SUPERCRITICAL MICROEMULSION CLEANING PROCESSES

Apart from obvious dry cleaning applications,potential applications of C02 based microemulsions indude (i) printed circuit board cleaning, (ii) extraction of contaminants firom soils, (in) cleaning of polymers, foams, aerogels, porous ceramics, and laser optics, (ivj regeneration of activated carbon beds or catalysts, and (v) the separation of dyestuffs from textiles. 

The high diffiisivities and lack of surface tension associated with pure supercritical fluids makes them ideal for cleaning narrow gaps (typically less than a few thousands of an inch) in circuit boards of high value such as for satellite applications. Many of the contaminants are, however, ionic and carbon dioxide alone is not effective at extracting these species. Residue from surfactants need not be a problem as final washings with pure CO2 would clean the boards of remaining surfactant. 

Supercritical fluid extraction with carbon dioxide has long been proposed as a method for the cleanup of soils, sediments and sludges that are contaminated with toxic substances. An attractive feature of this process is that very little solvent residue remains in the processed 

The opportunity to recover the surfactant and extractant following cleaning is a distinct advantage of a sup critical microemulsion over conventional water- or liquid-based systems. The low volatility 

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A potent, new solvent is evolving—a supercritical carbon dioxide microemulsion. A C02-based microemulsion is especially attractive since CO2 is very abundant, relatively inexpensive, and environmentally benign at this scale of use. Applications of this system to cleaning processes appear very promising. 

If large quantities are used for technical processes, e.g. for cleaning, the recovery and reuse of the microemulsion or at least of a considerable amount of the most expensive components is desired. Therefore, strategies are needed to separate contaminants from the organic microemulsion components. Separation is usually more complicated than from ordinary solvents and often requires several steps [39, 40]. In particular, the separation of waste materials from the surfactants is usually very difficult or often even impossible. The temperature-dependent phase behaviour of bicontinuous microemulsions, however, can sometimes be beneficially used for separation [41]. Easy separation, at least from the unpolar solvent, can be achieved from microemulsions with supercritical liquids [42]. 

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