Atmospheric Barriers: New Study Challenges Link Between Common Refrigerants and the Formation of TFA
Numerous studies to date have predominantly indicated that the degradation of a common refrigerant is contributing to the formation of trifluoroacetic acid (TFA). However, in a recent study published in Physical Chemistry Chemical Physics by Environmentally Applied Refrigerant Technology Hub (EARTH), investigators found no link between the common refrigerant, HFC-134a, and TFA under atmospheric conditions through the previously reported pathways.
Trifluoroacetic acid (CF3CO2H) is a water soluble and persistent organofluorine acid. The accumulation of TFA in the environment had been thought to be the direct result of the current refrigerants in use such as HFC-134a (CF3CH2F).
In the 1990s, concerns about ozone depletion from the use of chlorofluorocarbon refrigerants led to the use of hydrofluorocarbons (HFCs) as the latest generation of refrigerant. Today, HFC-134a is commonly used in automotive air conditioning, residential and commercial refrigeration, and medium temperature chillers. But concern is growing about the environmental impact of molecules released into the atmosphere when HFC-134a degrades, potentially creating TFA, which is being increasingly found in groundwater and rainwater, commonly referred to as acid rain.
“You can draw arrows from reactant to product, but that does not mean that reaction is going to be relevant under atmospheric conditions,” said Rui Sun, professor in the department of chemistry at the University of Hawai′i, and research faculty member with EARTH.
Leading this study was Allen Vincent, doctoral student in chemistry at the University of Hawai′i. “If refrigerants degrade in the atmosphere, can they form TFA in the environment?” asked Allen. “Under tropospheric pressures and temperatures using master equation simulations, what we found was that TFA cannot be formed from HFC-134a in the gas phase with the mechanism that had been proposed in studies previously. The energy barriers along the TFA-forming pathways are energetically inaccessible, thus leading to thermally stabilized intermediates.”
He added, “As chemists, energetics, mechanisms, and kinetics tell us how viable a chemical reaction is under certain conditions. While previous studies provided valuable insight into forming TFA from HFC-134a, without energetics, we simply do not know how relevant they are under atmospheric conditions.”
EARTH, an Engineering Research Center (ERC) funded by the U.S. National Science Foundation (NSF) and corporate investment, is undertaking studies on the environmental impact of refrigerants to understand how refrigerant molecules degrade, which can inform the development of future refrigerants. This research was funded by the NSF.
“Rigorous studies such as this are critically needed to properly inform industry, regulatory agencies, and society as we transition to lower global warming refrigerants,” said Mark B. Shiftlett, professor of chemical engineering at the University of Kansas and director of EARTH. “The EARTH Engineering Research Center is creating a sustainable refrigerant economy and innovations in air conditioning and refrigeration that secures U.S. leadership in workforce development and manufacturing.”
Moving forward, the EARTH research team is studying other refrigerant degradation molecules, as well as continuing their work on HFC-134a.
“Environmental assessment is important. This study showed that the HFC-134a molecule is not directly linked to the development of TFA when coupled with atmospheric conditions,” said Sun. “While this study looked at roughly 75% of the different atmospheric radicals that may directly connect HFC-134a with the accumulation of TFA, more variables need to be studied to determine the exact molecular pathway in the development of TFA.”
Please direct queries regarding this study to Prof. Rui Sun, ruisun@hawaii.edu.
EARTH Engineering Research Center
The Environmentally Applied Refrigerant Technology Hub (EARTH) is an NSF- and corporate-funded Engineering Research Center. EARTH is dedicated to revolutionizing how refrigerants are formulated, manufactured, applied, monitored, and recycled to dramatically reduce the environmental footprint of the global cooling sector. Led by the University of Kansas, this consortium of partner research universities includes the University of Notre Dame, University of Maryland, Lehigh University, University of South Dakota, and the University of Hawai′i.