Oxides of sulphur

It is extensively used industrially as a catalyst, notably in the oxidation of sulphur dioxide to the trioxide in sulphuric acid manufacture. It is an essentially acidic oxide, dissolving in alkalis to give vanadates however, addition of acid converts the anionic vanadate species to cationic species, by processes which are very complex, but which overall amount to the following ... 

For compounds containing carbon, hydrogen, oxygen, nitrogen halogens and sulphur. If the compound to be analysed contains sulphur in addition to the elements considered above, then oxides of sulphur will be formed, and a new... 

Oxides of sulphur and other sulphur compounds Oxides of nitrogen and other nitrogen compounds Oxides of carbon... 

Mechanism and sulphur oxidation Apart from its intrinsic interest the economic importance of acid corrosion and more lately interest in ore leaching, has stimulated considerable work on the oxidation of sulphur, Fe and Mn. It must be stressed that the Thiobacilli are obligate aerobes, i.e. that depend on molecular oxygen as a terminal electron acceptor. Possible reactions for the oxidation of sulphur are... 

These alloy coatings have advantages over tin in atmospheric exposure where there is heavy pollution by oxides of sulphur. They are cathodic to steel and anodic to copper. In industrial atmospheres, however, formation of a layer of lead sulphate seals pores and produces a generally stable surface and terne-plate has been used extensively as roofing sheet, especially in the USA. It is easily and effectively painted when additional protection is required. Copper heat exchangers in gas-fired water-heaters may be coated by hot dipping in 20% tin alloy . 

In the glass-bottle industry the bottles can be cooled in a dilute SOj/SO, atmosphere to increase chemical resistance. A similar effect has been noted with vitreous enamel. It has been postulated that a thin layer of —OH groups or — OH—HjO (hydronium) ions is adsorbed on the surface of a fired enamel. These ions are transformed into — OSO, or —OSO3 in the presence of oxides of sulphur which are more resistant to further acid attack. It is known that the acid resistance of a recently fired enamel improves on ageing, probably due to the enamel reaction with SOj/SO, in the atmosphere and it is quite common for the grading to improve from Class A to Class AA (BS 1344). 

Implications to Humans. Acidic precipitation has not been observed with concentrations that pose a concern to human exposure. The acidic airborne pollutants in the particulate or gaseous forms such as the oxides of sulphur and of nitrogen, and the associated photochemical oxidant ozone, are inhaled. This may lead to the irritation of the respiratory tract, and subsequently to impaired lung function, aggravated asthma and bronchitis. 

Wiberg has reviewed this oxidation and suggests that the complex of Mason and Kowalak is a mixed anhydride, cf. the oxidations of sulphur dioxide (p. 285) and formic acid (p. 316). The anhydride cannot be of neutral charge, however, as no acidity dependence is observed and a possibility is... 

Made industrially by catalytic oxidation of sulphur dioxide, its interaction with water gives sulphuric acid. 

According to the state of oxidation of sulphur or oxygen and the types of bonds,... 

Matros, Yu. Sh., Unsteady-state oxidation of sulphur dioxide in sulphuric acid production. Sulphur 183, 23 (1986). 

Wu, H., Zhang, S., and Li, C., Study of unsteady-state catalytic oxidation of sulphur dioxide by periodic flow reversal. Can. J. Chem. Eng. 74, 766-771 (19%). 

SAQ 4.2 By inspection alone, decide whether the oxidation of sulphur dioxide is thermodynamically spontaneous or not. The stoichiometry of the reaction is V202(g)... 

S02 and S03 are the only compounds considered in this section. S20 is a well-established356 oxide of sulphur, although there is apparently no information on the kinetics of its decomposition. Sulphur monoxide, SO, is a reactive intermediate which features in the decompositions of S02 and S03. 

From Eq. (a) step 1, it is obvious that the oxidation of sulphur dioxide takes place by iodine to yield sulphur trioxide and hydrogen iodide thereby consuming one mole of water. In other words, each one molecule... 

In SL-PC, a catalyst is supported on a solid matrix in the form of the film of a nonvolatile liquid phase adsorbed on the solid. The catalytic film can be, for example, a molten salt or a molten oxide (e.g., Deacon s catalyst (CUCI2/KCI) used to oxidize HCl with oxygen for the chlorination of ethylene in the synthesis of vinyl chloride. Figure 6.1 V2O5 for the oxidation of sulphurous to sulphuric anhydride). Alternately, it can be a liquid phase (e.g., ethylene glycol, PPh3, butyl benzyl phthalate, etc.) that contains a soluble catalytic species such as a metal complex. 

Kelly DP. 1988. Oxidation of sulphur compounds. Soc Gen Microbiol Symposium 42 65-98. 

So far, no reference has been made to the presence of more than one phase in the reactor. Many important chemicals are manufactured by processes in which gases react on the surface of solid catalysts. Examples include ammonia synthesis, the oxidation of sulphur dioxide to sulphur trioxide, the oxidation of naphthalene to phthalic anhydride and the manufacture of methanol from carbon monoxide and hydrogen. These reactions, and many others, are carried out in tubular reactors containing a fixed bed of catalyst which may be either a single deep bed or a number of parallel tubes packed with catalyst pellets. The latter arrangement is used, for exjimple, in the oxidation of ethene to oxiran (ethylene oxide)... 

This type of operation with heat exchange between the hot product stream and the cold incoming reactants is employed in many industrial reactors. Important examples include ammonia synthesis, methanol synthesis, the oxidation of sulphur dioxide, the water gas shift reaction and the synthesis of phthalic anhydride. 

Unlike the specifically bound metals which participate in reversible redox reactions extraneously bound transition metals are well able to induce uncontrolled oxidation of sulphur containing ligands The so called metal driven Haber Weiss reaction is responsible for the formation of oxidised sulphur species leading to sulphonic acid. For example ... 

Lagrange, J., C. Pallares, G. Wenger, and P. Lagrange, "Electrolyte Effects on Aqueous Atmospheric Oxidation of Sulphur Dioxide by Hydrogen Peroxide, Atmos. Environ., 27A, 129-137 (1993). 

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