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Environmental Foresight through Computational Chemistry: Hydrofluoroethers and Potential Impacts

Paul Blowers and Kyle Hollingshead. Chemical and Environmental Engineering, The University of Arizona, PO Box 210011, Tucson, AZ 85721-0011

Dr. Paul Blowers, Kyle Hollingshead, Benjamin Long, Bo-Gyeong Kim, Yan Zhu, Kimberly Seamans, and Zachary Ronan

Department of Chemical and Environmental Engineering

The University of Arizona

Environmental issues have traditionally been discovered in hindsight after time lags of years to decades of industrial or consumer use of new chemistries. While our choices of new materials and routes for accomplishing a technological goal are often driven to avoid newly discovered environmental issues, lack of data often prevents the best economic and planning decisions to be made when alternatives are introduced.

In this work, computational and estimative methods are used to predict several potential environmental impacts of hydrofluoroethers (HFEs). This class of compounds was first synthesized in the mid- to late-1990s and there are an increasing number of patents appearing in the United States for their use as solvents, refrigerants, blowing agents, and in consumer products. The environmental degradation pathways of HFEs have been hypothesized but not quantified or validated to date.

Our recent work predicted global warming potentials of a large number of HFEs. However, the definition of global warming potential assumes that all environmental impacts of a species are due to the presence of the original chemical released into the environment and that contributions from daughter species are negligible. In this previous work, we found that this assumption may not be valid for this class of compounds. Therefore, in this work we predict formation rates and atmospheric lifetimes of likely daughter species of HFEs in order to evaluate the environmental consequences of HFEs after initial degradation through hydroxyl radical hydrogen abstraction has occurred

This work also estimates water solubilities of the parent and daughter species to identify if rain-out is a primary route for removal from the troposphere, as others have hypothesized previously. We also estimate octanol-water partition coefficients as a proxy measure of estimating bioaccumulation potential. HOMO-LUMO energy gaps are estimated to potentially correlate with toxicity data as it is developed in the future. Finally, kinetic rate constants of the degradation pathways are estimated using transition state theory.

This complete set of evaluative tools gives more insight into potential environmental implications of implementing HFE technologies to replace hydrofluorocarbon (HFC) ones. In particular, we anticipate that when all these environmental impacts are considered using a holistic life cycle assessment approach, the original HFCs used may in fact be environmentally preferred over their HFE replacements.