Role of Asphaltene Origin in Its Adsorption at Oil–Water Interfaces

We have studied the interfacial properties of oil–water interfaces in the presence of asphaltenes from different sources, crude oil, bitumen, and coal. The study includes dynamic interfacial tension (DIFT) and interfacial compression rheology measurements. By comparison of DIFT for different concentrations, we show that the kinetics is dominated by interfacial reorganization. Some of the asphaltenes are found more interfacially active than others, but adsorption is irreversible for all. The interfacial rheological behavior is also varied: asphaltenes from petroleum with equal aliphatic and aromatic fractions and immature bitumen with a large aliphatic fraction and small aromatic fraction form flexible interfacial layers, whereas coal asphaltenes with a large aromatic fraction and small aliphatic fraction form rigid layers. As other asphaltenes, the petroleum and coal asphaltenes of the present study form layers that equilibrate rapidly below the critical nanoaggregate concentration (CNAC). The immature shale asphaltenes behave differently as the other asphaltenes studied above the CNAC. The interfacial layers have a marked nonlinear behavior, particularly pronounced for the coal asphaltenes, in which complex Lissajous’ diagrams indicate stacking upon compression. We discuss the overall interfacial behavior in terms of molecular differences between asphaltenes.