Abstract :
Several aspects related to light aromatic compounds in petroleum are discussed: relative abundance in crude oils, possible associations between their contents and those of other major petroleum components, generation in radical and acid clay-catalyzed reactions from model compounds representing various petroleum components (n-alkanes, isoprenoid alkanes, light naphthenic compounds, saturated polycyclic hydrocarbons, alkylaromatic compounds) and chemical mechanisms of aromatization during petroleum maturation. Model cracking reactions of various petroleum constituents indicate that light aromatic compounds are most likely formed during the petroleum catagenesis stage from a variety of sources, most importantly from compounds containing long n-alkyl and isoprenoid chains. The most probable sequence of events leading to aromatization includes cracking of saturated hydrocarbon chains to olefins, cracking of olefins to dienes, cyclization of dienes to cyclodienes and aromatization of cyclodienes. The molecular weight distribution of aromatic compounds in petroleum is most probably controlled by temperature and duration of the last stages of petroleum maturation. This distribution correlates with the distribution of n-alkanes as a function of their carbon number. Presented data on isomerization of individual aromatic compounds and aromatics distribution in crude oils suggest that aromatic compounds generated in cracking reactions undergo extensive isomerization and exchange of alkyl substituents. These reactions result in a nearly complete randomization of the types of alkyl substituents (mostly methyl and ethyl groups) and their positions in aromatic rings. These mixtures in most crude oils can be represented by thermodynamic equilibrium estimations for 200–300°C.
