Solvent supercritical fluid, comparison

The use of supercritical fluids in separation processes has received considerable attention in the past several years and the fundamentals of supercritical fluid (SCF) extraction and potential applications have been described in a recent review article (p. It is generally known that supercritical conditions enhance the dissolution of solid particles. In comparison with liquid solvents, supercritical fluids have a high diffusivity, a low density and a low viscosity, thus allowing rapid extraction and phase separation. Little information is available in the literature however, on mass transfer coefficients between supercritical fluids and solids. 

Shen, S. et al.. Comparison of solid-phase microextraction, supercritical fluid extraction, steam distillation, and solvent extraction techniques for analysis of volatile consituents in Fructus amomi, J. AOAC Int., 88, 418, 2005. 

Bergeron, C. et al.. Comparison of the chemical composition of extracts from Scutellaria lateriflora using accelerated solvent extraction and supercritical fluid extraction versus standard hot water or 70% ethanol extraction, J. Agric. Food Chem., 53, 3076, 2005. 

Teng, W.Y., Chen, C.C., and Chung, R.S., HPLC comparison of supercritical fluid extraction and solvent extraction of coumarins from the peel of Citrus maxima fmit, Phytochem. Anal, 16, 459, 2005. 

Yang Yu, Hawthorne B, Miller DJ. 1995. Comparison of sorbent and solvent trapping after supercritical fluid extraction of volatile petroleum hydrocarbons from soil. J Chromatogr A 699 265-276. 

Matthijs, N., Maftouh, M., Vander Heyden, Y. Chiral separation strategy in polar organic solvent chromatography and performance comparison with normal-phase liquid and supercritical-fluid chromatography. J. Sep. Sci. 2006, 29, 1353-1362. 

In a subsequent study, they used ethylene for a dual purpose, as a substrate as well as a supercritical fluid solvent. This notoriously unreactive olefin to PKR served nicely to give 2-substituted cyclopentenones. Reaction efficiency of each alkyne substrate can be tuned by changing catalyst precursors. Not only Co2(CO)8 but also the two cobalt clusters [Co4(CO)i2] and [Co4(GO)n P(OPh)3 ] work well for some substrates (Equation (8)). The comparison with Rautenstrauch s result clearly shows the beneficial effect of this approach. 

Figure 20.6—Supercritical fluid extraction. A comparison of the solvation strength of CO2 with classical solvents (Hildebrand scale) as a function of temperature and pressure is shown.

R Marsili, D Callahan. Comparison of a liquid solvent extraction technique and supercritical fluid extraction for the determination of a- and /8-carotene in vegetables. J Chromatogr Sci 31 422-428, 1993. 

Chlordane co2 Comparison of supercritical fluid extraction, accelerated solvent extraction and Soxhlet extraction [275, 277-280]... 

Taft permits direct comparison between the results for supercritical fluid solvents and the known behavior of liquid solvents. 

From the position of the absorbance maximum in different fluids, the corresponding it parameter values are readily calculated, allowing comparison of supercritical fluids at various experimental conditions with conventional liquid solvents. In Figure 4 the calculated it values are plotted vs the reduced density for the various fluids. Two sets of points have been plotted for CO one set of measurements were made by varying the pressure at constant temperature, the other is for various temperatures at constant pressure. 

X. Chaudot, A. Tambute and M. Caude, Comparison of supercritical fluid extraction with solvent sonication for chemical warfare agent determination in alkyd painted plates, J. High Resolut. Chromatogr., 21, 457-463 (1998). 

Therefore a much higher mass transfer coefficient can be expected for SFE. A comparison of countercurrent extraction columns using supercritical fluids with those using liquid solvents shows, however, that SFE-columns do not reach an efficiency as high as could be expected because of the solvent properties (table 2). 

Xu, Z. Godber, J.S. 2000. Comparison of supercritical fluid and solvent extraction methods in extracting gamma-oryzanol from rice bran. J. Am. Oil Chem. Soc. 77 547-551. 

Water can be used as the solvent in the presence of added surfactants. Reactions in ionic liquids and supercritical fluids are also feasible. A variety of reagents promote cychzation, which can be achieved at room temperature. Examples of compounds that promote and accelerate the reaction include A-methyhnorphohne A-oxide, trimethylamine A-oxide, phosphine oxides, dimethylsulfoxide, alkyl methyl snlfides, molecular sieves, and lithium perchlorate. A comparison of a few promoters is seen in Scheme 246. Promoters... 

Supercritical fluids (SCFs) have long fascinated chemists and over the last 30 years this interest has accelerated. There is even a journal dedicated to the subject— the Journal of Supercritical Fluids. These fluids have many fascinating and unusual properties that make them useful media for separations and spectroscopic studies as well as for reactions and synthesis. So what is an SCF Substances enter the SCF phase above their critical pressures P and temperatures (Tc) (Figure 4.1). Some substances have readily accessible critical points, for example for carbon dioxide is 304 K (31 °C) and is 72.8 atm, whereas other substances need more extreme conditions. For example for water is 647 K (374 °C) and P is 218 atm. The most useful SCFs to green chemists are water and carbon dioxide, which are renewable and non-flammable. However, critical data for some other substances are provided for comparison in Table 4.1. In addition to reactions in the supercritical phase, water has interesting properties in the near critical region and carbon dioxide can also be a useful solvent in the liquid phase. Collectively, carbon dioxide under pressurized conditions (liquid or supercritical) is sometimes referred to as dense phase carbon dioxide. 

Zhou, L.Y. Asharf-Khorassani, M. Taylor, L.T. Comparison of methods for quantitative analysis of additives in low density polyethylene using supercritical fluid and enhanced solvent extraction. J. Chromatogr., A 1999, 858, 209-218. 

Supercritical fluid extraction (SFE), usually with carbon dioxide and, often, with a modifier, has become of increasing interest in the last few years because of its selectivity, preconcentration effect, efficiency, simplicity, rapidity, cleanness, and safety, mainly concerning the extraction of organic compounds prior to separation and detection by chromatographic techniques. It has several advantages over classical solvent extractions, in comparison with recent extraction techniques. Approaches to obtain quantitative extractions, including fluid choice, extraction flow rate, modifiers, pressure, and temperature, are presented, as well as the potential for SFE to extract polynuclear aromatic hydrocarbons (PAHs) from soils, sediments, and biota. Improvements and new environmental applications are also reported. 

Tena, M.T., Valcarel, M., Hidalgo, PJ. and Ubera, J.L. 1997. Supercritical fluid extraction of natural antioxidants from rosemary comparison with liquid solvent sonication. Analytical Chem. 69 521-526. 

Comparison of Supercritical Fluid Solvents to Conventional Liquid Solvents... 

In another investigation, picosecond absorption studies were conducted on TPE singlet excited state in supercritical fluids. Studies were also carried out on ethyl-(Af,Af-dimethylamino)benzoate TICT (twisted intramolecular charge transfer) state for comparison with the TPE studies in supercritical fluids [62]. The decay rates of excited singlet of TPE were found to be correlatable with the solvent-induced changes. The results of this study indicated that the singlet excited state of TPE is twisted and is associated with a polar or zwitterionic character. 

Figure 21.8 Supercritical fluid extraction. Comparison of the solvation strength of the COj with respect to the usual solvents (HUdehrand scale) as a function of the temperature and pressure. The polarity of carhon dioxide in the supercritical state is comparable with that of hexane (for 100 atm and 35 °C). SPE is a method for which automation becomes a justified investment when the sample throughput is large. Above, sample extractor by supercritical fluids (Model SFE-703 reproduced courtesy of Dionex).

Gomez, A. Lopez, C. Martinez de la Ossa, E. "Recovery of Grape Seed Oil by Liquid and Supercritical Fluid Extraction A Comparison with Conventional Solvent Extraction", Chem. Eng. J., 1996,61,227. 

Cocks, S. et al. (1995) High-performance liquid chromatography comparison of supercritical-fluid extraction and solvent extraction of microbial fermentation products, y. Chromatog. A697, 115-122. 

H) have studied various supercritical fluids over a wide range of density and temperature conditions with the aim of allowing intercomparison of supercritical fluid solvents as well as comparison with conventional liquid solvents. Kim and Johnston (41) have also reported solvatochromic data using pure and binary mixtures of supercritical fluids. 

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