Application of spectral fluorescence microscopy for the characterization of Athabasca bitumen vacuum bottoms

The relationship between visible light region fluorescence properties and gross chemical composition of ten narrow cut subfractions of Athabasca bitumen separated by super critical fluid extraction has been studied. The objective of this investigation was to evaluate the potential for utilizing spectral fluorescence microscopy for empirically assaying the chemical composition (e.g. wt% saturates, aromatics, resins and asphaltenes) of the bitumen fractions. Two spectral parameters were used to characterize the bitumen fluorescence properties: Lambda max (Lmax in nm) or the wavelength of maximum emission intensity, and Q, which is the ratio of intensity at 650 nm to the intensity at 500 nm. Positive linear relationships with high r2 values were established for Lmax and Q parameters, which correlated with the wt% of resins plus asphaltenes, aromatic carbon, C/H atomic ratio and wt% of S. In addition, the fluorescence properties displayed a progressive red shift to longer wavelengths. Lmax and Q versus saturate/aromatic ratio and wt% saturates showed a negative linear relationship consisting of two distinct linear segments. Although Lmax and Q increased up to about 550 nm and 1.0, respectively, they showed a progressive red shift in the second segment that was accompanied by a decrease in both values. Weight per cent aromatics exhibited a polynomial (?) relationship with fluorescence properties, which may reflect variations in the proportion of mono- and di-aromatics relative to cata-condensed aromatics within the Athabasca bitumen subfractions.