Supercritical fluid separations extraction

The two SCFs most often studied—CO2 and water—are the two least expensive of all solvents. CO2 is nontoxic and nonflammable and has a near-ambient critical temperature of 31. UC. CO2 is an environmentally friendly substitute for organic solvents including chlorocarbons and chlorofluorocarbons. Supercritical water (Tc = 374°C) is of interest as a substitute for organic solvents to minimize waste in extraction and reaction processes. Additionally, it is used for hydrothermal oxidation of hazardous organic wastes (also called supercritical water oxidation) and hydrothermal synthesis. (See also Sec. 15 for additional discussion of supercritical fluid separation processes.)... 

Supercritical fluid separation processes operate at pressures ranging from 1000 to 4000 lb/in.2, pressures that might be considered high, especially in the foods and essential oils industries. However, because of the factors just listed, supercritical fluid extraction has become eco-... 

The preparation of high-purity tocopherols and phytosterols involves steps such as molecular distillation, adduct formation, liquid-liquid extraction, supercritical fluid extraction, saponification, and chromatography (175). The extraction of tocopherols from soybean oil deodorizer distillate by urea inclusion and saponification of free fatty acids resulted in good recovery of tocopherols (208). To improve the separation of sterols and tocopherols, Shimada et al. (209) used a lipase to esterify sterols with free fatty acids. Then the steryl esters and tocopherols were separated better by molecular distillation. Chang et al. (210) used supercritical fluid CO2 extraction to recover tocopherols and sterols from soybean oil deodorizer distillate. A patent by Sumner et al. (211) advocated treatment of the distillate with methanol to converted free fatty acids and other fatty acid esters to methyl esters that can then be removed by a stripping operation. Then separation of sterols and tocopherols could be carried out by molecular distillation. 

Since 1929, polychlorinated biphenyls (PCBs) have been produced and used as heat-transfer, hydraulic, and dielectric fluids. Because of their chemical and physical stability, PCBs have been found in many environmental samples. Generally, PCBs have been analyzed by GC with electron-capture detection. There are many reports on subcritical and supercritical fluid extraction of PCBs, but only a few on supercritical fluid separation of PCBs. 

For most applications, it is not possible to treat supercritical fluid separations, for example extraction, as a well-defined unit operation as is the case for simpler proctssts such as distillation. Instead, research is often needed to characterize the important properties for each specific separation or reaction. However, the recent advances in the molecular understanding of SCF solutions provide some general themes that can be utilized in a semi-quantitative manner to evaluate the potential of both research and applications. 

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. 

How does one evaluate the process viability of an SCF application We have touched on economics several times in the preceding chapters, but only superficially. As there are no hard and fast answers to questions of viability with traditional processes, so are there none with supercritical fluid extraction. Nevertheless, both of us are asked quite frequently How much will it cost To indicate why there is no single answer, we list below just a few of the parameters that influence the cost of a supercritical fluid separation process ... 

In some respects this patent is like the deFillippi and Vivian patent, U.S. 4,349,415 although the deFillippi patent claims all near-critici liquids and supercritical fluids for extracting all organics while this one claims propylene as the extractant for ethanol. Both patents describe that the solvent and the extracted organic are separated by distillation. The major difference is in the supply of energy to the reboiler in the solvent distillation column. U.S. 4,349,415 utilized vapor recompression while this one uses a heat pump. 

Removal of interfering species Masking or separation techniques (e.g., adsorption, absorption, hxiviation, supercritical fluid (SF) extraction, dialysis, liquid-liquid extraction (LLE), solid phase extraction (SPE), precipitation, etc). 

The capsaicinoids are extracted using different solvents and more recently ultrasound-assisted extraction [61], extraction by means of supercritical fluids [65], extraction by pressurized liquids [58] and enzymatic extraction [59], and analyzed by HPLC [64,93-95], GC [72-76], hyphenated systems as HPLC-MS [96-100], and GC-MS [77]. Normally the GC methods require derivatization of the compounds to make them sufficiently volatile for determination. There are many other reported papers have been found in the literature for the analytical separation, quantitation, and identification of naturally occurring capsaicinoids in different matrices. Select matrices are discussed here. 

The ability of small molecular fluids under nearcritical conditions to dissolve low-vapour-pressure solid materials was first discovered by Hannay et al. (1). Scheffer and coworkers (2) investigated extensively the solubility of naphthalene in near- and supercritical ethylene. Since then many researchers have started to study the possibilities of supercritical solvents and within the past two decades several research institutes have Investigated and developed the principles and technology of supercritical fluid separations. Commercial application can be found in areas as diverse as spice extraction, monomer purification, coal extraction, nicotine and caffeine extraction, fractionation of (co-) polymers or the extraction of oils from all kinds of natural products. Reviews of most of this work are... 

In 2010 and 2012 All-Russian School-Conference of Young Scientists Supercritical Fluid Technologies in the Decision of Environmental Problems. Plants Biomass Extraction was held on the base of North (Arctic) Federal University. Taking into account the major local directions of scientific work, the scope of the School-Conference included such issues as the properties of supercritical fluids, ScF extraction of plant biomass, chemical and biological processes in ScF media, ScF chromatography in analysis and separation of natural extracts. 

The use of separation techniques, such as gel permeation and high pressure Hquid chromatography interfaced with sensitive, silicon-specific aas or ICP detectors, has been particularly advantageous for the analysis of siUcones in environmental extracts (469,483—486). Supercritical fluid chromatography coupled with various detection devices is effective for the separation of siUcone oligomers that have molecular weights less than 3000 Da. Time-of-flight secondary ion mass spectrometry (TOF-sims) is appHcable up to 10,000 Da (487). 

The development of methods of analysis of tria2ines and thek hydroxy metabohtes in humic soil samples with combined chromatographic and ms techniques has been described (78). A two-way approach was used for separating interfering humic substances and for performing stmctural elucidation of the herbicide traces. Humic samples were extracted by supercritical fluid extraction and analy2ed by both hplc/particle beam ms and a new ms/ms method. The new ms /ms unit was of the tandem sector field-time-of-flight/ms type. 

Separation Techniques. Current methods for separating fatty acids are by solvent crystaUi2ation or by the hydrophili2ation process. Other methods that have been used in the past, or perhaps could be used in the future, are panning and pressing, solvent extraction, supercritical fluid extraction, the use of metal salts in assisting in separation, separations using urea complexes, and adsorption/desorption. 

ON-LINE COUPLING OF SUPERCRITICAL FLUID EXTRACTION WITH CAPILLARY ELECTRODRIVEN SEPARATION TECHNIQUES (SFE-CESTs)... 

Supercritical fluid extraction (SFE) has been extensively used for the extraction of volatile components such as essential oils, flavours and aromas from plant materials on an industrial as well as an analytical scale (61). The extract thus obtained is usually analysed by GC. Off-line SFE-GC is frequently employed, but on-line SEE-GC has also been used. The direct coupling of SEE with supercritical fluid chromatography (SEC) has also been successfully caried out. Coupling SEE with SEC provides several advantages for the separation and detection of organic substances low temperatures can be used for both SEE and SEC, so they are well suited for the analysis of natural materials that contain compounds which are temperature-sensitive, such as flavours and fragrances. 

A method which uses supercritical fluid/solid phase extraction/supercritical fluid chromatography (SE/SPE/SEC) has been developed for the analysis of trace constituents in complex matrices (67). By using this technique, extraction and clean-up are accomplished in one step using unmodified SC CO2. This step is monitored by a photodiode-array detector which allows fractionation. Eigure 10.14 shows a schematic representation of the SE/SPE/SEC set-up. This system allowed selective retention of the sample matrices while eluting and depositing the analytes of interest in the cryogenic trap. Application to the analysis of pesticides from lipid sample matrices have been reported. In this case, the lipids were completely separated from the pesticides. 

One example of normal-phase liquid chromatography coupled to gas chromatography is the determination of alkylated, oxygenated and nitrated polycyclic aromatic compounds (PACs) in urban air particulate extracts (97). Since such extracts are very complex, LC-GC is the best possible separation technique. A quartz microfibre filter retains the particulate material and supercritical fluid extraction (SPE) with CO2 and a toluene modifier extracts the organic components from the dust particles. The final extract is then dissolved in -hexane and analysed by NPLC. The transfer at 100 p.1 min of different fractions to the GC system by an on-column interface enabled many PACs to be detected by an ion-trap detector. A flame ionization detector (PID) and a 350 p.1 loop interface was used to quantify the identified compounds. The experimental conditions employed are shown in Table 13.2. 

Although on-line sample preparation cannot be regarded as being traditional multidimensional chromatography, the principles of the latter have been employed in the development of many on-line sample preparation techniques, including supercritical fluid extraction (SFE)-GC, SPME, thermal desorption and other on-line extraction methods. As with multidimensional chromatography, the principle is to obtain a portion of the required selectivity by using an additional separation device prior to the main analytical column. 

Figure 15.14 Separation of explosives exnacted from water by using SPE-SFE-GC at several SEE trapping temperatures, peak identification is as follows NG, nitroglycerin 2,6-DNT, 2,6-dinitrotoluene 2,4-DNT, 2,4-dinitrotoluene TNT, triniti otoluene IS, 1,3-tiichloroben-zene. Adapted Journal of High Resolution Chromatography, 16, G. C. Slack et al., Coupled solid phase extraction supercritical fluid extraction-on-line gas cliromatography of explosives from water , pp. 473-478, 1993, with permission from Wiley-VCH.

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