Thermodynamic and Phase Behavior of Supercritical Water: Environmentally Significant Organic Chemical Mixtures

The importance of equation of state models is fundamental to new technologies such as supercritical water oxidation for the destruction of organic pollutants. In order to be able to perform hazard and risk assessments, the parameters ofthermodynamic models are considered as information characteristics of chemicals that store the knowledge on their thermodynamic, phase and environmental behavior. Considering the extremely large number of existing chemicals, it is obvious that there is need for developing theoretically sound methods for the prompt estimation of their phase behavior in aquatic media at supercritical conditions. Recent developments of the global phase equilibria studies of binary mixtures provide some basic ideas of how the required methods can be developed based on global phase diagrams for visualization of the phase behavior of mixtures. The mapping of the global equilibrium surface in the parameter space of the equation of state (EoS) model provides the most comprehensive system of criteria for predicting binary mixture phase behavior. The main types of phase behavior for environmentally significant organic chemicals in aqueous environments are considered using structure-property correlations for the critical parameters of substances. Analytic expressions for azeotropy prediction for cubic EoS are derived. A local mapping concept is introduced to describe thermodynamically consistently the saturation curve of water. The classes of environmentally significant chemicals (polycyclic aromatic hydrocarbons - PAH, polychlorinated biphenyls - PCB, polychlorinated dibenzo-p-dioxins and furans, and selected pesticides) are considered and main sources of the property data are examined. Vapor pressure, heat of vaporization, and critical parameter estimations for pure components were chosen for seeking a correlation between the octanol–water partition coefficients K_OW and the EoS binary interaction parameters - k₁₂. The assessment of thermodynamic and phase behavior of representatives for different pollutants is given.