Solvents for Degreasing

Ketones or chlorinated hydrocarbons, especially trichloroethylene, perchloro-ethylene, or dichloromethane, are used to degrease metals [14.251], [14.252]. The chlorinated hydrocarbons used to degrease light metals are stabilized to prevent the metal-catalyzed elimination of hydrogen chloride. The solvent mixture [14.253]-[14.256] for metal degreasing are being replaced by aqueous systems [14.257], [14.258] due to more stringent environmental protection requirements. See also Section 8.2.1.2. 

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Particularly the chlorinated compounds have enjoyed range of applications vinyl chloride (chloro-ethene) as monomer for the production of PVC, tetra- and trichloroethenes as solvents for degreasing, and the insecticides l,l,l-trichloro-2,2-bis(p-chlorophenyl)ethane (DDT) and isomers of hexachlorocyclohexane (HCH) (benzene hexachloride). The biodegradation of fluorinated aliphatic compounds is generally different from the outlines that have emerged from investigations on their chlorinated, brominated, and even iodinated analogues. They are therefore treated separately in Part 4 of this chapter. 

Use alkaline cleaners instead of solvents for degreasing operations they can be treated on site and usually discharged to the sewer with permit authorization. 

Monochlorobenzene is a flammable clear liquid (fp, -45"C bp, 132°C) used as a solvent, solvent carrier for methylene diisocyanate, pesticide, heat transfer fluid, and in the manufacture of aniline, nitrobenzene, and phenol. The 1,2- isomer of dichlorobenzene (ortho-dichlorobenzene) has been used as a solvent for degreasing hides and wool and as a raw material for dye manufacture. The 1,4- isomer (para-dichlorobenzene) is also used in dye manufacture and as a moth repellant and germicide. All three isomers have been used as fumigants and insecticides. The 1,2- and 1,3-(meta) isomers are liquids under ambient conditions, whereas the 1,4- isomer is a white sublimable solid. Used as a solvent, lubricant, dielectric fluid, chemical intermediate, and formerly as a termiticide, 1,2,4-trichlorobenzene is a liquid (fp, 17°C bp, 213°C). 

Methylene chloride is used primarily as a solvent for degreasing and paint removal, and it is also used in aerosols and foam-blowing agents. Since 1985, new environmental regulation has had a major impact on this chemical. The consumption of methylene chloride has been reduced by 60 percent due to recycling and product substitutions. 

Other Chlorinated Ethylenes. Trichloroethylene was a major solvent for degreasing in the late 1960s and early 1970s. Since that time, its production has decreased from 500 million lb to 100 million lb in 1993 because of environmental pressures on the solvent users and replacement by 1,1,1-trichloroethane. Recently, trichloroethylene has recovered market share in metal cleaning due to the phasing out of 1,1,1 -trichloroethane in 1996. Also, the use as precursor for HFC-134a synthesis continues to increase. The production volume in 1998 was 245 million lb. 

Freons are commonly used as refrigerants and propellants in many types of aerosols. They are also used as selective solvents for degreasing. 

OTHER COMMENTS used as a solvent and extractant for resins, oils, fats, waxes, and chlorinated rubber used as a paint and varnish remover, and as a commercial solvent for degreasing metal parts useful in the synthesis of hexafluoropropylene has also been used in the synthesis of thiokol polysulfide elastomers if some branching of the polymer structure is required. 

Chlorinated hydrocarbons have been very much utilized as industrial solvents for degreasing, paint stripping and dry-cleaning. Mostly trichlorethylene CjHCl, alternatively methylene chloride (dichloromethane) CHjCl or tetrachlorethylene (per-chlorethylene) CClj CClj, have been used. 

Uses The major use for TRI is as a solvent for degreasing in the metal industry. Before use it is stabilized with acid acceptors such as amines, alcohols, epoxides and metal stabilizers. It is used also for degreasing in the textile industry, as an extractant, in solvent formulations for rubbers, paintstrippers and in paints, as intermediate for the production of dyes, colors, of fluorochloro-hydrocarbons and of fluoro-hydrocar-bons. 

Other Chlorinated Ethylenes, Trichloroethylene was a major solvent for degreasing in the late 1960s and early 1970s. Since that time, its production has decreased significantly because of environmental pressures on the solvent users and replacement by 1,1,1-trichloroethane. This decline is expected to continue. 

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