Impact of H-Bonds and Porphyrins on Asphaltene Aggregation As Revealed by Molecular Dynamics Simulations

The presence of metalloporphyrins alongside asphaltenes in heavy fractions of crude oil is a key issue in petroleum exploration and upgrading. These compounds are also expected to display interfacial activity in water/toluene mixtures, but the origin of this phenomenon remains uncertain. In this work, we use molecular dynamics simulations to investigate complex asphaltene mixtures constituted of 10 different molecules, under also multifaceted solvation conditions (toluene/n-heptane/water). We add nickel and vanadium (under the form of vanadyl) porphyrins with occasionally grafted polar lateral chains, in these mixtures. The aggregation behavior and interaction with water molecules (as a model to have insights from the interfacial activity of such molecules) are intimately linked to the type of porphyrin and to the molecular properties of the asphaltenes (mainly the presence of polar lateral chains). Vanadium porphyrins, even without polar lateral chains, can form H-bonds that might contribute to their presence within asphaltene nanoaggregates. Moreover, when polar lateral chains are present in asphaltene molecules, the systems display a supramolecular organization with several distinct interactions at the same time. The shapes of these systems do not totally agree with the traditional Yen-Mullins model. In the first part of this work, we finally propose that complex asphaltene systems in complex solvent mixtures seem to have a supramolecular behavior with non-negligent colloidal behavior as well. This should be indicative that Yen-Mullins and Gray's models of asphaltene self-assembly are neither conflictual nor antagonistic. They are two facets of a scale- and molecular structure-dependent complex mechanism.