Diamondoid hydrocarbons - Application in the chemical fingerprinting of natural gas condensate and gasoline

Diamondoids are a class of naturally occurring, saturated hydrocarbons in petroleum that consist of three or more fused cyclohexane rings, which results in a "diamond-like" structure. The diamondoids that can be found in light petroleum liquids (e.g., natural gas condensates), intermediate petroleum distillates (e.g., naphthas), and finished petroleum products (e.g., automotive gasoline) include adamantane (boiling point similar to190degreesC) and diamantane (boiling point similar to272degreesC), and their various substituted equivalents. Previous petroleum geochemistry studies indicate these naturally occurring compounds are extremely resistant to weathering. As such, their distribution and relative abundance in environmental samples can be useful in the chemical fingerprinting of light petroleum and gasoline. In this article, the application of diamondoids in the chemical fingerprinting of lower boiling petroleum in environmental samples is introduced and demonstrated. Specifically, the relative abundance of C0- to C4-alkylated adamantanes, as determined relative to comparably boiling C5-alkylated benzenes, is shown to be significantly greater in natural gas condensates than in gasoline-derived nonaqueous phase liquids (NAPLs) and modem automotive gasolines, which along with more conventional fingerprinting further allows for their distinction in the environment.