Analysis of organic sulfur and nitrogen in coal via tandem degradation methods. Final technical report, 1 September 1991--31 August 1992

Abstract

With the recent increase in concern for environmental issues and the implication of sulfur and nitrogen in coal combustion products as prime causes of acid rain, it has become clear that there is an urgent need for alternative methods for de g the nature of organic sulfur and nitrogen compounds in coal. The principal impediment to the molecular characterization of organic sulfur and nitrogen forms in coal is the polymeric nature of coal`s molecular structure, ordering coal insoluble and impossible to analyze by the necessary gas chromatographic (GC) methods. In our research, we apply mild chemical degradation techniques in order to render coal soluble in common organic solvents and thus amenable to standard GC characterization. The study also seeks to apply the degradative techniques to coal asphaltenes, since they are believed to be polymeric structures similar to the whole coal, but smaller and more readily analyzed. Of the degradation techniques used to date, oxidation by sodium dichromate provides the best chemical structural information. A variety of major sulfur compounds were detected in the dichromate oxidation products of demineralized IBC101 coal, including thiazoles (compounds which contains both sulfur and nitrogen) and a series of isomers of C{sub 2}-, C{sub 3}and C{sub 4}-alkylthiophene derivatives. Precise agreement between GC-MS and sulfur-selective GC-FPD data was obtained for these compounds, which probably originated as short alkyl chains on exterior portions of the original peat macromolecular structure that were sulfurized shortly after burial by H{sub 2}S. The results were further confirmed by the analysis of a non-Illinois Basin coal with nearly twice the organic sulfur content of IBC101.