Electrokinetic characterization of asphaltenes and the asphaltenes-resins interaction

The electrophoretic mobility of asphaltene particles formed by precipitation induced by the addition of n-heptane to asphaltene solutions in toluene was measured in water and in nonpolar media. Dispersed in water, the particles presented a negative electrophoretic mobility, whereas in toluene their mobility was positive and around 2.0 x 10(-9) m(2)/V s. When resins were present in the precipitating medium, a coprecipitation of these fractions occurred, indicating an adsorption or binding process of the resins on the nascent asphaltene particles. This interaction, however, did not significantly change the electrophoretic mobility of the asphaltene particles. In contrast with commercial dispersants, resins fail to stabilize asphaltene dispersions. This result indicate that the descriptions representing asphaltenes as a solid phase intrinsically insoluble in hydrocarbon media dispersed by adsorbed resins molecules does not accurately represent the structure of these fractions.