Superheated water extraction

Miller and Hawthorne [416] have developed a chromatographic method that allows subcritical (hot/liquid) water to be used as a mobile phase for packed-column RPLC with solute detection by FID, UV or F also PHWE-LC-GC-FTD couplings are used. Before LC elution the extract is dried in a solid-phase trap to remove the water. In analogy to SFE-SFC, on-line coupled superheated water extraction-superheated water chromatography (SWE-SWC) has been proposed [417]. On-line sample extraction, clean-up and fractionation increases sensitivity, avoids contamination and minimises sources of error. 

The ingenious process of melting suhlerranean sulfur with superheated water and forcing it to the surface with compressed air was devised and perfected by Herman Frasch in the period 1891-4. Oiiginally designed to overcome the problems of recovering sulfur from the caprock of salt domes far below the swamps and quicksands of Louisiana, the method is now also extensively used elsewhere To extract native sulfiu. ... 

Meluch et al.10 reported that high-pressure steam hydrolyzes flexible polyurethane foams rapidly at temperatures of 232-316°C. The diamines are distilled and extracted from the steam and the polyols are isolated from the hydrolysis residue. Good results were obtained by using reclaimed polyol in flexible-foam recipes at file 5% level. Mahoney et al.53 reported the reaction of polyurethane foams with superheated water at 200°C for 15 min to form toluene diamines and polypropylene oxide. Gerlock et al.54 studied the mechanism and kinetics of the reaction... 

Sulfur is widely distributed as sulfide ores, which include galena, PbS cinnabar, HgS iron pyrite, FeS, and sphalerite, ZnS (Fig. 15.11). Because these ores are so common, sulfur is a by-product of the extraction of a number of metals, especially copper. Sulfur is also found as deposits of the native element (called brimstone), which are formed by bacterial action on H,S. The low melting point of sulfur (115°C) is utilized in the Frasch process, in which superheated water is used to melt solid sulfur underground and compressed air pushes the resulting slurry to the surface. Sulfur is also commonly found in petroleum, and extracting it chemically has been made inexpensive and safe by the use of heterogeneous catalysts, particularly zeolites (see Section 13.14). One method used to remove sulfur in the form of H2S from petroleum and natural gas is the Claus process, in which some of the H2S is first oxidized to sulfur dioxide ... 

CO2 extraction has been prevalent for the isolation of essential oils and other natural lipophilic pigments like carotenoids. Hot water and superheated water extraction methods are used for analytical preparation of polar pigments. The technique is commonly referred to as subcritical water extraction because the practitioners of this approach come from SEE backgrounds. 

Gogus, E, Ozel, M.Z., Lewis, A.C. (2005) Superheated water extraction of essential oils of Origanum micranthum. J. Chromatogr. Sci. 43 87-91. 

The most important deposits of sulphur in the world arc those of Louisiana and Texas, U.S.A., where //. Franck s method of extraction is followed.2 This obviates the formation of sulphur dioxide and at the same time yields a product of such a degree of purity (in some wells as high as 99-9 per cent.) as to be suitable in most cases for direct use. A boring is made in the earth down to the sulphur stratum so that a continuous pipe can pass thence to the surface the pipe consists of throe concentric tubes (see lig. 1). Superheated water, c.g. at 150" is forced down the annular spaces A, A, between the outer tubes, in order to melt the sulphur in the neighbourhood of the cud of the boring. A blast of heated air down the inmost tube, II, then causes the molten sulphur to be carried up between the two inner tubes to the surface, where it is collected.3... 

Method by which elemental sulfur is mined or extracted. Sulfur is melted with superheated water (at 170°C under high pressure) and forced to the surface of the earth as a slurry. 

R.Tajuddin and R. M. Smith, On-line coupled superheated water extraction (SWE) and superheated water chromatography (SWC), Analyst 17 (2002), 883-885. 

Miniaturized retention has been accomplished by using solid-phase microextraction (SPME) to collect PAHs from soil, air particulate matter and urban particulates [62,165], and pyrethrins from pyrethrum flower [165] in the fibre after quantitative extraction with superheated water [62,166]. 

A number of alternatives to Soxhlet extraction have been described. By pressurized liquid or accelerated solvent extraction, the extraction efficiency can be enhanced. Superheated water extraction, taking advantages of the decreased polarity of water at higher temperature and pressure, has been used for liquid extraction of solid samples as well. 

Clifford AA, Basile A, Jimenez-Carmona MM, Al-Said SHR. Extraction of natural products with superheated water. Proceedings of the GVC-Fachaussschuss Hochdruckverfahrenstechnik, 1999 181-184. 

Basile A, Jimenez-Carmona MM, Clifford AA. Extraction of rosemary by superheated water. J Agric Food Chem 1998 46 5205-5209. 

Sulfur is extracted from underground deposits by the Frasch process, shown in Figure 21.15. In this process, superheated water (liquid water heated to about 160°C under high pressure to prevent it from boiling) is pumped down the outermost pipe to melt the sulfur (Figure 21.16). Next, compressed air is forced down the innermost pipe. 

Superheated Water Extraction or Subcritical Water Extraction (SWE)... 

When water is used as the solvent, PLE is referred to as superheated water extraction, subcritical water extraction (SWE), or pressurized (hot) water extraction (PWE). Hot water is very effective as an extraction solvent for PAHs from soil and sediment. Superheated water is water above the boiling point but below the supercritical point, and under sufficient pressure to maintain... 

When extracting with superheated water, soil samples do not require predrying. Water is the ideal solvent when performing immunoassay detection because it does not denature the reagents. However, a small amount of methanol can be added to prevent precipitation of the analytes on to container walls. 

Smith, R. M., Extractions with superheated water, J. Chromatogr. A, 975, 31-46, 2002. Hawthorne, S. B., Yang, Y., and Miller, D. J., Extraction of organic pollutants from environmental solids with sub- and supercritical water, Anal. Chem., 66, 2912-2920, 1994. 

Kipp, S., Peyrer, H., and Kleibohmer, W., Coupling superheated water extraction with enzyme immunoassay for an efficient and fast PAH. Screening in soil, Talanta, 46, 385-393, 1998. 

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