Vapor Pressures and Thermodynamic Properties of Complex Organic Mixtures

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This project is concerned with the question of vapor pressures of marginally volatile organic compounds (VOC) or Semi-Volatile Organic Compounds (SVOC). Few data exist on the vapor pressures of high molecular weight compounds, such as make up tars and combustion byproducts. Even fewer data exist for polycyclic aromatics that contain heteroatoms. Many of these types pf compounds are important as contaminants in Brownfields or Superfund sites. There is significant concern related to vapor exposures at sites, and vapor pressure is the key parameter that determines exposure concentrations. Likewise, vapor pressure is a key factor determining some modes of transport of contaminants off site, as well as a design parameter for thermal desorption processes. This project will address the paucity of such basic thermodynamic data, through a series of measurements designed to fill in key gaps. In addition, there is only limited understanding of the mixture rules governing vapor pressure and other thermodynamic properties of mixtures of such high molecular weight compounds. This study will also seek to address questions related to mixture behavior of systems of high molecular weight. When is it acceptable to use ideal mixing laws, such as Raoult's Law, to characterize the behavior of mixtures of contaminants? Finally, Brownfields and Superfund sites always contain a complex soil matrix, in addition to the mixture of contaminant organics. The question is, what role does the soil play in adsorbing the compounds of interest? In particular, what role does the small but significant carbon content of most soils play in determining vapor pressure of organic contaminants? At what conditions? A subsidiary question to those being examined in the adsorption portion of this work is, how high must temperatures of thermal desorption processes be, in order to reduce the residual vapor pressures of contaminants to acceptable levels? The approach in this project is primarily experimental, but will always keep a view towards the need to determine reliable property correlations. The project team is already experienced in two critical areas for success on this project- measurements of vapor pressures of low volatility compounds and their mixtures, and adsorption of organics onto carbons in inorganic matrices.