Preparative subfractionation of petroleum resins and asphaltenes. II. Characterization of size exclusion chromatography isolated fractions

In the first study of this series, resins and asphaltenes from stable and unstable crude oils have been separated by size exclusion chromatography in three molecular mass ranges (MM: high, medium, and low). In the present study, the isolated fractions were further characterized in order to correlate several of their structural properties with crude oil tendency to solid deposition. Elemental analysis (C,H,S,N), infrared spectrophotometry (IR), and proton nuclear magnetic resonance (H-1 NMR) were the characterization techniques performed in order to meet the objective. Hydrogen deficiency and aromaticity appear to be the main parameters governing the intrinsic stability for the studied samples. Oxygen compounds were observed to be more abundant within fractions isolated from unstable oils, particularly in resins and in the low MM range fractions both from resins and asphaltenes. However, causes for the presence of these oxygenates remain open to further study. Experimental evidence gathered during this work suggest the possibility of small compounds acting like natural dispersants of the larger components present in complex mixtures like asphaltenes.