Polycyclic aromatic hydrocarbons dissolution in supercritical carbon dioxide by molecular dynamics simulation

With the rapid development of industry, the problem of soil contamination has grown increasingly serious, posing a serious threat to the wellness of people. Polycyclic aromatic hydrocarbons (PAHs) are among the most common soil contaminants. Supercritical CO2 extraction has been widely used to treat PAHs in soils. Solute solubility in supercritical fluids is a fundamental thermophysical parameter that must be investigated and modeled. In this work, we employed molecular dynamics simulation to investigate the microscopic dissolution process in supercritical CO2 of four PAHs: naphthalene, anthracene, pyrene, and benzo(alpha)pyrene. We also looked into the implications of changing the ring number of PAHs on the ability of supercritical CO2 to dissolve PAHs by calculating the interaction energy, radial distribution function, and the coordination number between PAHs and supercritical CO2. The results indicated that the PAHs' capacity to dissolve in supercritical CO2 decreased gradually with the increase of ring number. The interaction energy between PAHs and supercritical CO2 decreases as the number of PAHs rings increases. Among them, the van der Waals interaction energy plays a decisive role in the dissolution of PAHs in supercritical CO2. As the number of PAHs rings increased, the positions of the first peak and valley of the radial distribution function remained the same, which appeared at about 4.3 angstrom and 6.1 angstrom, respectively. However, the magnitudes of the peaks and valleys decreased. As the number of PAHs rings increased, the coordination number of the C atoms of supercritical CO2 around the C atoms of PAHs decreased.