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7/31/2019 CFCs & HFCs
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1) Organic compound
- Carbon
- Chlorine
- Fluorine
2) Produced as a volatile derivative of
- Methane
- Ethane
- Formulae CClmF4-m & C2ClmF6-m (m is nonzero)
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3) A family of non-toxic
4) Inert chemical compounds bound tightly to forminert molecules
5) Invented in the late 1920s & early 1930s as a safer
alternative to :
- Sulfur dioxide & ammonia refrigerants
6) Some commercial names of CFCs
- Freon , Algofrene, Arcton, Daiflon, Eskimo, FCC,
Flon, Flugene, Forane, Fridohna, Genetron,
Isceon, Isotron, Kaiser,Ledon, Racon, & Ucon.
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7) Used worldwide in
- Aerosol sprays (banned in the U.S. & a fewnorthern European countries in the mid-70s)
- Coolants in refrigeration system & air
conditioners
- Solvents to clean electronic components
(eg washing micro-electronic chips)
- Blowing agents in the production of plastic
foams
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8) Chosen because
- Low toxicity
- Nonflammable
- Noncorrosive
- Nonreactive with other chemical species
- Desirable thermal conductivity & boiling point
9) Each kind of CFC has a different formula such as
- CFC 11: CCl3F (Trichlorofluoromethane)- CFC 12: CCl2F2 (Dichlorodifluoromethane)
- CFC 22: CHClF2 (Chlorodifluoromethane)
- CFC 113: C2Cl3F3 (Trichlorotrifluoromethane)
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1) A common subclass of Chlorofluorocarbon
2) Contain
- Carbon
- Hydrogen
- Chlorine- Fluorine
- Formulae CClmFnH4-m-n & C2ClxFyH6-x-y,
(m, n, x, & y are nonzero)
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3) Not found anywhere in nature
4) HCFC production increased after countries
agreed to phase out the use of CFCs.
5) However, most HCFCs are broken down in the
lowest part of the atmosphere which pose a much
smaller risk to the ozone layer.
6) Also a very potent greenhouse gas
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ultra-violet
radiationfrom the Sunis absorbed bystratosphericozone and,doesn't enter
thetroposphere.
ultra-violetlight is tooweak tobreakdown the
CFC's presentthere
However,significantamounts enteredthe stratospherewhere the ultra-violet radiationis strong enough
to break themdown into veryreactive chlorineand fluorineradical species.
Theseradicalsare capableof destroying
ozone
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This meansthat they arenot consumed
by thereaction butare recycledand cancontinue toreact with
other ozonemolecules todestroy themas well.
However,chlorineradicals (Cl)
react withozone simply todestroyit. They arevery efficientat removing
ozone becausethey act ascatalysts.
So as ozoneconcentrationsincrease, theamount ofozone destroyed
also increases.
Under
naturalconditions,ozone levelsare constant since theyare both
formed &destroyedby ultra-violet light.
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Molecular chlorine (Cl2) is a stable molecule which
does not react with the ozone.
However, when the CFC reach the ozone layer, 2
reactions happen.
The first involves homolytic breakdown of CFC
molecules under the influence of ultraviolet light
CCl2F2 CCl2F2 + Cl
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This reaction produces highly reactive chlorine
free radical
The atom may recombine with its original
molecule or may attack a molecule of the ozone
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1) Choose CFC - free products for your household
2) If you own or work for a business, ensure that
your
company supplies and products are as free ofCFCs
as possible
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4) Attempts have been made to develop compounds
which have low ozone depletion potential (ODP) to
replace CFCs as refrigerants, aerosol propellantsand solvents. Possible alternatives for CFCs
include:
Hydrochlorofluorocarbons (HCHCs) such as
CF3CHCl2
They break down more quickly in the atmosphere.
Though they have a lower percentage ofchlorine and hence a lower ozone depletion
potential than CFCs, they could damage ozone if
overuse.
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Hydrofluorocarbons(HCFs) such as CF3CH2F
They have no chlorine and thus are "ozone safe".
However, safety question on toxicity is still unsolved.
Hydrocarbons such as butane and propane
They are cheap and readily available. As they
contain no chlorine, they are "ozone safe". However,they are flammable and poisonous.
Water and steam
They are effective for some cleaning applicationsand thus can replace some CFCs as solvents incleaning.
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5) Installation of recovering and recycling units
to recycle CFCs from used refrigeration systems
and motor vehicle air conditioners to control theventing of CFCs into the atmosphere.
6) World wide help
Hong Kong joined the international effort to
protect the ozone layer by becoming a party to the
Protocol and introduced the Ozone Layer
Protection Ordinance (OLPO) in 1989. Theordinance empowers the government to control
the consumption of CFCs and other ozone
depleting substances through import/export
licensing control.
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As early as 1978, CFC aerosol propellants were
banned in some countries like Canada and United
States. The first international effort to protect theozone layer came in January 1978 when 24
countries signed the Montreal Protocol on
Substances That Deplete the Ozone Layer which
called for a cut back of the CFC production instages. The Protocol was amended in 1990 when 93
countries pledged to stop all production of CFCs
and other ozone depleting substances by 2000.
Since then, many industrialized nations have
agreed to a complete phase out as early as 1995.
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Done by,
Thava Muthasha
Ho Min YenGeetha Sarika
Nashwa