Dissolution of polycyclic aromatic hydrocarbons in supercritical water in hydrogen production process: A molecular dynamics simulation study

Rapid heating of coal particles in supercritical water (SCW) is the prerequisite for complete gasification, while there is a rapid precipitation of volatiles during this process. If the volatiles cannot be dissolved and diffused in time, side reaction is inclined to occur, especially coking. The solubility of the volatiles in SCW has not yet been studied because the composition is not simple and the corresponding interaction with SCW is complex. In this paper, polycyclic aromatic hydrocarbons (PAHs) were used as the volatile model compound. Molecular dynamics (MD) simulations focused on the dissolution of pure PAHs and PAHs mixtures in SCW were carried out. The investigation results indicated that the dissolution behavior of naphthalene was the most excellent in SCW, while heavy PAHs were sensitive to the thermodynamic state of water molecules. The light PAHs were liable to be dissolved, while heavy PAHs were more likely to be remained in the PAH droplet. Moreover, the increase of temperature and density has a positive impact on the dissolution of PAHs in the supercritical solvent. This work is prospective to provide a theoretical basis for ensuring efficient and complete gasification of coal and restraining side effects for hydrogen production. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.