1 / 11

Adapted from chemcases

ChloroFluoroCarbons (CFCs). Adapted from http://chemcases.com. Step Back in History. Why is refrigeration important?. Food preservation! Air conditioning!. Humans learned that various techniques such as salting, boiling, or storage in cold locations worked well.

kaiser
Download Presentation

Adapted from chemcases

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. ChloroFluoroCarbons (CFCs) • Adapted from http://chemcases.com

  2. Step Back in History Why is refrigeration important? Food preservation! Air conditioning! Humans learned that various techniques such as salting, boiling, or storage in cold locations worked well. In the mid 19th century, insulation and ice started to become the standard refrigeration method. Even in 1940s people would have ice delivered by horsecart.

  3. Mechanical Refrigeration In 1851 Dr. John Gorrie obtained a patent entitled, "An Apparatus for the Artificial Production of Ice in Tropical Climates". The invention was based on the well-known cooling effect produced by the evaporation of a liquid. By 1928, the engineering and design of a mechanical refrigerator was complete. Clausius-Rankin system All that was missing was a good chemical to use as the gas/liquid. 1) A gaseous refrigerant is compressed from a lower to a higher pressure, some of the energy supplied by the compressor transfers to the gas as heat. 2) The heat is removed from the and the refrigerant liquifies. 3) Passage of this liquid through an expansion valve lowers the pressure exerted on it, thereby causing some of the liquid to evaporate and cool the remaining liquid as a result. 4) In the evaporator the cold liquid-vapor mixture completely vaporizes, completing the cycle.

  4. Chemists to the Rescue A good refrigerant for food needs to Have a boiling point around −40 to −10 °C at 1 atm Be nontoxic and nonflammable Low vapor pressures The first examples used SO2 or NH3 Both are quite toxic and NH3 is quite flammable. Scientists at the company Frigidaire, Robert McNary, Thomas Midgley and Albert Henne, were tasked to find alternative gases. Found CF2Cl2 had the best properties and it quickly became the most popular refrigerant

  5. What is a CFC? CFCs are compounds made up of only carbons, fluorines, and chlorines. Dr. Roy Plunkett, at Dupont in 1938, was evaluating CF2=CF2 as a possible refrigerant when it spontaneously polymerized produce to poly TFE which we now call "Teflon".

  6. Atmospheric Chemistry Ozone layer is important for life to work, O3+ hv--> O2 + O* In 1973 Dr. James Lovelock reported that he detected a buildup of CFC-11 and CFC-12 in the atmosphere. In 1974 Sherwood Rowland and Mario Molina speculated that Cl* radicals could destroy ozone much more rapidly than other reactions. CF2Cl2 CF2Cl + Cl* Cl* + O3 ClO + O2O* + ClO  Cl* + O2 It has been estimated that one Cl radical can destroy up to 100,000 O3 molecules before it is depleted!

  7. Societal Uproar Initially, companies tried to discredit the scientific findings. In 1979, the US banned CFC-using aerosol products. In 1985, British scientists reported the first direct evidence of declines in atmospheric O3. In 1987, the Montreal Protocol was drafted as an international effort to reduce the use and production of ozone-depleting chemicals.

  8. Dilemmas in the Montreal Protocol First universally ratified treaty in United Nations history! If the agreement is adhered to, the ozone layer is expected to recover by 2050. One of the issues addressed by the Montreal negotiators was how not to impose a hardship on developing countries– they were given more time to comply. Nations such as China, Russia and India, which potentially are the world's largest CFC's users, benefit by being considered to be "developing" nations. What do you think?

  9. Developing Alternatives Refrigerants and propellants are still important, how do chemists design alternatives? Get rid of Cl and incorporate some C–H bonds instead. Hydrofluorocarbons (HFCs) and hydrochlorofluorocarbons (HCFCs) have gained popularity. HFC-134a CF3CH2F and HFC-125 CF3CF2H are now used for refrigeration. These new refrigerants for the 21st century cost 3-5 times as much to manufacture.

  10. A Rose by Any Other Name… All of these are the same compound HFC-134a!

  11. What about Greenhouse Gases? HFC-134a and HFC-125 are at least 1000 times worse greenhouse gases than CO2! Thoughts about climate change? The Kyoto Protocol has been drafted to attempt to address this issue. Why hasn’t it caught on? The USA senate voted 95-0 NOT to ratify the original Kyoto Protocol Canada withdrew from the Kyoto Protocol because it wouldn’t be able to meet any targets.

More Related