maryken 發問於 科學及數學地理學 · 1 十年前

chlorofluorocarbons (CFCs,氟氯碳化合物)

I want to know the meaning of chlorofluorocarbons......umm..like what is CFCs, and it have what harm(害處,串錯請不要見怪^_^")for us.

Plz answer me in English.

Thz a lot^^

1 個解答

評分
  • sc
    Lv 7
    1 十年前
    最愛解答

    The haloalkanes (also known as halogenoalkanes or alkyl halides) are a group of chemical compounds, consisting of alkanes, such as methane or ethane, with one or more halogens linked, such as chlorine or fluorine, making them a type of organic halide. They are known under many chemical and commercial names. As fire extinguishants, propellants and solvents they have or had wide use. Some haloalkanes (those containing chlorine or bromine) are believed to have negative effects on the environment such as ozone depletion. The most widely known family within this group are the chlorofluorocarbons (CFCs).

    Chloro fluoro compounds (CFC, HCFC)

    圖片參考:http://upload.wikimedia.org/wikipedia/commons/thum...

    CFC molecules

    Chlorofluorocarbons (CFC) are compounds containing chlorine, fluorine and carbon only, that is they contain no hydrogen. They were formerly used widely in industry, for example as refrigerants, propellants, and cleaning solvents. Their use has been regularly prohibited by the Montreal Protocol, because of effects on the ozone layer (see ozone depletion). They are also a powerful greenhouse gas, in terms of carbon dioxide equivalence (over a time period of one hundred years) between 5000 and 8100 per kg. [1]

    Hydrochlorofluorocarbons (HCFCs) are of a class of haloalkanes where not all hydrogen has been replaced by chlorine or fluorine. They are used primarily as chlorofluorocarbon (CFC) substitutes, as the ozone depleting effects are only about 10% of the CFCs.

    History

    Original development

    Carbon tetrachloride was used in fire extinguishers and glass "anti-fire grenades" from the late nineteenth century until around the end of World War II. Experimentation with chloroalkanes for fire suppression on military aircraft began at least as early as the 1920s.

    Development of alternatives

    圖片參考:http://upload.wikimedia.org/wikipedia/en/thumb/8/8...

    Work on alternatives for chlorofluorocarbons in refrigerants began in the late 1970s after the first warnings of damage to stratospheric ozone were published in the journal Nature in 1974 by Molina and Rowland (who shared the 1995 Nobel Prize for Chemistry for their work). Adding hydrogen and thus creating hydrochlorofluorocarbons (HCFC), chemists made the compounds less stable in the lower atmosphere, enabling them to break down before reaching the ozone layer. Later alternatives dispense with the chlorine, creating hydrofluorocarbons (HFC) with even shorter lifetimes in the lower atmosphere.

    However, by the time of the Montreal Protocol it was realised that deliberate and accidental discharges during system tests and maintenance accounted for substantially larger volumes than emergency discharges, and consequently halons were brought into the treaty, albeit with many exceptions.

    Phase out

    Use of certain chloroalkanes as solvents for large scale application, such as dry cleaning, have been phased out, for example, by the IPPC directive on greenhouse gases in 1994 and by the Volatile Organic Compounds (VOC) directive of the EU in 1997. Permitted chlorofluoroalkane uses are medicinal only.

    Finally, bromofluoroalkanes have been largely phased out and the possession of such equipment is prohibited in some countries like the Netherlands and Belgium, from 1 January 2004, based on the Montreal Protocol and guidelines of the European Union.

    Production of new stocks ceased in most (probably all) 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 specialised, uses. These programs recycle halon through "halon banks" coordinated by the Halon Recycling Corporation[3] to ensure that discharge to the atmosphere occurs only in a genuine emergency and to conserve remaining stocks.

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