VAPOR PRESSURES AND THERMODYNAMICS OF MODEL MIXTURES OF POLYCYCLIC AROMATIC COMPOUNDS MEASURED VIA THE KNUDSEN EFFUSION TECHNIQUE

摘要

The vast majority of systems in the environment are composed of mixtures,some easily defined and many that lack quantification due to their seemingly infinite number of constituents.There is a distinct lack of data in the literature concerning mixtures of high molecular weight organic compounds,hindering the modeling of volatilization from soil of discrete and complex mixtures.There are many relationships that predict the behavior of multi-phase and multi-component mixture.Raoult's law is often used to determine the contribution of individual components of a liquid or solid mixture to the total pressure exerted by the system.Prediction methods are often used to model the environmental fate and transport of polycyclic aromatic compounds(PACs),environmental pollutants frequently encountered at former manufactured gas plant sites.Mixtures of these PACs can result from processing or incomplete combustion of coal and other fossil fuels and are often present at very low concentrations.Vapor pressures may vary by orders-of-magnitude from compound to compound;the vapor pressures of some PACs vary from 10~(-2)to 10~(-12)atmospheres at ambient conditions.Even though the concentrations and vapor pressures of these compounds and mixtures of PACs are quite low,such mixtures can nevertheless represent a threat to air quality at contaminated sites through vaporization from soil of lower molecular weight compounds present in the mixtures.In addition,it is important to understand the vaporization behavior of these mixtures in thermal remediation scenarios.