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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. • Phase equilibria of PAHs and Sub-CW were studied by MD simulation. • Phase equilibria of PAHs and Sub-CW feature dissolution of Sub-CW in PAHs. • Solubility of Sub-CW in PAHs is sensitive to temperature change. • Opposite distributions of Hansen HSP hinder dissolution of Sub-CW in PAHs. • Electrostatic interaction promotes dissolution of Sub-CW in PAHs. [ABSTRACT FROM AUTHOR]

The phase equilibria of subcritical water (Sub-CW) and four-ring N-, S-containing heterocyclic aromatic hydrocarbons (hetero-PAHs) were investigated by molecular dynamics simulation. In a temperature range of 250–350 °C and a pressure range of 4.2–21 MPa, the mixture of hetero-PAHs and Sub-CW shows an equilibrium between water-rich and oil-rich liquid phases, characterized by a significant dissolution of water in the oil phase. The solubility of Sub-CW is 1.9–3.8 wt% in N-containing hetero-PAHs and 1.0 to 2.7 wt% in S-containing hetero-PAHs. Compared with polycyclic aromatic hydrocarbons (PAHs) with the same ring number, the presence of the thiophenic ring in hetero-PAHs leads to a decrease in the solubility of Sub-CW. The particularity of N-containing hetero-PAHs lies in the hydrogen bond between the pyridinic ring and water molecules, which increases the solubility of Sub-CW at temperatures below 300 °C. The solubility of Sub-CW in hetero-PAHs/PAHs can be correlated with the Gibbs solvation free energy of water dissolved in the oil phase and the cohesive energy density of the oil phase as parameters. • Phase equilibria of hetero-PAHs and Sub-CW were studied by MD simulation. • Phase equilibria feature dissolution of Sub-CW in hetero-PAHs rich phase. • The presence of thiophenic rings in hetero-PAHs decreases Sub-CW solubility. • The presence of pyridinic rings in hetero-PAHs increases Sub-CW solubility. • Hydrogen bonds play vital roles in Sub-CW solubility in N-containing hetero-PAHs. [ABSTRACT FROM AUTHOR]