Applications of Supercritical Water

From the macroscopic point of view, SCW is a non-polar solvent from a microscopic point of view, it is a molecule with a strong dipole of 1.85 Debye. Water in the supercritical state is able to react with different compounds. Therefore water is simidtaneously solvent and reactant in a variety of reactions. 

This chapter focuses on reactions that take advantage of the special properties or the tunability of properties of near- and supercritical water. These are on the one hand, synthesis reactions near the critical temperature of water, and on the other, decomposition reactions at higher temperatures. First of all, the properties of near-and supercritical water and their influence on chemical reactions will be discussed. 

Physico-Chemical Properties of Water at High Temperature and Pressure and their Relation to Applications 

Water is an ecologically safe substance widespread throughout nature. Below the critical point, the vapor pressure curve separates the liquid and gaseous phase. 

Here a continuous density variation from gas-like to liquid-like densities is not possible [2]. The vapor pressure ends at the critical point (Tc = 373 °C, pc = 22.1 MPa, P(- = 320 kg m ). Beyond the critical point, the density of SCW can be varied continuously from liquid-like to gas-like values without phase transition, over a wide range of conditions. 

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This can be used for the decomposition of chemical weapons. Another application is that the supercritical water is a special reaction medium to synthesize the new advanced materials and medicines. There appeared several reviews on the chemistry and application of supercritical water [62-66]. 

Research on the applications of supercritical water started in the Institute for Technical Chemistry in the early 90 s. At this time interest was focused on the oxidation of hazardous aqueous wastes in supercritical water (SCWO). Many industrial wastewaters containing highly toxic substances, which cannot be destroyed by biological treatment or disposed of, can be completely converted into harmless products [1-5],... 

A variety of chemical and biological reactions involving supercritical fluid technology are being explored and developed. They include polymerization reactions, biomass conversion, hydrogen production, applications of supercritical water oxidation, self-assembly applications, synthesis of specialty chemicals, manufacture of materials with tailored properties, and much more. These developments and new ones are expected to mature and be commercially deployed in years to come. 

Complete oxidation in supercritical water occurs at a high rate usually, complete conversion to carbon dioxide is achieved in the reaction time of about 1 min for most organics. New applications of supercritical water are emerging where only partial oxidation is carried out and oxygenated hydrocarbons are produced. Here, the reaction time has to be limited to the order of seconds. 

Dinjus, E. Kruse, A. Applications of Supercritical Water. In High Pressure Chemistry. Synthetic, Mechanistic and Supercritical Applications-,... 

Vogelaar, B.M., Makkee, M., and Moulijn, J.A. (1999) Applicability of supercritical water as a reaction medium for desulfurization and demetallisation of gasoil. Fuel Process. Technol., 61, 265. 

J.H. Wright, J.F. Paterson, Status and application of supercritical-water reactor coolant, in Ptoc. Am. Power Conf. 26—28 April 1966, Chicago vol. XXVm, 1%6, pp. 139—149. 

J. F. Patterson, Supercritical Technology Program, Final Report, WCAP-3394-8 (1968) (5) J. H. Wright and J. F. Patterson Status and Application of Supercritical-Water Reactor Coolant, Proc. of American Power Conference, Vol. 28, 139-149 (1966)... 

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