Mass transfer of polynuclear aromatic hydrocarbons from complex DNAPL mixtures

Parameters governing the rates of mass transfer of the individual components of four synthetic dense non-aqueous phase liquid (DNAPL) mixtures into the aqueous phase were evaluated. The DNAPL mixtures, composed of toluene and eight polynuclear aromatic hydrocarbons (PAHs), were designed to serve as models for coal tars and creosotes. The reactor employed provided a relatively stable interface between internally mixed but segregated aqueous and DNAPL phases. Two parameters, the aqueous phase concentration at equilibrium and the overall film mass transfer coefficient, were quantified by simulating aqueous concentration profiles with a mass-transfer-limited rate model using a statistical parameter search and data fitting routine. DNAPL phase activity coefficient values for the various compounds derived from equilibrium aqueous phase concentrations were typically within a factor of 2 of Raoult's law prediction of unity; refinement of fugacity ratio estimates for the solid PAHs brought the values even closer to unity. Film transfer coefficients for all components of the mixtures studied were similar in magnitude, in the range 0.8-3 x 10^-3 cm/s. No significant variations of the film transfer coefficient for naphthalene were noted across the DNAPL mixtures, aver which the mole fraction of this compound was varied from 0.05 to 0.25.