Research activities
PFAS Destruction Kinetics (US EPA)
We have developed detailed kinetic mechanisms for destruction of perfluorooctanoic acid (PFOA), perfluorooctanesulfonic acid (PFOS), and related “Per and polyfluoro alkyl substances” (PFAS). These compounds have become known as “forever chemicals” because they do not naturally degrade. Unfortunately, their adverse health effects and ability to bioaccumulate give them EPA Drinking Water Health Advisories limits as low as 4 parts per quadrillion. Our approach is to applying theory and computational quantum chemistry, tested with EPA’s incinerator data.
Fundamental Pyrolysis Kinetics of Polymers (DoD MURI)
Since 1994, we have worked experimentally and computationally to discern the elementary reaction kinetics and physics of polymer decomposition. Beyond the fundamental insights, we seek ways to generate useful chemicals from recycled polymers and biomass.
TGA/DSC and flash pyrolysis with GCxGC-ToFMS analyses have revealed key products and rates. Computational quantum chemistry has provided important bond energies and transitions states, and we have used our Reactive Molecular Dynamics method RxnMD and forcefield along with LAMMPS to identify the contributing role of polymer chain ratcheting to accumulate the energy needed to break the chains bonds.
Global models are useful for predicting general product yields for pyrolysis. However, they do not explain any of the elementary chemical reactions, which may become vital for maximizing the more desirable components. Knowing how to control specific reactions and specific products will allow better design of pyrolysis processes as well as better design of upgrading catalysts.
In previous work on the fundamental chemistry of biomass pyrolysis, Arnab Bose and Ankush Jain pyrolyzed and modeled hemicellulose monosaccharides and polysaccharides. Arnab and Jen Wang have developed data science to correlate and predict GC elution times for our GCxGC/ToF-MS. One method of analysis we used for cellulose was to compare the pyrolysis behavior of glucose monomer, which is easier to simulate than the full polymer. Vikram Seshadri identified several potential pathways for transforming glucose to levoglucosan, and in a landmark paper, we showed how OH groups within the cellulose can catalyze its conversion. Click here for more information on our work with pyrolysis.
Previous work: Molecular-Beam Mass Spectrometry
A powerful way to investigate flame and pyrolysis chemistry is by molecular-beam mass spectrometry (MBMS), which is capable of detecting reactive intermediate species involved in the many chemical reactions present in a flame. In 2011, Xueliang Yang and Vikram Seshadri constructed a new MBMS system for the Westmoreland laboratory at NC State, which we have used for studying gas-phase and surface catalytic and noncatalytic reactions. Click here for more information on our work with MBMS systems.
Previous work: Reaction pathways of combustion and flammability
Our group is known worldwide for using a combination of flame-sampling molecular beam mass spectrometry experiment and kinetic modeling to study low-pressure premixed laminar flat flames of different hydrocarbons. The objective has been to investigate the different reaction pathways for the fuel consumption and the initial aromatics formation at different flame conditions. The key reason for the stoichiometric effects are also investigated, considering the different flame temperatures and the different abundance of major radicals. Vernon Mascarenas and Chris Weber extended these models to predict flammability limits. Click here for more information on our work on aromatics formation in flames.