NITROGEN CHEMISTRY OF KEROGENS AND BITUMENS FROM X-RAY-ABSORPTION NEAR-EDGE STRUCTURE SPECTROSCOPY

X-ray absorption near-edge structure (XANES) spectroscopy studies have been conducted on several different kerogens and bitumens to identify all the different nitrogen chemical structures present. Virtually all of the nitrogen is present in aromatic forms; pyrroles are the most dominant type, followed by pyridines, pyridones, and aromatic amines. A considerable amount of porphyrinic nitrogen, characterized by significant spectral effects, is found in one of the bitumens. The pyridone fraction in the kerogens and bitumens is much larger than in petroleum asphaltenes, suggesting that petroleum generation is accompanied by the loss of pyridone, possibly by conversion to pyridines. Differences are found between the kerogens and bitumens from the same source rock, indicating that bitumen analysis cannot substitute for kerogen analysis at least for nitrogen chemistry. There is no qualitative difference in the types of nitrogen compounds between kerogens produced by HCl or HF digestion.