SMALL POPULATION OF ONE TO 3 FUSED-AROMATIC RING MOIETIES IN ASPHALTENES

The aromatic ring distributions of asphaltenes are examined with empha sis on one- to three-ring moieties by using fluorescence emission spec troscopy: such a nondestructive, bulk analysis of small aromatic moiet ies in asphaltene has not been achieved by any other method. Asphalten es are found to lack significant populations of these small rings comp ared to larger ring systems; increasing relative populations of small ring moieties are found for resins and maltenes, as expected. Addition ally, the one asphaltene with higher polarity possesses smaller aromat ic ring systems. Potential perturbations of asphaltene spectra by ener gy transfer effects are ruled out, using analyses based on fluorescenc e Lifetimes. Energy transfer, which yields red-shifted emission, is kn own to decrease fluorescence lifetimes. Fluorescence lifetimes of dilu te asphaltene solutions are shown to be intrinsic by comparison to tho se of deasphaltened crude oils; thus, fluorescence emissions of dilute asphaltene solutions are unaffected by energy transfer.