Waxy Crude Oil Emulsion Gel: Chemical Characterization of Emulsified Phase Extract Components

Emulsions of several waxy crude oils exhibiting similar properties were prepared and characterized to better understand the nature of their polar components. Both crude oils and their corresponding emulsions were analyzed by negative-ion electrospray Fourier transform ion cyclotron resonance mass spectrometry [ESI (-) FT-ICR MS]. The most abundant classes found in these crude oils were neutral N, acidic O, and O-2 heteroatomic compounds. The N class was present in higher relative abundance in all samples, followed by the O class (phenolic-like compounds). The O-2 class was minor in all crude oils, corroborating their low total acid number (TAN) values. The O/O-2 class ratios were directly correlated with their rheological properties. Higher O/O-2 class ratios were associated with crude oils that formed gel emulsions, indicating that O class compounds play an important role in gel emulsion stabilization. The identified phenolic compounds possess a structure that allows for (i) intermolecular hydrogen-bonding interactions that facilitate the formation of large aggregates and (ii) van der Waals interactions (e.g., pi stacking and solvophobic effects) that promote attraction of the large aggregates. We propose that the alignment of paraffins and the alkyl side chains of phenolic-like compounds contribute to the emulsion stability and affect the rheological behavior of the highly paraffinic crude oils. The analysis of the emulsion phase confirmed the presence of the O class (phenolic compounds) as well as the acidic O-2, O-4, O4S, and nitrogen-containing classes (NO and NO2), indicating the surface activity of compounds bearing at least one oxygen atom. These results suggest an enhanced activity of O-containing compounds in gel formation and the stabilization of emulsions of highly paraffinic crude oils.