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HFCs and Their Final Fate

HFCs and Their Final Fate. Becky Otter Chemistry 481 February 3, 2005. What are HFCs?. HFCs or hydrofluorocarbons are made of H,F, & C They are used as replacements for chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs). HFCs . 1,1,1,2-tetrafluoroethane or HFC-134a

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HFCs and Their Final Fate

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  1. HFCs and Their Final Fate Becky Otter Chemistry 481 February 3, 2005

  2. What are HFCs? • HFCs or hydrofluorocarbons are made of H,F, & C • They are used as replacements for chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs)

  3. HFCs • 1,1,1,2-tetrafluoroethane or HFC-134a • HFCs are used as replacements because have near-zero ozone depletion potentials (ODP), short atmospheric lifetimes, less or non-flammable, low global warming potentials (GWPs), are cheap, high volatility, and very low solubility in water. • Most importantly the C-H bonds allow the HFCs to react with OH radicals and breakdown (Tsai, Chemosphere 61, 2005 p1539-1547) CH2FCF3 HFC-134a

  4. Oxidation of HFC-134a HFC134-a CF3CFHO radical Pathway 1 CF3CFHO radical CF3COF TFA CF3COF Pathway 2 CF3CFHO radical CF3 radical CF3 radical

  5. What happens to HFCs after they are released into the environment? • HFCs remain in the lower atmosphere • There are several products of oxidation: TFA, HF, C3FOF, CO2, CF3OH, HCOF • Some HFCs (HFC-32, HFC-143a, & HFC-152a) can form flammable mixtures with air • Burning these compounds produces more toxic compounds and other GHGs adding to the Greenhouse Effect (Tsai, Chemosphere 61, 2005 p1539-1547)

  6. (Tsai, Chemosphere 61, 2005 p1539-1547)

  7. So What Does This Mean? • Since HFCs have very low solubility in water they do not stay in water very long thus not serving a large risk • COF2 is a irritating gas and can be hydrolyzed to HF which is moderately toxic to humans , however there isn’t information on the atmospheric concentration on the degradation product. • TFA is also a skin/tissue irritant because it is a strong carboxylic acid-it can be acutely toxic to the biosystem

  8. And Time Says? • Culbertson and associates wanted to see how the relative amounts of CF3 containing compounds in background air were changing over the past two decades • The HFCs in question where CF3H (HFC-23), CF3CH3 (HFC-143a), and CF3CH2F (HFC-134a) Cape Meares, OR Palmer Station, Antarctica Point Barrow, AK

  9. Table 1: Annual Average concentrations of CF3-containing trace gases in parts per trillion by volume ( Culbertson, et al Chemosphere 55, 2004 pg 1109-1119)

  10. Fig. 4. OR emissions Fig. 5. AK and Antarctica emissions Take home message: There has been a increase in the concentration of HFC in the atmosphere in OR, but only a slight difference has been seen in AK and Antarctica= Shows difference in where the emissions are coming from ( Culbertson, et al Chemosphere 55, 2004 pg 1109-1119)

  11. Table 2. Average calculated emissions in Greenhouse Gases yr−1 over five-year periods ( Culbertson, et al Chemosphere 55, 2004 pg 1109-1119)

  12. What they concluded: • That over the past 2 decades, the emission rates have increased thus the concentration of HFCs has increased • There is a difference seen between the two hemispheres most likely due to the fact that the Northern hemisphere emits more HFCs

  13. CONCLUSIONS • HFCs are in fact GHGs however I believe they have much less environmental impacts than CFCs and HCFCs • The products of oxidation are “rained out” and the atmospheric lifetime is relatively short for most HFCs-posing a much smaller environment impact than the alternatives • From experiments measuring concentrations of HFCs, there is an increase in the emission rates

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