Self-assembly and solubility properties of polyaromatic compounds studied by molecular dynamics simulation

In the present study, molecular dynamics (MD) simulations were used to systematically investigate the solubility properties of model compounds of asphaltenes and maltenes. These model compounds with different double bond equivalent (DBE) and carbon numbers were reconstructed from the vacuum residue of crude oil. Asphaltenes occupy a different compositional and molecular structure space from maltenes due to their significantly higher aromaticity than maltenes. The boundary of asphaltenes and maltenes was previously determined by Rodgers et al. from their experimental study on a given class of crude oils. Based on MD simulations using various types of model compounds, the Hildebrand solubility parameters (HSP) of these model compounds can be obtained. The results of simulation show the following trend: i) for a constant DBE value, the HSP values decrease with increasing alkyl chain lengths; and ii) for a constant alkyl chain length, the HSP values increase with increasing the DBE values. The HSP threshold value of solubility range was found to be delta s +/- 2.86 MPa1/2, which is a good indicator to distinguish the composition and structure boundary for asphaltenes and maltenes. The MD simulation results provided molecular-level theories to distinguish the compositional space of asphaltenes and maltenes and determine solubility properties of crude oils.