Hydrogenation of organic sulfur compounds

Nickel sulfide catalysts are used in the hydrogenation of organic sulfur compounds because, in most cases, metallic catalysts react with, and are poisoned by, organic sulfur compounds. Most of these hydrogenations are carried out at temperatures above 100°. 

Although iron molybdate, nickel molybdate as well as cobalt molybdate, are active in hydrogenation of organic sulfur compounds, their activities are much lower than that of cobalt molybdate. 

A major product in the combustion of all organic sulfur compounds is sulfur dioxide. Sulfur dioxide has a well-known inhibiting effect on hydrocarbon and hydrogen oxidation and, indeed, is responsible for a self-inhibition in the oxidation of organic sulfur compounds. This inhibition most likely arises from its role in the removal of H atoms by the termolecular reaction... 

The desulfurization of organic sulfur compounds with Raney Ni using far greater amounts than a catalytic is not a catalytic hydrogenolysis in the strict sense but involves a stoichiometric chemical reaction, since the catalyst itself is converted into nickel sulfide. However, since it has found many useful applications with Raney Ni (a hydrogenation catalyst), this reaction has been treated in this section. 

The influence of these inhibitors is known to increase in the following order saturated hydrocarbons, monoaromatics < condensed aromatics, oxygen compounds, hydrogen sulfide < organic sulfur compounds < basic nitrogen compounds. Three of these inhibitor classes are discussed here. 

E. The synthesis gas must be free of sulfur. This can be achieved by catalytic conversion of the sulfur of organic sulfur compounds to hydrogen sulfide which can be removed by known methods. 

Hydrogen bonding and metal complexation of organic sulfur compounds have been reported in two former review articles in the Chemistry of Functional Groups series26. Sulfonic acids are capable of completely protonating organic substrates in protic media with formation of stable sulfonate anions as shown in the previous section. 

In this section, a summary of the chemical principles involved with membrane reactors for desulfurization are overviewed. The details will be covered in the following sections. Electrochemical desulfurization technologies assisted by membranes have been extensively explored for the removal of sulfur that exists in sulfur compounds in fossil fuels and in SO2 form in flue gas. In principle, SO2 can be absorbed by an aqueous electrolyte solution and then electrochemically converted into species such as sulfate, hydrogen sulfide, and sulfur, among others, by oxidation or reduction processes, whereas the sulfur compounds in fossil fuels can be similarly removed. The universal reaction mechanism of the electrochemical cathodic reduction of organic sulfur compounds in gasoline and diesel is shown in Eqn (14.1) (Lam et al., 2012) ... 

Acetylene manufactured from carbide made in the United States and Canada normally contains less than 0.4 percent impurities other than water vapor. Apart from water, the chief impurity is air, in concentrations of approximately 0.2 percent and 0.4 percent. The remainder is mostly phosphine, ammonia, hydrogen sulfide, and in some instances, small amounts of carbon dioxide, hydrogen, methane, carbon monoxide, organic sulfur compounds, silicon hydrides, and arsine. Purified acetylene is substantially free from phosphine, ammonia, hydrogen sulfide, organic sulfur compounds, and arsine. The other impurities are nearly the same as in the original gas. 

The production of hydrogen sulfide during the p5Uolysis of organic sulfur compounds with calcium oxalate makes possible a reliable test for sulfur in organic compounds. 

Catal3dic hydrodesulphurization is based on the reaction of organic sulfur compounds with hydrogen as catalysts. During reactions, the organic sulfur compounds are first converted to the inorganic sulfur compounds such as H2S, and then removed by the absorption of zinc oxide. The reactions involved are summarized as follows. 

Hydrogen sulfide is generally a minor gaseous constituent produced by petrification of organic sulfur compounds, the action of sulfate-reducing bacteria, fossil fuels, combustion and petroleum refining. H2S in a dry atmosphere is only weakly corrosive. It dissociates into and HS , the later being a corrosive species. 

Processes described in this chapter include (1) thermal oxidation of VOCs and odors, (2) catalytic oxidation of VOCs and odors, (3) catalytic oxidation of sulfur compounds to sulfur oxides, (4) catalytic conversion of organic sulfur compounds to hydrogen sulfide, (S) conversion of carbon monoxide to carbon dioxide (shift conversion), (6) conversion of oxides of carbon to methane (methanation), and (7) conversion of acetylene to ethylene (selective hydrogenation). 

The principal chemical reactions taking place in the catalytic conversion of organic sulfur compounds to hydrogen sulfide can be expressed by the following equations ... 

The presence of hydrogen in, for example, hydrotreating and hydrocracking operations, increases the severity of high-temperature sulfidic corrosion. Hydrogen coverts organic sulfur compounds in feed stocks to hydrogen sulfide corrosion becomes a function of HjS concentration. 

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