APPLICATIONS: WATER AND SUPERHEATED WATER
Water has obviously been used over a long period for many processes and this is also true to a smaller extent for superheated water. The current interest is to use water for processes that have previously been done in different and more polluting ways and these uses have recently been patented.
Superheated water has been used in the food industry for cooking a little above 100°C and the final extractions of instant coffee are sometimes up to 120°C. The processing of wood pulp is carried out sometimes above 100°C as has the hydrolysis of starch to polysaccharides out at high temperatures for some time. Re-crystallizations in water contained in sealed tubes above 100°C have been carried out for 100 years or more. Superheated water has also been used for waste treatment by the so-called wet-air oxidation process (a similar process has also been carried out in supercritical water). Chemical reactions have also been carried out in superheated water and this work has been thoroughly reviewed recently.
In the context of the recent use of water for more environmentally friendly processes, extraction has attracted the most interest. Extraction of plant materials to produce flavours and fragrances and valuable compounds has been carried out, for example the superheated water extraction of biomass for a cosmetic product and the production of indigo from woad. Extraction has been carried out for the removal of metal ions from a polymer and the removal of organic compounds from a polymer, even though the polymer is water soluble, by exploiting phase behaviour.
There has been interest in the recycling of polymers by de-polymerisation, regeneration of rubber by de-vulcanisation and the clean-up of contaminated land.
A.A Clifford 04/12/2007