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INTRODUCTION:
The world is in the midst of the greatest environmental crisis
it has ever seen in the age of man.The Antarctic ice shelf is
melting, sea levels are rising, the ozone layer is getting
depleted. And,the greatest trouble, of course, is that man, the
reason the earth is in such a mess, has beensupremely uninterested
in doing something about these crises.However, the reality and
imminence of the dangers that lie ahead if the environment is not
taken
care of has, in the last few years, dawned upon man. Cases such
as Vanuatu have almostshocked humans into action.Many steps have
been taken by countries of the world to save the planet from man.
Here, wewill talk about the environmental problems that
conventional refrigerants cause and the impactthat eco-friendly
refrigerants have had in reducing the environmental ramifications
of usingrefrigeration systems.HISTORY
Till about 1984, all refrigeration systems domestic and
industrial used only a handful ofrefrigerants. However, around that
time, it was discovered that the refrigerants, although non-toxic
per se, were having an adverse effect on the environment in an
unprecedented way. Therefrigerants used were all basically
haloalkanes called CFCs. These were basically alkaneswith varying
numbers of hydrogen atoms replaced by halogens (in most cases,
Chlorine and
Fluorine).Two international treaties the Kyoto Protocol and the
Montreal Protocol were adoptedby a very large number of countries
in order to control global warming and ozone
depletionrespectively.MECHANISM:
The mechanism by which CFCs deplete the ozone layer is very
simple. The reaction is basicallythe photolysis of ozone in the
presence of Chlorine free radical. Oxygen in the stratosphere
isfound in three forms O (oxygen atom - monoatomic), O2 (oxygen gas
- diatomic), O3 (ozone -triatomic).These are in a state of dynamic
equilibrium.O3 + energy (hv) = O2 + OO + O3 = 2O2
O + O2 = O3All that the CFCs do is provide a free radical other
than the oxygen atom for reaction. Forexample, CFCl3 reacts in the
stratosphere in the following way:CFCl3 + hv= CFCl2 + ClCl + O3 =
ClO + O2ClO + O3 = 2O2 + ClThus, the Chlorine free radical is
regenerated at the end of the mechanism, thus perpetuatingthe cycle
and removing ozone from the system. It has been found that a single
chlorine atomcan react with 100,000 ozone molecules before it comes
back down to the troposphere. That isthe kind of damage that CFCs
can cause to the Earths ozone layer.GROUNDWORK:
This knowledge about the ozone depletion and the understanding
of its mechanism made the
need for eco-friendly refrigerants very clear. Before going
further, we need to define certainterms that are essential to the
understanding of the environmental impact of refrigerants.Ozone
Depletion Potential (ODP): The ODP of a refrigerant is a measure of
the propensity thata refrigerant has for depleting the ozone from
the stratospheric ozone layer (about 30-40km
above mean sea level) that absorbs a large portion of the UV and
other harmful radiationfrom the sun. It is formally defined as the
relative amount of degradation to the ozone layerthat the compound
can cause, with respect to trichlorofluoromethane (R-11 or CFC-11)
whichhas an arbitrarily fixed ODP of 1.0. Chlorodifluoromethane
(R-22), for example, has an ODP of0.05. CFC or R11 has the maximum
potential amongst chlorocarbons because of the presence
