Critical fluids

Wilding N B and Bruce A D 1992 Density fluctuations and field mixing in the critical fluid J. Phys. Condens. Matter 4 3087-108... 

The majority of practical micellar systems of Tionnal micelles use water as tire main solvent. Reverse micelles use water immiscible organic solvents, altlrough tire cores of reverse micelles are usually hydrated and may contain considerable quantities of water. Polar solvents such as glycerol, etlrylene glycol, fonnamide and hydrazine are now being used instead of water to support regular micelles [10]. Critical fluids such as critical carbon dioxide are... 

Super critical fluid chromatograph/infrared spectrometer... 

Pollution Prevention. Procedures haven been developed for recovery of composite ammonium perchlorate propellant from rocket motors, and the treatment of scrap and recovered propellant to reclaim ingredients. These include the use of high pressure water jets or compounds such as ammonia, which form fluids under pressure at elevated temperature, to remove the propellant from the motor, extraction of the ammonium perchlorate with solvents such as water or ammonia as a critical fluid, recrystalli2ation of the perchlorate and reuse in composite propellant or in slurry explosives or conversion to perchloric acid (166,167). 

Erequenfly, the term compressed fluid, a more general expression than supercritical fluid, is used. A compressed fluid can be either a supercritical fluid, a near-critical fluid, an expanded Hquid, or a highly compressed gas, depending on temperature, pressure, and composition. 

Polymers and Supercritical Fluids. Prior to the mid-1980s, Httie information was pubhshed regarding polymer processing with supercritical and near-critical fluids (1). In 1985, the solubiUties of many polymers in near- and supercritical CO2 were reported. These polymers were examined for thek abiUty to increase viscosity in C02-enhanced oil recovery (24). Since then, a number of studies have examined solubiUties of polymers in... 

Catchpole-Kinp examined binaiy diffusion data of near-critical fluids in the reduced density range of 1 to 2.5 and found that their data correlated with average deviations of 10 percent and a maximum deviation of 60 percent. They observed two classes of behavior. For the first, no correction fac tor was required R = 1). That class was comprised of alcohols as solvents with aromatic or ahphatic solutes, or carbon dioxide as a solvent with ahphatics except ketones as solutes, or... 

Flow-induced tube vibration occurs at critical fluid velocities through tube banks, and is to be avoided because of the severe damage that can result. Methods to predict and correct vibration problems may be found in Eisinger Trans. ASME J. Pressure Vessel Tech., 102, 138-145 [May 1980]) and Chen J. Sound Vibration, 93, 439-455 [1984]). 

Extraction from Aqueous Solutions Critical Fluid Technologies, Inc. has developed a continuous countercurrent extraction process based on a 0.5-oy 10-m column to extract residual organic solvents such as trichloroethylene, methylene chloride, benzene, and chloroform from industrial wastewater streams. Typical solvents include supercritical CO9 and near-critical propane. The economics of these processes are largely driven by the hydrophihcity of the product, which has a large influence on the distribution coefficient. For example, at 16°C, the partition coefficient between liquid CO9 and water is 0.4 for methanol, 1.8 for /i-butanol, and 31 for /i-heptanol. 

D. E. Maitire, Unified theoiy of adsoiption cliromatography with heterogeneous surfaces gas, liquid and super-critical fluid mobile phases , ]. Liq. Chromatogr. 11 1779-1807(1988). 

The reaction-catalysing properties of super-critical fluids are described, and some examples are demonstrated of the chemical recycling of waste plastics. 16 refs. Articles from this journal can be requested for translation by subscribers to the Rapra produced International Polymer Science and Technology. 

Silver(I) /3-diketonate derivatives have received significant attention due to the ease with which they can be converted to the elemental metal by thermal decomposition techniques such as metal organic chemical vapor deposition (MOCVD).59 The larger cationic radius of silver(I) with respect to copper(I) has caused problems in achieving both good volatility and adequate stability of silver(I) complexes for the use in CVD apparatus. These problems have been overcome with the new techniques such as super critical fluid transport CVD (SFTCVD), aerosol-assisted CVD (AACVD), and spray pyrolysis, where the requirements for volatile precursors are less stringent. 

Sanders N. 1993. Food legislation and the scope for increased use of near-critical fluid extraction operations in food, flavoring and pharmaceutical industries. In King MB and Bott TR, editors. Extraction of Natural Products Using Near-Critical Solvents. Glasgow Blackie Academic, pp. 34 19. 

Critical fluids are discussed in Chapter 5, where values of critical) are listed. 

Another growing technique is super-critical fluid chromatography. Recent references to soil analysis include the following applications aliphatic hydrocarbons, polyaromatic hydrocarbons, polychlorobiphenyls, dioxins, alkyl and aryl phosphates, chloro, organophosphorus, triazine, substituted urea, phenoxy acetic acid, Dacthal herbicides and insecticides and mixtures of herbicides and pesticides and mixtures of organic compounds. 

Spectro- photometry Lumines- Infrared cence spectroscopy HPLC Super critical fluid chroma- tography GLC GLC-m/s Pyrolysis ESR GLC Thin layer chromatography... 

Beckman EJ (1995) Polymer nanostructures via critical fluid processing. In Vincenzi-ni P (ed) Adv Sci Technol New Horizons for Materials, Techna Sri, p 151... 

Several emerging processes may be applicable for treatment of oily drilling muds prior to disposal. One process being tested in Europe involves the use of an electric distillation kiln to break down solids-laden oil-based drilling muds [13]. Another process uses critical fluid to extract oil and organics from oily sludges so that they can be landhlled [34]. Copa and Dietrich [14] treated a sample of spent drilling mud with wet air oxidation. The COD content was reduced by 45 to 64% and the dewaterability of the mud was improved. 

Moses, J. Abrishamian, R. Case study SITE program puts critical fluid solvent extraction to the test. Hazardous Waste Management Magazine 1988, JanjFeb. 

Figure 15.19 (a) Schematic preparation procedure and apparatus for Rh and PtRh nanoparticle catalysts from Rh and PtRh salt-impregnated silicates by super critical fluid CO2 treatment (b) phase diagram of super critical CO2 as functions of pressure and temperature. 

Achiral (separation of diastereomeric derivatives) and chiral (sepa-ration of enantiomers) chromatography gas chromatography high-performance liquid chromatography super- and sub-critical fluid chromatography thin-layer chromatography... 

The benefits from tuning the solvent system can be tremendous. Again, remarkable opportunities exist for the fruitful exploitation of the special properties of supercritical and near-critical fluids as solvents for chemical reactions. Solution properties may be tuned, with thermodynamic conditions or cosolvents, to modify rates, yields, and selectivities, and supercritical fluids offer greatly enhanced mass transfer for heterogeneous reactions. Also, both supercritical fluids and near-critical water can often replace environmentally undesirable solvents or catalysts, or avoid undesirable byproducts. Furthermore, rational design of solvent systems can also modify reactions to facilitate process separations (Eckert and Chandler, 1998). 

As regards the dynamics of the fluid composition, the experimental results are very difficult to understand [66,67]. We expect that, if the pore size b is very large, the diffusion constant should first behave as in bulk near-critical fluids, but it will cross over to a value of order kBTZb/Gntis 2, being the correlation length (see Eq. (6.67) below). It would also be interesting to find whether the time correlation function of c would be influenced by structural relaxation of network (see Sect 6.2). 

If to is of the order of the concentration decay rate, the inequality co < (rjs/p)q2 holds for most q in the integration as in the case of near-critical fluids. This allows us to set... 

SFC chromatographs represent hybrids between GC and HPLC instruments (Fig. 6.4). In order to deliver the supercritical fluid, syringe pumps or reciprocal pumps are used and maintained above the critical temperature using a cryostat regulated at around 0 "C. In instances where an organic modifier is used, a tandem pump is employed which has two chambers, one for the critical fluid and one for the modifier. The liquid then passes through a coil maintained above the critical temperature so that it is converted into a supercritical fluid. Stainless steel packed columns like those used in HPLC (1 to 4 mm in diameter) or fused silica capillary columns like those used in capillary GC (2 to 20 m in length, internal diameters as low as 50 pm and stationary phase film thickness of at least 1 pm) are used in SFC. 

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