SULFUR SPECIATION IN BITUMENS AND ASPHALTENES BY X-RAY-ABSORPTION FINE-STRUCTURE SPECTROSCOPY

The S L-edge and K-edge XANES spectra were collected on bitumen and asphaltene samples as well as model compounds in order to determine the feasibility of monitoring transformations of organic sulphur in bitumen during genesis, processing, and upgrading. Using the spectra of model compounds as fingerprints, it was possible to speciate the sulphur forms in bitumen and asphaltene. The reduced form of sulphur such as thiophenes are the predominant form of sulphur in the bitumen and asphaltene samples analyzed. No significant amounts of oxidized sulphur forms could be detected. Spectra collected using total electron yield and fluorescence yield were identical, confirming that there is no preferential partitioning at the bitumen/air interface, or oxidation during sample handling. Also important was the finding that bitumen could be analyzed at moderately high vacuum (10(-8) torr). Thus XANES represents a rapid, nondestructive mean of characterizing specific classes of compounds in complex matrices, such as bitumen.