Ozone depleting solvent replacement

There now exist alternatives or sufficient quantities of controlled substances for almost all applications of ozone-depleting solvents. Exceptions have been noted for certain laboratory and analytical uses and for manufacture of space shuttle rocket motors. HCFCs have not been adopted on a large scale as alternatives to CFC solvents. In the near term, however, they may be needed as the conventional substances in some limited and unique applications. HCFC-141b is not a good replacement for methyl chloroform (1,1,1 -trichloroethane) because its ODP is three times higher. Alternatives for specific uses of ozone-depleting solvents are briefly described below. 

Electronics cleaning - For most uses in the electronics industry, ozone-depleting solvents can be replaced easily and, often, economically. A wide choice of alternatives exists. If technical specifications do not require postsolder cleaning, noclean is the preferred technology. If cleaning is required, the use of water-soluble chemistry has generally proved to be reliable. There are however limitations, whereby water-soluble chemistry is not suitable for all applications. 

Dry cleaning - Several solvents exist to replace the ozone-depleting solvents that have traditionally been used by the dry cleaning industry. Perchloroethylene has been used for more than three decades. Petroleum solvents, while flammable, can be safely used when appropriate safety precautions are taken. They include white spirit, Stoddard solvent, hydrocarbon solvents, isoparaffins, and n-paraffin. A... 

Chlorinated rubber is soluble in aromatic solvents, and paints made from it dry by solvent evaporation alone. In contrast to the vinyls, there is less difficulty in formulating systems that are suitable for brush application. It has excellent resistance to a wide range of chemicals and to water, but as it is extremely brittle it needs to be plasticised. To preserve chemical resistance it is necessary to use inert plasticisers such as chlorinated paraffin wax. Due to the presence of ozone depleting solvents, chlorinated rubber coatings are being phased out and largely replaced by vinyl acrylic coatings which have very similar performance and can be formulated from lower aromatic or aliphatic solvents. 

A variation on this procedure has been developed and constitutes passing fluorine through a dry column of AcOK. The AcOF thus formed was then usually dissolved in a suitable solvent, such as CFC13257. Recently it was discovered that this ozone-depleting solvent can be replaced by acetonitrile with no ill effects on the formation of AcOF nor on its reactions with various n centers258. 

SkyKleen [Solutia], TM for an aviation solvent that is a replacement for chlorinated or ozone depleting solvents such as MEK (methyl ethyl ketone), 1,1,1, trichlorethane, isopropyl alcohol, and acetone. It contains no halogenated materials. 

Oynasolve XD 27-2 is an experimental solvent that was developed for cleaning and defluxing of printed circuit boards. Oynasolve XD 27-2 is a non-chlorinated, non-fIcunmable, non-carcinogenic, non-ozone depleting solvent designed as a replacement for CFCs. 

Table 19.3. List of acceptable replacement chemicals for ozone-depleting solvents ODS) ...

Electrically conductive adhesives, primarily silver-filled epoxies, are finding uses as replacements for solder in surface-mounting components on printed-circuit boards and in flip-chip attachments. There are several driving forces for this application, a major one being the trend to eliminate lead and tin-lead solders because they may be health hazards. Also associated with the use of solder, is the need to eliminate ozone-depleting solvents presently used to clean and remove flux residues. Electrically conductive polymer... 

Production of hydrogen fluoride from reaction of Cap2 with sulfuric acid is the largest user of fluorspar and accounts for approximately 60—65% of total U.S. consumption. The principal uses of hydrogen fluoride are ia the manufacture of aluminum fluoride and synthetic cryoHte for the Hall aluminum process and fluoropolymers and chlorofluorocarbons that are used as refrigerants, solvents, aerosols (qv), and ia plastics. Because of the concern that chlorofluorocarbons cause upper atmosphere ozone depletion, these compounds are being replaced by hydrochlorofluorocarbons and hydrofluorocarbons. 

Perfluorocarbons are chemically inert, are nonflammable and have low toxici-ties. Unlike the halofluorocarbons, perfluorocarbons are not ozone-depleting and have been used as CFC replacements [7], However, perfluorocarbons have very long lifetimes in the atmosphere (>2000 years) [8] and this has consequences for their use as solvents since any process has to take into account the fact that any loss of solvent to the atmosphere is extremely undesirable. 

Perfluorocarbons are a class of organic compounds in which all of the hydrogen atoms are replaced with fluorine atoms. They possess unique properties that make them very useful as dispersants, carrier solvents, and processing solvent additives. Their lack of chlorine or bromine atoms results in zero-ozone-depletion potential. 

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. 

Tetrafluoroethane is a hydrofluorocarbon (HFC) or hydro-fluoroalkane (HFA) aerosol propellant (contains hydrogen, fluorine, and carbon) as contrasted to a CFC (chlorine, fluorine, and carbon). The lack of chlorine in the molecule and the presence of hydrogen reduces the ozone depletion activity to practically zero. Hence tetrafluoroethane can be considered as an alternative to CFCs in the formulation of metered-dose inhalers (MDIs). It has replaced CFC-12 as a refrigerant since it has essentially the same vapor pressure. Its very low Kauri-butanol value and solubility parameter indicate that it is not a good solvent for the commonly used surfactants for MDIs. Sorbitan trioleate, sorbitan sesquioleate, oleic acid, and soya lecithin show limited solubility in tetrafluoroethane and the amount of surfactant that actually dissolves may not be sufficient to keep a drug readily dispersed. 

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