Estimation of Henryʹs constants for aqueous systems at elevated temperatures

The treatment and removal of dilute organic contaminants from water require methods for estimating the vapor–liquid equilibrium behavior of these mixtures. Highly hydrophobic solutes may exhibit a maximum in Henryʹs law constant that is difficult to predict using traditional activity coefficient models. This paper examines the application of an activity coefficient model fitted specifically for dilute aqueous systems (UNIFAC-ENV) to make predictions for the infinite dilution activity coefficients at ambient conditions. The use of activity coefficient based mixing rules for equations of state to extend the range of the UNIFAC-ENV predictions to the temperatures typical for steam stripping conditions (80–140°C) is also evaluated. Application of this approach to Henryʹs law data for trichloroethylene in water indicates that these models require temperature dependent interaction coefficients to accurately predict the highly non-ideal solution behavior observed.