COMPARISON OF PYROLYTIC AND X-RAY SPECTROSCOPIC METHODS FOR DETERMINING ORGANIC SULFUR SPECIES IN COAL

Three methods for speciating and quantifying the forms of organically bound sulfur in coal, one based on chemical reactivity, and the other two based on direct measurement by X-ray absorption spectroscopies, are described and compared. One is based on the isothermal flash pyrolysis of coals as a function of temperature. The other two are based on spectra taken by X-ray absorption near-edge structure (XANES) spectroscopy and X-ray photoelectron spectroscopy (XPS). Data on aliphatic sulfur content of Rasa coal determined by the pyrolysis method are reported. With minor modification in the pyrolysis method, these three methods, used to characterize organically bound sulfur for the same suite of coal samples in terms of sulfidic and aromatic or thiophenic forms, give similar values. The pyrolysis method utilizes a specialized coal feeder, temperature-controlled fluidized sand bed, and a suitable analyzer such as a gas chromatograph with a sulfur-sensitive photodetector for H2S, CS2, and COS. The XANES method requires the availability of a synchrotron light source, and the XPS method requires the appropriate spectrometer. All three methods show that sulfur-containing low-rank coals tend to be high in sulfidic sulfur, whereas higher rank coals tend to contain mostly thiophenic sulfur forms.