Montreal protocol, solvents restricted

The second Montreal Protocol (1990) restricted the production and use of 1,1,1-TCA because of its high ODP, ultimately leading to its phase out by 2005. Metal cleaning is one of the important end uses of C2 chlorinated solvents, and emission of these solvents is a major issue. The metal industry has improved operations to recover these solvents and minimize emissions into the atmosphere. A similar trend is ongoing in dry cleaning operations to reduce the use of PCE. Phase-out of PCE is well underway. 

Recently several patents have been issued (16—18) describing the use of 1,2-dichloroethylene for use in blends of chlorofluorocarbons for solvent vapor cleaning. This art is primarily driven by the need to replace part of the chlorofluorocarbons because of the restriction on their production under the Montreal Protocol of 1987. Test data from the manufacturer show that the cleaning abiUty of these blends exceeds that of the pure chlorofluorocarbons or their azeotropic blends (19). 

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. 

Solvents restricted under the Montreal Protocol are categorized as Class 1 or Class II compounds, many of which are listed in table 7.3. Class I componnds have already undergone a major phase-ont, whereas Class II componnds will be completely phased out of use by 2030. 

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

Also, regulations are helping to reduce the solvent content of adhesives."" The use of chlorinated solvents, frequently used in primers and for cleaning, has been discontinued based on the Montreal Protocol. From June 1998, the production of a pair of shoes in Europe should not involve the use of more than 20 g of solvent. This is only partially successful solution since shoe production is expected to move out of developed countries to less restrictive jurisdictions. Solvent Emission Directive will continue to restrict solvent use in Europe. 

NCI3 is much less volatile than chlorine, and so it tends to accumulate in suction chiller bottoms (Section 9.1.6.4A) and in chlorine vaporizers (Section 9.1.8.7) or other vessels from which chlorine is withdrawn as vapor. One method for its removal as a waste from suction chillers has been the dilution of the bottoms with a chlorinated organic. The standard choice for this duty has been carbon tetrachloride. With the use of this solvent restricted under the Montreal protocol, other materials have been suggested as replacements. Chloroform is one possibility, but it is important to note that it (b.p. 61 °C) is more volatile than nitrogen trichloride. Section 17.4.2 outlines problems that can arise with replacement solvents. Section 9.1.11.2E discusses alternative proeesses for the safe destruction of NCI3. 

Many compounds have been used as SCFs. However, after the Montreal Protocol in 1987, the use of ozone-damaging compounds was banned and the use of SCFs was restricted to green compounds only. Among these solvents, carbon dioxide (CO2), which has a aitical tanperature of 31.1°C and a critical pressure of 72.8 bar, is most conunonly onployed. CO2 is nontoxic, nonflanunable, noncorrosive, inexpensive, abundant, and an environmentally friendly compound. 

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