Effect of Precipitating Conditions on Asphaltene Properties and Aggregation

Asphaltene, resin, and maltene physical isolation procedures involving different alkane precipitants and solvent/sample ratios were applied in this work to Athabasca bitumen vacuum residue. Samples were characterized by solubility profiling, size exclusion chromatography, fluorescence spectroscopy, X-ray photoelectron spectroscopy and density–viscosity analyses. Isolated fractions were found to display systematic property changes. Thus, it was found that denser, more polar, higher molecular weight (MW), more viscous, red-shifted fluorescence materials were sequentially ranked as follows: solvent extracted asphaltenes, C7 (unwashed) asphaltenes, C5 (unwashed) asphaltenes, resins, and maltenes. Intermolecular aggregation for these fractions was determined to follow the same order. Decreasing contents of resins in the same order were found to increase aggregation phenomena. This work further reports on aspects of possible practical interest, i.e., the liquid nature of asphaltenes at 300 °C and the possible existence of oxidative reactions affecting fraction isolation that follow standard methods which do not contemplate inert atmospheres. Preliminary assessment of chemical functionalities within isolated fractions highlighted the possible enrichment of pyrrolic compounds within resins and oxygen functionalities in asphaltenes.