Small Population of One to Three Fused-Aromatic Ring Moieties in Asphaltenes

Abstract

The aromatic ring distributions of asphaltenes are examined with emphasis on one- to three-ring moieties by using fluorescence emission spectroscopy: such a nondestructive, bulk analysis of small aromatic moieties in asphaltene has not been achieved by any other method. Asphaltenes are found to lack significant populations of these small rings compared to larger ring systems; increasing relative populations of small ring moieties are found for resins and maltenes, as expected. Additionally, the one asphaltene with higher polarity possesses smaller aromatic ring systems. Potential perturbations of asphaltene spectra by energy transfer effects are ruled out, using analyses based on fluorescence lifetimes. Energy transfer, which yields red-shifted emission, is known to decrease fluorescence lifetimes. Fluorescence lifetimes of dilute asphaltene solutions are shown to be intrinsic by comparison to those of deasphaltened crude oils; thus, fluorescence emissions of dilute asphaltene solutions are unaffected by energy transfer.