Ozone-depleting solvents, Montreal Protocol

Table 7.3. Ozone-depleting solvents restricted under the Montreal Protocol.

Many of the commonly used solvents for precision cleaning are being eliminated due to their suspected involvement in reduction of the earth s ozone layer. Production of these chemicals, known as ozone depleting substances (ODS), is being eliminated by an international treaty known as the Montreal Protocol. This is an international agreement, first proposed in 1987 and entered into force in 1989, which limits production of chlorofluorocarbons (CFCs) and halons due to concerns that these substances were damaging the earth s ozone layer. The Montreal Protocol was modified in 1990 and again in 1992 to completely eliminate the production of chlorofluorocarbons, carbon tetrachloride, methyl chloroform (1,1,1 -trichloroethane) and halons by 1996. 

Finally, nitromethane has been used in large quantities as a stabilizer for 1,1,1-trichloroethane. The use of this degreasing solvent is expected to decHne and disappear under the provisions of the Montreal Protocol (116), which bans ozone-depleting substances, of which this is one. 

The demand for trichloroethylene grew steadily until 1970. Since that time trichloroethylene has been a less desirable solvent because of restrictions on emissions under air pollution legislation and the passage of the Occupational Safety and Health Act. Whereas previously the principal use of trichloroethylene was for vapor degreasing, currentiy 1,1,1-trichloroethane is the most used solvent for vapor degreasing. The restrictions on production of 1,1,1-trichloroethane [71-55-6] from the 1990 Amendments to the Montreal Protocol on substances that deplete the stratospheric ozone and the U.S. 

Several of the commercially available 16,000 chlorinated and brominated compounds have already been regulated or harmed, CFCs, DDT and chlorinated biphenyls are typical examples. Many others are being phased out according to the Montreal Protocol on Substances that Deplete the Ozone Layer. This includes chlorinated solvents, methyl bromide and halons (e.g. CF3Br). The milder ozone destroyers, hydrochlorofluorocarbons (HCFCs) will also, eventually, be phased out. 

Prior to their current phase-out, chlorofluorocarbons (CFCs) were widely used as processing solvents for various materials. CFCs were well suited for many medical applications owing to their high solvency, nonflammability, good materials compatibility, and low toxicity. The uses for CFCs include a silicone deposition solvent, a fluoropolymer dispersion liquid, and processing solvents. However, the Montreal Protocol phase-out of ozone-depleting substances has required that alternative dispersants and solvents be found. Limitations of most available alternatives include flammability, low volatility, poor solvency, and poor materials compatibility. 

Trichloroethane was a major solvent, particularly for cold and vapor degreasing. It was phased out for emissive uses in the United States in 1996 because of its ozone depletion potential. The only application left is as chemical precursor for HCFC-141b and HCFC-142b. However, both are subject to phaseout schedule of the Montreal Protocol,... 

Hence, perfluorocarbons offer environmentally-friendly alternatives to common organic solvents with the potential for long lifetimes in industrial processes and are especially suitable for long, high temperature reactions. Furthermore, they are excellent substitutes for chlorinated solvents, like carbon tetrachloride, which are being phased out under the international agreement called the Montreal Protocol on Substances that Deplete the Ozone Layer and this has been demonstrated in their use as solvents in photooxidations [29] and brominations [30] of alkenes. 

In conjunction with the Montreal Protocol, the Clean Air Act of 1990 further defined the production and use of these ozone depleting materials. This act also created a program to identify alternatives to Class I and Class II ozone-depleting substances and to publish a list of acceptable and unacceptable substitutes. This is known as the Significant New Alternatives Policy or SNAP. Under the SNAP rules, it is illegal to replace a Class I or Class II substance with an unacceptable substance or process. Supercritical fluids are acceptable alternatives for solvent applications under the SNAP rules. 

Title VI of the CAA deals with chemicals, CFCs, and other ozone depleting substances (ODS) that can cause deterioration of the stratospheric ozone layer. Some of these chemicals are used as solvents in cleaning operations (cleaning of metals, electronics, and precision equipment), coatings, adhesives, and inks. Their production and use have been banned both domestically and internationally (except for a few countries). An unprecedented international effort by 20 countries and the Commission of the European Communities resulted in the 1987 Montreal Protocol. The Montreal Protocol became effective on January 1, 1989. In the U.S., the CAA Amendments of 1990 were the domestic response to such a critical environmental issue of global proportions and provided EPA with the regulatory agenda. 

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