Supercritical pressure

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... 

Fe(CN)6]3-(aq) + 6 H20(1). substrate The chemical species on which an enzyme acts, superconductor An electronic conductor that conducts electricity with zero resistance. See also high-temperature superconductor. supercooled Refers to a liquid cooled to below its freezing point but not yet frozen, supercritical fluid A fluid phase of a substance above its critical temperature and critical pressure. supercritical Having a mass greater than the critical mass. 

Carbon dioxide can be liquefied under high pressure (supercritical CO2). Several reactions have been done using supercritical CO2 as the medium, but special apparatus is required. This medium offers many advantages," and some disadvantages, but is an interesting new area of research. 

Although critical pressures are many times greater than atmospheric pressure, supercritical fluids have important commercial applications. The most important of these is the use of supercritical carbon dioxide as a solvent. Supercritical CO2 diffuses through a solid matrix rapidly, and it transports materials well because it has a lower... 

Supercritical fluid extraction (SFE) is a technique in which a supercritical fluid [formed when the critical temperature Tf) and critical pressure Pf) for the fluid are exceeded simultaneously] is used as an extraction solvent instead of an organic solvent. By far the most common choice of a supercritical fluid is carbon dioxide (CO2) because CO2 has a low critical temperature (re = 31.1 °C), is inexpensive, and is safe." SFE has the advantage of lower viscosity and improved diffusion coefficients relative to traditional organic solvents. Also, if supercritical CO2 is used as the extraction solvent, the solvent (CO2) can easily be removed by bringing the extract to atmospheric pressure. Supercritical CO2 itself is a very nonpolar solvent that may not have broad applicability as an extraction solvent. To overcome this problem, modifiers such as methanol can be used to increase the polarity of the SFE extraction solvent. Another problem associated with SFE using CO2 is the co-extraction of lipids and other nonpolar interferents. To overcome this problem, a combination of SFE with SPE can be used. Stolker et al." provided a review of several SFE/SPE methods described in the literature. 

Critical points vary widely. Table 6.1 shows a representative sample of critical parameters and it is immediately obvious why carbon dioxide is widely used. With a critical temperature just above room temperature and a critical pressure that is relatively low, the amount of energy needed to render carbon dioxide supercritical is comparatively small. Fluoroform (CHF3) and difluoromethane also have easily attainable critical parameters, but they are much more expensive than carbon dioxide. Despite its high critical temperature and pressure, supercritical water (SCH2O) is used widely as a destructive medium since it is highly acidic. 

Some of these salts would dissolve under high pressure supercritical conditions, but these conditions require pressures that are substantially above those of the SCWO reactors of the GATS design. 

Institut fiir Physikalische Chemie und Elektrochemie, Universitat Karlsruhe, KaiserstraBe 12, 7500 Karlsruhe Chemical Kinetics / Combustion / Flames / High Pressure / Supercritical Fluids... 

Recent experimental results on thermodynamic properties of high pressure supercritical fluids have opened up the possibility to study combustion and flames at very high pressures and in unusual environments. Stationary diffusion flames have been produced up to 2000 bar in dense aqueous mixed fluid phases. 

The physico-chemical effect of high pressure, especially in the supercritical state, to enhance the solubility and phase conditions of the components involved. Supercritical hydrogenation, or enzymatic syntheses are offer new steps with high pressure. Supercritical water oxidation at high pressure represents an efficient method for the decontamination of wastes. 

By utilizing the rapid expansion of supercritical solutions, small-size particles can be produced from materials which are soluble in supercritical solvents. In this process, a solid is dissolved in a pressurized supercritical fluid and the solution is rapidly expanded to some lower pressure level which causes the solid to precipitate. This concept has been demonstrated for a wide variety of materials including polymers, dyes, pharmaceuticals and inorganic substances. 

A supercritical fluid is defined as a substance that is above its critical temperature and pressure. It exhibits remarkable liquid-like solvent properties and, therefore, high extraction efficiency. Such common gases as carbon dioxide and nitrous oxide have been successfully employed as supercritical fluids in the extraction of organics from solid matrices. The solid sample is placed in an extraction vessel into which the pressurized supercritical fluid is pumped. The organic analytes dissolve in the supercritical fluid and are swept out of the extraction chamber... 

The recent introduction on the market of a new category of health-promoting functional food has created a need to develop appropriate novel technologies in order to optimise the desired beneficial properties of bioactive ingredients. To this end, novel techniques, such as high hydrostatic pressure, supercritical fluid extraction, microencapsulation and pulsed electric field techniques may provide feasible options in the future (Korhonen, 2002). 

Supercritical fluids are found in numerous applications thanks to their properties which vary with temperature and pressure. Supercritical fluids are put in contact with various compounds which also have physico-chemical properties dependant on temperature and pressure. Consequently, mixtures of these compounds with the supercritical solvent must be expected to behave in a complex way. For a binary mixture, for example, several types of phase equilibrium exist solid-fluid for low temperatures, solid-fluid-liquid when temperature rises, and liquid-fluid. 

Carbon dioxide can be used as a reaction solvent when pressurized (supercritical carbon dioxide, SCCO2). Carbon dioxide is nontoxic, inexpensive, abundant, and easily recycled. These properties have made it attractive as an extraction solvent. The low critical temperature of CO2 (Ti ) 31.1 °C ensures that SCCO2 is a safe solvent for many applications. " There are solubility issues that suggest SCCO2 is a rather polar solvent. For example, many systems with hydrocarbon chains are... 

A recent development in liquid-liquid extraction has been the use of supercritical fluids as the extraction-solvent. Carbon dioxide at high pressure is the most commonly used fluid. It is used in processes for the decaffeination of coffee and tea. The solvent can be recovered from the extract solution as a gas, by reducing the pressure. Supercritical extraction processes are discussed by Humphrey and Keller (1997). 

Once the coal is converted to hydrogen, captured C02, and electricity, the C02 must be transported to the site of sequestration. C02 can be transported as a compressed gas, a liquid, a solid, or in a high-pressure supercritical state. If a pipeline right-of-way is available, economic considerations show a clear advantage for C02 transport in the supercritical state,- pipelines delivering nearly 50,000 t/day of supercritical C02 have operated safely... 

Supercritical Fluid Extraction This process generally involves the use of CO2 or light hydrocarbons to extract components from liquids or porous solids [Brunner, Gas Extraction An Introduction to Fundamentals of Supercritical Fluids and the Application to Separation Processes (Springer-Verlag, 1995) Brunner, ed.. Supercritical Fluids as Solvents and Reaction Media (Elsevier, 2004) and McHugh and Krukonis, Supercritical Fluid Extraction, 2d ed. (Butterworth-Heinemann, 1993)]. Supercritical fluid extraction differs from liquid-liquid or liquid-solid extraction in that the operation is carried out at high-pressure, supercritical (or near-supercritical) conditions where the extraction fluid exhibits... 

Rapid expansion of supercritical solutions (RESS) processing is used to prepare microspheres. Microencapsulation takes place when a pressurized supercritical solvent containing the shell material and the active ingredient is released through a small nozzle the abrupt pressure drop causes the desolvation of the shell material and the formation of a coating layer around the active ingredient (74). A prerequisite for this technology is that the compounds effectively dissolve in the SCF, which limits its application. 

Supercritical fluid chromatography (SFC)ls Uses HPLC packed columns and a mobile phase of pressurized supercritical fluids (i.e., carbon dioxide modified with a polar organic solvent). Useful for nonpolar analytes and preparative applications where purified materials can be recovered easily by evaporating the carbon dioxide. HPLC pumps and GC-type detectors are often used. 

Supercritical CO2 has been considered as a potential alternative to conventional solvents due to its relative non-toxicity and non-flammability, as well as its low critical temperature and pressure. Supercritical fluid extraction (SFE) has been used for example in the extraction of fatty acids from diverse matrices such as grape seeds , ginseng seeds, wood pulp , and infant formula . The absence of oxygen and light during the supercritical extraction process helps prevent degradation of the extract. For example, Tipsrisukond, et al." found... 

Supercritical Carbon Dioxide - Refers to carbon dioxide that has been heated to above its critical temperature and pressure. Supercritical CO2 is a potent solvent for a great many organic substances. It is also a suitable medium for polymerization of fluorinated monomers. 

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