Extraction supercritical

Supercritical extraction involves the use of a gaseous solvent medium at a temperature just above its critical temperature while increasing the pressure to the critical pressure for that solvent. Under these conditions, the solvent has the properties of both gas and liquid, diffusing like a gas while having the density of a liquid (Anon., 1989). 

Applications of the technique in the food industry include decaffeination of coffee, flavour extraction from hops, extraction of spice oils, and separation of glycerides from edible oils and fats (Logsdail, 1983). 

For food use, the gaseous solvent used is normally carbon dioxide (CO2) as this will not contaminate the foodstuff. The critical temperatures and critical pressures of CO2 and some other solvents are given in Table 2.9. 

Logsdail (1983) considered that the main advantages of the technique over other solvent extraction methods were that it was more versatile, suitable for the extraction of heat-sensitive materials, highly selective, extracted low-volatile components easily and allowed easy recovery of solvent. 

The use of the system to reduce the cholesterol content of butterfat has been developed (Anon., 1989). It was considered that eventually the cholesterol level in butterfat could be reduced by 90%. Currently, reductions of 15% have been achieved commercially using a single-stage extraction, and reductions of 30% have been achieved with a multi-stage process. 

The efficiency of extractors and the equivalent number of equilibrium stages depends on internal design and other factors. Detailed description of extractor equipment is provided by Najim (1989) and is outside the scope of this book. 

In absorbers or strippers, components are transferred from the vapor phase to the liquid phase or vice versa. In liquid-liquid extraction, components are transferred from one liquid phase to the other. In supercritical extraction, components (the solute) are transferred from the liquid phase to the supercritical phase (the solvent) at equilibrium with the liquid. 

One of the benefits of using supercritical fluids as the solvent is the strong dependence of the solubility of the solute on the solvent density. This is a property that could be exploited for facilitating the separation of the solute from the solvent as it leaves the column, by dropping its pressure or raising its temperature, thereby lowering its density and the solubility of the solute. As a result, the extract separates into a liquid solute and a vapor solvent. Another favorable property of supercritical fluids as solvents is the high diffusivity of the solute in these fluids compared to that in liquids. Supercritical fluids also have a substantially lower viscosity than liquids. Because of these properties the mass transfer rate of the solute 

For a supercritical fluid to be suitable as a solvent in extraction, a high solubility of the solute is required, tf the objective is to separate components, the solvent should also have selective dissolution properties. Moreover, the pressure effect on the solubility is a factor. High compression costs may be incurred if the conditions for desirable solubility require excessively elevated pressures. The critical temperature of a potential solvent is also important. If the solvent is to be around its critical point for optimal performance, it is preferred that its critical temperature not be too far from ambient temperature. 

Among the practical applications of supercritical extraction is the use of supercritical carbon dioxide as the solvent in a number of processes. Carbon dioxide has several favorable properties as a supercritical solvent. It is nontoxic, low-cost, and noncorrosive. Its critical temperature is 304.2 K, which is near ambient. These properties are especially desirable in food processing, for the extraction of food components that must not be exposed to high temperatures. Examples are the removal of caffeine from coffee and the extraction of oil from beans and corn. 

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Supercritical Extraction. The use of a supercritical fluid such as carbon dioxide as extractant is growing in industrial importance, particularly in the food-related industries. The advantages of supercritical fluids (qv) as extractants include favorable solubiHty and transport properties, and the abiHty to complete an extraction rapidly at moderate temperature. Whereas most of the supercritical extraction processes are soHd—Hquid extractions, some Hquid—Hquid extractions are of commercial interest also. For example, the removal of ethanol from dilute aqueous solutions using Hquid carbon dioxide... 

Due to possible environmental problems with acetone, new technologies are being developed for the production of deoiled lecithins involving treatment of Hpid mixtures with supercritical gases or supercritical gas mixtures (10—12). In this process highly viscous cmde lecithin is fed into a separation column at several levels. The supercritical extraction solvent flows through the column upward at a pressure of 8 MPa (80 bar) and temperature between 40 and 55°C. The soy oil dissolves together with a small amount of lecithin. 

Fig. 11. Schematic of a residuum oil supercritical extraction (ROSE) process using compressed pentane to separate vacuum resids into asphaltenes (high...

Residuum oil supercritical extraction-petroleum deasphalting Polymer fractionation Edible oils fractionation Analytical SGF extraction and chromatography Reactive separations... 

These values are as much as one hundred times larger than those typically observed in conventional liquids. The improved transport rates in SCFs versus liquid solvents are important in practical appheations including supercritical extraction. Furthermore, carbon dioxide diffuses through condensed-hquid phases (e.g., adsorbents and polymers) faster than do typical solvents which have larger molecular sizes. 

De Franpa, L.F. et ah. Supercritical extraction of carotenoids and lipids from buriti (Mauritia flexuosa), a fruit from the Amazon region, J. Supercrit. Fluids, 14, 247, 1999. 

Removal of reaction products can shift the equilibrium, forcing the reaction to go to completion. This can be effected by evaporation of products from the reaction mixture (reactive distillations), extraction (including supercritical extraction) of products from the reaction mixture (reactive extractions), or membrane processes. Counter- and cocurrent operation also falls within this category. If the reaction is equilibrium-limited or inhibited by reaction products countercurrent operation outperforms cocurrent operation. 

Residuum oil supercritical extraction (ROSE) (petroleum deasphalting) Polymer and edible oils fractionation CO2 enhanced oil recovery Analytical SCF extraction and chromatography Infusion of materials into polymers (dyes, pharmaceuticals)... 

Temperature-Controlled Residuiun Oil Supercritical Extraction (ROSE) The Kerr-McCee ROSE process has been used worldwide for over two decades to remove asphaltenes from oil. The extraction step uses a hquid solvent that is recovered at supercritical conditions to save energy as shown in Fig. 20-21. The residuum is contacted with butane or pentane to precipitate the heavy asphaltene fraction. The extract is then passed through a series of heaters, where it goes from the liquid state to a lower-density SCF state. Because the entire process is carried out at conditions near the critical point, a relatively small temperature change is required to produce a fairly large density change. After the light oils have been removed, the solvent is cooled back to the liquid state and recycled. 

Some typical applications in SFE of polymer/additive analysis are illustrated below. Hunt et al. [333] found that supercritical extraction of DIOP and Topanol CA from ground PVC increased with temperature up to 90 °C at 45 MPa, then levelled off, presumably as solubility became the limiting factor. The extraction of DOP and DBP plasticisers from PVC by scC02 at 52 MPa increased from 50 to 80 °C, when extraction was almost complete in 25 min [336]. At 70 °C the amount extracted increased from 79 to 95 % for pressures from 22 to 60 MPa. SFE has the potential to shorten extraction times for traces (<20ppm) of additives (DBP and DOP) in flexible PVC formulations with similar or even better extraction efficiencies compared with traditional LSE techniques [384]. Marin et al. [336] have used off-line SFE-GC to determine the detection limits for DBP and DOP in flexible PVC. The method developed was compared with Soxhlet liquid extraction. At such low additive concentrations a maximum efficiency in the extractive process and an adequate separative system are needed to avoid interferences with other components that are present at high concentrations in the PVC formulations, such as DINP. Results obtained... 

The number of reports on on-line TLC analysis of extracts is quite limited. Stahl [16,29] described a device for supercritical extraction with deposition of the fluid extract on to a moving TLC plate. On-line SFE-TLC provides rapid and simple insight into the extraction performance. Its strength is that the extract is deposited on a plate, which means that detection is a static process. Limitations of SFE-TLC are that quantification is difficult, and that the stability of components on the support material or in the presence of oxygen may be a problem. For additives in beverages (such as benzoic... 

Shing, K. S. Chung, S. T., Computer-simulation methods for the calculation of solubility in supercritical extraction systems, J. Phys. Chem. 1987, 91, 1674-1681... 

Esquivel MM, Bemardo-Gil MG and King MB. 1999. Mathematical models for supercritical extraction of olive husk oil. J Supercrit Fluids 16(1) 43—58. 

ROSE (1) [Residuum Oil Supercritical Extraction] A process for extracting asphaltenes and resins from petroleum residues, using supercritical propane or isobutane as the extractant. Developed by Kerr-McGee Corporation in 1979 and sold to the MW Kellog Company in 1995, at which time 25 units had been licensed. 

The effects of added C02 on mass transfer properties and solubility were assessed in some detail for the catalytic asymmetric hydrogenation of 2-(6 -meth-oxy-2 -naphthyl) acrylic acid to (Sj-naproxen using Ru-(S)-BINAP-type catalysts in methanolic solution. The catalytic studies showed that a higher reaction rate was observed under a total C02/H2 pressure of ca. 100 bar (pH2 = 50bar) than under a pressure of 50 bar H2 alone. Upon further increase of the C02 pressure, the catalyst could be precipitated and solvent and product were removed, at least partly by supercritical extraction. Unfortunately, attempts to re-use the catalyst were hampered by its deactivation during the recycling process [11]. 

Supercritical extraction is an important methodology for extracting organics from soil. As the name implies, the solvent is kept in its liquid state but above its boiling point by keeping it under pressure. Figure 12.8 shows a simplified supercritical carbon dioxide extraction setup. It is possible and common to have pumps, in addition to the one shown, to add chemical modifiers to the solvent, to increase extraction efficiency, or to extract a specific organic component [6,9-12],... 

An example of a supercritical C02 extraction is given in Procedure 12.3. Note that methanol is added as a modifier and that extraction is rapid, taking only 15 minutes. Supercritical extractions are used when the analyte is difficult to extract, as when it is strongly associated with soil solid, and when it is particularly desirable to have an extract free of solvent contamination that might interfere with subsequent analysis. 

Supercritical extractions such as that illustrated in Procedure 12.3 have been used to extract phenols, organochlorine, organophosphate compounds, and amines from soil [9,10,12],... 

Other supercritical extractions using inorganic gases have also been carried out, most notably, those using nitrous oxide, N20. These have not, however, been used as extensively as supercritical C02 extraction [9-12],... 

All of the solvents that are liquid at STP can be used in the extraction of organics in conjunction with any extraction equipment. In addition to using these same solvents, supercritical extraction using C02 or N20 may also be carried out. Both C02and N20 will change to gas when the pressure is removed and thus will leave the sample free of solvent. 

Describe the basic efficiencies of simple extraction, supercritical extraction, and Soxhlet extraction. 

Explain why cleanup of supercritical extraction products is usually not... 

Brady BO, Kao CPC, Dooley KM, Knopf FC, Gambrell RP. Supercritical extraction of toxic organics from soils. Ind. Eng. Chem. Res. 1987 26 261-263. 

Burford et al. [3] reported a coupled supercritical extraction-gas chromatographic method that can quantitatively extract and determine both gasoline and diesel range hydrocarbons from contaminated soils. The direct transfer of the extract to a gas chromatograph reduced analysis times to about 80min, compared to the 18h required for conventional sonication analysis. 

Hawthorne et al. [53] compared supercritical extraction with chlorodifluoromethane, nitrous oxide and carbon dioxide for the extraction of polychlorobiphenyls and polyaromatic hydrocarbons from soil. Chlorodifluoromethane provided the highest recoveries while methanol modified carbon dioxide gave a 90% recovery of polychlorobiphenyls from soil. 

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