Investigation of the Effect of Sulfur Heteroatom on Asphaltene Aggregation.
Résumé
The authors present mol. dynamics simulations (MDS) for interpreting the mol. aggregation of four different asphaltene mol. models. These simulations are based on recent small-angle x-ray scattering (SAXS) and small-angle neutron scattering (SANS) expts. from Eyssautier and co-workers (Eyssautier, J. et. al. (2011)) which proposed a discoidal asphaltene nanoaggregate structure of 0.67 nm height and its chem. compn. Basically, the authors have studied the sulfur atom position in the asphaltene structure. π-π is the main type of contact, and it seems to be responsible for the parallel orientation of mols. This geometry is also corroborated by the cosine of angles between the polyarom. cores. However, the polar side chain is also important to the aggregation, because it occurs in the systems during all of the simulations. Three systems, namely, systems 1T, 2T, and 4T, are in good agreement with exptl. work, indicating an av. height \textless0.8 nm. Concerning the place occupied by the sulfur atom in the mol., when it is grafted directly to the conjugated core, no effect can be deducted from the stability of dimers and trimers and all of the other studied parameters. This is not the case when sulfur is located in the lateral chain, where it has a particular affinity with oxygen and hydrogen atoms of the acid chain ends of neighboring mols. Consequently, probably these configurations of the sulfur atom are more likely to be problematic in the oil industry. [on SciFinder(R)]