Evaluation of the affinity of asphaltene molecular models A1 and A2 by the water/oil interfaces based on a novel concept of solubility parameter profiles obtained from MD simulations

Abstract

Crude oils are formed of asphaltenes that are species soluble in certain solvents such as toluene. The distribution of asphaltene models and their mixtures in water/n–heptane and water/toluene systems were explored with MD simulations. A1 and A2 asphaltene models were used for the exploration of the affinity of these compounds by the water/oil interfaces. For this, a novel concept called solubility parameter profiles was used to characterize the polarity of the regions present in water/n–heptane and water/toluene systems. Molecules of asphaltene models, n–heptane, and toluene were described with the GROMOS53A6 force field and CHELPG atomic charges, and water molecules with the SPC model. The prediction of the affinity of A1 and A2 asphaltene models at interfaces was determined using the total solubility parameter differences calculated between these species and solvent molecules. Calculated solubility parameters show a good correlation with experimental values. Total solubility parameter differences equal to Δδtotal = 3.76 MPa0.5 and Δδtotal = 0.36 MPa0.5 at the water/n–heptane interface suggest that asphaltene models have a good affinity by the water/n–heptane interface in comparison with the water/toluene interface whose values were Δδtotal = 5.82 MPa0.5 and Δδtotal = 9.94 MPa0.5 for A1 and A2 asphaltene models, respectively. It was demonstrated that the affinity of asphaltenes by a specific region of the immiscible system is controlled by the electrostatic and dispersive contributions associated with the solubility parameter profiles.