Precision cleaning with supercritical carbon dioxide for the elimination of organic solvents and the reduction of hazardous wastes

摘要

Private and governmental industrial facilities use chlorofluorocarbons and chlorocarbons for the cleaning of a variety of items. The Montreal Protocol (1987) and amendments to this act will phase out the use of chlorofluorocarbons, or CFCs, by the year 2000 because they are toxic, carcinogenic, and implicated in the depletion of the Earth's ozone layer. The United States has pledged to eliminate these substances by 1995. To stay competitive in the global market, US industries require an economical replacement. Supercritical fluids, which have been used in food, fragrance, and petroleum processes for years, are attractive replacement solvents because of their low environmental impact, high diffusivities, low viscosities, and temperature-pressure dependence of solvent strengths. In the case of nontoxic and nonflammable carbon dioxide (CO(sub 2)), its critical temperature and pressure are readily accessible with well-established process technology and equipment. In addition, applications using a supercritical fluid such as CO(sub 2) are generally safer and environmentally benign. Extractions using supercritical CO(sub 2) use less energy than distillation and incineration processes and are less expensive than liquid extraction processes using toxic and costly organic solvents. Finally, CO(sub 2) has a very high volatility compared to virtually any organic extractant which facilitates its separation from extract solutions for extract recovery and CO(sub 2) recycle. Data will be presented on the successful removal of cutting and machine oils, silicone oils, body oils, and hydraulic fluids from a variety of industrial substrates with supercritical CO(sub 2) to, at, or below precision cleaning levels (less than 10 micrograms of contaminant per square centimeter of surface). The applicability of this technique to commercial operations was evaluated in this area of contaminant removal, surface interactions, operational costs, and waste reduction and elimination.