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Review date: July 24, 2003
PNNL-SA-27883

Surfactants and Microemulsion in Supercritical Fluids

K Jackson and JL Fulton. In Supercritical Fluid Cleaning. Narita, McHardy Eds. Noyes, in press.

Abstract: A new class of cleaning solvents is described in which the unique solvent power of a supercritical fluid is united with the broad solvation capabilities of a reverse microemulsion. The application of these systems to cleaning processes is discussed. A reverse microemulsion has a structure similar to that of a conventional water-based surfactant system with the exception that the nanometer-sized structures are inverted—the core of the micelle is an ultra-small droplet of water and the exterior is the oil or supercritical fluid phase. The advantages of supercritical micro emulsions over conventional liquid or aqueous based systems are 1) energy savings (no drying is required), 2) environmental benefits since the gases may be benign and the contaminants or surfactants can more easily be recovered, 3) microemulsions have a high capacity of oils or other lipophilic materials, 4) the selectivity for the contaminants may be adjusted by density manipulation, and 5) improved cleaning or extraction efficiency because of the high diffusivity and low viscosities inherent in supercritical fluids.

A potent, new solvent is evolving—a supercritical carbon dioxide microemulsion. A CO2-based microemulsion is especially attractive since CO2 is very abundant, relatively inexpensive, and environmental benign at this scale of use. Applications of this system to cleaning processes appear very promising.

The range of industrial applications that supercritical microemulsions aspires to cover is extensive and includes areas such as separations, reactions, and spray coatings, (paints, lacquers, enamels, and varnishes). Applications to cleaning could include dry cleaning, the separation of dyestuffs, the extraction of contaminants from soils, the regeneration of activated carbon/catalysts, and the removal of strongly polar or ionic species from printed circuit boards, polymers, foams, aerogels, porous ceramics, and laser optics. the combination of colloidal technology with the technology of supercritical fluids greatly enhances potential applications in cleaning processes.