Supercritical water oxidation

Water possesses vastly different properties as a reaction medium in its supercritical state than in its standard state. The diagram in Fig. 14.7 is that of a pure substance and shows the regions of temperature and pressure where the substance exists as a solid, liquid, gas, and supercritical fluid. The supercritical point for water is met at a temperature of 400°C and above and at high pressure (about 25 MPa). At the supercritical point, water behaves as a nonpolar dense gas, and hydrocarbons exhibit generally high solubility. However, the solubility of inorganic salts is very low in such liquid. Note that the dielectric constant of water is 80 at the standard state reaches approximately 0 at the supercritical point the Aw of 10 14 at the standard state reaches approximately 10-24 at the supercritical point. 

Supercritical water oxidation Involves mixing chemical agents with water that has been pressurized and heated to a point at which organic compounds become soluble. (Above 705 degrees Fahrenheit, and a pressure above 221 atmospheres, or 3,205 pounds per square inch.) Solution is oxidized at an elevated temperature, producing carbon dioxide and inorganic acids and salts. 

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Two Other chemical processes that rely on hydrothermal processing chemistry are wet oxidation and supercritical water oxidation (SCWO). The former process was developed in the late 1940s and early 1950s (3). The primary, initial appHcation was spent pulp (qv) mill Hquor. Shordy after its inception, the process was utilized for the treatment of industrial and municipal sludge. Wet oxidation is a term that is used to describe all hydrothermal oxidation processes carried out at temperatures below the critical temperature of water (374°C), whereas SCWO reactions take place above this temperature. 

S. H. Timbedake, G. T. Hong, M. Simson, and M. ModeU, "Supercritical Water Oxidation for Wastewater Treatment Preliminary Study of Urea... 

The formation of acids from heteroatoms creates a corrosion problem. At the working temperatures, stainless steels are easily corroded by the acids. Even platinum and gold are not immune to corrosion. One solution is to add sodium hydroxide to the reactant mixture to neutralize the acids as they form. However, because the dielectric constant of water is low at the temperatures and pressure in use, the salts formed have low solubiHty at the supercritical temperatures and tend to precipitate and plug reaction tubes. Most hydrothermal processing is oxidation, and has been called supercritical water oxidation. 

Fig. 12. Typical flow diagram of a hydrothermal oxidation process (HO), also known as supercritical water oxidation (SCWO) (73,105).

Reaction vessels for supercritical water oxidation must be highly corrosion resistant because of the aggressive nature of supercritical water and oxidation reaction products at extreme temperatures and pressures. Supercritical oxidation of PCBs and some chlorinated hydrocarbons can be difficult... 

The two fluids most often studied in supercritical fluid technology, carbon dioxide and water, are the two least expensive of all solvents. Carbon dioxide is nontoxic, nonflammable, and has a near-ambient critical temperature of 31.1°C. CO9 is an environmentally friendly substitute for organic solvents including chlorocarbons and chloroflu-orocarbons. Supercritical water (T = 374°C) is of interest as a substitute for organic solvents to minimize waste in extraction and reaction processes. Additionally, it is used for hydrothermal oxidation of hazardous organic wastes (also called supercritical water oxidation) and hydrothermal synthesis. 

Hydrotheimal oxidation (HO) (also called supercritical water oxidation) is a reactive process to separate aqueous wastes into water, CO9, nitrogen, salts, and other byproducts. It is an enclosed and complete water-treatment process m ng it more desirable to the public than incineration (Fig. 22-25) (Tester et al., op. cit. Gloyna and Li,... 

FIG. 22-25 Hydr othermal-oxidation process (also called supercritical water oxidation) for wastewater purification. (Cowtesy Eco-Waste Technologies.)... 

Supercritical Water Oxidation (SCWO) Wet oxidation occurring in supercritical water at temperatures greater than 374°C (705°F) and pressures greater than 221 bar (3204 psig). 

SCWO Supercritical Water Oxidation TKN Total Kjeldahl Nitrogen TOC Total Organic Carbon TSS Total Suspended Solids WAO Wet Air Oxidation... 

Supercritical fluid extraction — During the past two decades, important progress was registered in the extraction of bioactive phytochemicals from plant or food matrices. Most of the work in this area focused on non-polar compounds (terpenoid flavors, hydrocarbons, carotenes) where a supercritical (SFE) method with CO2 offered high extraction efficiencies. Co-solvent systems combining CO2 with one or more modifiers extended the utility of the SFE-CO2 system to polar and even ionic compounds, e.g., supercritical water to extract polar compounds. This last technique claims the additional advantage of combining extraction and destruction of contaminants via the supercritical water oxidation process."... 

FIG. 20-18 Physical properties of water versus temperature at 240 bar. [Reprinted from Kritzer and Dinjus, An Assessment of Supercritical Water Oxidation (SCWO) Existing Froblems, Tossibh Solutions and New Reactor Concepts Chem. Eng. ].,vol. 83(3), pp. 207-214, copyright 2001, withpermission form Elsevier ]... 

SC WO [supercritical water oxidation] A generic name for processes which destroy organic wastes in water by oxidation under supercritical conditions. The first such process was MODAR, invented in 1980. Since then, several other companies have introduced competing processes. 

Supercritical technology, 23 242,13 449 Supercritical water (SCW) properties, waste detoxification and, 14 108 Supercritical water oxidation (SCWO), 24 16-17... 

Area 100—Reverse Assembly/Munitions Access, 71 Area 200—Hydrolysis of Agent and Energetics, 77 Area 300—Supercritical Water Oxidation, 78 Area 400—Gas-Phase Chemical Reduction, 81... 

Agent Hydrolysis and Treatment of Metal Parts (Steps 8, 10, 13, and 16), 115 Treatment of Hydrolysates and Dunnage by Supercritical Water Oxidation (Steps 11, 12, and 14), 116 Assessment of Integration Issues, 118 Component Integration, 118 Process Operability, 119 Monitoring and Control Strategy, 119 Maintenance Issues, 119 Process Safety, 120 Worker Health and Safety, 121 Public Safety, 121... 

TACOM TBA TCLP THC TNB TNBA TNT TOC TRBP TW-SCWO Tank-Automotive and Armaments Command tributylamine toxicity characteristic leaching procedure total hydrocarbons trinitrobenzene trinitrobenzoic acid trinitrotoluene (an energetic material) total organic carbon thermal reduction batch processor transpiring-wall supercritical water oxidation... 

Figure ES-2 is a block diagram of the Eco Logic technology process. The primary treatment destroys the agent and the energetic materials by hydrolysis with caustic or water. Flowever, the hydrolysis products (hydrolysates) must be further treated prior to final disposal. For this secondary step, Eco Logic proposes to use a transpiring-wall supercritical water oxidation (SCWO) reactor design. The following major operations are included ...

General Atomics Modified reverse assembly cryofracture for projectiles. Hydrolysis supercritical water oxidation (SCWO). Hydrolysis, SCWO. Hydrolysis thermal treatment to 5X. Shredded destroyed in SCWO. 

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