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APPLICATIONS: SUPERCRITICAL FLUIDS

The initial application of supercritical fluids, and probably still its most productive, is extraction with carbon dioxide. It makes most economic sense for high-value materials, such as pharmaceutical precursors. For low-value materials it is only viable if carried out on a very large scale. The most prominent applications are the decaffeination of coffee and the extraction of hops as part of the beer-making process (although this is often carried out with liquid carbon dioxide). A related process is the ‘cleaning’ of seeds, such as rice, which is carried out in the Far East. Dry-cleaning is also carried out commercially. The advantages of supercritical carbon dioxide in these processes are speed due to rapid diffusion, less pollution in the working and general environment, less solvent residues in products, less solvent disposal costs.

Chromatography using supercritical carbon dioxide has been carried out on an analytical scale in niche applications and it has also been carried out on a small production scale for high value products and chiral separations. Efficient simulated simulated bed units are available. Because of more rapid diffusion, greater chromatographic efficiencies are possible.

A number of other processes have been and are being researched, with the hope of useful applications, which have not yet been notably achieved. These include fractionation of liquid mixtures, chemical reactions, metals processing, impregnation and dyeing of polymers and synthetic fibres, particle formation and the fabrication of minute electronic devices.

Other substances have been researched as supercritical fluids. One example of possible importance is the production of biodiesel using supercritical methanol.

Carbon dioxide under pressure is used to enhance the extraction of gas and oil from wells. This is related to the use of carbon dioxide to accomplish carbon capture and storage.

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