Precision Surface Cleaning with Supercritical Carbon Dioxide: Issues, Experience, and Prospects

anufacturing industries have traditionally relied on chloM rofluorocarbons (CFCs) and other halogenated solvents for precision cleaning of metals, plastics, composites, ceramics, electronic components, and other materials. In 1991, for example, the Environmental Protection Agency estimated that approximately 170 million pounds of CFC-113 and methyl chloroform were used by US . industries for vapor degreasing operations.' The use of these solvents is being phased out because of their role in stratospheric ozone depletion, and a number of alternative cleaning technologies and solvents are in various stages of development and use. Many of these alternative technologies are limited in their application and present new problems, including high solvent and operating costs (e&, estimates for perfluorocarbon solvents are as high as $15/lb); toxicity (e& VOCs and HCFCs); flammability (e& hydrocarbons, alcohols, and ketones); and the generation of wastewater streams (aqueous and semiaqueous systems). No single solvent alternative or cleaning technology developed to date has been found to have the near-universal application of CFCs for precision cleaning applications. Supercritical carbon dioxide (CO,) has been identified as a promising solvent alternative to CFCs for a variety of precision cleaning applications, primarily because of its low cost, low toxicity, nonflammability, and environmental acceptability. This article presents recent experience working with CO, as a cleaning solvent to reduce the technology to commercial practice.