Kinetic sulfur compounds

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. 

Many optically active hypervalent chalcogen compounds, particularly sulfur compounds, have been synthesized and proposed as important key intermediates in various reactions of the chalcogen compounds.46 Since the synthesis of spirosulfurane by Kapovits and Kalman,47 many optically active spir-osulfuranes were isolated in the last decade. Spirosulfurane 28 was separated into enantiomers by kinetic resolution using a chiral host molecule and found to be optically stable by Drabowicz and Martin.48 Spirosulfurane 29 was separated into enantiomers by chromatographic method by Allenmark and Claeson, and characterized by chiroptical methods.49 Optically active... 

Surprisingly, despite requiring two analyte molecules to produce one S2 molecule, the kinetics of the chemiluminescent reaction are first order with respect to the sulfur compound. This can be explained if every H2S or CH3SH molecule is consumed in the reaction and every S atom recombines to form S2, through the use of an excess of OCIO to maintain pseudo-first-order reaction conditions [81]. The limit of detection for this analysis was found to be 3 ppbv for H2S. 

MacLeod, H., Jourdain, L., Poulet, G., and LeBras, G. Kinetic study of reactions of some organic sulfur compounds with OH radicals, Atmos. Environ., 18(12) 2621-2626, 1984. 

For proper kinetic evaluation of the conversion selectivity in such a case, it is necessary to find means for distinguishing the relative contributions of the various pathways to the formation of products. A systematic method for distinguishing parallel and sequential formation of products will be described, and results of HDS of such multiaromatic sulfur compounds will be discussed in these terms. For ease of understanding the following discussion, we define the various rate constants as follows. 

In seeking new and improved ways for achieving the ultralow levels of sulfur in the fuels of the future, it is important to understand the nature of the sulfur compounds that are to be converted (especially PASCs), as described in Section III. It is equally important to understand how these transformations occur through interactions with catalytic surface species, the pathways involved during these transformations, and the associated kinetic and thermodynamic limitations. These considerations dictate the process conditions and reactor process configurations that must be used to promote such transformations. In this section, we describe the reactor configurations and process conditions being used today what is known about the catalyst compositions, structure, and chemistry and what is known about the chemistry and reaction pathways for conversion of PASCs in conventional HDS processes. 

C.F. Cullis and M.F.R. Mulcahy. The Kinetics of Combustion of Gaseous Sulfur Compounds. Combust. Flame, 18 225-292,1972. 

Most liquid chromatographic experiments performed with PAD employ alkaline mobile phases or use postcolumn addition of base to get the electrode at the appropriate pH for the formation of the oxide. The exceptions to this are the detection of carbohydrates and alcohols in acidic media and the detection of sulfur compounds. The oxidation of carbohydrates and alcohols is not oxide catalyzed, and since they exhibit a stronger adsorption to piatinum than gold, they can be determined under acidic conditions. Sulfur compounds are adsorbed at oxide-free surfaces, and the kinetics for detection are favorable even at pH values below 7. 

Sugioka and Aomura (133) provide kinetic evidence indicating that the rate-determining step in the hydrocracking of aliphatic sulfur compounds over silica-alumina is catalyzed by Brdnsted acid sites. Conversions of reactants were measured by use of a pulse reactor hydrogen was used as the carrier gas. They found that reactivities of mercaptans are in the following order ... 

Kinetic studies using individual sulfur compounds have usually indicated that simple first-order kinetics with respect to sulfur is the predominant mechanism by which sulfur is removed from the organic material as hydrogen sulfide. However, there is still much to be learned about the relative rates of reaction exhibited by the various compounds present in petroleum. 

Nevertheless, the development of general kinetic data for the hydrodesulfurization of different feedstocks is complicated by the presence of a large number of sulfur compounds each of which may react at a different rate because of structural differences as well as differences in molecular weight. This may be reflected in the appearance of a complicated kinetic picture for hydrodesulfurization in which the kinetics is not, apparently, first order (Scott and Bridge, 1971). The overall desulfurization reaction may be satisfied by a second-order kinetic expression when it can, in fact, also be considered as two competing first-order reactions. These reactions are (1) the removal of nonasphaltene sulfur and (2) the removal of asphaltene sulfur. It is the sum of these reactions that gives the second-order kinetic relationship. 

In addition, the sulfur compounds in a feedstock may cause changes in the catalyst upon contact and, therefore, every effort should be made to ensure that the kinetic data from such investigations are derived under standard conditions. In this sense, several attempts have been made to accomplish standardization of the reaction conditions by presulfiding the catalyst, passage of the feedstock over the catalyst until the catalyst is stabilized, obtaining the data at various conditions, and then rechecking the initial data by repetition. 

If each type of sulfur compound is removed by a reaction that was first-order with respect to sulfur concentration, the first-order reaction rate would gradually, and continually, decrease as the more reactive sulfur compounds in the mix became depleted. The more stable sulfur species would remain and the residuum would contain the more difficult-to-remove sulfur compounds. This sequence of events will, presumably lead to an apparent second-order rate equation which is, in fact, a compilation of many consecutive first-order reactions of continually decreasing rate constant. Indeed, the desulfurization of model sulfur-containing compounds exhibits first-order kinetics, and the concept that the residuum consists of a series of first-order reactions of decreasing rate constant leading to an overall second-order effect has been found to be acceptable. 

One of the major drawbacks to defining the influence of the feedstock on the process is that the research with respect to feedstocks has been fragmented. In every case, a conventional catalyst has been used, and the results obtained are only valid for the operating conditions, reactor system, and catalyst used. More rigorous correlation is required and there is a need to determine the optimum temperature for each type of sulfur compound. In order to obtain a useful model, the intrinsic kinetics of the reaction for a given catalyst should also be known. In addition, other factors that influence the desulfurization process such as (1) catalyst inhibition or deactivation by hydrogen sulfide, (2) effect of nitrogen... 

The liquid phase reaction kinetics and mechanisms of oxidation of biogenic sulfur compounds (H2S, RSH, C 2, OC, CH3SCH3, CH3SSCH3) by various environmental oxidants (02,... 

---