Asphaltene Solubility in Common Solvents: A Molecular Dynamics Simulation Study

Solubility of all proposed molecular models of asphaltene in various solvents is studied through molecular dynamics simulation to find the structural parameters which have a determining effect on asphaltene solubility. It is found that higher numbers of aromatic rings and heteroatoms such as oxygen, nitrogen, and sulphur in the molecular structure of asphaltenes raises their solubility in the solvents, whereas the length of aliphatic group, which increases the chain length, lowers their solubility. In addition, a cubic correlation equation for evaluating the asphaltene solubility parameter as a ratio of number of aromatic rings in the asphaltene molecular core to the number of carbon atoms in the asphaltene side chains is proposed. The results indicate that the relative energy difference (RED) of asphaltene models and isopropyl benzene, as a solvent, is the lowest compared with other solvents. To elucidate the mechanism of asphaltene dissolution in the common solvents the solubility of two asphaltene structural models in three solvents, including isopropyl benzene, toluene, and heptane, were studied by evaluating the radial distribution functions (RDFs) of the asphaltenes, and the results confirm that asphaltene has the highest solubility in isopropyl benzene.