Calorimetric Study of Ionization and Oxidation Reactions in Supercritical Water.

The investigation of chemical reactions in the supercritical region of water requires a knowledge of the thermodynamic quantities equilibrium constants, enthalpy changes, entropy changes, and heat capacity changes associated with water dissociation and solute-solute interaction in this region. In this study, these quantities have been determined to 350 or, in some cases, to 370 deg C for water ionization and alkali and alkaline earth chloride ion interaction. The determinations were made using a high precision flow calorimeter designed and constructed to withstand the corrosive and high temperature conditions encountered in the study. The results are consistent with a model involving water molecules as active participants in the reactions. As temperature increases, the percentage of water molecules participating in hydrogen bonding decreases with resulting large effects on enthalpy changes, entropy changes and heat capacity changes values for chemical reactions. The equilibrium constants and enthalpy changes values provide essential information for the design of processes intended to operate under supercritical water conditions.