Long-chain aliphatic nitriles in pyrolysates of young kerogen: implications for the intermediates in petroleum hydrocarbon formation.

Abstract

Gas chromatographic/mass spectrometric examination of products from laboratory thermal degradation of kerogen from a young marine sediment (Tanner Basin off California), revealed a series of long-chain nitriles whose carbon-chain lengths range from 12 to 26. These compounds appeared after the relatively mild thermal conditions of 310–350°C for 5–116 hrs and disappeared before major n-alkane generation. We hypothesise that n-alkanes are generated at the expense of long-chain fatty nitriles which in turn are formed via fatty acid amide-linked structures in kerogen. Heating of standard long chain (C18) fatty acid amides with kerogen produced n-alkanes with no odd/even predominance. The heating experiments showed that these nitrogen compounds have a strong potential for producing a series of normal hydrocarbons. Consequently, nitrogen-linked long-methylene-chain structures in kerogen analogous to fatty acid amides/fatty nitriles can act as one of the precursors of petroleum hydrocarbons.