A molecular dynamics simulation on dissolution of subcritical water in heavy oil: (I) Effect of polycyclic aromatic hydrocarbons

Abstract

Molecular dynamics simulations were applied to characterize the dissolution of subcritical water (Sub-CW) in polycyclic aromatic hydrocarbons (PAHs). The phase equilibria of Sub-CW/PAHs are characterized by the dissolution of Sub-CW in PAHs.The solubility of Sub-CW increases with temperature but is relatively insensitive to pressure changes. Furthermore, an increase in PAH scale leads to a decrease in Sub-CW solubility. The PAH-rich phase can be divided into an interface region and a bulk region, and the water concentrations in the two regions differ greatly. The Hansen solubility parameters of PAHs and Sub-CW exhibit opposite distributions, hindering the mutual solubility between the two. The dissolution of Sub-CW is promoted by the destruction of intermolecular hydrogen bonds of water at increasing temperature, but is ultimately inhibited by the difference in dispersion properties between PAHs and Sub-CW. According to the Gibbs solvation free energy, the electrostatic interaction between PAHs and Sub-CW favors the dissolution of Sub-CW. Meanwhile, the van der Waals interaction shows different effects.