ABSTRACT
Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 315 Need for New Solvents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 316 Liquid and Supercritical Carbon Dioxide. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 317
Carbon Dioxide. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 317 Phases of CO2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 317
Liquid CO2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 317 Supercritical CO2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 318
Industrial Cleaning. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 318 Condensed-Phase CO2 Cleaning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 319
Supercritical Fluid Extraction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 319 Supercritical CO2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 320
Engineering Condensed-Phase CO2 Cleaning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 321 Details of Condensed Phases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 322
Solubility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 322 Cosolvents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 322 Substrate Compatibility. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 323 Effect of Mixing on Supercritical CO2 Cleaning. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 324
Economics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 325 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 326 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 326
INTRODUCTION
The use of carbon dioxide (CO2), either liquid CO2 (LCO2) or supercritical CO2 (SCCO2), cleaning has been shown through extensive laboratory and pilot testing to be potential alternatives for manufacturers looking for new precision and parts cleaning systems. The use of carbon dioxide as an extraction solvent has slowly found acceptance, and also close
to commercialization are applications for supercritical and liquid CO2 in the electronics industry. Although much of the potential for supercritical or liquid carbon dioxide lies in fairly exotic applications, CO2 solvent technology is already commercial in the comparatively mundane fields of dry cleaning and spray painting. The technology is especially well suited for precision cleaning applications in which parts have intricate geometries or for applications in which parts are sensitive to water or high temperature. CO2 cleaning appears to be compatible with a majority of substrates encountered in manufacturing, including most metal and glass, and many plastics. Mixing generally appears to improve the efficiency of the CO2 cleaning process, as does the incorporation of cosolvents with condensed-phase CO2.
