Solubility of Potassium Hydroxide and Potassium Phosphate in Supercritical Water

The solubilities of potassium hydroxide and dibasic potassium phosphate in supercritical water solutions have been measured at temperatures from 400 to 525 C and pressures from 22.1 to 32.0 MPa. The solubility of potassium hydroxide varied from 61 mg/kg at 525 C and 22.1 MPa to 594 mg/kg at 450 C and 30.4 MPa. The solubility of dibasic potassium phosphate varied from 2 mg/kg at 450 C and 26.8 MPa to 416 mg/kg at 400 C and 27.1 MPa. The solubility was found to vary directly with pressure and inversely with temperature. Results were fit to a semiempirical solvation model to yield predictive equations for solubility as a function of water density. These studies were motivated by applications for electrolyte solubility data in the supercritical water oxidation process. Supercritical water oxidation (SCWO) is an emerging technology for the thermal destruction of organic compounds in wastewaters and sludges.