Theoretical modeling of molecular interactions of iron with asphaltenes from heavy crude oil

The interaction of metallic iron with a model asphaltene molecule in the presence of water and electron-donor additives was modeled by using a quantum mechanics parametric method, CATIVIC. Results of Fe–asphaltene interactions show the formation of bonds on aromatic rings and directly on heteroatoms and so a decrease of CC, NC, and SC bond energies (bond activations) and the formation of metal–asphaltene complexes. Values of diatomic energies (DE), equilibrium bond distances (EBD), and diatomic bond energies (DBE) show that the most significant bonds arise when the interaction is directly on heteroatoms (N, S) and the highest activation is in the CS bonds. Electronic charge transfer occurs from the metal to hydrocarbon, except when interaction is on the N atom. Important metalO bond is observed when water interacts with Fe–asphaltene complex, leading to some activation of OH bonds. Negative charge on the system, in the presence of H2O, will decrease FeO and FeN bonds and will reinforce FeS ones. Comparison with previous work shows that, in general, hydrogenation and carbon–heteroatom bond activations due to metal interaction in the presence of water follow the trend: nickel > iron.

Adsorption mode of Fe on site E of asphaltene fragment F1. Final location of water molecule and Fe after interaction with H2O–[F1–Fe]0. Note that Fe was initially on site A. Figure optionsDownload as PowerPoint slide