Sulfidation kinetics

The interaction of H2S, organic sulfides, and other sulfur compounds may involve a number of consecutive steps including reversible molecular adsorption of the sulfur compound, its dissociation, reorientation or reconstruction of the metal surface, formation of a 2-D surface sulfide, and at still higher H2S/H2 ratios, formation of a three-dimensional (3-D) (bulk) metal sulfide. Kinetic information about these processes may generally be helpful in elucidating the adsorption mechanism. Unfortunately, such quantitative kinetic information is not adequately available, with one exception, formation of bulk sulfides (9, 96). 

The influence of temperature on the sulfidation kinetics of Ni36Al at a constant sulfur partial pressure of 6.4X10-7 bar is shown in Fig. 3a. The sulfidation kinetic follows the parabolic rate law over the whole temperature range and the sulfidation rate increases with increasing temperature. From the Arrhenius plot of the parabolic rate constants for sulfidation of Ni36Al in Fig. 3b we calculate an apparent activation energy of 58kJ/mol. 

The sulfidation kinetics of the investigated nickel aluminides except Ni25Al approximately follows the parabolic rate law in H2-H2S atmospheres between 750 and 950 °C. 

Light S. and Davis J. (1997) Disproportionation of aqueous sulfur and sulfide kinetics of polysulfide decomposition. 

In a recent paper, sulfidation kinetics of Mn—li and Mn—Cr alloys have been studied [61], and the doping effects have... 

Kai] Corrosion tests Oxidation and sulfidation kinetics... 

Organic sulfur compounds such as sulfurized spermaceti oil, terpene sulfides, and aromatic disulfides have been used. Encumbered phenols such as di-tertiary-butylphenols and amines of the phenyl-alphanaphthylamine type are effective stopping the kinetic oxidation chain by creating stable radicals. 

The equilibrium is more favorable to acetone at higher temperatures. At 325°C 97% conversion is theoretically possible. The kinetics of the reaction has been studied (23). A large number of catalysts have been investigated, including copper, silver, platinum, and palladium metals, as well as sulfides of transition metals of groups 4, 5, and 6 of the periodic table. These catalysts are made with inert supports and are used at 400—600°C (24). Lower temperature reactions (315—482°C) have been successhiUy conducted using 2inc oxide-zirconium oxide combinations (25), and combinations of copper-chromium oxide and of copper and silicon dioxide (26). 

The rate of dissolution is limited by oxygen availabiUty rather than by cyanide concentration. When oxygen solubiUty is reduced by water salinity or by consumption by ore constituents such as sulfide minerals, enrichment of the air with oxygen or addition of hydrogen or calcium peroxide improves leaching kinetics and decreases cyanide consumption (10). 

Chemical Properties. Although hydrogen sulfide is thermodynamically stable, it can dissociate at very high temperatures. The decomposition thermodynamics and kinetics have been reviewed and the equihbrium constant for the reaction has been deterrnined (101,102) ... 

SolubiHty of carbon dioxide in ethanolamines is affected by temperature, amine solution strength, and carbon dioxide partial pressure. Information on the performance of amines is available in the Hterature and from amine manufacturers. Values for the solubiHty of carbon dioxide and hydrogen sulfide mixtures in monoethanolamine and for the solubiHty of carbon dioxide in diethanolamine are given (36,37). SolubiHty of carbon dioxide in monoethanolamine is provided (38). The effects of catalysts have been studied to improve the activity of amines and provide absorption data for carbon dioxide in both mono- and diethanolamine solutions with and without sodium arsenite as a catalyst (39). Absorption kinetics over a range of contact times for carbon dioxide in monoethanolamine have also been investigated (40). 

The kinetics of formation and hydrolysis of /-C H OCl have been investigated (262). The chemistry of alkyl hypochlorites, /-C H OCl in particular, has been extensively explored (247). /-Butyl hypochlorite reacts with a variety of olefins via a photoinduced radical chain process to give good yields of aUyflc chlorides (263). Steroid alcohols can be oxidized and chlorinated with /-C H OCl to give good yields of ketosteroids and chlorosteroids (264) (see Steroids). /-Butyl hypochlorite is a more satisfactory reagent than HOCl for /V-chlorination of amines (265). Sulfides are oxidized in excellent yields to sulfoxides without concomitant formation of sulfones (266). 2-Amino-1, 4-quinones are rapidly chlorinated at room temperature chlorination occurs specifically at the position adjacent to the amino group (267). Anhydropenicillin is converted almost quantitatively to its 6-methoxy derivative by /-C H OCl in methanol (268). Reaction of unsaturated hydroperoxides with /-C H OCl provides monocyclic and bicycHc chloroalkyl 1,2-dioxolanes. 

Yang, Yonghua and Eric R. Allen, Biofiltration Control of Hydrogen Sulfide. 2. Kinetics, Biofilter Performance, and Maintenance, yAWA. vol. 44, p. 1315. 

Effect of HjS, Carbon Oxides, Etc. Hydrogen sulfide in the treat gas has an inhibiting effect on the kinetics of hydrotreating. Being a product of the desulfurization reactions, HjS must diffuse from the catalyst surface into the bulk gas stream. Any HjS present beyond that formed, further slows down the rate of diffusion with a consequent decrease in the amount of desulfurization for a given amount of catalyst. Therefore, additional catalyst would be required. 

Transition elements, for which variable valency is energetically feasible, frequently show non-stoichiometric behaviour (variable composition) in their oxides, sulfides and related binary compounds. For small deviations from stoichiometry a thermodynamic approach is instructive, but for larger deviations structural considerations supervene, and the possibility of thermodynamically unstable but kinetically isolable phases must be considered. These ideas will be expanded in the following paragraphs but more detailed treatment must be sought elsewhere. " ... 

Although desulfurization is a process, which has been in use in the oil industry for many years, renewed research has recently been started, aimed at improving the efficiency of the process. Envii onmental pressure and legislation to further reduce Sulfur levels in the various fuels has forced process development to place an increased emphasis on hydrodesulfurization (HDS). For a clear comprehension of the process kinetics involved in HDS, a detailed analyses of all the organosulfur compounds clarifying the desulfurization chemistry is a prerequisite. The reactivities of the Sulfur-containing structures present in middle distillates decrease sharply in the sequence thiols sulfides thiophenes benzothiophenes dibenzothio-phenes (32). However, in addition, within the various families the reactivities of the Substituted species are different. 

Parallel and reversible reactions. The isomerization of allyl phenyl sulfide is a degenerate rearrangement made detectable by isotopic labeling of one end of the allyl group, permitting kinetic monitoring by NMR techniques.12... 

Here we illustrate how to use kinetic data to establish a power rate law, and how to derive rate constants, equilibrium constants of adsorption and even heats of adsorption when a kinetic model is available. We use the catalytic hydrodesulfurization of thiophene over a sulfidic nickel-promoted M0S2 catalyst as an example ... 

The kinetics and mechanism of the growth of anodic silver sulfide films on silver metal in aqueous sulfide solutions has been studied under potentiodynamic conditions [162], The Ag2S film formation was presumed to proceed as... 

Birss VI, Wright GA (1981) The kinetics of the anodic formation and reduction of phase silver sulfide films on silver in aqueous sulfide solutions. Electrochim Acta 26 1809-1817 Petrov GV, Belen ku AM (2005) Interactions in the silver selenide-water system. Russ J Appl Chem 78 53-56... 

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