Molecular Basis of Asphaltene Stability

The instability of asphaltenes in crude oils, manifested in their precipitation, is a major production issue that may arise both during the recovery and processing of petroleum feedstocks. The purpose of this study was to investigate the molecular structure of asphaltenes in order to shed light on the causes of their precipitation. To this end, the molecular structures of stable (remaining in the solution) and unstable (precipitated) asphaltenes were characterized by EPR, NMR, and IR spectroscopy. Using crude oil asphaltenes and air-blown asphalt as objects for the study, only weak increasing and decreasing trends were observed in the content of aromatics and oxygenates, respectively, in the unstable asphaltene fraction. The stable and unstable asphaltenes were found to differ in adsorption capacity. It was shown that the species adsorbed on asphaltenes are rich in moieties of aromatic acid esters, and that removing these species further eliminates the structural-group composition differences between stable and unstable asphaltenes. The study findings suggest that the stability of asphaltenes in crude oils can be controlled by introducing synthetic aromatic acid esters structurally similar to natural surfactants.