Guidelines for Phase Separations in High-Temperature and Supercritical Water Solutions: A Report on a Workshop Organized by the U.S. Army Research Office and the Forschungzentrum Karlsruhe, 7-9 July 1999

Abstract

Approved for public release; distribution unlimited. AbstractThe U.S. Army is developing supercritical water oxidation for destruction of military toxic materials. The properties of high-temperature aqueous solutions are not, in most cases, well known. Understanding the phase behavior of these solutions will facilitate design and efficient operation of high-temperature water reactors. A U.S. Army workshop held at the Forschungzentrum Karlsruhe in July 1999 assembled experts on phase behavior to develop guidelines that, in the absence of more complete knowledge of solution properties, will aid reactor designers and operators. The experts presented papers on model systems, properties of high-temperature aqueous solutions, and chemistry in high-temperature water. Following these presentations, the experts developed some of the desired rules of thumb and made recommendations for research to develop these guidelines further. This workshop report includes the presentation papers, guidelines, and recommendations for research. Distribution 67Report Documentation Page 71 Participants in the workshop 2Hong, Model Systems P-T-x diagram for Type la systems and Type lb systems 122. T-x diagram for NaCI-H 2 0 at 250 bar 13 3. P-T projection of solidus for NaCI-H 2 0 14 4. P-T-x diagrams for Type 2a systems, and Type 2b systems 14 5. T-x projection of phase diagram for ternary systems of Type 1: subtype A, subtype B, and subtype C 16 6. P-T projection of eutonic curve for NaCl-Na 2 S04-H 2 0 system ... 177. Temperature progression of phase diagrams at 225 bar for NaCINa 2 S04-H 2 0 system 17 Supercritical water (SCW) oxidation (SCWO) provides a powerful means to transform toxic organic materials into simple, relatively inert oxides. Water at high temperatures and pressures is an active medium, however, and its properties and those of its solutions are only partially understood. Indeed, two principal challenges to broad use of this technology are (1) the materials requirements for the reactor and the heatup and cooldown sections, and (2) the incomplete understanding of and ability to predict the phase behavior of SCW solutions.Phase separations have the potential to impair the operation of an SCWO reactor (1) by dramatically changing transport properties (especially in the presence of dynamically separating liquid and solid phases), (2) by generating solid particles that may plug reactor orifices and deposit on reactor surfaces, and (3) by producing a highly corrosive electrochemical environment. Objectives for This WorkshopWe sought to develop (or recommend methodologies to develop) guidelines/rules of thumb for phase separations in organic/salt/gas/aqueous solutions in SCWO processing for defined sets of feed compositions. Useful speculations about these phase separations are in the areas not only of equilibrium thermodynamics (e.g., solubility), but also of the kinetics of phase separation and growth (e.g., the problem of heterogeneous nucleation). The phase separation guidelines are intended to indicate regions of safe (pr...

PVTx Measurements and Crossover Equation of State of Pure n-Hexane and Dilute Aqueous n-Hexane Solutions in the Critical and Supercritical Regions

“…Thermodynamic properties of hydrocarbons in water at high temperatures and high pressures are of considerable interest in a number of industrial applications. Since water's dielectric constant varies from a room-temperature value of 80 to a value of 5 at its critical point, it can solubilize most nonpolar organic compounds including most hydrocarbons and aromatics at temperatures starting at 473 and extending to the critical point. , Therefore, supercritical water (SCW) has been proposed as a solvent and as a reaction medium for a number of technological applications such as coal conversion, organic synthesis, environmentally friendly destruction of toxic and hazardous wastes, − including chemical weapons and the cleanup of nuclear processing sites, − SCW oxidation processes, , and extraction of organics from environmental solids. − Water + hydrocarbon systems may also serve as model systems that are useful for the development of processes such as the hydrolysis of plastic, synthetic fibers, or polycarbonates for recycling …”