High molecular weight aromatic nitrogen and other novel hopanoid-related compounds in crude oils

Abstract

Aromatic nitrogen and other novel hopanoid-related compounds were tentatively identified in biodegraded crude oils from the Liaohe Basin, NE China. They include naphthohopanes, pyridino-, quinolino-, acridino- or benzoquinolino-, and naphthoquinolinohopanes. The nitrogen-containing hopanoids occur in substantial quantities in the biodegraded oils, with around 14 ppm of a single compound of the pyridino- and quinolinohopanoids, whereas the compounds with more rings, acridino- or benzoquinolino- and naphthoquinolinohopanes, are much less abundant, with a maximum concentration less than 2 ppm and 1 ppm, respectively. These novel highly cyclised compound series may be viewed as representatives of new classes of components whose natural distribution and biogeochemical significance remain to be determined, although the possibility of diagenetic modification of known hopane precursors (as known for sulfur-containing hopanoids) cannot be ruled out. Alternatively, inorganic nitrogen (ammonium ion) which is abundant in oil field waters, sourced by clay water equilibria, could be incorporated into biohopanoids to lead to these novel compound classes. In addition, hopanes and hopanoic acids were detected up to C 40 and C 37, respectively, as were as the common aromatic benzohopanes. These biodegraded oils are strongly enriched in hopanoids, with contents of the aliphatic hopanes up to 6.3% of the whole oil.