Sulfur, forms in coal

It is generally accepted that there are several forms of mineral sulfur, other than sulfate and pyritic, present in coals. Mossbauer studies of inorganic sulfur forms in coal have shown the presence of pyrrhotite (FeS) (2), and the presence of other sulfides such as sphalerite (ZnS), and chalcopyrite (CuFeS2) have been reported by other workers (3). Several investigators have reported as much as 1% sphalerite in some northwestern Illinois coals (4-6). The presence of elemental sulfur has also been reported (7-9V The failure to account for these mineral sulfur forms results in high values for organic sulfur using the ASTM method. 

Innershell absorption spectroscopy of amino acids. J Phys Chem A 106 3153-3168 Kelemen SR, Gorbaty ML, George GN, Kwiatek PJ, Sansone M (1991) Thermal reactivity of sulfur forms in coal. Fuel 70 396-402... 

George, G. N., Gorbaty, M. L, Kelemen, S. R., and Sansone, M. (1991). Direct determination and quantification of sulfur forms in coals from the Argonne Premium Sample Program, Energy Fuels 5, 93-97. 

Sulfur constitutes about 0.052 wt % of the earth s cmst. The forms in which it is ordinarily found include elemental or native sulfur in unconsohdated volcanic rocks, in anhydrite over salt-dome stmctures, and in bedded anhydrite or gypsum evaporate basin formations combined sulfur in metal sulfide ores and mineral sulfates hydrogen sulfide in natural gas organic sulfur compounds in petroleum and tar sands and a combination of both pyritic and organic sulfur compounds in coal (qv). 

Iron pyrite, FeS2, is the form in which much of the sulfur exists in coal. In the combustion of coal, oxygen reacts with iron pyrite to produce iron(III) oxide and sulfur dioxide, which... 

With the unique reactor and smart particle designs, the oxygen carrying capacity and recyclability of the iron-based chemical looping particles have been radically improved, and OSU s SGR process has shown a great potential for commercialization. Its pilot-scale demonstration is currently under way. In addition, the sulfur present in coal is expected to react with Fe and form FeS. Flence, the SGR process has the capability of removing... 

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

Sulfur in Coal. Sulfur occurs in coal in two forms (I) organic sulfur, which is chemically bonded to the coal, and (2) pyritic sulfur, which occurs... 

Sulfur (total sulfur) sulfur found in coal as iron pyrites, sulfates, and organic compounds. It is undesirable because the sulfur oxides formed when it bums contribute to air pollution, and sulfur compounds contribute to combustion-system corrosion and deposits. 

Yurovskii (48) recognized the importance of elemental sulfur in the formation of pyritic and organic sulfur compounds and suggested that the elemental sulfur found in coal today is a primary substance formed during coal formation. However, this view is unsupported by recent data (47). 

Geochemical studies of sulfur in coal provide information on the forms, distribution, and origin of sulfur in coal. The variation of sulfur content in coal is controlled by geologic conditions during coal formation. This is... 

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. 

Assuming that the composition of the sulfur forms in the asphaltene samples and the Rasa coal is approximated by the simple two component mixture of dibenzothiophene and dibenzylsulfide models, an estimate of the relative molar quantities of sulfide and thiophenic forms can be obtained as described above and from Figure 3. These approximate values are listed in Table II. 

It is evident that detectable quantities of sulfur form in the pristine coals in less than two months. The rate of formation of sulfur appeared to be enhanced significantly when the coal was suspended above water in a closed desiccator. Clearly, a broad array of factors such as particle size, air currents and so forth will influence the rate of sulfur production, but there is no doubt that it is a facile process. 

Until recently, there have been only a few reports of aliphatic sulfur structures in coal (1,12). These results together with the experiments of Gorbaty et al. (11), give further support for the presence of labile (presumably aliphatic) sulfur moieties in high-organic sulfur-containing coals. In the previous sulfur study (1), one bituminous coal was analyzed for organic sulfur forms both by the... 

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. 

Casagrande et al. (1977) found pyrite in peat formed in a marine environment to constitute over 15% of the sulfur present while the pyrite level in freshwater peat was an order of magnitude lower. Carbon-bonded sulfur accounted for 50% of the total sulfur in marine peat, but 70% in freshwater peat. Ester-sulfate constituted 25% of the sulfur in both cases. These authors concluded that the total sulfur found in coal can be incorporated in the peatforming stage. 

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