Supercritical fluids materials

N.N. Supercritical Fluids - Material and Natural Products Processing, Nice/France, 1998, Institut National Polytechnique de Lorraine... 

J. Hawari, A. Halasz, L. Dusseault, J. Kumita, E. Zhou, L. Paquet, G. Ampleman, S. Thiboutot, Proc. 5th Meeting on Supercrit. Fluids Materials and Natural Products Processing, Nice, (ed. M. Perrut, P. Subra), (1998) 161. 

Verillon F, Boutant R, Proceedings of the Fifth Meeting on Supercritical Fluids, Materials, and Natural Products Processing, March 23-25, 1998, Nice, France (1998). 

Weber A, Tschernjaew J, Kummel R. Coprecipitation with compressed antisolvents for the manufacture of microcomposites. Proceedings of the 5th meeting on Supercritical Fluids Materials and Natural Products Processing, Nice,... 

Murata T, Nakagawa K, Kimura A, Otoda N, Shimoyama I (1995) Design of the cell and gas-handling system for the X-ray absorption study of supercritical fluid material. Rev Sci Instrum 66 1437-1439 Myneni SCB (2000) X-ray and vibrational spectroscopy of sulfate in earth materials. Rev Mineral Geochem 40 113-172... 

Kerst, A.W. and SchlQnder, E-U, (1998) Fluid dynamics and liquid side mass transfer at high pressures in Proc. 5 Meeting on Supercritical Fluids Materials and Natural Product Processing, Pemit, M and Supra, P., (eds.) 457-462. 

Eig. 1. Schematic pressure—temperature diagram for a pure material showing the supercritical fluid region, where is the pure component critical point... 

A paiticularly attiactive and useful feature of supeicritical fluids is that these materials can have properties somewhere between those of a gas and a hquid (Table 2). A supercritical fluid has more hquid-hke densities, and subsequent solvation strengths, while possessiag transport properties, ie, viscosities and diffusivities, that are more like gases. Thus, an SCF may diffuse iato a matrix more quickly than a Hquid solvent, yet still possess a Hquid-like solvent strength for extracting a component from the matrix. 

Materials. Supercritical fluids offer many opportunities in materials processing, such as crystallization, recrystallization, comminution, fiber formation, blend formation, and microceUular (foam) formation. 

Supercritical and Freeze Drying. To eliminate surface tension related drying stresses in fine pore materials such as gels, ware can be heated in an autoclave until the Hquid becomes a supercritical fluid, after which drying can be accompHshed by isothermal depressurization to remove the fluid (45,69,72) (see Supercritical fluid). In materials that are heat sensitive, the ware can be frozen and the frozen Hquid can be removed by sublimation (45,69). 

Supercritical Atomization. Atomization can be obtained by mixing a supercritical fluid (SCF) with the material to be atomized. This process reduces volatile organic compound (VOC) emissions as the SCF acts as a solvent and replaces some of the hydrocarbon solvents in the material (see... 

Supercriticalfluid solvents are those formed by operating a system above the critical conditions of the solvent. SolubiHties of many solutes ia such fluids often is much greater than those found for the same solutes but with the fluid at sub atmospheric conditions. Recently, there has been considerable iaterest ia usiag supercritical fluids as solvents ia the production of certain crystalline materials because of the special properties of the product crystals. Rapid expansion of a supercritical system rapidly reduces the solubiHty of a solute throughout the entire mixture. The resulting high supersaturation produces fine crystals of relatively uniform size. Moreover, the solvent poses no purification problems because it simply becomes a gas as the system conditions are reduced below critical. 

Supercritical fluid extraction (SFE) has been extensively used for the extraction of volatile components such as essential oils, flavours and aromas from plant materials on an industrial as well as an analytical scale (61). The extract thus obtained is usually analysed by GC. Off-line SFE-GC is frequently employed, but on-line SEE-GC has also been used. The direct coupling of SEE with supercritical fluid chromatography (SEC) has also been successfully caried out. Coupling SEE with SEC provides several advantages for the separation and detection of organic substances low temperatures can be used for both SEE and SEC, so they are well suited for the analysis of natural materials that contain compounds which are temperature-sensitive, such as flavours and fragrances. 

The usual means of identifying and quantifying the level of these additives in polymer samples is performed by dissolution of the polymer in a solvent, followed by precipitation of the material. The additives in turn remain in the Supernatant liquid. The different solubilites of the additives, high reactivity, low stability, low concentrations and possible co-precipitation with the polymer may pose problems and lead to inconclusive results. Another sample pretreatment method is the use of Soxhlet extraction and reconcentration before analysis, although this method is very time consuming, and is still limited by solubility dependence. Other approaches include the use of supercritical fluids to extract the additives from the polymer and Subsequent analysis of the extracts by microcolumn LC (2). 

One example of normal-phase liquid chromatography coupled to gas chromatography is the determination of alkylated, oxygenated and nitrated polycyclic aromatic compounds (PACs) in urban air particulate extracts (97). Since such extracts are very complex, LC-GC is the best possible separation technique. A quartz microfibre filter retains the particulate material and supercritical fluid extraction (SPE) with CO2 and a toluene modifier extracts the organic components from the dust particles. The final extract is then dissolved in -hexane and analysed by NPLC. The transfer at 100 p.1 min of different fractions to the GC system by an on-column interface enabled many PACs to be detected by an ion-trap detector. A flame ionization detector (PID) and a 350 p.1 loop interface was used to quantify the identified compounds. The experimental conditions employed are shown in Table 13.2. 

Entries on new materials, including re-cyclate plastics, fullerenes, hard-surfaced polymers, dendrimers, transflective materials, rapid prototyping materials, silicone nitride, supercritical fluids, bulk molding compounds, conversion coatings, folic acid, replacements for chloro-fluorocarbons ... 

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... 

The current state of analytical SPE was critically reviewed and no major changes of the technique have been observed. Overviews of the developments of the extraction technologies of secondary metabolites from plant materials refer to three types of conventional extraction techniques that involve the use of solvents, steam, or supercritical fluids. Each technique is described in detail with respect to typical processing parameters and recent developments. Eollowing the discussion of some technical and economic aspects of conventional and novel separation processes, a few general conclusions about the applicabilities of the different types of extraction techniques are drawn. ... 

The efficiency of drilling operations can be increased using a drilling fluid material that exists as supercritical fluid or a dense gas at temperature and pressure conditions occurring in the drill site, such as carbon dioxide. 

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