Thermodynamics of Interactions at Infinite Dilution between Asphaltenes and a Surfactant or Crude Oil Resins

We present a thermodynamic study of the interactions between asphaltenes and a surfactant and between asphaltenes and resins of crude oil at 303.15 K in toluene solution, using a recent thermodynamic scheme, which allows the study of multicomponent systems at infinite dilution. The specific partial volumes and the specific partial adiabatic compressibility coefficients at infinite dilution were calculated from the experimental measurements of densities using vibrating tube instruments and of speeds of sound. Systems containing asphaltenes and the surfactant tert-octylphenol in solution in toluene behave in the same way as systems containing noncharged polymeric particles and a cationic surfactant in water. Therefore, it can be concluded that the main interactions in these systems are the solvophobic interactions and that these interactions only affect the surface of the asphaltene aggregates. To study the interactions between asphaltenes and resins, we developed an alternative method to separate the resins fractions. This method is quicker, cheaper, and more accurate than the usual method based on chromatography columns. Systems composed of asphaltenes and resins in solution in toluene present a similar sequence of interactions as systems composed of a protein and a ionic surfactant in solution in water.