Role of Compounds Adsorbed onto Asphaltenes in Stabilizing Water–Oil Emulsions

This study employs IR spectroscopy to investigate the compositional features of an asphaltene fraction that promotes the formation of stable water–oil emulsions. Emulsification was achieved by mixing distilled water with toluene and heptol solutions of asphaltenes. This asphaltene fraction was found to be enriched in ester fragments and monoaromatic compounds. During standard crude oil deasphaltenization, heptane-soluble compounds became trapped in—or adsorbed onto—the asphaltenes. These compounds were subsequently isolated from the asphaltenes through repeated dissolution of the asphaltenes in toluene and washing in n-heptane, and then characterized. They accounted for up to 20 wt % of the asphaltene mass and consisted predominantly of resins (60–80 wt %). Their structural group composition closely resembled that of the asphaltene fraction responsible for the emulsifying properties of crude oil. We suggest that the surface-active behavior of crude oil arises from resin-like monoaromatic compounds enriched in ester groups, which exhibit a strong affinity for asphaltenes.