MOLECULAR DIFFUSIVITY OF POLYCYCLIC AROMATIC-HYDROCARBONS IN AQUEOUS-SOLUTION

Measured molecular diffusion coefficients of several polycyclic aromatic hydrocarbons (PAHs) in aqueous solution indicate that available techniques largely overestimate the diffusivities of compounds with three or more aromatic rings. The molecular diffusivities of benzene, toluene, naphthalene, phenanthrene, anthracene, benz[a]anthracene, and pyrene were measured in water at temperatures ranging from 4 to 40-degrees-C using a modified open tube elution method. An experiment was conducted to assess the effects and interactions of solute concentration, temperature, and salinity on PAH aqueous molecular diffusivity. Aqueous diffusion coefficients increased with temperature and decreased with molar volume of the diffusing species. No significant effects of solute concentration (12.5-50% saturation) and salinity (0-35 ppt) were observed. The experimental data have been used to formulate a new predictive equation for estimation of aqueous molecular diffusivity of aromatic chemicals as a function of temperature.