Supercritical water oxidation and other destructive processes

5 Supercritical water oxidation and other destructive processes 

The use of supercritical water for the destruction of toxic materials dates back to a patent by Modell [12]. There are now more than 10 pilot-scale systems, mostly in the USA, but also in Germany. An authoritative review of progress in the decade following the Modell patent has been published 

A variety of pure compounds, mixtures and materials have been studied in such systems and have been found to be destroyed by 99.99% [24]. The 

However, in some cases incomplete oxidation products, such as ammonia and acetic acid, are produced [25]. In the oxidation of phenol, small quantities of the undesirable products dibenzofuran and dibenzo-/ -dioxin have been obtained [26]. The use of catalysts have been studied, with a view to improving the efficiency of the oxidation process. A mixture of CeO and Mn02 present in the reaction vessel was found to increase the rate of oxidation of acetic acid a difficult substrate [27]. The same catalyst was found to reduce the amounts of undesirable by-products from the oxidation of phenol [28]. 

Solid materials, such as sewage sludge, have been oxidised successfully in supercritical water [24]. The economical destruction of biomass waste is now only a possibility in the longer term. The same is true of plastic waste, although special cases exist, for example when the waste is radioactive. The latter was the motivation of a study of the oxidation of poly- 

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