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
| CHF3 | HFC-23 |
| CHCl2CF3 | HCFC-123 |
| CH2FCClF2 | HCFC-133b |
| CH3CHClF | HCFC-151a |
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.
Aerosol; Air Pollution; Air Pollution Control; Air Quality; Carcinogen; Ozone Layer Depletion; Pollution; Pollution Control
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.
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