Solvation of asphaltenes in supercritical water: A molecular dynamics study

To improve the understanding of the condensation of asphaltenes in supercritical water (SCW), the solvation of asphaltenes under SCW environments was investigated with molecular dynamics simulation. The simulation results indicate that the repulsive van der Waals interaction has a primary influence on the nature and the magnitude of the interaction between asphaltenes and SCW. A cavity short-range solvent structure surrounding asphaltenes thus is formed, and the solvation free energy (G(sol)) of asphaltenes in SCW has a positive sign in most cases. The scale of cavities and the value of G(sol) both are determined mainly by the bulk density of water. By the repulsive asphaltenes/SCW interaction and the attractive pi pi aromatic interaction, the aggregation of asphaltenes in SCW occurs spontaneously. The asphaltene clusters formed, containing asphaltene monomers and nanoaggregates, present a coke-like supramolecular structure. Benefiting from excellent diffusivity in SCW, the aggregation of asphaltenes in SCW can be accomplished rapidly. (C) 2016 Elsevier Ltd. All rights reserved.