(110f) Predicting Gas-Phase Transport Properties of PFAS for Incineration Models Using Quantum Chemistry, Correlations, and Molecular Simulation

Transport-property parameters are being predicted via quantum chemistry and correlations. Modeling the destruction of per- and polyfluorinated substances (PFAS) “Forever Chemicals” by incineration requires transport properties. In this work, we have gathered transport-property parameters and tested sensitivity on a separately developed kinetics model for PFAS substances.

The essential six species parameters besides mass are linearity (atom, linear, or nonlinear), Lennard-Jones diameter and well depth, dipole moment, dipole polarizability, and rotational relaxation collision number. The dipole moment and polarizability parameters have been calculated using quantum chemical methods in Gaussian 16.¹ Structure optimization calculations are run at the B3LYP/6-31G(d,p) level, then later upgraded to M06-2X-D3(0)/def2-TZVP as selected in a separate study on predicting species thermochemistry.² Lennard-Jones parameters are calculated using Joback’s group-additivity method. Rotational relaxation collision number represents the efficiency of a rotating molecule colliding with another molecule and losing rotational energy; based on the complexity of the PFAS molecules, it is unity. These parameters are applied to different reacting flows and incinerator conditions, showing the potential impact of uncertainties.

The perfluoroalkyl chain is long and relatively linear, raising questions about appropriateness of using the Lennard-Jones spherical potential. As a result, molecular simulations of the diffusivity are being carried out in LAMMPS. The resulting diffusivities are compared to values found using the Lennard-Jones parameters and differences are explored.

[1] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman, G. Scalmani, V. Barone, G.A. Petersson, H. Nakatsuji, et al. Gaussian 16, Revision A.03. Gaussian, Inc., Wallingford CT, 2016.

[2] H. Ram, T.P. Sadej, C.C. Murphy, T.J. Mallo, P.R. Westmoreland, "Thermochemistry of Species in Gas-Phase Thermal Oxidation of C2 to C8 Perfluorinated Carboxylic Acids," J. Phys. Chem. A 128:7 (2024) 1313–1326. DOI: 10.1021/acs.jpca.3c06937.