2. Supercritical water

2.1 Properties of supercritical water

In the (pressure-temperature) diagram of a pure substance, the coexistence line between the gas and liquid phases ends at the critical point of that substance. For values above this critical pressure and temperature, a single phase exists—known as the “supercritical region”—in which there is no discontinuity when transitioning to the liquid or gaseous state through changes in pressure or temperature. In general, fluids in the supercritical state have specific, common, and interesting properties, such as a relatively high density—sometimes close to that of liquids—low viscosity similar to that of gases, and good mass transfer coefficients. This gives them attractive solvent and transport properties and justifies the use of this solvent in chemical...