Supercritical fluid processing method

Watson MS, Whitaker MJ, Howdle SM, Shakesheff KM. Incorporation of proteins into polymer materials by a novel supercritical fluid processing method. Adva Mate 2002 14 1802-1804. 

In our laboratory, we have modified the supercritical fluid processing method known as RESS (Rapid Expansion of Supercritical Solution) (7 J-7S) by expanding the supercritical solution into a liquid solvent, or RESOLV (Rapid Expansion of a Supercritical Solution into a Liquid SOLVent), to produce nanoscale semiconductor and metal particles (7, 9, 19-22). For the solubility of metal salts, supercritical ammonia, THF, and acetone were used in the rapid expansion at relatively higher temperatures. The nanoparticles thus obtained were small (less than 10 nm), with relatively narrow size distributions. In an effort to replace the organic solvents with C02-based systems for RESOLV at ambient temperatures, we used a water-in-C02... 

Chromatography. GC is the most common anal)d ical method used but liquid and supercritical fluid chromatographic methods are being increasingly developed. Like titration the sample is destroyed in the analysis process. The ideal situation depicted in Figure 8.8 cannot normally be applied for titration or chromatographic analysis since the analysis equipment needs to be close to the sampling device. This is often termed at-line analysis. 

Rapid solidification and devitrification of amorphous metals and metallic glasses Combustion-flame chemical vapor condensation processes (Kear) Induction-heating chemical vapor condensation processes DC and RF magnetron sputtering, inclusive of the method of thermalization Laser ablation methods Supercritical fluid processing... 

Another approach to separate carpet components is to use a supercritical fluid (SCF) method in a batch process. - The solubility of the polymer changes with the variation in pressure and temperature of the SCF. Sikorski discloses that the individual polymers in carpet can be extracted sequentially using a SCF such as COj by increasing temperature and pressure. However, high temperatures (170-210 °C) and pressures (500-1000 atm) are required to dissolve the various polymers in the SCF solvent. Another development enables the separation of... 

Recently, much attention has been paid to the preparation of nanometer particle catalysts. Several methods have been developed to prepare nanometer particles. The liquid phase method could be better for the preparation of catalyst with nanometer size [1]. A main problem for this preparation process is how the aggregation of fine particles can be avoided, espedsdly at the dr3dng step. The key is to reduce surface tension. Alcoholate method was developed for it in which alcoholate hydrolysis instead of aqueous solution to make the sol(gel) was used to avoid surface tension, i.e. avoid vapor-liquid interface freeze drying method, in which the solution is first firozen and then sublimated to remove it, and supercritical fluid drying method, in which the solvent is solved in a supercritical fluid to remove it, were also developed. Although these methods have successfully reduced or avoided the effect of surface tension, the preparation cost including raw material, special equipment and time is increased. 

Woo JS, Kim HJ, Kim Y (2006) Method for the preparatin of paclitaxel sohd dispersion by using the supercritical fluid process and paclitaxel solid dispersion prepared thereby, Google Patents Yeo S-D, Kiran E (2005) Formation of polymer particles with supercritical fluids a review. J Supercrit Fluids 34(3) 287-308... 

It is possible to get drug delivery devices with drug action by using supercritical fluid processes such as impregnation [34-39], SAS [40-44] and RESS [45-52], among other methods [53-55]. 

The WAG process has been used extensively in the field, particularly in supercritical CO2 injection, with considerable success (22,157,158). However, a method to further reduce the viscosity of injected gas or supercritical fluid is desired. One means of increasing the viscosity of CO2 is through the use of supercritical C02-soluble polymers and other additives (159). The use of surfactants to form low mobihty foams or supercritical CO2 dispersions within the formation has received more attention (160—162). Foam has also been used to reduce mobihty of hydrocarbon gases and nitrogen. The behavior of foam in porous media has been the subject of extensive study (4). X-ray computerized tomographic analysis of core floods indicate that addition of 500 ppm of an alcohol ethoxyglycerylsulfonate increased volumetric sweep efficiency substantially over that obtained in a WAG process (156). 

Mixtures can be identified with the help of computer software that subtracts the spectra of pure compounds from that of the sample. For complex mixtures, fractionation may be needed as part of the analysis. Commercial instmments are available that combine ftir, as a detector, with a separation technique such as gas chromatography (gc), high performance Hquid chromatography (hplc), or supercritical fluid chromatography (96,97). Instmments such as gc/ftir are often termed hyphenated instmments (98). Pyrolyzer (99) and thermogravimetric analysis (tga) instmmentation can also be combined with ftir for monitoring pyrolysis and oxidation processes (100) (see Analytical methods, hyphenated instruments). 

Separation Techniques. Current methods for separating fatty acids are by solvent crystaUi2ation or by the hydrophili2ation process. Other methods that have been used in the past, or perhaps could be used in the future, are panning and pressing, solvent extraction, supercritical fluid extraction, the use of metal salts in assisting in separation, separations using urea complexes, and adsorption/desorption. 

The coupling of supercritical fluid extraction (SEE) with gas chromatography (SEE-GC) provides an excellent example of the application of multidimensional chromatography principles to a sample preparation method. In SEE, the analytical matrix is packed into an extraction vessel and a supercritical fluid, usually carbon dioxide, is passed through it. The analyte matrix may be viewed as the stationary phase, while the supercritical fluid can be viewed as the mobile phase. In order to obtain an effective extraction, the solubility of the analyte in the supercritical fluid mobile phase must be considered, along with its affinity to the matrix stationary phase. The effluent from the extraction is then collected and transferred to a gas chromatograph. In his comprehensive text, Taylor provides an excellent description of the principles and applications of SEE (44), while Pawliszyn presents a description of the supercritical fluid as the mobile phase in his development of a kinetic model for the extraction process (45). 

Chromatography is a physical method of separation in which the components to be separated are distributed between two phases, one of which is stationary (the stationary phase), while the other (the mobile phase) moves in a definite direction. A mobile phase is described as a fluid which percolates through or along the stationary bed in a definite direction . It may be a liquid, a gas or a supercritical fluid, while the stationary phase may be a solid, a gel or a liquid. If a liquid, it may be distributed on a solid, which may or may not contribute to the separation process. ... 

Braga et al. ° compared the efficiencies of several processes, i.e., hydrodistillation, low pressnre solvent extraction, and Soxhlet and supercritical fluid extraction. For each process, the inflnences of several parameters (duration, temperature, nature of solvent) were also evalnated. These authors concluded that the Soxhlet method performed with ethanol/isopropanol 1/100 v/v for 2 hr and 30 min was the most effective. Snn et al. nsed solid phase extraction to concentrate (nine times) a... 

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."... 

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