ABSTRACT

With the aim of improving understanding of aromatic hydrocarbon formation by transformation of alkanes during maturation, the C₂₃, C₂₈, C₂₉, C₃₁ and C₃₆ n-alkanes and pristane were separately heated at 350–500°C in a closed system for 72 h to determine the aromatic hydrocarbon species and their characteristics formed by pyrolysis. Analysis of the obtained pyrolysates using gas chromatography-mass spectrometry showed that pyrolysis of different alkanes formed similar aromatic hydrocarbons with increasing maturity, regardless of whether they were straight chain or isoprenoid. Monoaromatic compounds were preferentially formed first, followed by various dicyclic and polycyclic aromatics. Many common aromatic hydrocarbons were detected in the pyrolysates, and their distribution suggests that alkanes are an important aromatic hydrocarbon source in petroleum formed by high maturity. Some aromatic hydrocarbons that are known to originate from biological precursors could also be formed by pyrolysis, so more attention to sample maturity is required when such compounds are used as source indicators. With increasing temperature, the aromatic hydrocarbons mainly underwent polymerization and desubstitution reactions, resulting in an elevated amount of polyaromatics and fewer substituted aromatic compounds.