Organic phase resistance to dissolution of polycyclic aromatic hydrocarboncompounds

The dissolution of naphthalene, phenanthrene, and pyrene from viscous organ ic phases into water was studied in continuous-flow systems for time period s ranging from several months to more than 1 year. By selecting nonaqueous phases ranging from low viscosity to semisolid, i.e., from a light lubricat ing oil to paraffin, the governance of mass transfer was shown to vary from water phase control to nonaqueous phase control. An advancing depleted-zon e model is proposed to explain the dissolution of PAHs from a viscous organ ic phase wherein the formation of a depleted zone within the organic phase increases the organic phase resistance to the dissolution of PAHs. The expe rimental data suggest the formation of a depleted zone within the organic p hase for systems comprising a high-viscosity oil (similar to 1000 cP at 40 degrees C), petrolatum (petroleum jelly), and paraffin. Organic phase resis tance to naphthalene dissolution became dominant over aqueous phase resista nce after flushing for several days. Such effects were not evident for low viscosity lubricating oil (86 cP at 40 degrees C). The transition from aque ous-phase dissolution control to nonaqueous-phase dissolution control appea rs predictable, and this provides a more rational framework to assess longt erm release of HOCs from viscous nonaqueous phase liquids and semisolids.