Hydrochlorofluorocarbons

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Hydrochlorofluorocarbons

Hydrochlorofluorocarbons (HCFCs) are compounds made up of hydrogen , chlorine , fluorine, and carbon atoms . HCFCs and their cousins, 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 , and/or contribute to an unnatural warming of the planet's climate, 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 non-flammable, non-toxic, non-corroding gases. In addition to their widespread use as coolants, they were used in the manufacturing of hundreds of products, such 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 of aerosol products.

By 1974, however, researchers discovered that CFCs emitted to the atmosphere slowly traveled to the upper-altitude layer known as the stratosphere, higher than about 15 mi (25 km) above Earth's surface. The 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.

The good news and the bad news

HCFC compounds react differently from CFCs. This is because the 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 two 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 are expected to replace 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 much more expensive to manufacture than CFCs, and they 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 carbon dioxide , 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 our quality of 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 phaseouts for HCFCs and HFCs by the year 2020 if possible, and no later than 2040.

Other research is increasing the 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 are using 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.

Resources

books

Duden, Jane. The Ozone Layer. New York: Crestwood House, 1990.

Fisher, David E. Fire and Ice. New York: HarperCollins, 1990.

Fisher, Marshall. The Ozone Layer. New York: Chelsea House Publishers, 1992.

Gay, Kathlyn. Air Pollution. New York: Franklin Watts, 1991.

Jahn, F., M. Cook, and M. Graham. Hydrocarbon Exploration and Production. Developments in Petroleum Science. Vol. 46. The Netherlands: Elsevier Science, 2000.

periodicals

MacKenzie, Debora. "Cheaper Alternatives for CFCs." NewScientist (June 30, 1990): 39-40.

Wallington, Timothy J., et al. "The Environmental Impact of CFC Replacement-HFCs and HCFCs." Environmental Science & Technology 28 (1994): 320A-326A.

Sally Cole-Misch

KEY TERMS

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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 the 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 the earth, also known as the lower atmosphere.
Ultraviolet radiation: —Radiation similar to visible light but of shorter wavelength, and thus higher energy.