Molecular Mechanics and Microcalorimetric Investigations of the Effects of Molecular Water on the Aggregation of Asphaltenes in Solutions

Abstract

The interaction of two model asphaltene molecules from the Athabasca sand oil with a water molecule in a toluene solution was studied by means of molecular mechanics calculations. It was found that water forms bridging H bonds between the heteroatoms of asphaltenes with a considerable span in energies. The stronger H bond found has energies higher than those corresponding to the stacking of the aromatic areas of the same asphaltene molecules. This shows that the water molecule may generate additional mechanisms of aggregation of asphaltenes in toluene solution, as found experimentally. The H bond mechanism depends on the heteroatoms involved, the extension of the aromatic regions, and the steric interference present in the asphaltene molecules. The simulation results have been compared with experimental values of enthalpy of association of two different petroleum asphaltenes obtained by titration calorimetry. A simple dimer dissociation model was used to derive the information about the heat and the constant of dissociation from asphaltenes of Mexico and Alaska obtained from the calorimetric data. The association enthalpies calculated were found to be in excellent agreement with those measured, although the simulation only employed the interaction between averaged molecular structures.

Asphaltene adsorption on quartz sand in the presence of pre-adsorbed water

“…This latter view supports other results from simulation and experiment, that low water concentrations promote asphaltene nanoaggregation in toluene solution [13], which is suggested to involve intermolecular H-bonded water bridges and asphaltene heteroatoms, e.g.…”

Calorimetric Evidence about the Application of the Concept of CMC to Asphaltene Self‐Association

“…The main technique applied is isothermal titration calorimetry (ITC). However, it has never had an extended application to petroleum species (Dietz, Blaha, and Li 1977;Andersen et al 2001;Murgich et al 2002;Merino-Garcia and Andersen 2003). The advantage of this ITC technique above others is that it allows the determination of both the CMC and the enthalpy of surfactant micellization in a single experiment.…”

Asphaltene Aggregation in Aqueous Solution Using Different Water Models: A Classical Molecular Dynamics Study

“…The polar heteroatoms of the asphaltene are involved in the formation of the H bonds with water. Murgich et al 40 performed molecular mechanics calculations and titration calorimetry experiments to investigate the H bonds between asphaltene heteroatoms and water. The study showed that water enhances the association of asphaltene monomers to form dimers because of the formation of H bonds with water molecules.…”