hydrofluorocarbons (HFCs) ARE a group of organic compounds that contain carbon, fluorine, and hydrogen. They are by-products of industrial manufacturing and were introduced as a replacements for chlorofluorocarbons and other ozone-depleting substances. However, though HFCs have zero ozone depletion potential (ODP), they have intrinsic and significant global warming potential (GWP), typically in the range of 1,000 to 3,000 times that of CO2. Thus, they are among the six key greenhouse gases listed in the Kyoto Protocol for emission reduction. Other greenhouse gases listed by the protocol are CO2, CH4, N2O, PFCs, SF6, and HFCs. Industry and government are collaborating on research and development, communication, and other activities to find new technologies, designs, and processes to manage these emissions.
The emissions management is occurring through non-regulatory means, voluntary measures, and industry-government collaborations. The air-conditioning and commercial refrigeration industry has particularly contributed to the success of the management process.
HFCs are generally colorless and odorless gases at environmental temperatures and are mostly chemically unreactive. They are non-flammable, having very low toxicity; they are recyclable, and highly energy efficient. There has been a significant growth in the market for HFCs because they have been identified as important alternative fluids for many end users. They find applications in refrigeration and air-conditioning, foam-blowing, general aerosols, solvent cleaning, firefighting, and metered-dose inhaling. They are preferred due to certain physical and chemical characteristics, especially their low toxicity and low flam-mability. The main sources of atmospheric HFCs are traceable to their sources of application. Two other major emitters are chemical plants making HCFC 22 (where HFC-23 is emitted as a by-product) and HFCs. There are several points in the lifecycle of HFC-using products at which emissions can occur. A computer model uses four emission factors to characterize the HFC emissions, namely fluid manufacturing, product manufacturing, product life, and disposal loss factors.
Examples of HFCs include trifluoromethane (HFC-23), difluoromethane (HFC-32), fluoromethane (HFC-
41), 2-chloro-1,1,1,2-tetrafluoroethane (HFC-124), 1,1,2,2,2-pentafluoroethane(HFC-125),1,1,2,2-tetraflu-oroethane (HFC-134), 1,1,1,2-tetrafluoroethane (HFC-134a,), 1,1-difluoroethane (HFC-152a), 1,1,1,2,3,3,3-heptafluoropropane (HFC-227ea). HFC-23 is created as a byproduct in the production of HCFC-22. Small amounts are also used in semiconductor manufacture and as fire-extinguishing agents. 1,2,2,2-tetrafluoroeth-ane (HFC-134a) is now used in place of CFC-12, gaining importance as a replacement for CFCs in automotive air conditioners.
HFC-134a is also used as a refrigerant in most new refrigerators and in commercial chillers. Leakage from these sources, which occurs primarily during servicing of the units, rather than during normal operation, is much less than from automotive air-conditioners. Short-term uses of HFC-134a, on the other hand, are becoming an important source of emissions. 1,1-diflu-oroethane (HFC-152a) is used as a blowing agent, an ingredient in refrigerant blends, and in fluoropolymer manufacturing applications. Other HFCs with considerable radiative forcing potential include HFC-125, HFC-143a, HFC-227e, and HFC-236fa. In addition to replacing HCFC-22 in stationary air conditioning and refrigeration applications, HFCs are expected to gain new markets as foam-blowing agents.
The opportunities to reduce global warming emissions from HFC end-use markets could be considered from four perspectives, namely the minimization of emissions throughout the lifecycle of a product, usage of a zero/low GWP alternative fluid, usage of an alternative technology, and the minimization of indirect emissions of CO2 from energy used by HFC users. These approaches should be considered from the viewpoints of practical feasibility, environmental effectiveness, and economic impact before the most cost-effective emissions-reduction strategy can be developed.
In some end-use markets, such as refrigeration, there may be significant opportunities for adoption of emissions-reduction techniques. In others, such as aerosols, emission reduction may not be a viable option. HFC emissions should not be considered in isolation, but in relation to emissions of other global warming gases. In some cases, the use of HFCs can reduce CO2 emissions; therefore, an appraisal of total global warming impact must be made to properly understand the best fluids or technologies to apply.
sEE ALso: Aerosols; Greenhouse Gases; Pollution, Air.
BIBLIoGRAPHY. Opportunities to Minimise Emissions of Hydrofluorocarbon from the European Union (March Consulting Group, 1998); W. Schwarz and A. Leisewitz, Emissions and Reduction Potentials of Hydrofluorocarbons, Perfluorocarbons and Sulphur Hexafluoride in Germany (German Federal Environmental Agency, 1999).
Akan Bassey Williams Covenant University
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