Chlorofluorocarbon (CFC) is an
organic compound that contains carbon, chlorine, and fluorine, produced as a
volatile derivative of methane and ethane. A common subclass is the
hydrochlorofluorocarbons (HCFCs), which contain hydrogen, as well. Freon is
DuPont's brand name for CFCs, HCFCs and related compounds. Other commercial
names from around the world are Algofrene, Arcton, Asahiflon, Daiflon, Eskimo,
FCC, Flon, Flugene, Forane, Fridohna, Frigen, Frigedohn, Genetron, Isceon,
Isotron, Kaiser, Kaltron, Khladon, Ledon, Racon, and Ucon. The most common
representative is dichlorodifluoromethane (R-12 or Freon-12).
Chlorofluorocarbons (CFCs) are a
family of chemical compounds developed back in the 1930's as safe, non-toxic,
non-flammable alternative to dangerous substances like ammonia for purposes of
refrigeration and spray can propellants. Their usage grew enormously over the
years. One of the elements that make up CFCs is chlorine. Very little chlorine
exists naturally in the atmosphere. But it turns out that CFCs are an excellent
way of introducing chlorine into the ozone layer. The ultraviolet radiation at
this altitude breaks down CFCs, freeing the chlorine. Under the proper
conditions, this chlorine has the potential to destroy large amounts of ozone.
This has indeed been observed, especially over Antarctica. As a consequence,
levels of genetically harmful ultraviolet radiation have increased.
Production of new stocks ceased
in most countries as of 1994 However many countries still require
aircraft to be fitted with halon fire suppression systems because no safe and
completely satisfactory alternative has been discovered for this application.
There are also a few other, highly specialized uses. These programs recycle
halon through "halon banks" coordinated by the Halon Recycling
Corporation to ensure that discharge to the atmosphere occurs only in a genuine
emergency and to conserve remaining stocks.
Development
of alternatives for CFCs
Work on alternatives for
chlorofluorocarbons in refrigerants began in the late 1970s after the first
warnings of damage to stratospheric ozone were published. The
hydrochlorofluorocarbons (HCFCs) are less stable in the lower atmosphere,
enabling them to break down before reaching the ozone layer. Nevertheless, a
significant fraction of the HCFCs do break down in the stratosphere and they
have contributed to more chlorine buildup there than originally predicted. Later
alternatives lacking the chlorine, the hydrofluorocarbons (HFCs) have an even
shorter lifetimes in the lower atmosphere. One
of these compounds, HFC-134a, is now used in place of CFC-12 in
automobile air conditioners. Hydrocarbon refrigerants (a propane/isobutane
blend) are also used extensively in mobile air conditioning systems in
Australia, the USA and many other countries, as they have excellent
thermodynamic properties and perform particularly well in high ambient
temperatures. One of the natural refrigerants (along with Ammonia and Carbon
Dioxide), hydrocarbons have negligible environmental impacts and are also used
worldwide in domestic and commercial refrigeration applications, and are
becoming available in new split system air conditioners
HFC-23 (CHF3);
HFC-134a (CF3CFH2); HFC-507 (a 1:1 azeotropic
mixture of HFC 125 (CF3 CHF2) and HFC-143a (CF3CH3));
HFC 410 (a 1:1 azeotropic mixture of HFC-32 (CF2H2)
and HFC-125 (CF3CF2H))
Refrigerators from the late 1800s
until 1929 used the toxic gases, ammonia (NH3), methyl chloride (CH3Cl), and
sulfur dioxide (SO2), as refrigerants. Several fatal accidents occurred in the
1920s because of methyl chloride leakage from refrigerators. People started
leaving their refrigerators in their backyards. A collaborative effort began
between three American corporations, Frigidaire, General Motors and DuPont to
search for a less dangerous method of refrigeration.
In 1928, Thomas Midgley, Jr.
aided by Charles Franklin Kettering invented a "miracle compound"
called Freon. Freon represents several different chlorofluorocarbons, or CFCs,
which are used in commerce and industry. The CFCs are a group of aliphatic
organic compounds containing the elements carbon and fluorine, and, in many
cases, other halogens (especially chlorine) and hydrogen. Freons are colorless,
odorless, nonflammable, noncorrosive gases or liquids.
Chlorofluorocarbons (CFCs) are highly stable compounds
that were used as propellents in spray cans and in refrigeration units. They are
several organic compounds composed of carbon, fluorine, chlorine, and hydrogen.
CFCs are manufactured under the trade name Freon .
The invention of
chlorofluorocarbons (CFCs) in the late 1920s and early 1930s stemmed from the
call for safer alternatives to the sulfur dioxide and ammonia refrigerants used
at the time, CFCs found wide application
after World War II.
Chloroflourocarbons were first
created in 1928 as non-toxic, non-flamable refrigerants, and were first produced
commercially in the 1930's by DuPont. The first Chlorofluorocarbon was CFC-12, a
single carbon with two chlorines and two Fluorines attached to it.
These halogenated hydrocarbons, notably
trichlorofluoromethane (CFC-11, or F-11) and dichlorodifluoromethane (CFC-12, or
F-12), have been used extensively as aerosol-spray propellants, refrigerants,
solvents, and foam-blowing agents. They are well-suited for these and other
applications because they are nontoxic and nonflammable and can be readily
converted from a liquid to a gas and vice versa.
Chlorofluorocarbons or CFCs (also known as Freon) are
non-toxic, non-flammable and non-carcinogenic. They contain fluorine atoms,
carbon atoms and chlorine atoms. The 5 main CFCs include CFC-11 (trichlorofluoromethane
- CFCl3), CFC-12 (dichloro-difluoromethane - CF2Cl2), CFC-113 (trichloro-trifluoroethane
- C2F3Cl3), CFC-114 (dichloro-tetrfluoroethane - C2F4Cl2), and CFC-115 (chloropentafluoroethane
- C2F5Cl).
CFCs have been found to pose a serious environmental
threat. Studies undertaken by various scientists during the 1970s revealed that
CFCs released into the atmosphere accumulate in the stratosphere, where they had
a deleterious effect on the ozone layer. Stratospheric ozone shields living
organisms on Earth from the harmful effects of the Sun's ultraviolet radiation;
even a relatively small decrease in the stratospheric ozone concentration can
result in an increased incidence of skin cancer in humans and in genetic damage
in many organisms. In the stratosphere the CFC molecules break down by the
action of solar ultraviolet radiation and release their constituent chlorine
atoms. These then react with the ozone molecules, resulting in their removal.
CFCs have a lifetime in the atmosphere of about
20 to 100 years, and consequently one free chlorine atom from a CFC molecule can
do a lot of damage, destroying ozone molecules for a long time. Although
emissions of CFCs around the developed world have largely ceased due to
international control agreements, the damage to the stratospheric ozone layer
will continue well into the 21st century.
In 1978 The Montreal
Protocol was adopted as a framework for international cooperation regarding CFC
control on the basis of the Vienna Convention for the Protection of the Ozone
Layer.
