Hydrochlorofluorocarbons

Why HCFCs?

Benefits and costs of HCFCs

The future of HCFCs

Resources

Hydrochlorofluorocarbons (HCFCs) are compounds consisting of hydrogen, chlorine, fluorine, and carbon atoms. HCFCs and hydrofluorocarbons (HFCs) were created in the 1980s as substitutes for chlorofluorocarbons (CFCs) for use in refrigeration and a wide variety of manufacturing processes. Because all three of these classes of compounds either destroy the stratospheric ozone layer essential to life on Earth or contribute to global warming, international agreements have been signed to eliminate their production and use by either the year 2000 (CFCs) or 2040 (HCFCs and HFCs).

Why HCFCs?

Thomas Midgley, an organic chemist working at the Frigidaire division of General Motors, created chlorofluorocarbons in 1928 as a safe and inexpensive coolant for use in refrigerators and air conditioners. CFCs are nonflammable, nontoxic, noncorroding gases. In addition to their widespread use as coolants, they were used in the manufacturing such products as contact lenses, telephones, artificial hip joints, foam for car seats and furniture, and computer circuit boards. CFCs have also been used as a propellant in aerosol products.

By 1974, however, researchers discovered that CFCs emitted to the atmosphere slowly accumulated in the stratosphere, higher than about 15 mi (25 km) above Earth’s surface. CFCs are degraded in the stratosphere by solar ultraviolet radiation, and this releases chlorine radicals that attack ozone molecules. Although ozone in the lower atmosphere is a harmful pollutant, in the stratosphere it acts to shield organisms at the surface of Earth from the harmful effects of solar ultraviolet radiation.

When ultraviolet radiation in the stratosphere degrades CFCs or HCFCs, the chlorine released acts to consume ozone molecules, which contain three oxygen atoms, into separate chlorine-oxygen and two-oxygen molecules (the latter is known as oxygen gas). Because the chlorine atoms can persist in the stratosphere for more than a century, they are recycled through the ozone-degrading reactions. One chlorine atom can destroy up to 100,000 molecules of stratospheric ozone.

The use of CFCs as aerosol propellants was banned in the United States, Canada, Switzerland, and the Scandinavian countries in 1978, as the dangers posed by their use were increasingly understood. By the early 1980s, companies such as DuPont, the world’s largest manufacturer of CFCs, were creating alternate, less-damaging compounds, including HCFCs and HFCs.

Benefits and costs of HCFCs

HCFC compounds react differently from CFCs because HCFCs contain a hydrogen atom, which causes these chemicals to decompose photochemically before they reach the stratosphere. HFCs do not contain chlorine and thus do not attack the ozone layer. HCFCs and HFCs survive in the atmosphere for 2 to 40 years, compared with about 150 years for CFCs.

As a result of their shorter persistence and different molecular composition, HCFC and HFC compounds

KEY TERMS

Chlorofluorocarbons (CFCs) —Chemical compounds containing chlorine, fluorine and carbon. CFCs were a key component in the development of refrigeration, air conditioning, and foam products.

Greenhouse gases —Gases that contribute to the warming of Earth’s atmosphere. Examples include carbon dioxide, HCFCs, CFCs, and HFCs.

Hydrofluorocarbons (HFCs) —Chemical compounds that contain hydrogen, fluorine, and carbon atoms.

Montreal Protocol on Substances that Deplete the Ozone Layer —An agreement signed by 43 countries in 1987, and amended and signed by 90 nations in 1990, to eliminate the production and use of compounds that destroy the ozone layer.

Ozone —A gas made up of three atoms of oxygen. Pale blue in color, it is a pollutant in the lower atmosphere, but essential for the survival of life on Earth’s surface when found in the upper atmosphere because it blocks dangerous ultraviolet solar radiation.

Ozone layer —A layer of ozone in the stratosphere that shields the surface of Earth from dangerous ultraviolet solar radiation.

Stratosphere —A layer of the upper atmosphere above an altitude of 5–10.6 mi (8–17 km) and extending to about 31 mi (50 km), depending on season and latitude. Within the stratosphere, air temperature changes little with altitude, and there are few convective air currents.

Troposphere —The layer of air up to 15 mi (24 km) above the surface of Earth, also known as the lower atmosphere.

Ultraviolet radiation —Radiation similar to visible light but of shorter wavelength, and thus higher energy.

have replaced CFCs in most major uses, including the production of foams for insulation, furniture, and vehicle seats, and as a coolant in refrigerators and air conditioners.

HCFCs and HFCs are more expensive to manufacture than CFCs and still negatively affect Earth’s atmosphere to some degree. Although HCFCs destroy 98% less ozone in the stratosphere than do CFCs, HCFCs and HFCs are still greenhouse gases that may contribute to global warming. In comparison to a more common greenhouse gas, CFCs are about 4,100 times more efficient in their global warming potential, while HFCs are 350 times more effective.

The future of HCFCs

CFCs and HCFCs have contributed to the quality of modern life, particularly as valuable components in refrigeration and computer technology. However, their impact on the atmosphere has prompted several countries to agree to stop producing them. The Montreal Protocol on Substances that Deplete the Ozone Layer was signed by 43 countries in 1987 to limit and eventually eliminate the production and use of CFCs. When additional evidence emerged that the ozone layer was being damaged more quickly than originally thought, more than 90 countries signed an amendment to the Montreal Protocol in 1990. In the year 2000, CFCs were banned from use and guidelines included new phase-outs for HCFCs and HFCs by the year 2020 if possible, and no later than 2040.

Research results suggest that there is a need to develop acceptable alternatives to HCFCs. In laboratory tests, male rats exposed to 5,000 parts per million (ppm) of HCFCs over a two-year period (equivalent to what humans working occupationally with the compound might experience over 30-40 years) developed tumors in the pancreas and testes. The tumors were benign and did not result in death for the tested rats. Nevertheless, this research resulted in the recommended eight-hour occupational exposure levels to HCFCs for humans being reduced from 100 ppm to 10 ppm.

Two possible alternatives to HCFCs are already being used successfully. Refrigerators that use propane gas, ammonia, or water as coolants are being tested in research laboratories, and use up to 10% less energy than typical models using CFCs as a coolant. Telephone companies are experimenting with crushed orange peels and other materials to clean computer circuit boards, as substitutes for another important use of CFCs and HCFCs. Certain microorganisms are also being tested that degrade HCFCs and HFCs, which could help in controlling emissions of these compounds during manufacturing processes involving their use.

See also Greenhouse effect; Ozone layer depletion.

Resources

BOOKS

Anslyn, E.V. and D.A. Dougherty. Modern Physical Organic Chemistry. Herndon, VA: University Science Books, 2005.

Hobbs, P.V. Introduction to Atmospheric Chemistry. New York: Cambridge University Press, 2006.

Sally Cole-Misch

Hydrochlorofluorocarbons

The term hydrochlorofluorocarbon (HCFC) refers to halogenated hydrocarbons that contain chlorine and/or fluorine in place of some hydrogen atoms in the molecule. They are chemical cousins of the chlorofluorocarbons (CFCs), but differ from them in that they have less chlorine. A special subgroup of the HCFCs is the hydrofluorocarbons (HFCs), which contain no chlorine at all.

A total of 53 HCFCs and HFCs are possible.

The HCFCs and HFCs have become commercially and environmentally important since the 1980s. Their growing significance has resulted from increasing concerns about the damage being done to stratospheric ozone by CFCs.

Significant production of the CFCs began in the late 1930s. At first, they were used almost exclusively as refrigerants. Gradually other applications—especially as propellants and blowing agents—were developed. By 1970, the production of CFCs was growing by more than 10% per year, with a worldwide production of well over 662 million lb (300 million kg) of one family member alone, CFC-11.

Environmental studies began to show, however, that CFCs decompose in the upper atmosphere . Chlorine atoms produced in this reaction attack ozone molecules (O₃), converting them to normal oxygen (O₂). Since stratospheric ozone provides protection for humans against solar ultraviolet radiation , this finding was a source of great concern. By 1987, 31 nations had signed the Montreal Protocol, agreeing to cut back significantly on their production of CFCs.

The question became how nations were to find substitutes for the CFCs. The problem was especially severe in developing nations where CFCs are widely used in refrigeration and air-conditioning systems. Countries like China and India refused to take part in the CFC-reduction plan unless

developed nations helped them switch over to an equally satisfactory substitute.

Scientists soon learned that HCFCs were a more benign alternative to the CFCs. They discovered that compounds with less chlorine than the amount present in traditional CFCs were less stable and often decomposed before they reached the stratosphere . By mid 1992, the United States Environmental Protection Agency (EPA) had selected 11 chemicals that they considered to be possible replacements for CFCs. Nine of those compounds are HFCs and two are HCFCs.

The HCFC-HFC solution is not totally satisfactory, however. Computer models have shown that nearly all of the proposed substitutes will have at least some slight effect on the ozone layer and the greenhouse effect . In fact, the British government considered banning one possible substitute for CFCs, HCFC-22, almost as soon as the compound was developed. In addition, one of the most promising candidates, HCFC-123, was found to be carcinogenic in rats.

Finally, the cost of replacing CFCs with HCFCs and HFCs is expected to be high. One consulting firm, Metroeconomica, has estimated that CFC substitutes may be six to 15 times as expensive as CFCs themselves.

See also Aerosol; Air pollution; Air pollution control; Air quality; Carcinogen; Ozone layer depletion; Pollution; Pollution control

[David E. Newton ]

RESOURCES

PERIODICALS

Johnson, J. "CFC Substitutes Will Still Add to Global Warming." New Scientist 126 (April 14, 1990): 20.

MacKenzie, D. "Cheaper Alternatives for CFCs." New Scientist 126 (June 30, 1990): 39–40.

Pool, R. "Red Flag on CFC Substitute." Nature 352 (July 11, 1991): 352.

Stone, R. "Ozone Depletion: Warm Reception for Substitute Coolant." Science 256 (April 3, 1992): 22.