Subcritical water applications

Applications Subcritical water extractions with suitable adjustments to the temperature (up to 250 °C)... 

Numerous organic transformations have been carried out in subcritical water under conventional thermal conditions [35]. The application of microwave heating... 

Table 1.2. Applications of subcritical water extraction to the determination of organic compounds in soil (from author s own files)...

An example of the application of subcritical water extraction-solid-phase microextraction is that of Crescenzi et al. [122] (see above). 

Other applications of subcritical water extraction-solid-phase microextraction are the determination of terbuthylazine and its metabolites [123], polycyclic aromatic hydrocarbons [124,125] and polychlorobiphenyls [63]. Yang and Her [193] collected 1-chloronaphthylene, nitrobenzene and 2-chloro-toluene in soil on a hydrophobic polyisobutylene disc prior to analysis by attenuated total reflectance Fourier transform infrared spectroscopy. 

Application of pressurized hot water (subcritical water) as the extraction medium Extraction of moderately and nonvolatile, thermally stable organic pollutants from a variety of solid and semisolid environmental matrices Extraction of metals such as copper and lead from spent industrial oils with acidified pressurized hot water extraction (PHWE) 76-78,79... 

One special application of SEE involves its joint use with subcritical water to extract Dacthal and its acid metabolites from soil the herbicide is converted to monoacid and diacid derivatives that are more readily soluble in water than the parent compound. Thus, following extraction of Dacthal with supercritical CO, at 400 bar at 150°C for 15 min, its monoacid and diacid metabolites were extracted from soil in 10 min, using subcritical water conditions (viz. 200 bar and 50°C). The metabolites were trapped in situ on a strong anion-exchange disc placed over the exit frit in the extraction cell and subsequently combined with Dacthal by placing the disc into the GC autosampler vial containing the SEE extract to allow their simultaneous elution from the disc and deriva-tization to their ethyl esters. Only a single sample was analysed also, because the disc-catalysed alkylation reaction did not transesterify Dacthal, its speciation was maintained [180]. 

The special features of the uses of supercritical water justify dealing with them in a separate section. No commercially available or laboratory-made extractor can operate in a continuous manner under the conditions required by supercritical water. In fact, most of the few reported applications allegedly involving supercritical water extraction actually used subcritical water conditions with not more than two extractions in the supercritical state this can readily be inferred from the equipment used — stainless steel SF extractors can hardly withstand the drastic conditions needed for work with supercritical water. As a... 

Recent work describing the use of subcritical water as a chromatographic mobile phase has been reported. Water heated to 100-200°C, pressurized to 20-50 bar, can be used as a reversed-phase chromatography eluant. This application exists somewhere in the boundary region between pSFC and HPLC. Stationary phases that have been used successfully for subcritical... 

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. 

Garcaa-Sema, J., Garcia-Verdugo, E., Hyde, J., et al. (2007). Modelling residence time distribution in chemical reactors A novel generalised n-laminar model Application to supercritical CO2 and subcritical water tubular reactors, J. Supercrit. Fluid, 41, pp. 82—91. 

Given the concerns about the use of toxic organic solvents in food chemistry, many new techniques have been developed to overcome or minimize this problem. For instance, environmentally clean extraction techniques, such as those based on the use of compressed fluids (pressurized liquids, PLE supercritical fluids, SFE and subcritical water, SWE or PHWE), are widely used as alternatives to conventional procedures, such as solid—liquid extraction (SEE), liquid—liquid extraction (LLE), and the like. These alternative processes have in common the use of lower amount of solvents (from hundred milliliters to few milliliters), the lack of toxic residues, higher efficiency extraction (in terms of yields and energy used), and the improved selectivity of the process. SFE has been used in food analysis as a sample preparation technique, mainly for lipophilic compounds, while PLE has been extensively used for many compositional food applications, because the selectivity of this technique... 

Properties of substances highly depend on temperature. As an extreme example, water can be considered. We know very well the behaviour of normal water, but it is less familiar that water heated up near to its critical temperature behaves like a completely different solvent. Subcritical water and supercritical water are unpolar liquids and able to dissolve fats. Why should not we utilise the extraordinary properties of such solvents in electrochemistry The methods presented in this book further down will show that we can do experiments of this kind even with everyday instruments, without application of external pressure or spending a lot of heat energy. Examples for the novel experimental facihties offered by the scientific field named here modem thermoelectrochemistry or alternatively in sim thermoelectrochemistry will be presented in this book. 

The problem of determining where a hydraulic jump will occur is a combined application. In the case of supercritical flow on a mild slope, for instance, the tail water depth y2 is determined by the uniform flow depth jo for that slope. The rate of flow and the application of Eq. (10.133) then fix yu and the length of the M3 curve required to reach this depth from the upstream control may be computed from Eq. (10.123). Similarly, in the case of subcritical flow on a steep slope, the initial depth is equal to y0, the tail water depth is given by Eq. (10.133), and the length of the Si curve to the jump from the downstream control is computed from Eq. (10.123). For application of the hydraulic jump to design problems, and for analysis of the jump in circular and other nonrectangular sections, the reader is referred to more extensive treatises on the subject [42],... 

With an increased interest and awareness of the impact of society and industry on the environment, there has been a significant attempt in recent years to reduce or replace the usage of organic solvents. Much early work in this area concentrated on the application of supercritical and subcritical carbon dioxide, but in recent years superheated (or subcritical/pressurized hot) water (SHW) has become of interest for both chromatography and extraction [43,54], The earliest work was reported by GuUlemin et al. [55], who used the term thermal aqueous liquid chromatography. As well as using SHW for the separation of... 

One of the few DPHSE applications using an extractant other than water is that involving the extraction of spice red pepper oil with subcritical propane for the determination of the carotenoid and tocopherol contents [177]. 

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