Refrigerants, other than CFCs

The discussion of liquefaction of chlorine (Section 9.1.7.2B) also pointed out that new systems operate on refrigerants other than the CFCs that were the industry standard for many years. Many existing systems have also been converted to the newer materials. HCFCs, such as R-22, have much lower ozone depletion potentials than the CFCs but... 

Other refrigerants, including CFCs Rll and R12, HCFC R22, HFC R32 and hydrocarbons such as butane have been evaluated in detail by Critoph [3,4] but are significantly worse in performance than methanol or ammonia. In 1996, these two refrigerants are the only ones used in the major laboratories working on carbon adsorption cycles. 

Table 1 lA presents tabulations of the safety of important refrigerants, but this list does not include aU available refrigerants. Table 11-5 summarizes a limited list of comparative hazards to life of refrigerant gas and vapor. The current more applicable refrigerants from the m or manufacturers of the CFC and HCFC refrigerants and their azeotropes/ blends/mrxtures are included, but the list excludes the pure hydrocarbons such as propane, chlorinated hydrocarbons such as methyl chloride and others, inorganics, ammonia, carbon dioxide, etc. See Table 11-6. The CFC compounds have a longer and more serious ozone depletion potential than the HCFC compounds, because these decompose at a much lower atmospheric level and have relatively short atmospheric lifetimes therefore, they do less damage to the ozone layer. Table 11-7 summarizes alternate refrigerants of the same classes as discussed previously. Table 11-8 correlates DuPont s SUVA refrigerant numbers to the corresponding ASHRAE numbers.

To provide some historical perspective, Table 12.2 gives the distribution of sales by use for CFC-11 and CFC-12, broken down into aerosol propellants, blowing agents, refrigerants, and other uses, from 1976 to 1992. On a global basis, the use as aerosol propellants accounted for more than half of the sales of CFC-11 and CFC-12 in 1976. Essentially all of this as well as most of that used in other applications has been released into the atmosphere. 

Nonfluorine CFC substitutes have been considered, but few are fully satisfactory. For example, we could go back 50 years to the use of anhydrous ammonia as a refrigerant, but NH3 is as toxic now as it ever was. Cyclopentane could be used as a foam-blowing agent, but it is less effective than HCFC-141b and besides would contribute to the volatile organic compound load in the troposphere, which is the root cause of ozone pollution (Section 8.3.2). On the other hand, supercritical CO2 is emerging as an alternative to CFCs in various steps in the preparation of fluorocarbon polymers (Section 8.1.3). 

Ozone is O3. The ozone layer is a region of the stratosphere that contains higher concentrations of ozone than other parts of the atmosphere. The ozone layer is important for human health because it blocks ultraviolet radiation from the sun, and this helps to protect us from skin cancer. Research in the 1970s revealed that several gases used for refrigeration and other purposes were depleting the ozone layer. Many of these ozone-destroying molecules are short alkyl halides known as chlorofluorocarbons or CFCs. 

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