Uses

The existing and potential uses of supercritical carbon dioxide (scCO2) fall into several areas:

Supercritical Fluid Extraction
ScCO2 is used to dissolve a required material from a mixed resource.

Decaffeination of coffee beans
image: coffee beans

Some people like the taste of coffee, but not the effects of the caffeine. The decaffeination process should not remove flavouring components, and must not leave residues of solvents used. ScCO2 can be "tuned" to extract only the caffeine, and any remaining traces of carbon dioxide will diffuse out of the product. Find out more about this process.

 

Hop extraction in brewing

image: beer can

The addition of hops to beer (which began in the 15th century) is responsible for the flavour of "bitter". Flavour can be extracted using pressurised hot water, but is not very efficient. With other solvents, like methanol and dichloromethane, there is a risk traces will remain in the hop extract. ScCO2 is a much better alternative and is now widely used.

 

Treatment of toxic waste
image: toxic waste
Many organic compounds are soluble in scCO2, and this can be exploited to remove toxic materials from waste. The safe oxidation of toxic waste chemicals can also be carried out in supercritical water (temperatures above 350 °C, pressure higher than 200 atmospheres).

 

 

 

 

 

 

 

 

 

 

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Flavour Extraction
As the supercritical carbon dioxide (scCO2) passes through the extractor, the required flavouring compounds are selectively dissolved in it, and leave the extractor with the scCO2. When pressure is released in a separator vessel, the flavouring compounds precipitate out. The flavouring compounds are separated from the carbon dioxide, which is pressurised for re-use.
diagram: flavour extraction with supercritical carbon dioxide
diagram: flavour extraction with supercritical carbon dioxide
diagram: flavour extraction with supercritical carbon dioxide diagram: flavour extraction with supercritical carbon dioxide diagram: flavour extraction with supercritical carbon dioxide
diagram: flavour extraction with supercritical carbon dioxide

Chemical Synthesis
There are many possible reactions that can be carried out in supercritical carbon dioxide (scCO2) where it is used either as a solvent or as one of the reagents too. The ability to control its solvent properties means that the desired product is obtained with fewer co-products. This in turn leads to simpler product separation.

Friedel Crafts This type of reaction typically generates a lot of waste, as the catalyst cannot be recovered and reused. By using scCO2, a different, recoverable catalyst can be used, and the desired product has a higher yield. Find out more
Polymers The use of scCO2 is paving the way for better ways of making high quality polymers without the use of environmentally undesirable organic solvents. Click here for more detail
Asymmetric Synthesis Several pharmaceutical products are based on compounds that exist as two optical isomers, but only one form is required. Usually both isomers are made, and then separated, but research has shown synthesis in scCO2 can yield one isomer almost exclusively. Find out about this

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image: commercial extraction plant
image: supercritical reactor

Solvent replacement
Solvents are used in many different ways, for example in household products and industrial cleaning. Whilst the high pressures needed for supercritical carbon dioxide (scCO2) make it impractical for domestic use, there are several commercial applications where it can be used with considerable benefit.
Water is also used in very large quantities by some industries, but cannot be discharged unless it is free from contamination. There are several areas where scCO2 may be introduced as an alternative, significantly reducing water use.
Find out more by following this link

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