Sulfur stoichiometries

De Beer et al. (7) also mention that disulfide species found on exposure of sulfided catalysts to air (46) can cause incorrect assessment of sulfur stoichiometry. Again, however, this can be attributed to adsorbed H2S on their catalyst and its overall contribution to the sulfur content of well-purged samples was found to be small (33). 

Sulfur stoichiometry did not agree with simple conversion of Mo03 to MoS2 and initial results were closer to a one-to-one replacement of O for S (see Section IV.B). 

Prior to methanation, the gas product from the gasifier must be thoroughly purified, especially from sulfur compounds the precursors of which are widespread throughout coal (23) (see Sulfurremoval and recovery). Moreover, the composition of the gas must be adjusted, if required, to contain three parts hydrogen to one part carbon monoxide to fit the stoichiometry of methane production. This is accompHshed by appHcation of a catalytic water gas shift reaction. 

The mechanism for sulfonation of hydrogenated fatty esters is accepted as a two-stage process. A rapid sequence of reactions leads to the formation of intermediates having approximately 2 1 stoichiometry of sulfur trioxide to ester. In the subsequent slower and higher temperature aging step, the SO is released for further reactions and the starting material conversion proceeds to completion (133). 

The amount of combustion ait is tightly controlled to maximize sulfur recovery, ie, maintaining the appropriate reaction stoichiometry of 2 1 hydrogen sulfide to sulfur dioxide throughout downstream reactors. Typically, sulfur recoveries of up to 97% can be achieved (7). The recovery is heavily dependent on the concentration of hydrogen sulfide and contaminants, especially ammonia and heavy hydrocarbons, ia the feed to the Claus unit. 

Another boron sulfide, of stoichiometry BS2, can be made by heating B2S3 and sulfur to 300°C under very carefully defined conditions. It is a colourless, moisture-sensitive material with a porphine-like molecular structure, BgSig, as shown in Fig. 6.29b. An alternative route to BgSie involves the reaction of dibromotrithiadiborolane with trithiocarbonic acid in an H2S generator in dilute CS2 solution ... 

The seven known sulfur fluorides are quite different from the other halides of sulfur in their stability, reactivity and to some extent even in their stoichiometries it is therefore convenient to... 

Consistent with this, experiments using HS" labelled with radioactive (p. 661) show that acid hydrolysis of the 8203 produces elemental sulfur in which two-thirds of the activity is concentrated. Thiosulfates can also he made by boiling aqueous solutions of metal sulfites (or hydrogen sulfites) with elemental sulfur according to the stoichiometry... 

Basically, the oxidation of iron pyrite, FeS2, results in the production of iron(III) sulfate and sulfuric acid, H2SO4. However, two overall reaction stoichiometries are possible and each will yield a different acid generation capacity (e.g., Langmuir, 1997 Baird, 1995) ... 

The [3Fe-4S] core is now considered an unique basic iron-sulfur core whose structure was determined in D. gigas Fdll 56, 84) (as well as in aconitase 85-87) and A. vinelandii Fd (57, 59, 80)). The cluster in these proteins have Fe-Fe and Fe-S distances around 2.8 and 2.2 A and the core described as a cuboidal geometry with one comer missing (Fe S stoichiometry of 3 4). 

Besides complexes of thiosemicarbazones prepared from nitrogen heterocycles, iron(III) complexes of both 2-formylthiophene thiosemicarbazone, 26, and 2-acetylthiophene thiosemicarbazone, 27, have been isolated [155]. Low spin, distorted octahedral complexes of stoichiometry [Fe(26)2A2]A (A = Cl, Br, SCN) were found to be 1 1 electrolytes in nitromethane. Low spin Fe(27)3A3 (A = Cl, Br, SCN) complexes were also isolated, but their insolubility in organic solvents did not allow molar conductivity measurements. Infrared speetra indicate coordination of both via the azomethine nitrogen and thione sulfur, but not the thiophene sulfur. The thiocyanate complexes have spectral bands at 2065, 770 and 470 cm consistent with N-bonded thiocyanato ligands, but v(FeCl) and v(FeBr) were not assigned due to the large number of bands found in the spectra of the two ligands. 

The S-methyldithiocarbazates of both 2-formylquinoline, 18, and 1-formyliso-quinoline, 19, when mixed with cobalt(II) salts in ethanol-dimethoxypropane, yield [Co(L-H)2]N03 and [Co(L-H)2]2[CoA4], where A = Cl, Br, I, NCS, or NCSe [145]. Magnetic and spectral data support these stoichiometries and bonding is via the ring nitrogen, azomethine nitrogen, and thiol sulfur. More recently [146], [Co(19-H)2]2[CoCl4] has been shown to have d-d bands consistent with the presence of both cobalt centers. 

Formylthiophene thiosemicarbazone, 26, forms nickelfll) complexes of stoichiometry of [Ni(26)2]A2, [Ni(26)A2], Ni(26-H)A, and [Ni(26-H)2] where A = Cl, Br, I, NCS etc. [211]. Except when A = NCS in the first two types of complexes, the rest are diamagnetic and planar. The thiosemicarbazone moiety bonds NS, but there is no indication whether the Ni(26-H)A complexes are dimeric, or the thiophene sulfur completes the coordination sphere, which is less likely. 

Formylthiophene thiosemicarbazone, 26, as well as the N-methylfhio-semicarbazone, and N-phenylthiosemicarbazone, each yield complexes of stoichiometry [Ni(26-H)2] from heated aqueous alcohol solutions brought to above pH = 7 with ammonia [209]. All complexes are four-coordinate, diamagnetic and the thiophene sulfur does not bond to the nickel(II) center. 

Equation A may now be used to determine the diffusivity of sulfur dioxide in the gas mixture. The flux ratios may be determined from the reaction stoichiometry. 

---