Direct determination of total organic sulfur in coal

RILEY ET AL. Direct Determination of Total Organic Sulfur in Coal... 

A method for the direct determination of the organic sulfur in coal using extraction with hot nitric acid was developed. The method yields total organic sulfur values that are much closer to the sulfur values found in deep cleaned coals and with greater precision than the organic sulfur values obtained by ASTM Method D 2492. 

There are methods for the direct determination of organic sulfur in coal (3.4), but details regarding individual molecular structures are much harder to obtain. Much of the research designed to obtain this information has concentrated on the analysis of coal extracts (5.6) and pyrolysis products (7.8). Unfortunately the sulfur species from pyrolysis processes may be highly modified and usually account for only a very small percentage of the total sulfur in the coal. 

It appears that adding to all these difficulties is the lack of a satisfactory method for the direct determination of organic sulfur in coal that could be routinely applied to all coals under all conditions. The commonly used ASTM procedure (7) for organic sulfur is an indirect method, based on the difference between the total sulfur and the total inorganic... 

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. 

A procedure for the direct determination of the sulfate, sulfide, pyritic, and organic sulfur in a single sample of coal has been reported by McGowan and Markuszewski (17). The method uses various strengths of perchloric acid as the selective oxidizing agent. The results obtained for the analysis of three coals were comparable to ASTM results and the relative standard deviations for nine sulfate, four pyritic, six organic, and four total recovered sulfur determinations were 2.7, 3.4, 2.4, and 2.4%, respectively. 

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