Reproduced with permission,
CFC-12, or CCl2F2, is used in air-conditioning systems, refrigerators, and freezers. It is one of the most widely used chlorofluorocarbons, and it is one of the most damaging to the ozone layer.
HFC-134a, or CF3CFH2, is a leading candidate to replace CFC-12. It is a hydrofluorocarbon and contains no chlorine, so it offers no threat to the ozone layer.
The numbering system for CFCs and related compounds looks confusing, but it does have a method, called the "rule of 90." To get the chemical formula from the number, one adds 90 to it; the digits of the resulting number give the number of carbon, hydrogen, and fluorine atoms. For instance, adding 90 to 134 gives 224. Thus HFC-134a has two carbon atoms, two hydrogen atoms, and four fluorinc atoms. The "a" refers to how the atoms are arranged; HFC-134b is a different substance.
The numbering system apparently was invented at Du Pont in the early 1930s. Du Pont scientists did much of the early work on CFCs, and their numbering system became standard. According to Du Pont lore, the system was deliberately made confusing to give Du Pont scientists a step up on the competition.
The two substances, CFC-12 and HFC-134a, are similar. Their boiling points are within a few degrees of each other, and their molecular weights differ by less than 20%. Neither is flammable. HFC-134a is close enough to CFC-12 that it should perform the same refrigeration functions with little loss of efficiency.
The differences between the two chemicals will cause some headaches, however. HFC- 134a must be run through a refrigeration system at a higher pressure than CFC12, so current refrigerators and air conditioners will have to be either fitted with stronger compressors or else replaced. In the case of commercial refrigerators, which are meant to last for 30 years or more, it will be smarter to refit them. It would not be economical, though, to refit home refrigerators and automotive air conditioners, so they will be allowed to wear out and then be replaced with new models designed for HFC-134a. The automobile industry expects to spend $100 million to retool its assembly lines to make the new air-conditioning compressors.
A second problem is that HFC-134a will not work with the existing lubricants used in refrigeration systems. Chlorine makes CFCs soluble in oils, but HFC-134a is not soluble in the oils used now. If HFC-134a is to replace CFC-12, a new lubricant must be found. Further, while CFC-12 is proven to be nontoxic, toxicology studies on HFC-134a remain incomplete.
The major drawback of HFG134a at the moment, though, is that no good manufacturing process exist for it. CFC-12 is easy to make--basically, one takes carbon tetrachloride (CCI) and adds hydrofluoric acid at high temperature and pressure. No such simple process appears available for HFC-134a, and several companies are looking into different processing techniques. * RP.