Molecular Dynamics Simulation On Degradation Of Nitrobenzene Via Supercritical Water Oxidation

Supercritical water oxidation (SCWO) is a newly-developed, highly-effective technology for the treatment of hazardous organic wastewater. However, there are disadvantages in the experimental study due to the high reaction temperature and pressure condition requirements. In this paper, the properties of supercritical water oxidation system with nitrobenzene were investigated using the Molecular Dynamics (MD) simulation method.The suitable parameters of MD simulation for the sub-critical and supercritical water system were optimized. The calculated results of self-diffusion coefficients of water were in good agreement with the experimental results. The relative errors were no more than 5 percent. The self-diffusion coefficients of sub-critical and supercritical water were investigated systemically. The effects of temperature and pressure on hydrogen bond and the geometry of water molecules were investigated respectively.Based on the mechanism of hydroxyl radical reactivity with nitrobenzene in supercritical water, the formation of [OHC6H5NO2]Ï€?, which is diffusion-controlled, is the first step. However,the diffusion-controlled rate constant of this step is related to the infinite dilute diffusion coefficients of the reactants. Therefore, the infinite dilute diffusion coefficients of nitrobenzene and hydroxyl in supercritical water were first investigated by MD simulation in the temperature range of 643.2~843.2K and pressure range of 23~29MPa, by which, the diffusion-controlled rate constant for the addition of hydroxyl radical to nitrobenzene could be calculated by the Smoluchowski equation. The results provided valuable information to the reaction kinetics of nitrobenzene in SCWO processes.Cohesive Energy Density (CED) is an important property of a substance which can characterize intermolecular force. In this paper, the changing trend of Cohesive Energy Density was investigated to estimate the phase behaviour of the binary mixture. In order to ensure the validity of the simulation method, the CO2-ethanol system was chosen as an instance, and the results agreed with the experiment results. Henceforth, the phase behaviour of H2O-ethanol system was simulated.