How were FREONS developed for use in refrigeration? What were the advantages of these chlorofluorocarbons over previously used cryogens? Outline why the use of FREONS has now been discontinued.© BrainMass Inc. brainmass.com December 24, 2021, 7:05 pm ad1c9bdddf
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Refrigeration in the early 1930s was done primarily with ammonia, methyl chloride, sulphur dioxide, propane and isobutane. Each of these refrigerants had serious drawbacks in terms of safety. Methyl chloride (CH3Cl) was by far the most dangerous because of the hydrogen atoms not being strongly enough bonded to the carbon, causing it to ignite. The statistically safer ammonia and sulphur dioxide were unpopular because leakages were so noxious. Propane and isobutane are highly flammable but in fact rarely ignited when used for refrigeration.
Thomas Midgeley, Jr. of General Motors was charged with finding a safer alternative. He turned to the periodic table to find families of elements forming stable compounds with the desired vapor pressures. He concluded that carbon-halogen compounds might be sufficiently stable. Midgeley reasoned that compounds which did not include hydrogen, as methyl chloride did, would be more stable and certainly non-flammable. His reasoning proved correct and CFCs (compounds containing chlorine, fluorine and carbon only) became the new standard in refrigeration.
However, their vapor pressures are high enough that they eventually escape into the atmosphere, where they contribute to global warming. They remain in the atmosphere until they reach the stratosphere by means of convection (physical mixing of masses of the atmosphere). There they are decomposed by photolysis. Chlorine from the decomposition process destroys ozone. Since ozone in the stratosphere acts as a filter to remove much of the UV-b in from solar radiation, ozone depletion will likely lead to adverse effects on plants and animals. For this reason CFCs are being phased out and replaced with compounds whose constituents do not react with ozone.© BrainMass Inc. brainmass.com December 24, 2021, 7:05 pm ad1c9bdddf>