Supercritical fluid water, comparison

Although hydrogenation reactions in ILs are stiU in many ways in their infancy, as are those in other alternative solvents such as fluorous phases and supercritical fluids, some comparisons can be made. Water has now been evaluated extensively as an immobilization solvent for biphasic hydrogenation reactions and while there are many excellent systems, water is limited by substrate solubility and the fact... 

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. 

S.B. Hawthorne, C.B. Grabanski, E. Martin and D.J. Miller, Comparison of Soxhlet extraction, pressurized liquid extraction, supercritical fluid extraction and subcritical water extraction for environmental solids recovery, selectivity and effects on sample matrix. J. Chromatogr.A 892 (2000) 421 133. 

Figure 9. Comparison of the extractabilities of hyoscyamine (A) and scopolamine (B) hydrochloride using water basified with diethylamine (10% v/v) with those of pure water. SFE conditions at 60 C, 34.0 MP [39]. Reprinted from J. Chmmatogr. A, 863, Y. H. Choi et al., Strategies for supercritical fluid extraction of hyoscyamine and scopolamine salts using basified modifiers, 47-55,1999, with permission from Elsevier Science.

Combination of static subcritical water extraction and solid-phase microextraction Comparison of CHC1F2, N2O and CO2 extractants. CHC1 F2 gave highest recovery, methanol-modified CO2 gave 90% recovery Combination of supercritical fluid extraction with off-line Fourier transform infrared spectroscopy... 

Alzaga, R., G. Durand, D. Barcelo, and J.M. Bayona (1994). Comparison of supercritical fluid extraction and liquid-liquid extraction for isolation of selected pesticides stored in freeze-dried water samples. Chromatographia, 38(7-8) 502-508. 

Eskilsson, C.S., K. Hartonen, L. Mathiasson, et al. 2003. Pressurized hot water extraction of insecticides from process dust—comparison with supercritical fluid extraction. J. Sep. Sci. 27 59-64. 

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. 

Solid-phase extraction (SPE) is nearly always required prior to the supercritical fluid extraction of PAHs from liquid samples alternatively, samples can be spiked to a solid material such as diatomaceous earth. A comparison of SPE, SFE, SPE-SFE and liquid-liquid extraction (LEE) for the removal of PAHs from drinking water revealed the SPE-SFE combination to provide the best results and LLE the poorest [188]. 

M. Modell and M. Svanstrom, Comparison of Supercritical Water Oxidation and Incineration for Treatment of Sewage Sludges, 6th Conference on Supercritical Fluids and Their Applications, September 9-12, Maiori, Italy, 2001. 

Because the extraction efficiency was determined by the direct comparison of dye concentration in the spiked dyebadi before and after the extraction, the higher SFE recoveries (e.g. efficiency >99%) should have relative standard deviations <1%. For the purpose of this study, >99% of recovery is sufficient to illustrate the effectiveness of the SFE technique. According to our experiments, no decomposition or breakdown of these disperse dyes was observed during SFE at the specified experimental conditions described atove. The restrictor flow rates of SC-CO2 often dominate the success of SFE, and can be varied to provide information on the dynamics of the extraction process. It is known that if the flow of supercritical fluid is sufficient to sweep the ceil void volume, the effectiveness of the extraction is enhanced. In fact, changing the flow rate is a simple way to determine the extraction efficiency (7). In this study, no obvious difference in extraction efficiency was observed at the SC-C02 flow rate of 2.0, and S.O mL/min. It is also noted that SFE of samples with high concentrations of water tends to plug fused silica restrictors 19). Therefore, a restrictor temperature controller was used in our experiments to avoid restrictor plugging. 

One of the most intensively examined type of pesticides handled under PBl conditions were the chlorinated phenoxy acids and their esters which were determined in water [82-86] and soil samples [83, 86]. Even results of an interlaboratory comparison study of 10 chlorinated phenoxy acids using PBl or TSP ionisation were published by Jones et al. [37] [87]. Statistically significant differences were observed between the interfaces and under these conditions PBl was found to have a better precision than TSP [87]. Betowsld et al. [88] observed thermal degradation induced by residence time in the ion source and the influence of ion source temperature in the ionisation of the chlorinated phenoxy acid derivatives 2,4-D and MCPA. Several authors successfully examined a large number of different carbamate pesticides [67, 89, 90] and their transformation products by PBl-LC-MS [89, 90], by PBl-FIA-MS (flow injection analysis) [67] or by supercritical fluid chromatography (SEC) PBl-interfaced to MS [91],... 

SEE is today not the only hyphenated extraction technique available. Both microwave-assisted solvent extraction (MAE) and pressurized fluid extraction (PEE) have evolved in parallel with SFE during the last decade. A thorough comparison of the different techniques can be found in the analytical literature, and will assist in choosing an appropriate technique for a specific application. These newer techniques offer both speed and simplicity, while some of the main benefits of SFE are still inherent to the usage of supercritical fluids as MAE and PFE utilize liquid solvents. More recently, subcritical water extraction has also been introduced as an environmental friendly alternative but the reader is referred to the analytical literature on this research topic. 

Amigo, S.G. Falcon, M.S.G. Yusty, M.A.L. Lozano, J.S. Supercritical Uqud extraction of polycycHc aromatic hydrocarbons from U ver samples and determination by HPLC-FL. Fresenius J. Anal. Chem. 2000, 367 (6), 572 578. Hawthorne, S.B. Grabanski, C.B. Martin, E. Miller, D.J. Comparison of Soxhlet extraction, pressurized liquid extraction, supercritical fluid extraction and subdritical water extraction for environmental solids Recovery, selectivity and effects on sample matrix. J. Chromatogr. A, 2000, 892, 421 33. 

Other separation techniques, such as capillary electrophoresis (CB) and supercritical fluid chromatography (SBC), have been shown to perform well for the separation of phenols. Several papers describing the use of CB for the separation of phenolic compoimds in water samples have been published lately [97-100]. The majority of these employ UV detection, but BSP-MS in the negative-ion mode [101] and indirect fluorescence detection [102] have also been used. In one study, a comparison between HPLC and CB was performed to assess their suitability for the determination of the 11 priority pollutants in water [16]. The authors claim that CB gave a shorter analysis time and smaller matrix effects. However, it was not possible to achieve the desired detection limits without a preconcentration on solid-phase material. 

Da Porto, C Decorti, D Natolino, A. Water and ethanol as co-solvent in supercritical fluid extraction of proanthoc anidins from grape marc A comparison and a proposal. J. of Supercritical Fluids 2014, 87, 1-8. 

The derived correlation can be used for supercritical fluid heat transfer calculations, in circular and other flow geometries, for heat exchangers, steam generators, nuclear reactors and other heat transfer equipment, for future comparison with other datasets, and for verification of computer codes and scaling parameters between water and modeling fluids. This correlation can be also used for supercritical carbon dioxide and other fluids. However, its accuracy might be less in these cases. Some specifics of pressure-drop calculations were also listed in the paper. 

So far, a relatively limited number of works has been published on the oxidation of light alkanes under SC conditions, mostly on the oxidation of methane in supercritical water (SCW). The role of water, which under SC conditions even at moderate temperatures, below 600 °C, cannot be considered as an inert component, is of special interest. Unfortimately, only a few experimental studies have been performed on the oxidation of methane in other than water SC fluids, a comparison with which would be very interesting for understanding the role of the state of the medium in these reactions. 

Comparison of the supercritical temperature and pressure conditions of some candidate fluids for industrial exploitation Q igure 3.1) may exclude those requiring extreme conditions, such as water, and others on environmental (SFg) or cost grounds (xenon). 

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