Association Kinetics for Perfluorinated n-Alkyl Radicals

Area of Science:

• Chemical Kinetics
• Environmental Chemistry
• Computational Chemistry

Background:

• Radical-radical reactions are key in per- and polyfluoroalkyl substances (PFAS) pyrolysis and oxidation.
• Unbranched perfluoroalkyl chains' unimolecular dissociation and association reactions significantly impact gas-phase thermal decomposition.
• Experimental data for these reactions are scarce and uncertain, hindering accurate modeling.

Purpose of the Study:

• To investigate the chemical kinetics of association/decomposition reactions for C2-C4 unbranched n-perfluoroalkanes.
• To provide reliable theoretical predictions for these reactions, addressing the lack of experimental data.
• To generate data suitable for comprehensive chemical kinetic models of PFAS thermal destruction.

Main Methods:

• Utilized state-of-the-art ab initio transition-state-theory-based master-equation calculations.
• Employed variable-reaction-coordinate transition-state theory (VRC-TST) for microcanonical and canonical rates.
• Applied composite quantum chemistry and a connectivity-based hierarchy for thermochemistry; direct dynamics for collision parameters.

Main Results:

• Calculated microcanonical and canonical rates for association reactions of C2-C4 perfluoroalkanes.
• Determined temperature- and pressure-dependent rate constants for association and dissociation reactions.
• Generated data in standardized formats for integration into chemical kinetic models.

Conclusions:

• The study provides essential theoretical kinetic data for key PFAS decomposition pathways.
• The generated data can improve the accuracy of models predicting PFAS behavior in thermal processes.
• This work addresses a critical knowledge gap in PFAS environmental chemistry and remediation.