Effects of organic solutes properties on the volatilization processes from water solutions

Effects of organic solutes properties, including Henryʹs law constant (H), molecular weight (M), molar volume at normal boiling point (Vb), and solubility (S), on the usefulness of rate estimation by reference to a reference substance (i.e., reference substance concept) and on the evaporation rate were investigated by measuring the volatilization rate constant of organic solutes under different environmental conditions, including mixing and surfactants. It was found that if benzene was used as a reference substance, the ratio of the solute rate to that of benzene (F) becomes insensitive to water mixing, whether the solute possessed high or low Henryʹs law constant. In the presence of surfactants, however, the F value changes sharply as the solute solubility decreases. For benzene, toluene, ethylbenzene, and xylenes (BTEX), the F values are essentially constant irrespective of the presence of other chemicals (including organic compounds, surfactants, and salinity) and of the variation in temperature. On the other hand, the volatilization rates are closely related to molecular weight (solubility) in the existence of mixing (surfactants). Three different approaches, i.e., mass-transport theory, modified Knudsen equation, and reaction rate concept, were used to evaluate the dependence of solute volatilization rates on solute properties. It was concluded that the interaction between solute properties and environmental parameters might play a key role in the volatilization process of organic solutes under different environmental conditions.