DETERMINATION OF THE CHEMICAL ENVIRONMENT OF SULFUR IN PETROLEUM ASPHALTENES BY X-RAY ABSORPTION-SPECTROSCOPY

Sulphur K-edge X-ray absorption spectra are analysed for a diverse series of petroleum asphaltenes. The spectra of the asphaltenes are interpreted by fitting with a linear superposition of model compound spectra. This analysis procedure is shown to work quite well in a stringent test case. The reduced forms of sulphur, thiophenes and sulphides dominate in all of the asphaltenes. Generally, the sulphoxide group is the most dominant form of the oxidized sulphur. Comparison of the X-ray data with the elemental composition of the asphaltenes shows that the sulphur and oxygen are preferentially bonded to each other. The inverse dependence of the oxygen-sulphur correlation with the fraction of sulphur which is sulphide suggests that oxidation of sulphur occurs preferentially at the sulphide group.