crystal samples at high pressures. The use of surfaces having a variety of orientations allows the study of reactions that are surface structure sensitive 6Uid provides insight into the nature of the catalytic site. Here we have shown that the ammonia synthesis... 

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 ... 

Irrespective of the exact configuration around the promoter atom, we have a detailed picture of the Co-Mo-S phase on the atomic scale. Figure 9.23 summarizes schematically what a working Co-Mo/A1203 hydrodesulfurization catalyst looks like. It contains MoS2 particles with dimensions of a few nanometers, decorated with cobalt to form the catalytically highly active Co-Mo-S phase. It also contains cobalt ions firmly bound to the lattice of the alumina support, and it may contain crystallites of the stable bulk sulfide Co9S8, which has a low activity for the HDS reaction [49]. 

Ruthenium carbonyl-derived catalytic systems have also been studied in hydrodesulfuration [118, 119], Highly active catalysts for the hydrodesulfuration of diben-zothiophene have been obtained by supporting on alumina MHRu3(CO)n (M = group 1 metal), which was the product of the reaction between Ru3(CO)i2 and MOH. The activity increased from Li to Cs [119]. 

Whitehurst, Isoda, and Mochida write about catalytic hydrodesulfurization of fossil fuels, one of the important applications of catalysis for environmental protection. They focus on the relatively unreactive substituted di-benzothiophenes, the most difficult to convert organosulfur compounds, which now must be removed if fuels are to meet the stringent emerging standards for sulfur content. On the basis of an in-depth examination of the reaction networks, kinetics, and mechanisms of hydrodesulfurization of these compounds, the authors draw conclusions that are important for catalyst and process design. 

Terpene catalytic hydrodesulfurization was performed in a pilot-plant reactor at 200°C, 1 atm. The volume of catalyst was 70 cm the liquid hourly space velocity of terpene 0.4 h"1 and the hydrogen to terpene molar ratio of 7. The catalysts were pretreated in situ in a flow of N2 at 260°C then sulfided in H2S/H2 (1 9) from 260°C to 370°C. After 5 h-on-stream, the catalysts were cooled down to the reaction temperature in H2S/H2. The hydrocarbons were analyzed by GC on a CP Wax 57 CB capillary column at 65°C and the sulfur contents were determined by microcoulometry using the ASTM D312077 norm. The... 

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