DIRECT DETERMINATION AND QUANTIFICATION OF SULFUR FORMS IN COALS FROM THE ARGONNE PREMIUM SAMPLE PROGRAM

Sulfur K edge X-ray absorption near edge structure spectroscopy (XANES) and X-ray photoelectron spectroscopy (XPS) have been developed for the direct determination and quantification of the forms of organically bound sulfur in nonvolatile petroleum and coal samples. Both techniques were used to characterize organically bound sulfur forms in coals from the Argonne Premium Coal Sample Program. XANES and XPS spectra were taken of a number of model compounds, mixtures of model compounds, and coal samples. A third-derivative analysis of the XANES spectra involving curve reconstruction was required to account for the presence of pyrite and aromatic sulfur. Curve resolution of the XPS spectra allowed approximate quantification of the surface aliphatic and aromatic components. XPS spectra showed little evidence of oxidized sulfur forms despite the presence of iron oxides and hydroxyoxides in the iron 2p spectra. Pyritic iron was identified only in Illinois No. 6 coal. The measured quantity of pyritic iron was used to interpret the sulfur 2p XPS spectrum. Both XANES and XPS show a monotonic increase of aromatic sulfur, defined as sulfur bound to two sp2-hybridized carbons, with increasing rank in the Argonne premium samples.