Industrial applications, supercritical

The criteria which would be most desirable for industrial application of a separation process involving a supercritical gas may be established by comparing Figs. 3IB, 3ID, and 32. The largest cost in such a process is likely to be that of gas compression. Therefore, the maximum separation possible of the two solvents should occur for the addition of a given amount of gas, and the total pressure required to dissolve this gas should be small. This is the case if the tie lines slope toward the 1-3 binary line and if the gas is readily soluble. In terms of the Margules parameters and Henry s constant, these favorable criteria are ... 

SCFs will find applications in high cost areas such as fine chemical production. Having said that, marketing can also be an issue. For example, whilst decaffeina-tion of coffee with dichloromethane is possible, the use of scCC>2 can be said to be natural Industrial applications of SCFs have been around for a long time. Decaffeination of coffee is perhaps the use that is best known [16], but of course the Born-Haber process for ammonia synthesis operates under supercritical conditions as does low density polyethylene (LDPE) synthesis which is carried out in supercritical ethene [17]. 

From an industrial point of view, homogeneous catalysis has significant advantages concerning selectivities and due to mild reaction conditions [47]. In fact, there is only a limited munber of processes established in industrial applications because of the disadvantageous separabihty of the catalyst from substrate and product. A possible and convenient solution for this limitation can be the application of supercritical carbon dioxide as part of a reaction system due to the following ... 

A special area of HP NMR in catalysis involves supercritical fluids, which have drawn substantial attention in both industrial applications and basic research [249, 254, 255]. Reactions in supercritical fluids involve only one phase, thereby circumventing the usual liquid/gas mixing problems that can occur in conventional solvents. Further advantages of these media concern their higher diffusivities and lower viscosities [219]. The most commonly used supercritical phase for metal-catalyzed processes is supercritical CO2 (SCCO2), due to its favorable properties [256-260], i. e., nontoxicity, availability, cost, environmental benefits, low critical temperature and moderate critical pressure, as well as facile separation of reactants, catalysts and products after the reaction. 

Ionic liquids (ILs) are, together with water and supercritical fluids, one of the few alternative media for environmentally friendly processes, which seem to have more possibility of industrial application in the next 10 years. The range of demonstrated or proposed applications of ILs is extraordinary, going from their use as nonvolatile, non-flammable solvents in organic synthesis to catalysts, materials for aiding separations and gas capture, advanced heat transfer fluids, lubricants, antistatics, and so on [2 ]. Surpassing in magnitude the number of potential uses is the number of possible IL compositions, estimated to be in the billions [5]. The term ionic liquids includes all compounds composed exclusively by ions that are liquid... 

The first exceptional system that we review is carbon dioxide [15-21], Supercritical (sc) CO2 finds numerous industrial applications as a green solvent, and this practical consideration stimulates interest in its radiation chemistry. Though the studies of sc CO2 are recent, this system is particularly interesting because of the simplicity of the solvent molecule and extensive gas phase and matrix isolation studies of the corresponding ions (see below). 

Finally, the industrial application of a technique based on the precipitation by a supercritical anti-solvent is discussed it can be economically attractive only with high-value products, such as pharmaceutical ones. 

Preliminary studies [1,2] suggest that the use of supercritical CO2 allows size- and shape-control of polymeric particles, in particular in the production of protein-loaded microparticles [3], However, to realise an industrial application of such a production, a reasonable economic income has to be expected. 

M. Perrut, Supercritical Fluid Applications Industrial Developments and Economic Issues, Proceedings of the 5th International Symposium on Supercritical Fluids, Atlanta, Georgia, USA, 2000. 

Particle design is presently a major development of supercritical fluids applications, mainly in the paint, cosmetic, pharmaceutical, and specialty chemical industries [4CM-2]. The particle formation of functional pigments with biodegradable polymer has been successfully performed by gas-saturated solution (GSS) process using scC02 and PEG in a thermostatted stirred vessel [43]. The average diameter of the particles obtained by GSS at different conditions (40 and 50 °C, 10-30 MPa) is about 0.78-1.472 pm. 

The physical properties of supercritical fluids tend to lie between those of gases and liquids. The increased density relative to a gas, and the decreased viscosity relative to a liquid, allow supercritical fluids to be used as excellent solvents in many laboratory and industrial applications (19-25). Also, some notable solvation peculiarities of supercritical fluids have been discovered. For example, supercritical water can dissolve nonpolar oils because the dielectric constant of supercritical water decreases drastically near the critical point (26). 

Pinkston, J.D., Bowling, D.J., and Delaney, T.E. 1989. Industrial applications of supercritical-fluid chromatography-mass spectrometry involving ohgometric materials of low volatility and thermally labile materials. Journal of Chromatography, 474 97-111. 

In addition to common organic solvents, supercritical fluids (scf s) can be used for a great variety of extraction processes [158 165], Supercritical fluid extraction (SFE), mostly carried out with SC-CO2 as eluant, has many advantages compared to extractions with conventional solvents. The solvent strength of a supercritical fluid can easily be controlled by the pressure and temperature used for the extraction at a constant temperature, extraction at lower pressures will favour less polar analytes, while extraction at higher pressures will favour more polar and higher molar mass analytes. As supercritical fluids such as CO2 and N2O have low critical temperatures (tc = 31 °C and 36 °C, respectively), SFE can be performed at moderate temperatures to extract thermolabile compounds. Typical industrial applications using SC-CO2 include caffeine extraction from coffee beans [158] as well as fat and oil extraction from plant and animal tissues [165]. For some physical properties of supercritical solvents, see Section 3.2. 

Table 10.4 Industrial applications of supercritical and liquid carbon dioxide...

Gas flow processes through microporous materials are important to many industrial applications involving membrane gas separations. Permeability measurements through mesoporous media have been published exhibiting a maximum at some relative pressure, a fact that has been attributed to the occurrence of capillary condensation and the menisci formed at the gas-liquid interface [1,2]. Although, similar results, implying a transition in the adsorbed phase, have been reported for microporous media [3] and several theoretical studies [4-6] have been carried out, a comprehensive explanation of the static and dynamic behavior of fluids in micropores is yet to be given, especially when supercritical conditions are considered. Supercritical fluids attract, nowadays, both industrial and scientific interest, due to their unique thermodynamic properties at the vicinity of the critical point. For example supercritical CO2 is widely used in industry as an extraction solvent as well as for chemical... 

Industrial applications of supercritical fluids had humble beginnings. The observation of the supercritical phase was first cited in 1822 by Cagniard de la Tour.f In the said work, the disappearance of the gas-liquid boundary by visual inspection of a sealed glass container at elevated temperatures was noted. Following this, in 1879, Hannay and Hogarth reported the ability of an SCF to dissolve low-pressure solid materials. They observed that pressure increases resulted in increased dissolution of metal chlorides in SC ethanol, whereas pressure decreases caused dissolved materials to precipitate as a snow. This increased solubility was later determined to be higher than the solubility predicted by vapor pressure alone. 

At present, the most promising process seems to be the supercritical antisolvent precipitation, which is the most widely applied " and has been recently proposed on a semi-industrial scale. However, despite the fact that many works have been published on SAS precipitation, only a limited number of them have focused on the mechanisms controlling particle formation and on the role of the process parameters on the morphology and on the dimensions of the precipitated powders. This lack of information can be one of the main factors hampering the industrial application of this process. 

The attractiveness of supercritical carbon dioxide extraction is shown by the already existing industrial applications of hop extraction, decaffeination of tea and coffee, defatting of cocoa powder, and extraction of herbs and spices and is also demonstrated by the large number of patent applications and scientific publications in recent years. 

Perrut, M. Supercritical fluid applications Industrial developments and economic issues. Ind. Eng. Chem. Res. 2000, 39, 4531-4535. 

A fluid is supercritical when it is compressed beyond its critical pressure (Pc) and heated beyond its critical temperature (r, ). Supercritical fluid technology has emerged as an important technique for supercritical fluid extraction (SFE). In many of the industrial applications, it has replaced conventional solvent-based or steam extraction processes, mainly due to the quality and the purity of the final product and environmental benefits. 

In many industrial applications, supercritical fluids are poised to replace the conventional solvents, mainly due to the quality and purity of the final products and environmental benefits. There are various supercritical fluids available, as listed in Table 1. 

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