Sulfur forms determination

Table III. Mole Percent Sulfide and Thiophenic Sulfur Forms Determined From Analysis of the XPS Sulfur 2p Signal...

Abstract This chapter first explains the natural flotability of some minerals in the aspect of the crystal structure and demonstates the collectorless flotaiton of some minerals and its dependence on the h and pH of pulp. And then the surface oxidation is analysed eletrochemically and the relations of E to the composition of the solutions are calculated in accordance with Nemst Equation. The E h-pH diagrams of several minerals are obtained. Thereafter, electrochemical determination such as linear potential sweep voltammetry (LPSV) and cyclic voltammetry (CV) and surface analysis of surface oxidation applied to the sulphide minerals are introduced. And recent researches have proved that elemental sulfur is the main hydrophobic entity which causes the collectorless flotability and also revealed the relation of the amount of sulfur formed on the mineral surfaces to the recoveries of minerals, which is always that the higher the concentration of surface sulphur, the quicker the collectorless flotation rate and thus the higher the recovery. 

Sulfur dioxide in the sample causes a negative interference of approximately 1 mole of ozone per mole of sulfur dioxide, because it reduces the iodine formed by ozone back to potassium iodide. When sulfur dioxide concentrations do not exceed those of the oxidants, a method commonly used to correct for its interference is to add the amount of sulfur dioxide determined by an independent method to the total detector response. A second method is to remove the sulfur dioxide from the sample stream with solid or liquid chromium trioxide scrubbers. Because the data on the performance or these sulfur dioxide scrubbers are inadequate, the performance for each oxidant system must be established experimentally. 

Direct Determination and Quantification of Sulfur Forms in Heavy Petroleum and Coal... 

This work has demonstrated that organically bound sulfur forms can be distinguished and in some manner quantified directly in model compound mixtures, and in petroleum and coal. The use of third derivatives of the XANES spectra was the critical factor in allowing this analysis. The tentative quantitative identifications of sulfur forms appear to be consistent with the chemical behavior of the petroleum and coal samples. XANES and XPS analyses of the same samples show the same trends in relative levels of sulfide and thiophenic forms, but with significant numerical differences. This reflects the fact that use of both XPS and XANES methods for quantitative determinations of sulfur forms are in an early development stage. Work is currently in progress to resolve issues of thickness effects for XANES spectra and to define the possible interferences from pyritic sulfur in both approaches. In addition these techniques are being extended to other nonvolatile and solid hydrocarbon materials. 

The mechanisms of nucleophilic displacements on tricoordinated sulfur are not yet fully understood. The stereochemistry can be determined by studying the relative configuration of starting materials and products.63 The substituents attached to tricoordinated sulfur form a tetrahedron with the lone pair occupying one of the apices (10) but, unlike its nitrogen-containing analog, the sulfur... 

In the method for determining the forms of sulfur in coal (ASTM D-2492 ISO 157), the sulfate and pyrite sulfur are determined directly, and the organic sulfur is taken as the difference between the total sulfur and the sum of the sulfate and pyrite sulfur. 

In the determination of sulfate, 2 to 5 g of the analysis sample is mixed with HC1 (2 volumes concentrated HC1 + 3 volumes of water), and the mixture is gently boiled for 30 minutes. After filtering and washing, the undissolved coal may be retained for the determination of pyrite sulfur, or it may be discarded and a fresh sample used for pyrite sulfur. Saturated bromine water is added to the filtrate to oxidize all sulfur forms to sulfate ions and ferrous ions to ferric ions. After boiling to remove excess bromine, the iron is precipitated with excess ammonia and filtered. This precipitate must be retained for the determination of nonpyrite iron if a fresh sample of coal was used for the determination of the pyrite iron. The sulfate is then precipitated with ISaCE, and the BaSC>4 is determined gravimetrically. 

The utility of sulfur K-edge X-ray absorption spectroscopy for the determination and quantification of sulfur forms in nonvolatile hydrocarbons has been investigated. X-ray Absorption Near Edge Structure (XANES) spectra were obtained for a selected group of model compounds, for several petroleum asphaltene samples and for Rasa coal. For the model compounds the sulfur XANES was found to vary widely from compound to compound, and to provide a fingerprint for the form of sulfur involved. The use of third derivatives of the spectra enabled discrimination of mixtures of sulfide and thiophenic model compounds, and allowed approximate quantification of the amount of each component in the mixtures, in the asphaltene samples and the coal. These results represent the first demonstration that nonvolatile sulfide and thiophenic sulfur forms can be distinguished and approximately quantified by direct measurement. 

Several papers in this book and in the recent literature (3) discuss use of pyrolysis techniques coupled with gas chromatography and mass spectrometry to determine forms of organically bound sulfur, but these methods introduce an uncertainty due to the possible interconversion of these sulfur forms during the heating step. For example, it has been shown that when benzyl sulfide was heated to 290°C, tetraphenyl thiophene, hydrogen sulfide and stilbene were produced (4). Coupled with heat and mass transport limitation considerations, particularly for viscous liquids and solids, it is not unreasonable to question whether at least some of the thiophenic forms observed by these techniques were produced during the analysis and may not have been present in the original sample. 

The tentative quantitative determinations of sulfur forms appear to be consistent with the chemical behavior of the asphaltene and coal samples. Further work is in progress to extend these techniques to other nonvolatile and solid hydrocarbon materials. 

Determination of the Effects of Separation Processes on Organic Sulfur Forms in Model Compounds. Three substituted dibenzothiophenes were subjected to the coal preparation and maceral separation processes. The model compounds used are shown below. 

Samples of raw and cleaned coals produced at the Ames Laboratory and obtained from TRW have been characterized for the mineral matter content and distribution among various particle sizes. The sulfur forms before and after treatment have been determined by conventional ASTM techniques and a direct SEM method. 

During the reaction, elementary sulfur forms at the surface of the colloidal particle. Denote the fraction of the newly formed sulfur atoms which will be blocked by surfactant as Pb. Naturally, the value of Pb may be determined by expression... 

The pH is controlled by various reactions and the presence of different compounds. In fresh water systems the carbonate system C02—HC03—C03 plays a primary role in determining the pH. In other cases the presence of H2S or its oxidized form, sulfuric acid, determines low pH. The pH value is an important parameter in water quality assessment in relation to corrosion problems and taste. 

Aspiras, R. B., D. R. Keeney, and G. Chesters. 1972. Determination of reduced inorganic sulfur forms as suphide by zinc-hydrochloric acid distillation. Anal. Lett. 5 425-432. 

It can thus be seen that zwitterions IV and V would be stabilized by the interaction of the alcohol with them, and the ozonide would have no opportunity to form and decompose abnormally. Whether zwitterions IV and V are formed in equal amounts depends upon the groups which are attached to the double bond and the carbon atom to which the ozone molecule initially adds. The final products, VI and VII, may be considered as hemiperacetals or hemiperketals and could be isolated only under special conditions. However, they can be easily decomposed with either sulfurous acid or sodium bisulfite and the ketones or aldehydes formed determined quantitatively as their 2,4-dinitrophenylhydrazones. 

The freezing-point depression constant of pure H2SO4 is 6.12 K kg mol . When 2.3 g of ethanol (C2H5OH) is dissolved in 1.00 kg of pure sulfuric acid, the freezing point of the solution is 0.92 K lower than the freezing point of pure sulfuric acid. Determine how many particles are formed as 1 molecule of ethanol goes into solution in sulfuric acid. 

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