Estimation of polychlorinated biphenyl fugacity ratios

Area of Science:

• Environmental Chemistry
• Thermodynamics
• Chemical Physics

Background:

• Comparing solubilities and vapor pressures of homologous series is complicated by crystal structure variations.
• Fugacity ratios, comparing solid and liquid states, are typically derived from fusion thermodynamic data.
• Polychlorinated biphenyls (PCBs) are a group of persistent organic pollutants with diverse structures.

Purpose of the Study:

• To investigate the relationship between fusion enthalpy and fusion entropy for polychlorinated biphenyls (PCBs).
• To develop and validate methods for estimating fugacity ratios for PCB congeners.
• To provide a comprehensive list of fugacity ratios for all 209 PCB congeners.

Main Methods:

• Correlating fusion enthalpy with fusion entropy for 41 PCBs.
• Calculating fugacity ratios using linear and nonlinear regression models based on fusion data.
• Comparing estimated fugacity ratios with those calculated directly from fusion enthalpy.

Main Results:

• Strong linear correlations were found between fusion enthalpy and fusion entropy for non-ortho-, mono-ortho-, and diortho-PCBs.
• Estimated fugacity ratios closely matched calculated values for specific groups of PCBs (ortho-chlorinated below 380 K, non-ortho-PCBs).
• Nonlinear regression improved fugacity ratio estimation for ortho-chlorinated PCBs with melting points above 380 K.

Conclusions:

• Fusion enthalpy-entropy correlations offer a viable approach for estimating PCB fugacity ratios.
• Regression models provide accurate estimations, particularly for congeners where direct calculation is challenging.
• The study provides essential fugacity ratio data for all 209 PCB congeners, aiding environmental fate assessments.